National Aeronautics and Space Administration

S p a c e Te l e s c o p e S c i e n c e I n s t i t u t e

F A L L 2 0 0 9 V O L 2 6 I S S U E 0 2

NEWSLETTER

H ubble servicing missions are special events. Each is unique—and all are complex—drawing on the full range of human imagination to convert vision to reality. Thousands of person-years of work meld

together the very best of NASA’s programs of human spaceflight and scientific exploration. The missions themselves last only a few intense, stressful days, but for those fortunate enough to participate in these grand endeavors—each playing a small role in a grand, choreographed dance with the stars 350 miles above the surface of the Earth—the experience is beyond any other, and will remain etched in our memories forever.

As originally envisioned, the goals of Servicing Mission 4 (SM4) were ambitious, to say the least. They included installations of a new wide-field camera and an ultraviolet spectrograph, each designed to increase Hubble’s prodigious observing power by factors of ten or more. They included new batteries for power, a full set of six new gyros and a refurbished Fine Guidance Sensor (FGS) for Hubble’s exquisite pointing, and a cooling system and thermal blankets to regulate temperature. All these upgrades were shoe-horned into the minute-by-minute schedules of five six-and-a-half-hour spacewalks (or extravehicular activities, EVAs).

In addition to module replacements, the electrical failures of the Space Telescope Imaging Spectrograph (STIS) in 2001 and 2004 gave rise to the idea of repairing an instrument in place. This would call for specialized tools to capture numerous screws and replace a faulty electronics board. The STIS repair was a daunting task that, thanks to the creative minds of task developers, the ingenuity of the tool designers, and countless hours of training by the astronauts, eventually became believable and do-able. The STIS repair alone, even under the best of circumstances, would require nearly a full EVA to accomplish, so officially including this goal was a major decision point. At the end of the day, a consensus

emerged that the unique science capabilities of STIS—longslit spectroscopy to study exoplanet atmospheres, black holes, and other objects; and high-resolution ultraviolet spectroscopy to study the gas-phase composition and kinematics of all types of astronomical objects—offered science that was just too important to pass up. The manifest was scrubbed to remove important, but lower-priority items, like the cooling system, to make room for this precious instrument repair.

The cancellation of SM4—on January 16, 2004, which was one year after the launch of Space Shuttle Columbia and the tragic loss of seven astronauts—shattered hopes for a sustained and vastly improved Hubble. Nevertheless, in April 2005 the new NASA administrator, Michael Griffin, directed the Hubble program to recommence developing SM4. Its actual execution would depend on whether an engineering analysis of the shuttle safety improvements made a compelling case that it was safe to fly. Much work on SM4 hung in the balance, but everyone agreed that the potential danger to the astronauts was the foremost consideration.

National Aeronautics and Space Administration

Kenneth Sembach, sembach@stsci.edu

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Servicing Hubble

Jet in the Carina Nebula taken with Hubble’s WFC3 detectorCredit: NASA, ESA, and the Hubble SM4 ERO Team)

The Space Shuttle Atlantis’ remote manipulator system robotic arm lifts the Hubble Space Telescope from the cargo bay and is moments away from releasing the orbital observatory to start it on its way back home to observe the universe. (Image/caption credit: NASA)

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Servicing Hubblefrom page 1

Hubble was showing its age. The gyros were failing, and the FGSs were degrading. One of the two sets of electronics powering the CCD cameras in the Advanced Camera for Surveys (ACS) failed in June 2006. Hubble’s fate seemed to rest on ever-thinning ice.

Yet, even this dark cloud had a silver lining. The delayed decision gave precious time to test and improve the new instruments. Superior infrared detectors became available for the new Wide Field Camera 3, offering increased quantum efficiency and better dark noise characteristics, far exceeding the original

requirements. Nevertheless, whether those detectors would ever fly on Hubble remained unknown.The reinstatement of the mission in October 2006 set up the next twist of fate on the Hubble

team’s emotional roller coaster. The second set of electronics on ACS failed in January 2007, leaving both ACS CCD cameras crippled. This was a huge loss because the ACS wide-field camera accounted for roughly 70% of the Hubble science program at the time. Although at first a repair of ACS seemed out of the question, a plausible plan emerged, built on the tools and training for the STIS repair. To work, however, a task of extraordinary complexity would have to be developed and perfected in time for the planned launch of SM4, just a bit more than a year away.

Like the STIS repair, the ACS repair would entail removing tiny screws. It would also require its own set of specialized tools, to cut an aluminum grid, to capture screws, to replace electronics boards, and to reroute power lines outside the instrument. Once again, the schedule was closely examined and its priorities assessed. The already full timeline would become even more challenging if a second instrument repair was squeezed into what little space could be found in the five EVAs. But science was once again a powerful motivating factor in the decision process. Having both ACS and WFC3 on-line would provide astronomers with the two most powerful astronomical imaging instruments ever flown—and their simultaneous operation would open new avenues to scientific discovery.

Fast-forward to a planned launch of SM4 in October 2008. Less than three weeks prior to the launch date and after more than 18 years of operation, an electrical component failed in the science-data formatter, which is part of the instrument-control unit. All communications

with the instruments pass through this unit, and if the redundant system failed, there would no way to command the instruments—nor to retrieve any data, even if the instruments could be commanded. The risk of operating Hubble for a prolonged period after SM4 with only the redundant set of electronics, and without further backup, was unacceptable.

The Hubble project again developed an action plan, this time to refurbish and qualify for flight a replacement for the instrument-control unit. The launch date was revised to May 2009. The schedule was examined and rearranged again. This time, however, the baseline plan could not accommodate all of the new subsystems, instrumentation, and instrument repairs. There was only so much that

could be planned for the 32.5 hours of EVA time. One of the instrument repairs (ACS or STIS) would likely have to be dropped, with the choice depending on events as they unfolded during the mission itself.

During SM4, I was stationed at Goddard Space Flight Center as part of the management team, and I had an up-close view of the mission from inside the operations center. I participated in the planning shift—the team of engineers, scientists, managers, and staff that reacted to the events of each day and replanned activities for the next day. We all hoped each activity would go according to plan, but we knew what to do in case of discrepancies. Indeed, we had trained for months, working our way through all sorts of possible anomalies, and learning to work as a team. We were ready. The entire Hubble team was ready. And our heroes in space were ready—ready for whatever surprises Hubble could summon. And surprises did arise: stuck bolts, slightly misaligned hardware, an obstinate handle, and anomalous readings during an instrument functional test.

Personally, I couldn’t sleep more than three or four hours a night during the mission. The moment my head hit the pillow each night (actually, morning), I was sound asleep. Like clockwork, that sleep came to an end as abruptly as it started. Subconsciously I couldn’t bear the thought of not knowing

what was happening, despite knowing full well that my sleep schedule made no difference whatsoever to the activities overhead. I was compelled to arrive early in the operations center, to observe first hand and absorb the energy of the day’s events.

In this close-up scene featuring astronaut John Grunsfeld performing a spacewalk to work on the Hubble Space Telescope, the reflection in his helmet visor shows astronaut Andrew Feustel taking the photo as he’s perched on the end of the Canadian-built remote manipulator system arm. The mission specialists are performing the first of five STS-125 spacewalks and the first of three for this duo. (Image/caption credit: NASA)

While standing on the end of Atlantis’ remote manipulator system arm, astronaut Michael Good, STS-125 mission specialist, uses a power tool to perform work on the Hubble Space Telescope. (Image/caption credit: NASA)

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At Goddard, I had the luxury of watching the faces around me as the EVA activities proceeded. I saw them turn ashen on several occasions (a stuck bolt—really?), only to see the healthy hues return when it was clear we were back on track. I watched as teams sprang into action to provide long-distance support to our counterparts at Johnson Space Center and to the astronauts above. I saw the joy and relief on the faces of all those who witnessed the first signs that a newly installed or repaired instrument was alive and well.

At the end of the fifth EVA, I shared the disbelief and the groundswell of emotion evoked by the amazing accomplishments of that week in May. We knew the astronauts would strive to do what they could to repair Hubble. While it seemed improbable that they would accomplish more than the baseline schedule, looking back now, it somehow seemed equally improbable that they would not rise to the challenge of doing it all. When so many people share the same hopes and dreams, truly awesome things can be accomplished.

I am so proud to have been part of this team of teams, to have been able to work alongside my friends and colleagues during the mission, and to have been able to contribute to its success, even if only in small ways, by doing my best in a complex sequence of events that was far too large for any individual to grasp in its entirety.

It was an amazing week, filled with emotion. For many that I observed, it was their final encounter with Hubble. For some, it was a new beginning—both literally and figuratively—as Hubble was released and sent on its way to begin its on-orbit checkouts. That verification has now concluded, with the proof of Hubble’s capabilities and the work of thousands of people over the last ten years reflected in the stunning pictures made public on September 9.

Hubble itself now begins life anew, more powerful than ever before. More powerful than it would have been had the mission not been cancelled in 2004, and eventually delayed until 2009. Even more powerful than originally envisioned, there are great days ahead for Hubble, making new discoveries to amaze and challenge us.

Astronaut Andrew Feustel, STS-125 mission specialist, navigates near the Hubble Space Telescope on the end of the remote manipulator system arm, controlled from inside Atlantis’ crew cabin. Astronaut John Grunsfeld signals to his crewmate from just a few feet away. Astronauts Feustel and Grunsfeld were continuing servicing work on the giant observatory, locked down in the cargo bay of the shuttle. (Image/caption credit: NASA)

The crewmembers for the STS-125 mission pose for the traditional in-flight portrait on the middeck of the Earth-orbiting Space Shuttle Atlantis. Pictured on the front row are astronauts Scott Altman (center), commander; Gregory C. Johnson, pilot; and Megan McArthur, mission specialist. Pictured on the back row (left to right) are astronauts Michael Good, Mike Massimino, John Grunsfeld and Andrew Feustel, all mission specialists. (Image/caption credit: NASA)

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The Master of HubbleEthan Schreier, ejs@aui.edu

R odger Doxsey passed away on October 13. He had been at the Institute for 28 years, almost exactly. I know because I hired him, and he actually started work at STScI shortly before I moved to Baltimore myself.

All STScI staff know that Rodger was a mainstay of the Institute, and he was so from the start. He helped create the Institute, and went on to help create the complex systems that made Hubble the success it was. He stayed with the Institute—and with Hubble—for the reminder of his professional career.

Rodger was totally dedicated to Hubble’s mission—through its crises, its challenges, and its magnificent accomplishments. He was a key player in making the first servicing mission, the one that fixed Hubble, a success, and which, in turn, made Hubble into one of the world’s most impressive tools for research and discovery. And he was still active in preparing for the last servicing mission, despite his advancing illness.

Rodger was also dedicated to the Institute itself, and to its mission of producing the best science that Hubble could do, using a dedicated team of scientists, engineers, and support staff, who thoroughly knew what the scientific community wanted and needed.

I first met Rodger in 1971. He was a new graduate student at MIT, and I was barely two years out of MIT myself, working with Riccardo Giacconi and his group at American Science and Engineering in Cambridge. We had just discovered that many, indeed most, of the X-ray sources we saw were variable. I went across to MIT, to convince the astronomers getting ready to launch a rocket that they should modify their detectors to better study the variability. Rodger was the young student who helped implement the changes.

Our paths kept crossing over the next decade, as he worked on two other X-ray astronomy satellites at MIT, and I worked on two other X-ray satellites at Harvard. While Rodger and I did not work closely together at that time, we both were doing research in X-ray astronomy, we both shared a group of friends and colleagues, and we both were involved with the operations of our respective satellites.

In 1981, when Riccardo was named first director of STScI, he asked me to come and lead the operations and data processing group. Surveying the scene, it did not take long to realize I would need to organize two teams, one for each area, and decided that operations was going to need its own lead. When I approached Rodger, he did

not hesitate—he recognized a challenge when he saw one.The rest is history. Rodger moved to Baltimore and immediately became a key player at the Institute,

helping in all aspects of the wonderful venture of creating a new Institute that could conduct the science program of Hubble. Rodger was, in the words of the Institute’s first Director, a “force of nature.” He was the strongest demonstration of the power of “technical truth” (also in the words of Riccardo) in addressing all manner of problems. It is impossible to recount his contributions—they ranged from the sublime to the ridiculous: from overseeing the total rewrite of the operations ground system, to writing an accounting program in FORTRAN, because the Institute’s initial business systems could not produce accurate budget forecasts. Rodger was brilliant, even-handed, and totally honest with all his coworkers, inside the Institute and outside. When Rodger offered an opinion, people listened.

Rodger eventually became truly the “master of Hubble.” More than any other single individual in the world, Rodger knew what made Hubble tick, and knew the systems that supported and controlled Hubble. This was recognized throughout the community.

Rodger was, as so many people know, a private person. But that does not mean that he did not communicate his feelings, his passions, his dedication. Indeed, Rodger and I developed a deep relationship based on total trust. In the first year or two of the Institute, I commuted from Cambridge, usually spending four days of each week in Baltimore. Much of the time, Rodger and I worked in the growing Institute all day, then had dinner together, then worked some more. We did not always

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have deep discussions, but we developed a strong bond, based on a shared understanding of our goals—and I think our personal strengths and weaknesses. We knew that that we could always be honest about work issues, and even personal problems we chose to share. When Rodger and Vicki got together, Rodger felt it was important for me to know, and immediately told me. This was a wonderful, unique relationship. I am so glad that they were there for each other through the years.

I think all people who knew Rodger—it is still hard to not say know Rodger—will agree he was a unique person: his honesty, his comprehensive, encyclopedic knowledge about Hubble, his fierce dedication to technical truth, his ability to engender trust from everyone who worked with him. His imprint on Hubble, on the Institute, indeed on the international research enterprise, and on so many of us as individuals, will last a long time.

“More than any other single individual in the world, Rodger knew what made Hubble tick, and knew the systems that supported and controlled Hubble. This was recognized throughout the community.”

ACS StatusLinda Smith, lsmith@stsci.edu and David Golimowski, golim@stsci.edu

D uring the third extravehicular activity of Servicing Mission 4 (SM4), on 16 May 2009, astronauts John Grunsfeld and Drew Feustel successfully repaired the Advanced Camera for Surveys (ACS), which had failed in January 2007. Through a breath-taking series of

maneuvers, Grunsfeld deftly removed four circuit boards, one by one, from the Wide Field Channel (WFC) CCD (charge-coupled device) Electronics Box (CEB), and replaced them with a new module (CEB-R). He then attached a new low-voltage power supply for the CEB-R to a nearby handrail and connected the new power harnesses. The aliveness test, which followed immediately, showed that the first-ever on-orbit, board-level repair had been successful—the WFC is back in business! The WFC passed its functional test, and the first bias frames showed an even lower read noise than before the failure.

We had hoped that the High Resolution Channel (HRC) might also be restored by powering from the WFC CEB-R. This restoration was not successful, however, probably because the original failure caused a permanent short circuit in a location that could not be bypassed with the CEB-R.

The Solar Blind Channel (SBC), which was not affected by the failure of the CCD circuitry, has been used without interruption since January 2007.

First light for the WFC was achieved on 13 June, when the barred spiral galaxy NGC 6217 (see Fig. 1) was observed as part of a test to measure the cross-talk between CCD amplifiers.

After annealing (heating and cooling) the CCDs to repair hot pixels due to radiation damage, we began a campaign to optimize WFC performance by using the CEB-R’s Application-Specific Integrated Circuit (ASIC) to vary the bias, clock voltages, and data-transmission timing. The results show that the performance of the WFC CCDs under command of the new CEB-R—in terms of read noise, linearity, pixel full-well depth, and amplifier cross-talk—meets or exceeds the performance of the old CEB with the default settings used before January 2007. As expected, the dark current, hot-pixel fraction, and charge-transfer efficiency (CTE) have degraded after 28 months additional exposure to Hubble’s trapped-radiation environment.

The first set of bias and dark reference files, together with a table of the performance characteristics of each amplifier, have been delivered to the Calibration Database System for use in processing post-SM4 ACS data. More details on the performance of

ACS are available at http://www.stsci.edu/hst/acs/documents/newsletters/ACS_WFPC2_STAN_0909/.

In summary, the ACS repair during SM4 has fully restored the imaging and grism capabilities of the WFC. Its performance is equal to or better than that before repair, after adjusting for 28 more months of exposure to radiation. It is clear that ACS/WFC is back and will once again provide spectacular new images and exciting science results.

Figure 1: First-light image of the barred spiral galaxy NGC 6217. The orbital verification program for ACS/WFC ended in mid-July and General Observer (GO) programs have been executing since then.

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COS Delivers Sensitive Ultraviolet SpectroscopyRachel Osten, osten@stsci.edu, for the COS team

T he Cosmic Origins Spectrograph (COS) is Hubble’s third-generation ultraviolet spectrograph. It was installed on Hubble on May 16, 2009, during the third extra-vehicular activity of Servicing Mission 4. COS is designed to perform high-sensitivity, medium- and low-resolution

spectroscopy of astronomical objects in the 1150–3200 Å wavelength range. COS significantly expands the spectroscopic capabilities of Hubble at ultraviolet wavelengths, providing observers with unparalleled opportunities for observing faint point sources of ultraviolet light. The primary science objectives of the mission are the study of the origins of large-scale structure in the Universe, the formation and evolution of galaxies, the origin of stellar and planetary systems, and the cold interstellar medium. The COS near-ultraviolet (NUV) and far-ultraviolet (FUV) detectors have now been released for science, and the early observations illustrate COS’s capabilities (Figs. 1–2.)

The Institute’s COS team, in collaboration with the COS Instrument Definition Team, led by Principal Investigator James Green of the University of Colorado, participated in the on-orbit verification and initial calibration of the instrument. By the end of September 2009, a total of nearly 2800 individual exposures in 415 (259 external) orbits of COS observations had been executed in the process of activating the instrument.

Several early COS programs were dedicated to characterizing the on-orbit performance of the FUV and NUV detectors. The measured FUV dark rate meets expectations, and the NUV dark rate is 11 counts cm-2 s-1, which is about three times lower than pre-launch predictions. Other programs obtained flat-field images and verified the ability to achieve high signal-to-noise ratios.

We are characterizing the on-orbit line-spread function (LSF). The line-spread function quantifies the response of the mirror, grating, and detector to the wavelength of an input photon. On-orbit observations indicate that the LSF has a narrow core with a non-Gaussian contribution extending into wings of many pixels. We will provide the observers with more quantitative information in the near future.

We have performed initial, on-orbit measurements of the sensitivity of the COS detectors. The sensitivities of all FUV modes and detector segments are within 10–20% of the values expected from ground testing. On-orbit measurements with the B segment (short wavelength segment) of the detector with the G140L grating have confirmed some modest sensitivity at wavelengths shorter than 1150 Å, because the reflectivity of the MgF2 coatings is still non-zero in that wavelength range. Assessment of COS sensitivity of this regime will be made available to the user community in updates to the instrument handbook (IHB) and instrument science reports (ISRs).

The measured sensitivities of most modes in the NUV range are within 10–15% of the values predicted from ground tests. Two of the NUV gratings displayed time-dependent sensitivity loss on the ground; initial on-orbit measurements of the efficiencies of these gratings are consistent with pre-launch trends. It is expected that this loss of efficiency will not continue on orbit. Also, the NUV detector suffers from some vignetting when observing external targets, which can decrease the sensitivity by

Figure 1: COS observation of supernova remnant N132D–P3, obtained with the G130M and G160M modes. The full spectrum is shown. Several ionization states of oxygen are observed, and emission from Si IV is detected for the first time near the O IV lines. The oxygen and silicon exhibit a common velocity. A velocity offset of the carbon species suggests that the carbon is spatially distinct from the O-rich knot. The supernova explosion occurred nearly 3000 years ago, and yet the COS spectrum detects material that still has not mixed with interstellar material. The geocoronal lines of H I and O I have been removed. Credit: Kevin France and James C. Green (CASA/University of Colorado).

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COS Deliversfrom page 7

as much as 20% at one edge of the detector. Vignetting is uniform for all three stripes, and the effect is now included in the NUV flat-field reference file.

All the COS target-acquisition modes work as planned, and have demonstrated the ability to center the target to within 10–20 milli-arcseconds. For acquisitions using the bright-object aperture, we now recommend exposing to achieve a signal-to-noise ratio of 60, rather than 40 as originally prescribed.

We are delivering new reference files, updating the IHB, and preparing new ISRs to document the COS instrument as it commences science operations. Updates based on the on-orbit performance of the instrument will be made available through our web pages (http://www.stsci.edu/hst/cos/ ).

Calibration activities will continue through Cycle 17. We will monitor dark frames, sensitivity, internal/external wavelength scales, and NUV imaging performance. Also, we will continue to improve the calibration software and reference files.

Observers who obtain COS data prior to the completion of these on-orbit calibrations should be aware that they may need to revise their analysis once the final performance characteristics are determined. Areas of active investigation and characterization include the COS line-spread function, flat fields, and wavelength solutions. If you have any specific concerns about your COS data, please contact help@stsci.edu with questions.

We expect the Call for Proposals for Cycle 18 to be released on December 4, 2009.

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Figure 2: COS spectrum of absorption from intervening gas clouds along the line of sight towards quasar PKS0405–123. The exposure time was about one-fourth as long—and the signal-to-noise ratio is higher—as other UV spectrographs on the same target. This advantage has enabled the detection of 3–5 times as many lower-density filaments of hydrogen in the cosmic web than previously detected along this line of sight. Credit: Charles Danforth (CASA/University of Colorado), Keith Noll (STScI), James C. Green, Cynthia Froning, Brian Keeney (CASA/University of Colorado).

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STIS Performance after Servicing Mission 4Charles R. Proffitt, proffitt@stsci.edu, Paul Goudfrooij, Michael A. Wolfe, Daniel Lennon, Wei Zheng,

Ralph C. Bohlin, and Alessandra Aloisi

T he Space Telescope Imaging Spectrograph (STIS) had been originally installed in the Hubble Space Telescope in February 1997. On May 16, 2001, the primary side-one package of support electronics failed, but STIS was able to continue operations using the redundant side-

two electronics until August 3, 2004, when an electrical malfunction in a power supply stopped STIS operations. On May 17, 2009, during the fourth EVA of Servicing Mission 4, astronauts Michael Good and Mike Massimino undertook an eight-hour spacewalk and replaced the STIS circuit board containing a failed component. This repair restored the STIS side-two electronics. All three of the STIS detectors are now being used for science observations.

In most respects, after the 2009 repair STIS operates in much the same way as it did prior to the 2004 failure. Most changes are close to what was expected. The degradation of the STIS charge-coupled device (CCD) by radiation damage and the modest changes in optical throughput are consistent with extrapolations of previously observed trends. The biggest surprise is in the dark count rate for the near-ultraviolet (NUV), multi-anode, micro-channel array (MAMA) detector. That dark rate is several times larger than had been expected, and is only slowly decreasing back towards its expected range.

Changes in CCD CTIThe STIS CCD is a 1024 × 1024 pixel, thinned, backside-illuminated Scientific Image Technology

(SITe) CCD, with sensitivity from below 2000 Å up to about 11000 Å. In a space environment, CCD detectors accumulate radiation damage, which over time leads to increasing dark current, more hot pixels, and increased charge-transfer inefficiency (CTI). After twelve years on orbit, the effects of such radiation damage on the STIS CCD have become substantial.

CTI measures the fraction of the charge in a given pixel that is not transferred to the next row during the readout. The CTI is, in practice, always greater than zero because some of the charge is caught in “traps” in the pixel, and left behind—not transferred to the readout amplifier. CTI depends on the amount of charge in the pixel and on how many of the traps are already filled. Losses increase substantially when the source is faint and the background is low. By design, a CCD transfers charge many times along columns before it reaches the readout register. Therefore, even a small increase in CTI can have a large effect on the measured count rate near the center of the detector. For n transfers, the fraction of detected charge will be (1 – CTI)n. In Figure 1, we show how STIS’s measured charge-transfer inefficiency has changed over the years. For very faint sources near the center of the detector, the majority of the counts collected by the detector can easily be lost during readout.

Charge lost during a transfer will often reappear during a later transfer. This can lead to substantial “tails” from bright pixels caused by cosmic rays, or from hot pixels, which can cause considerable noise. Some years ago, to ameliorate this problem new “E1” aperture positions were defined for the long slits of STIS. The new positions place the target near row 900 of the CCD, which is much closer to the readout register and reduces the number of transfers during the readout by about a factor of four. In addition to reducing CTI losses, the new positions substantially reduce contamination by the CTI “tails” of cosmic rays and hot pixels. Another benefit is the noticeably lower dark current near the edge of the detector.

While the calstis software does include an algorithm to correct the extracted flux of a point source spectrum for CTI effects, it cannot restore the lost signal to noise. Therefore, we strongly recommend

Figure 1: Measured CTI values over the history of STIS. Each color gives the results for a different source-count level in units of electrons per pixel along the dispersion direction, but integrated over a box perpendicular to the dispersion.

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using the E1 aperture positions for all but the very brightest or most-extended spectroscopic point sources. Also, while the STIS spectroscopic exposure-time calculator does not currently include correction for CTI effects, the effects can be estimated using an IRAF script available at: http://www.stsci.edu/hst/stis/software/scripts/cteloss_descrip.html/.

Additional information about the STIS CCD CTI and the algorithm for correcting the fluxes of point-source spectra can be found in Goudfrooij et al. (2006 PASP, 118, 1455).

CCD dark currentThe CCD dark current has increased over time due to radiation damage. Since the STIS CCD lacks

a working temperature sensor or controller, the dark current also fluctuates with the temperature. (The CCD housing temperature is used as a surrogate for the unavailable CCD-chip temperature.) Figure 2 shows the dark current scaled to a housing temperature of 18 C as a function of time at both the center of the CCD and near row 900 at the E1 aperture position.

Time-dependent sensitivity changesAll STIS modes have shown wavelength-dependent changes in sensitivity over time. We believe these

changes are due to contaminants on the optical surfaces within STIS. Initial throughput measurements show the post-repair optical throughput is within 2% of values expected from the extrapolation of trends observed in 2004.

NUV MAMA dark count rateThe STIS NUV MAMA, while otherwise performing well, currently exhibits a dark count rate several

times higher than had been expected based on its behavior prior to the 2004 failure of STIS.The NUV MAMA dark count rate is dominated by a phosphorescent glow from the detector window.

Impurities in the window have meta-stable states that are populated by cosmic-ray impacts. These states are depopulated by thermal excitation to states that decay quickly by emitting a UV photon. The rate at which the meta-stable states depopulate is very sensitive to temperature. Therefore, we had expected a temporary increase in the NUV MAMA dark count rate as the excess population of meta-stable states—that had built up over the years that STIS was inactive—cleared out at the higher

STIS Performancefrom page 9

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Figure 2: The measured median dark current in units of e-/pixel/s is shown as a function of time for a position near the center of the detector (right) and near the E1 aperture positions at row 900 (left). The red line shows an extrapolation of the late-2004 values to the current epoch.

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temperature of a fully powered STIS. (The strong temperature dependence also causes the dark rate to vary by a factor of two over several hours.)

The previous behavior of the NUV MAMA dark counts (see STIS ISR 1999-02) had led us to expect an initial dark rate of 2500–3500 counts/s over the whole detector, which should then have declined with an e-folding time of a week or so, reaching the predicted range of between 900 and 1800 counts/s within about a month of the initial detector turn-on. This modeling led to our prediction of a mean NUV MAMA dark rate of 0.0013 counts/s/pixel for Cycle 17.

However, we instead found for the NUV MAMA detector an initial global dark rate of between 9000 and 18000 counts/s, (a mean of 0.013 counts/s/pixel). We suspect that a new group of meta-stable states became populated during the 4.5 years that STIS was inoperative and cold. This new excess dark rate does appear to be declining, but with an apparent time scale much longer than that of the states with which we have previous experience. Initial measurements suggest an e-folding time of about 100 days, but since we do not understand the detailed physics of these new states, or how many different time scales might be involved, the future evolution of the NUV MAMA dark current remains highly uncertain.

While the impact is minimal for most programs observing sufficiently bright targets, observations of targets with a count rate comparable to the background are significantly impacted. For example, with a dark current of 0.0013 c/pixel/s, for an E230H echelle observation at 2300 Å of a source with a flux of 1 × 10-13 ergs/cm2/Å/s, the source count rate in the extraction region would be about 2.5 times higher than the dark count rate, and it would require about 4500 s to reach S/N = 10 per resolution element. However, with a dark current of 0.011 c/pixel/s, the source counts in the extraction region would only be about 30% as large as the dark counts, and it would require over 14,000 s to reach the same S/N. For a target ten times brighter, the required exposure time would only increase by about 30%, from about 330 s to 430 s, to reach S/N = 10. Observers using the STIS NUV-MAMA in TIME-TAG mode will also need to consider the excess dark count rate when calculating the number of photon events expected in order to be able to set the buffer time properly during the instrument readout.

WFC3 CommissioningJohn W. MacKenty, mackenty@stsci.edu

A fter eleven years of design, development, testing, launch delays, modifications, and more testing, Wide Field Camera 3 (WFC3) was launched on space shuttle STS-125 on May 11, 2009. After a heart-stopping moment

when the Wide Field Planetary Camera 2 was reluctant to leave the radial bay of Hubble, installation of WFC3 proceeded smoothly. The instrument passed all of its engineering checkout activities and, after 21 days of waiting for the detector packages to fully outgas, the detectors were successfully cooled to their planned operating temperatures on June 11. Testing, optical alignment, and initial calibration followed (briefly interrupted by a few images of an impact event on Jupiter) with WFC3 performing as well as or better than expected.

Key findings about WFC3 from the commissioning process include (1) the throughput of both channels range from 5 to 15 percent above prelaunch predictions, (2) the near-infrared channel can indeed continue operating inside the South Atlantic Anomaly, and (3) the detector noise levels are as expected from ground testing. As of mid-September, WFC3 is actively conducting science observations and beginning its Cycle 17 calibration program.

Observers and proposers are referred to the “Late Breaking News” section of the Institute WFC3 web site (http://www.stsci.edu/hst/wfc3/), where initial results and several useful, early calibrations are available, such as the geometric distortion files required to run the MultiDrizzle software.

Stephan’s Quintet HST WFC3/IRC F140W

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Webb Flight Structure Delivered

The flight structure for the Webb integrated science instrument module has been delivered to NASA. In the next two years, the science instrument teams will use this structure for ambient and cryogenic testing of the flight instruments, which are now under construction. (Initial testing will use engineering models of the instruments, which will soon be delivered to NASA.) The composite structure was created by Alliant Techsystems (ATK) at its Magna, Utah facility where the Webb Telescope’s backplane is also being assembled. These two structures must hold the science instruments and mirror segments during the rigors of launch and retain their shape and strength as they cool from room temperature to ~40K. (Image credit: NASA, Chris Gunn)

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News from the Multi-mission Archive at Space TelescopeRachel Somerville, somer@stsci.edu, for the MAST team

MAST User Survey and Users Group MeetingIn order to get feedback from our users, MAST conducted a user survey in May–June 2009. We

thank everyone who answered the survey. The results can be viewed at http://archive.stsci.edu/surveyresults/2009/index.html/, and our responses to some of the comments and questions are at http://archive.stsci.edu/surveyresults/2009/response2009.html/.

We also held our annual MAST Users Group (MUG) meeting, on July 9, 2009. The current MUG members are Steve Howell (chair), Mike Crenshaw, Duilia de Mello, Casey Papovich, Evgenya Shkolnik, and Ben Williams. We thank all the MUG members for their service, helpful insights, and suggestions. The presentations from the MUG meeting and the MUG report are available at http://archive.stsci.edu/mug/index.html/.

MAST bibliographic searchMAST has a new tool enabling users to search for papers that have made use of MAST data. You

can modify your search based on mission, author, title words, journal, or year. The MAST-wide search form is available at http://archive.stsci.edu/bibliography/index.html/. A more Hubble-specific version, which also allows you to narrow your search to specific instruments, is available at http://archive.stsci.edu/hst/bibliography/.

Kepler data to be hosted at MASTKepler, a NASA strategic mission, was launched into an Earth-trailing heliocentric orbit on March 6,

2009. It will stare at a 105-square-degree region of the sky in the constellations of Cygnus and Lyra. The goal of the mission is to obtain precise, long-term light curves of up to 100,000 cool stars and to search for periodic signatures of transits of planets as small as the Earth. A secondary objective is to study rapid oscillations of the target stars in order to determine their ages, radii, and chemical compositions. A general overview of the mission and more details about the scientific objectives can be found at the Kepler mission website (http://kepler.nasa.gov/ ). The post-commissioning phase of the mission began on May 12, 2009. Since then, Kepler has monitored the same field in the sky almost continuously and will continue to do so for most of its nominal lifetime of three-and-a-half years.

MAST is very pleased to be hosting the data from the Kepler mission, and to announce that the MAST Kepler website (http://archive.stsci.edu/kepler/ ) is now public. Users may query the 6-million-row Kepler target search form to select potential targets known to be on the CCD detector. They can also query the Kepler input catalog to search through 13 million objects in or near the Kepler field of view.

During its commissioning phase, Kepler monitored over 50,000 stars brighter than V = 13.8 magnitudes as calibration targets. The Kepler science team plans to release the resulting light curves of several thousands of these stars in fall 2009. As the mission proceeds, the team will periodically “deselect” stars as exoplanetary monitoring candidates. As it does so, MAST will provide access to lists of targets and/or data. These data will be announced on the MAST Kepler webpage as they become available. In addition, data for these stars will become available for download through the MAST Kepler data search and retrieval page.

New High-Level Science ProductsHigh-level science products (HLSPs) are community contributed, fully processed (reduced, co-added,

cosmic-ray cleaned, etc.) images and spectra that are ready for scientific analysis. MAST is pleased to announce the availability of several new HLSPs, which can be accessed through the HLSP page (http://archive.stsci.edu/hlsp/index.html/).

The ACS Nearby Galaxy Survey (ANGST)ANGST (PI J. Dalcanton) is a carefully crafted Hubble imaging survey that was designed to establish

a legacy of uniform, multi-color photometry of resolved stars for a volume-limited sample of nearby galaxies. The galaxy sample spans a range of environments, morphological types, luminosities, and star-formation rates. The survey includes new observations with the Advanced Camera for Surveys (ACS), and new Wide Field Planetary Camera (WFPC2) imaging taken after the failure of ACS in January 2006. It is supplemented with archival data. Continued

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MAST Newsfrom page 13

The Space Telescope A901/902 Galaxy Evolution Survey (STAGES)STAGES (PI M. Gray) is a large-area (~0.5 × 0.5 degree), deep survey of the complex Abell

901(a,b)/902 multiple-cluster system at z = 0.165. The Hubble component consists of an 80-tile imaging mosaic in F606W. With multiwavelength data available from COMBO-17, Spitzer, XMM-Newton, GALEX, 2dF, and GMRT, the survey goals included linking galaxy morphology with other properties such as age, star-formation rate, nuclear activity, and stellar mass. The HLSPs available at MAST include the reduced Hubble/ACS images for each of the 80 tiles in the F606W ACS mosaic, as well as postage stamps for all galaxies in the field and the complete output of GALFIT profile fitting. Visit the STAGES homepage http://www.nottingham.ac.uk/astronomy/stages/ for more information about the survey or to download the STAGES master catalog.

Carina NebulaIn 2008, the Hubble Heritage Team obtained WFPC2 mosaic data for NGC 3324 with the [O III]

and [S II] filters (F502N and F673N). This area is adjacent to the large ACS H-alpha survey of the Carina Nebula and other smaller nearby fields. The resulting color-composite image was released in October 2008 to commemorate the 10th anniversary of the team, and the NGC 3324 data have now been released as HLSPs. Max Mutchler and his team are producing HLSPs for the remaining and much larger set of Carina Nebula data, which should be released later in 2009.

Deep Optical photometry of six fields in the Andromeda GalaxyUsing ACS, T. Brown (STScI) and collaborators obtained deep optical images reaching well below

the oldest main-sequence turnoff in six fields of the Andromeda Galaxy. The fields fall at four positions on the southeast minor axis, one position in the giant stellar stream, and one position on

Figure 2: Image from Hubble Heritage release of NGC 3324.

Figure 1: Mosaic of NGC 300 from the ANGST project

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the northeast major axis. The goal of the project was to probe the star-formation history in these various different parts of the Andromeda Galaxy.

The Hubble Legacy Archive—third data release The Hubble Legacy Archive (HLA) is a relatively new resource at MAST. It is designed to

optimize science from Hubble by providing online, enhanced data products and advanced browsing capabilities. The project is a collaboration between the Institute, the Space Telescope European Coordinating Facility (ST-ECF), and the Canadian Astronomy Data Centre (CADC). The HLA contains ACS, WFPC2, and NICMOS images, ACS and WFPC2 source lists, ACS and NICMOS extracted grism spectra, and prototype ACS mosaics. The HLA also provides access to the standard Hubble data products when HLA-enhanced products have not yet been created. Some advantages and features of the HLA include:

• online data that can be downloaded immediately• a footprint service that allows users to determine which data are available in a given region of the sky• composite images (stacked, color, mosaics)• improved absolute astrometry• source lists• extracted spectra from ACS and NICMOS grism data

The third data release (DR3) of the HLA occurred in May, 2009. New data products released in DR3 include:

• NICMOS drizzled combined images • ACS extracted grism spectra for 1235 objects (provided by ST-ECF) • WFPC2 source lists (DAOPhot and SExtractor) • Sample prototypes of ACS multi-visit mosaics

Enhancements to the user interface include:• User position lists accepted in a variety of input formats • Selected datasets (e.g., from clicking on footprints) can be added to cart• Selection of datasets can be used for sorting and filtering (e.g., to show selected data at the

top of the table) • Cart can be used to retrieve both DADS and HLA data products • Cart includes estimated download data volume • GALEX catalog is available for overlay in interactive display • Advanced contrast controls in interactive display can be used to change color balance

For more information, or to access the HLA, visit http://hla.stsci.edu/.

The FUSE archival siteFollowing the end of operations of FUSE (Far Ultraviolet Spectroscopic Explorer ), the FUSE team at the

Johns Hopkins University and MAST personnel have worked together to design a renovated “archival” website, which will provide a long-term home for FUSE data and data products (http://archive.stsci.edu/fuse/ ). The site not only includes access to enhanced data products, but also contains new documentation written specifically for archival users.

GALEX NewsThe Galaxy Evolution Explorer (GALEX ) is a NASA mission using microchannel plate detectors to

obtain direct images in the near ultraviolet (NUV) and far ultraviolet (FUV), with a grism to disperse light for spectroscopy. Since its launch in 2003, GALEX has carried out a series of surveys in the imaging and spectroscopic mode, as well as conducting a guest-investigator program. The GALEX project has released discrete sets of public data—known as GALEX Releases (GRs)—with the latest being GR5. GR5 was substantially augmented in January 2009.

In addition to its standard search forms, MAST has developed a powerful interface to search and browse GALEX data, called GalexView (http://galex.stsci.edu/galexview/). GalexView was recently updated to version 1.4. Users can enter a target name or coordinates and radius, and the graphical interface displays a background image and location of sources in the various GALEX surveys. The source properties are listed in a table below the image. New features include a histogram function, which displays a graphical histogram of a selected column (such as source magnitude).

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Keeping up with MASTWe are constantly improving our interface and making new tools and data available. Would you like to

keep up on MAST news in between Institute newsletters? Here are a few ways to do that:• Read MAST NEWS in the right sidebar of the main MAST webpage, and the separate news bars for the HLA and GALEX. A longer view of the news items can be seen by clicking on the “NEWS” headline.• Read MAST archive newsletters—contact archive@stsci.edu to sign up. (Previous MAST newsletters are archived at http://archive.stsci.edu/archive_news/.)

MAST Newsfrom page 15

Figure 3: Screenshot from the GalexView Interface to GALEX data at MAST.

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The Hubble Metrics and Bibliographic DatabaseJill Lagerstrom (library@stsci.edu), Daniel Apai, Karen Levay, and Elizabeth Fraser

F or nearly two decades, the Hubble Space Telescope has provided astronomers with scientific data from new observations. New knowledge based on the analysis of these observations is

communicated in many ways among astronomers and to the public. The ultimate, official record of research and discovery is the publication of results in peer-reviewed journals.

To assess and help maximize the scientific impact of Hubble, a new metrics team at the Institute—Daniel Apai, Jill Lagerstrom, Karen Levay, and Elizabeth Fraser—identifies and tracks Hubble-based papers in peer-reviewed journals. To qualify, a paper must use Hubble data as part of its scientific analysis. The team is assembling a database comprising approved proposals, refereed publications based on the data, and all papers that cite them. We can use this database to trace and quantify the evolution of astronomical projects from the proposal phase through execution and publication, to their impact on the astronomical literature. This knowledge, in turn, provides useful information for refining science policies, such as strategies for time allocation.

Observatories have traditionally characterized their contributions by counting not only the number of papers they have published, but also the number of papers that have cited them. We refer to the former as “productivity” and to the latter as “impact.” As of September 2009 we have identified more than 8,300 papers, and more than 287,000 citations.

We completed the database for 1998–2008 in August 2009, and our study of it reveals several interesting points. One is the strong demonstration of the increasing role of the Hubble archive (see White, R. L., et al. 2009, in Astro2010: The Astronomy and Astrophysics Decadal Survey, Position Papers, no. 64), served through the Multi-mission Archive at STScI (MAST). Figure 1 shows that approximately half of recent papers that analyze Hubble data use archival data, rather than only observations made by the authors of the paper.

Throughout its history, Hubble’s instruments have been upgraded, replaced, and repaired by five servicing missions. Figure 2 shows the historical productivity of Hubble’s various instruments, including the Fine Guidance Sensor, which has produced exciting results despite not being an official scientific instrument. For almost ten years, Wide-Field Planetary Camera 2 was Hubble’s most productive instrument, up to the installation of the Advanced Camera for Surveys, which provided superior imaging for many projects.

The bibliographic database offers an opportunity to evaluate the impact of proposals across different topics and as a function of program size. The time-allocation committee (TAC) has historically selected a wide range of programs of various sizes, ranging from those that require just a few Hubble orbits to others that require hundreds. Smaller programs generally observe a small number of specific targets, while larger programs are generally designed to create surveys. The analysis of our database shows that the smallest programs receive the highest number of citations per orbit (8 cits/orbit). However, the largest programs, while less productive per unit of telescope time (2 cits/orbit), are the most efficient in producing highly cited data sets.

It is interesting to evaluate the impact of programs observed through allocations of director’s discretionary (DD) time. About 8% of the telescope’s time is allocated by the director, typically for small, high-impact programs, often with a time-critical aspect. Table 1 shows that DD programs, both small and large, are more productive than Guest Observer (GO)

Figure 1: The number of refereed articles per year. “Not archival” denotes guest-observer papers. “AR” denotes papers based on archival data; “Partly Archival” are papers that combined GO and archival data.

Figure 2: Number of refereed publications per Hubble instrument, with important events highlighted.

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programs (0.17 vs. 0.14 papers/orbit). The most striking difference, however, is in the average impact of DD and GO papers: DD papers—both large and small—receive twice as many citations as GO papers! The enhanced productivity and higher impact indicate that the DD program is a very important component of the Hubble time-allocation strategy, likely due to its flexibility and rapid response.

Our database can also tell us something about the Hubble papers produced by the various scientific fields. In Cycles 12 and 13, the largest number of orbits was allocated to studies of galaxies, and this field has consistently been the most productive (per orbit allocated) and highly cited (per paper). Solar

system, which received a smaller time allocation than galaxies (and typically required smaller programs, 3–5 orbits), has been the second-highest category in cits/orbit. Solar-system papers also received the fewest citations on average. Cosmology, in turn, has been the topic in which papers received the highest number of citations on average, but the field is less productive per orbit, requiring 20 orbits for a typical paper.

Our database contains only papers that analyze Hubble data, and does not contain many publications that use

Hubble-derived information less directly. In order to measure Hubble’s broader influence in the scientific literature we also counted additional articles that mention Hubble in the four major journals (Astronomical Journal, Astronomy and Astrophysics, Astrophysical Journal, Monthly Notices of the Royal Astronomical Society ) between 1998 and 2003. Table 2 shows that Hubble instruments influenced at least 21% of major astronomy journal articles published during this time period, of which 8% directly analyze Hubble data, while 13% refer to the telescope in various ways, such as referring to past observations, calling for new observations, or referring to previously published results to provide context for a new scientific discovery.

The historical record tells us how the advent of new Hubble instruments has shaped astronomical knowledge. We look forward to seeing how the newly restored Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph, as well as the new instruments, Cosmic Origins Spectrograph and Wide Field Camera 3, accelerate Hubble’s productivity, impact, and influence on the astronomical literature.

The details of the Hubble bibliographic database and its analyses will be described in a future paper (Apai et al. 2010, in prep.). Visit the Hubble bibliographic database at http://archive.stsci.edu/hst/bibliography/. You can search it to find up-to-the-minute statistics about publications, and a complete description of our methodology for collecting and identifying Hubble papers. We send out a biweekly listing of newly found papers using Hubble data. To receive this notification, please email library@stsci.edu.

Table 1: Comparison of the productivity and impact of the GO and director’s discretionary (DD) programs between Cycle 5 and Cycle 17. All programs are shown in the upper section of the table; programs smaller than 30 orbits are compared in the lower section. The DD programs are slightly more productive than GO programs, but have twice the impact.

All Programs Orbits Papers Citations Papers/Orbits Cits/Orbits Cit/Papers

GO 51,442 7,007 209,133 0.14 4.1 29.8DD 4,323 719 44,970 0.17 10.4 62.5

Prog <30 orbits Orbits Papers Citations Papers/Orbits Cits/Orbits Cit/Papers

GO 22,385 4,807 127,115 0.215 5.68 26.4DD 1,136 374 19,573 0.329 17.2 52.3

Hubble Metricsfrom page 17

Table 2: Number of papers published in the four major journals from 1998 to 2003. “HST papers” denotes papers that use Hubble data for a scientific analysis. “Other HST mentions” denotes papers that mention Hubble in some additional way (referring to published results, calls for more observations, etc.) In total, for this time period, Hubble influences nearly 21% of the articles found in the four major journals.

Journal Total Papers HST Papers Other HST Mentions

ApJ 15,045 10.4% 13.3%MNRAS 6,056 5.4% 15.1%AJ 3,095 19.5% 18.4%A&A 11,878 3.6% 10.6%

Total 36,074 8.1% 13%

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Hubble Fellowship Program NewsRon Allen, rjallen@stsci.edu

The Hubble Fellowship Program supports outstanding postdoctoral scientists whose research is related

to the scientific mission of the Hubble Space Telescope. The research may be theoretical, observational, or instrumental. This program is funded by NASA and is open to applicants of any nationality. The fellowships are tenable at U.S. host institutions of the fellows’ choice, subject to a maximum of one new fellow per host institution per year. The duration of the fellowship is up to three years.

2009 Hubble Fellows SymposiumEach year, the Hubble Fellows present the

results of their research at a symposium at the Institute. The Hubble Fellows Symposia are unique in that they include the latest research, not from just one field, but from all fields in astronomy. They are an excellent opportunity to hear about the latest hot topics and to talk with young experts at work on them. Attendance is open to all in the professional astronomical community.

This year the symposium was held at the Institute from March 9–11, 2009. Regrettably we had to miss the personal participation of four Hubble Fellows who had conflicts; Beth Biller (HF07; IfA), Rachel Mandelbaum (HF06; IAS), Dominik Riechers (HF07; Caltech), and Jay Strader (HF07, Harvard).

The presentations by the Fellows were rounded out with summaries from several scientists at NASA or at the Institute. In particular, we were pleased to welcome the participation of the Institute’s Giacconi Fellows Asaf Pe’er and Alceste Bonanos, as well as Dr. Eric Smith from NASA Headquarters.

The program and recorded video of the symposium are available at: http://www.stsci.edu/institute/itsd/information/streaming/archive/.

Selection of the 2009 Hubble FellowsThe 2009 Hubble Fellow Selection Committee met

at the Institute on January 12–13 to consider the 237 applications that were received by the deadline on November 6, 2008.

This year, at NASA’s request, the Hubble Fellowship Program was generalized to include the scientific goals addressed not only by Hubble, but also by any of the missions in NASA’s Cosmic Origins Program. These missions presently include: the Hubble Space Telescope, Spitzer Space Telescope, Stratospheric Observatory for Infrared Astronomy, the Herschel Space Observatory, and the James Webb Space Telescope. The selection criteria will otherwise remain the same. The number of Hubble Fellowships to be awarded for 2009 was increased to 17, and the selection committee was therefore enlarged somewhat in order to account for the additional workload. The 15-member committee was chaired by Prof. James Bullock (University of California, Irvine). Offers were made, and by mid-February the list of 2009 Hubble Fellows was complete; see Table 1. They will take up their new fellowships in the fall of 2009.

Figure 1: Participants in the 2009 Hubble Fellows Symposium, including fellows who were appointed in 2006, 2007, and 2008, as well as the Giacconi Fellows at the Institute. In the foreground to the left is Hubble Fellow Program Manager, Ron Allen, and to the right is the Institute’s Deputy Director, Mike Hauser.

2009 Hubble Fellow PhD Institution Host Institution

Stephen Ammons UC Santa Cruz 2009 U Arizona

Misty Bentz Ohio State 2007 UC Irvine

Tabetha Boyajian Georgia State 2009 Georgia State

Kevin Covey U Washington 2006 Cornell

Kristian Finlator U Arizona 2009 UC Santa Barbara

Mario Juric Princeton 2007 Harvard

Evan Kirby UC Santa Cruz 2009 Caltech

Adam Kraus Caltech 2009 U Hawaii

Adam Leroy UC Berkeley 2006 NRAO

Daniel Marrone Harvard 2006 U Chicago

Karin Oberg Leiden 2009 Smithsonian

Jose Prieto Ohio State 2009 OCIW Pasadena

Brant Robertson Harvard 2006 Caltech

Lisa Winter U Maryland 2008 U Colorado Boulder

John Wise Stanford 2007 Princeton

Shelley Wright UC Los Angeles 2008 UC Berkeley

Joshua Younger Harvard 2009 Inst. for Advanced Studies

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Institute Participation in the Astro2010 Decadal Survey ProcessRoeland P. van der Marel, marel@stsci.edu, Marc Postman, postman@stsci.edu, and Harry Ferguson,

ferguson@stsci.edu

E very ten years, the National Research Council of the National Academy of Sciences performs a survey of the state and future of astronomy and astrophysics in the United States. One of the goals is to set the priorities for science and investments in the coming decade. The previous

survey was completed in 2000 under the leadership of Christopher McKee and Joseph Taylor. It led, among other things, to a positive recommendation on the scientific potential of the Next Generation Space Telescope, since renamed the James Webb Space Telescope. This year saw the start of the Astro2010 survey, led by Roger Blandford, and organized by the Council’s Board on Physics and Astronomy, in cooperation with the Space Studies Board.

This year it has been a high priority for the Institute to contribute to Astro2010 and assist in the creation of a vision for the future of astronomy in the United States. As one of the country’s leading institutions for optical and infrared astronomical research from space, the science and facilities in this subject area were a prime focus. Nevertheless, Institute astronomers—eight of whom serve on various Astro2010 panels—have a wide range of interests and expertise. As a result, their written contributions covered almost all aspects of astronomy, including ground-based observatories, high-energy observations, theory, computing, technology, infrastructure, and the diversity and nature of the astronomical workforce. Among the large collection of community submissions to Astro2010—including activity proposals and papers on science, the state of the profession, and technology—a total of 83 documents included Institute authors, 29 as first author.

In March 2009, the Institute organized a workshop, sponsored by the Association of Universities for Research in Astronomy, entitled “Beyond JWST: The Next Steps in UV-Optical-NIR Space Astronomy.” The goal was to engage the community in discussing its long-term goals for space-based astronomy and astrophysics. The meeting provided the community with an opportunity to look forward on a 25-year horizon to identify the scientific opportunities enabled by large and very large space telescopes. The 170 registered participants made the workshop quite a success, with lots of fruitful discussion. The workshop program was strongly science based, with topics covering: detection and characterization of exoplanets; the solar system; local galactic neighborhood; star formation and evolution; IGM and chemical evolution of the universe; galaxy formation and evolution; and cosmology: dark matter/lensing/dark energy. There were posters and short summaries on future NASA mission concepts proposals, and also on advanced technological possibilities for future telescopes. A concise summary of the presentations is described in the accompanying article on the workshop by Marc Postman. A longer summary was also submitted to the Astro2010 Survey, and is available at: http://www.stsci.edu/institute/conference/beyondjwst/images/beyond_jwst_summary.pdf/

A consortium of regional astronomy and space-science institutions also hosted an Astro2010 town hall at the Johns Hopkins University ( just across the road from the Institute). The Astro2010 committee had emphasized the importance of diverse, comprehensive input from the astronomical community. Town hall meetings can provide such input, especially on broad research topics that may not be ideally suited to white papers or other forms of input. The meeting was open to the public, and astronomers were encouraged to bring their ideas and opinions. The majority of the meeting was in the form of an open discussion on each of the three major themes into which Astro2010 is organized: science frontiers, infrastructure and state of the profession, and program priorities. There was time also for short, individual “open mike” statements as an additional opportunity for those whose research interests may not have been suitably covered otherwise. Representatives from Astro2010 attended. Afterwards, the organizing committee of the town hall submitted a summary of the inputs received during the meeting to Astro2010.

The scope of the science white papers submitted to the Survey by Institute astronomers spanned all of the five science panels of Astro2010, ranging from planetary systems and star formation to cosmology and fundamental physics. All the white papers submitted to the survey are available through the ADS abstract service. They provide a wonderful review of what is hot and fascinating in contemporary astronomy. As an interesting illustration, Figure 1 shows a graphical representation of the most prominent words in the white paper titles.

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The activity proposals in which Institute astronomers were involved also spanned a large range of topics and wavelengths, though primarily limited to facilities within the scope of the panel on electromagnetic observations from space. A list of all Institute contributions to Astro2010 is available at http://www.stsci.edu/~marel/decadal/sthome.html.

The state of the profession and technology papers submitted by Institute astronomers addressed several high-level infrastructure, technology, and workforce issues. These included the importance of diversifying the next generation of astronomers, using education and public outreach as a key avenue for inspiring and educating the next generation, the high impact of—and expected future demands on—data archives, the growth path for astronomical data-reduction software, and the relative prospects and benefits of ground- and space-based optical observations in the coming decades.

One paper, co-authored with representatives from the Chandra X-ray Center and the Spitzer Science Center, discussed the value of observatory-class missions. It highlights the virtues of a flexible mix of general-purpose capabilities, allowing investigations in a wide range of areas, as exemplified by Chandra, Hubble, and Spitzer. There are few areas of astrophysics that have not been profoundly affected by such facilities. Their continuing contributions—to science, the astrophysics community, and the nation—remain strong after some 33 years of combined service. These “great observatories” continue to serve as a model for what is possible when the astronomical community comes together to create a coherent vision for humanity’s progressive understanding of the Universe.

Figure 1: Graphical representation of the most prominent words in the titles of science white papers submitted to the Astro2010 Decadal Survey. Created with the tools at http://www.wordle.net/.

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CONFERENCE REPORT: Observational Signatures of Black-Hole MergersJeremy Schnittman, schnittm@pha.jhu.edu

W hat happens when the supermassive black holes (BHs) at the centers of merging galaxies spiral together and collide? Will we be able to see an explosion? Will we be able to “hear” the burst of gravitational waves (GWs)? Will the surrounding gas and stars be disrupted,

or even ejected from the galaxy? This past spring, the Institute hosted a conference of an unusually diverse group of astronomers and astrophysicists with the goal of answering these tough questions. Motivated in large part by recent advances in the numerical relativity community, the past couple of years have seen a remarkable number of new papers published on the potential observational signatures of colliding BHs.

According to Einstein’s general theory of relativity, which describes the behavior of gravity in the universe, even the enormous amount of energy released in GWs during a BH merger will not produce any significant electromagnetic signal (i.e., photons). In fact, this is precisely why it is so difficult to directly detect GWs, because they interact so weakly with ordinary matter. At present, much of the best observational evidence for BH mergers is circumstantial: most, if not all, galaxies appear to host supermassive BHs at their centers; galaxy mergers are observed to be relatively common, with most galaxies undergoing at least one major merger during their lifetimes; and almost no galaxies show evidence for the presence of two supermassive BHs, suggesting that when galaxies merge, their central black holes must also merge on a relatively short timescale.

The conference began with a session dedicated to the topic of galaxy mergers in the context of large-scale cosmological simulations, including the relations expected (and observed!) between the galactic nuclei and their central BHs. Moving to smaller time and distance scales, the “merger mechanisms” session addressed one of the oldest questions in the field: how exactly do two supermassive BHs come together to merge following the galaxy merger? Also known as “the final parsec problem,” the difficulty is bridging the gap between classical gravitational interactions with the stars in the galaxy, which cause the two BHs to sink to the central region of the galaxy within about a parsec of each other, to the point at which relativistic gravitational wave losses grow large enough to take over—around a hundredth of a parsec. One of the most promising mechanisms involves massive disks of gas and dust, which provide enormous drag forces on the orbiting BHs, accelerating their orbital decay.

Over the millions of years it takes just to get the two BHs close enough to merge, they will interact strongly (albeit non-relativistically) with the surrounding gas and stars near the center of the galaxy. Furthermore, detailed calculations of the merger itself suggest that during the final plunging orbit when the two black holes become one, the asymmetric emission of GWs can impart a recoil, or “kick,” to the final BH. This could send it flying through the host galaxy at thousands of kilometers per second, dragging with it the

Figure 1: Hubble image of the merging galaxies NGC 4038 and NGC 4039, also known as the “Antennae Galaxies.” Such mergers trigger massive bursts of star formation and likely lead to strong active galactic nuclear activity. Over a period of hundreds of millions of years, the supermassive black holes originally at the centers of each galaxy will spiral together and eventually merge. During the final hour of this merger, an enormous flux of gravitational waves will be emitted. A NASA supercomputer simulation of these waves is shown in the inset. (Images courtesy of STScI and NASA/GSFC)

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nearby material and plowing through anything in its path. In both cases, it seems quite likely that a strong electromagnetic signal would be generated.

One major question addressed at the conference was how to characterize and then detect such a signal. The centers of galaxies are already known for their dynamic and energetic activity, even without the presence of two black holes. How might we distinguish between binary BHs and “regular” BHs? Will the high orbital velocities of the binary expel the surrounding gas, or alternatively, might they actually enhance accretion and the production of energetic particles and radiation? After the merger and resulting kick, will the final BH resemble an active galactic nucleus (AGN)? Again, how might we distinguish between post-merger AGN and normal AGN?

In addition to the numerous talks on direct signatures of BH mergers, there was an entire session dedicated to indirect measurements of BH mergers and evolution. In particular, a number of speakers discussed how one might use observations of BH spin (which, along with mass, completely describes the physical properties of a black hole) to infer its merger history. Finally, the conference concluded with an exciting panel discussion highlighting the future capabilities of a number of major missions planned for the coming decade.

As might be accurately concluded from this brief summary, the subject of BH mergers has many more questions than answers right now. The meeting at the Institute was an important first step in formulating the questions and focusing the direction of the field. Even more important, it was a fantastic catalyst to bring together many astronomers and astrophysicists from a wide range of specialties to share their ideas and stimulate even more questions for the future.

WORKSHOP REPORT: Beyond JWST: the Next Steps in Ultraviolet–Optical–Near-IR Space AstronomyMarc Postman, postman@stsci.edu

O n March 26–27, 2009, over a hundred astronomers from around the nation and the world met at the Institute to discuss future directions in ultraviolet–optical–near-infrared (UVOIR) space astrophysics in the era after

the James Webb Space Telescope. Information about the meeting—the program, list of participants, and videos and electronic versions of all the presentations and posters—can be found at: http://www.stsci.edu/institute/conference/beyondjwst/.

What emerged from this meeting was an inspiring narrative of where modern astrophysics—enabled by advanced observations from space—can lead human discovery.

Space science stands at an exciting and challenging threshold. Within the next two decades NASA could have the capabilities to search for life on exoplanets orbiting other stars, and to observe with unprecedented clarity the complex processes that drive the evolution and structure of galaxies. For the first time in human history, we have within our grasp the ability to unravel how, across the vast expanse of cosmic time, our corner of the universe became a safe harbor for the emergence of life. We may be able to answer the profound question, “Are we alone?”

Observational astrophysics is a photon-limited field. The paradigm-shifting discoveries in the 2010–2030 era will require ever more capable instruments and facilities. The next big steps—both for characterizing extrasolar planets and for pursuing the fields of star and galaxy formation and evolution—require observations at high angular resolution of sources with flux densities as low as a few to tens of nano-Janskys. As hallmarks of this convergence, the key photometric and spectroscopic signatures for the search for life, for founding a comprehensive theory of star formation, and for understanding interactions between galaxies and the cosmic web, all lie in the UVOIR wavelength range 0.1–2.5 microns.

Figure 1: The power of UV spectral diagnostics is shown in this diagram by Seth Redfield (2006). In the study of the local interstellar medium, all but two of the key diagnostic lines are in the UV.

Continuedpage 24

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Beyond JWSTfrom page 23

Science opportunitiesUVOIR region of the electromagnetic spectrum is a window on many fundamental astrophysical

processes. UVOIR measurements have a track record of robust, often unique, diagnosis of the forces and phenomena that govern far-flung astronomical environments, and that control the formation and evolution of a variety of objects. Today’s knowledge of myriad topics—for example, the life-cycle of stars, the appearance and growth of structure in the universe, the physics of jets on many scales, the connection between galactic nuclei and supermassive black holes, the chemistry and dynamics of atmospheres of other planets, and the physics of protoplanetary disks—is largely due to UVOIR observations. The purpose of the “Beyond JWST” workshop was to survey the horizon of science opportunities for the next generation of UVOIR space observatories. Workshop participants agreed

that the most compelling observations 25 years from now will require increased angular resolution, higher dynamic range for image contrast, and better sensitivity over current—or currently planned—facilities in the UVOIR wavelength range.

The following sections offer some highlights and key questions from the workshop, organized by science area. These issues and opportunities are ripe for investigation in the next 20 years. We include representative observations that must await the advanced capabilities of a future era.

The Solar SystemExploration of our Solar System is in a golden age. Planetary orbiters, fly-bys, and landers have

brought spectacular and historic discoveries. But there is still a lot to learn:• How and why do planetary systems form?• How do planets evolve into habitable worlds?• What is the history of life in the Solar System?

Our Solar System provides many “laboratories” where we can search for the answers to these questions in unprecedented detail.

Yet much of planetary science relies on remote sensing with telescopes on—and in—orbit about the Earth. This will continue to be true in the coming decades.

Representative Observations: Understanding Planetary AtmospheresEuropa: Auroral emissions from Europa’s tenuous O2 atmosphere were first detected by Hubble

in the ultraviolet (135.6 nm) with limited S/N and spatial resolution (McGrath et al. 1994). Its heterogeneous distribution suggests a complex atmosphere. Does Enceladus-like venting contribute to the peculiar spatial distribution? Similar or better observations will provide valuable support for the NASA Europa Mission in the 2020s by assisting in the search for endogenic activity.

Pluto: CH4, N2, and CO are currently detected or inferred in Pluto’s thin atmosphere. Models predict C4H2, C6H2, HC3N, and C4N. Their abundances strongly constrain photochemical processes. But these species will not be detectable by the New Horizons spacecraft. The presence of these molecules in Pluto’s

tenuous atmosphere is detectable with a spectrograph capable of sensitive observations in the mid-UV. Hubble sensitivity is marginal. Io: Io has a

complex and variable SO2 atmosphere. It is observable via strong absorptions in mid-UV and Ly-alpha, and emission features in FUV. Spatially resolved mapping of the full disk at multiple epochs

Figure 2: Left: Hubble image of Jupiter following the 1994 impact of comet P/Shoemaker-Levy 9. Center: Mars at perigee in 1999. Right: Uranus with its moon Ariel as seen in 2006. (Image credits: NASA, ESA, Hubble Comet Team, S. Lee/University of Colorado, Jim Bell/Cornell University, Mike Wolff/Space Science Institute, L. Sromovsky/University of Wisconsin, Madison, H. Hammel/Space Science Institute, and K. Rages/SETI).

Figure 3: Oxygen emission from Europa’s atmosphere as mapped by Hubble at ultraviolet wavelengths (McGrath et al. 2004).

Figure 4: A mosaic image of Io composed of data from the Voyager 1 and Galileo spacecraft. (Image Credit: NASA, JPL).

Figure 5: Image sequence of Saturn and its aurorae taken by Hubble in 2004. (Image Credit: NASA, ESA, J. Clarke/Boston Univ., Z. Levay/STScI)

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is possible, but Hubble’s sensitivity is marginal, making it inefficient. Improved UV sensitivity will greatly improve our understanding of Io’s complex interaction with the Jovian magnetosphere.

Giant-planet aurorae: Combined Hubble and Cassini observations are very effective in revealing physics behind Saturn’s aurora. UV imaging and spectroscopy of aurora in outer gas giants is essential for tracking the influence of solar wind across the Solar System. To further our understanding of the influence of the solar wind on the outer Solar System, we will need UV imaging and spectroscopic capabilities into the 2020 decade.

The Search for Life in the Galaxy“Four hundred years after Galileo’s

discoveries via the first astronomical use of the telescope, the world’s astronomers are once again using powerful new instrumentation to make startling discoveries of and about new planets, quite literally other worlds, which promise to once again transform our understanding of the nature of the Earth and of life’s and humanity’s places in the cosmos.” - Ed Turner, March 2009

Representative Observations: Characterizing Exosolar Terrestrial PlanetsIf one can sufficiently suppress the light from the star about which an exoplanet orbits, then optical

and NIR broadband photometry and low-resolution spectroscopy can reveal much information about the planet’s atmospheric composition, habitability, surface geography, potential biological activity, rotation period, and weather patterns.

Characterization of exoplanets in the habitable zones of long-lived stars requires a space telescope that has the sensitivity, high-contrast imaging performance, and the angular resolution (i.e., inner working angle) to study tens of systems. In Figure 8, the blue bars show the total number of such stars for which R = 70 spectrum of an Earth-twin could be obtained in <500 ksec. The red bars show the number of such stars that could be observed 3× each in a 5-year mission without exceeding 20% of total observing time available to community. These numbers assume every known F, G, or K star within 30 parsecs has an Earth-like planet in

Figure 6: Absorption features from O3, O2, and H2O dominate the reflected visible and near-IR spectrum of Earth (Turnbull et al. 2006). These signatures readily distinguish the Earth from the other planets in the Solar System as a site where biological activity is occurring. (Image of Earth from Apollo 17 Crew, NASA.)

Figure 7: Left: Model of the variation in the broadband optical (BVRI ) reflectivity as a function of time for Earth (Ford et al. 2003). Variations of up to 30% are due to changes in albedo as the planet rotates, putting different mixtures of land and sea into the observer’s line of sight. Right: Variations in the intensity of polarized visible and NIR light (Figure credit: E. Turner).

Continuedpage 26

the HZ. However, the fraction of stars with Earth-like planets may be considerably less than 1, arguing in favor of larger telescopes as the number of accessible systems scales approximately as the cube of the aperture size.

• Are there other worlds which resemble the earth?• If so, how common are they? • How are they similar? How are they different?• Are any of them life-bearing?• If so, what forms does alien life take?

The Local Interstellar MediumThe region of space within 250 pc of

the Sun is a rich environment. It contains ~10 million stars, hundreds of known exoplanets, a broad range of interstellar gas phases from very low (20 K) to very high (107 K) temperatures, several star-forming regions, and dozens of resolved stellar debris disks. Galactic stellar and interstellar science programs in the future will likely focus on understanding the interactions between all these components.

Key directions for future ISM and stellar research include:• How do stars and their planets interact with the interstellar medium

that surrounds them?• How does the local interstellar medium modulate cosmic-ray flux?• How does stellar activity alter habitability and life?

Representative Observations: Heliopause and Exo-heliospheresBetter understanding of the interaction between the ISM and exo-heliospheres (astrospheres) is

an important focus for future studies. It will help us understand the role the ISM plays in affecting the Habitable Zones around stars. Astrosphere structure can be determined from very high resolution Ly-alpha absorption spectroscopy. Such observations allow us to study both the structure of the astrospheres around nearby stars and our local heliosphere.

The Assembly of GalaxiesResolved stellar populations are cosmic clocks that can

be used to trace the evolution of chemical abundance, stellar mass, and kinematics as functions of time and position within a galaxy. This information provides critical verification of and constraints on models for both star and galaxy formation.

The key questions that can uniquely be addressed through the study of resolved stellar populations in both the Milky Way and other galaxies are:

• What is the formation time and assembly history of galaxies?• How much energy is input into the ISM from stellar birth and death?• Does the initial distribution of stellar masses depend on environment?• What are the masses of undetected transient precursors?

Figure 8: Histogram shows the number of spectral type F, G, K star systems for which an SNR = 10 spectrum of an Earth-twin in the Habitable Zone could be obtained as a function of space-based telescope aperture size (Postman et al. 2009).

Beyond JWSTfrom page 25

Figure 9: Map of the local Solar Neighborhood from Lallement et al. (2003).

Figure 10: The heliosphere is defined by the LISM properties (e.g., plasma temperatures, H I gas densities). The LISM modulates galactic cosmic-ray (CR) flux on solar system bodies (e.g., Florinski & Frisch 2003). The CR flux can influence cloud cover, lightning intensity, and surface mutation rates (Scalo et al. 2007). The CR flux can also alter ozone and methane biomarker strength on fairly short timescales (Grenfell et al. 2007). The structure of the heliosphere is easily altered by ISM-induced compression.

Figure 11: Excess UV Ly-alpha absorption due to the hydrogen “walls” from both our heliosphere and the astrosphere of a nearby star encodes information on the properties of the stellar wind, magnetic field, and exoplanetary cosmic-ray field (Wood 2004).

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Representative Observations: Star formation histories beyond the Local GroupThe accuracy with which a spatially resolved star-formation history (SFH) can be reconstructed

depends critically on how many phases of stellar evolution can be detected. The most accurate reconstructions require detection of individual stars on the giant branch, as well as individual dwarf stars, like the Sun, near the turn-off of the main sequence.

If both blue and far-red broadband photometry is available to measure the stellar color-magnitude relation, the degeneracy between metal abundance and age can be broken, enabling an accurate SFH to be measured and enabling individual components of a galaxy to be “tagged” by age and metallicity.

To perform such observations beyond the Local Group—essential for accessing the full range of star-forming environments—one needs a large UV-Optical space telescope. The circles in Figure 15 show the distance out to which a space telescope of the indicated aperture can obtain SNR = 5 V- and I- band photometry down to solar analog stars in 100 hours of exposure time. The 8-m and 16-m telescope limits assume a diffraction limit at 500 nm.

Figure 12: Stellar populations in M31 as revealed through Hubble observations (center and right). (Images courtesy: T. Brown/STScI)

Figure 13: NGC 300 as seen with the Hubble/ACS. (Image courtesy: J. Dalcanton/University of Washington)

Figure 14: A solar analog star in M31 as seen in an HST/ACS image. (Image credit: T. Brown/STScI)

Figure 15: The projected galaxy distribution over 24 Mpc region centered on the Milky Way Galaxy. Giant Ellipticals are denoted by orange ovals, giant spirals by blue swirls, and dwarf galaxies by green dots. (Image credit: T. Brown/STScI)

Continuedpage 28

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The Cosmic WebMost of the matter in the Universe is located in intergalactic space outside

of galaxies. Understanding how gas in the intergalactic medium (IGM) gets into galaxies, and how galaxies respond to inflow, lies at the heart of understanding galactic evolution. Depending on the mass of the galaxy halo, infalling gas may be shocked and heated, or accrete in cold mode along narrow filaments. Gas can also be removed from galaxies via tidal and ram pressure stripping, or during the accretion of gas-rich dwarfs onto giant galaxies.

Metal-enriched gas introduced into the IGM by these processes will be dynamically cool. All of these accretion and gas removal theories have observational consequences (see Figure 18) that can be tested if the distribution of gas in the cosmic web around galaxies can be characterized through UV absorption and emission line spectroscopy. The key questions are:

• How is intergalactic matter assembled into galaxies?• To what degree does galaxy feedback regulate and enrich the IGM?• Where and when do these processes occur as a function of time?

Representative Observations: Mapping the IGM–Galaxy InterfaceThe observational challenge is to probe a suitably large number of background

sources and with enough diagnostic power (i.e., spectral resolution) to identify and characterize the processes at work at the IGM–galaxy interface (regions within a few hundred kpc of a galaxy). Dramatically increased absorption-line sensitivity at UV and optical wavelengths is crucial for reaching the required background source densities. There are ~100 quasars per square degree that are brighter than a GALEX FUV flux of 24th magnitude. At this sampling density, one can select sight lines next to thousands of examples of any common galaxy, group, or cluster, yielding a high-resolution map of the gas

and metals surrounding these structures. One will also want to systematically target individual nearby galactic coronae and groups of galaxies, for which it would be possible to observe the production sites of heavy elements (star-forming regions, SNe, emission nebulae), follow the processes by which the elements are transported within galaxies, and trace the expulsion of metals into the IGM.

Gravitational LensingThe images of galaxies lying behind foreground galaxies

and clusters of galaxies can be significantly distorted due to gravitational lensing.

The amplitude of the distortion, and the number of “multiple images” of a background source produced, provide fundamental constraints on the distribution of matter

in the foreground objects. This, in turn, allows the mass profile of the foreground “lensing” object to be derived with unprecedented accuracy. In the case of strong lensing, usually seen in the direction of massive galaxy clusters, the lensing signatures also provide unique constraints on cosmological parameters and on the structure of very distant background galaxies. The highly stable, diffraction-limited imaging that an optical space-based telescope provides on moderately wide angles (3–10 arcminutes) enables us to address these key questions:

Figure 16: Image courtesy: K. Sembach/STScI, M. Shull/University of Colorado.

Figure 17: Slice through the dark-matter distribution as modeled by the Millenium Simulation Project, MPIA.

Beyond JWSTfrom page 27

Figure 18: IGM gas temperature distribution for cosmological models with and without supernova feedback (Cen & Ostriker 2006).

Figure 19: With space telescopes having apertures in excess of eight meters, one could also use multiple quasars and distant galaxies as background continuum sources to dissect the gas distribution in fields known to have galaxies and gas at the same redshift.

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• How is dark matter distributed on scales of 10 kpc to 5 Mpc?• What is the link between x-ray gas and dark matter?• What is the distribution of dark matter halo masses and radii?

Representative Observations: Precision Substructure MappingThere are two key science goals from detected strong lensing in clusters: (i) substructure mapping and

(ii) constraints on dark energy from multiple sets of multiple images. For both these applications, high

angular resolution is key as the accuracy of the derived substructure map and the constraints on dark energy both scale (non-linearly) with the number of multiply-imaged systems that can be detected (as shown in Figure 21).

While adaptive optics systems on large ground-based telescopes will likely produce intermediate Strehl ratios in the NIR over 1 or 2 arcminutes, one requires very stable, ~10 milli-arcsec point-spread functions on scales of 5–10 arcminutes from a space-based optical telescope to make the next major leap in studying sub-galactic scale structure: detection of hundreds of multiple images of background galaxies.

The deep Hubble/ACS image of Abell 1689 has about 100 sets of multiple images. This yields a mass map that has a resolution of 0.6 arcsec, which translates to a lower mass limit on the detected sub halos of 2 × 1011 Msun. The next frontier requires us to improve this limit downwards by at least one order of magnitude (to see if there is a substructure “crisis” in LDCM on cluster scales). This requires detecting ~1,000 sets of multiple images. Such capability requires a five to tenfold improvement in angular resolution in the optical band over that available with Hubble.

Figure 20: Gravitational lensing distorts the images of galaxies lying beyond a large mass like a cluster of galaxies. Images here show Hubble observations of lensing in Abell 2218 (top, A. Fruchter), CL2244–02 (center, P. Natarajan), and CL0024+16 (bottom; M. Jee). (Image Credits: NASA, ESA)

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Figure 21: High angular resolution is key as the accuracy of the derived substructure map and the constraints on dark energy both scale (non-linearly) with the number of multiply-imaged systems that can be detected (Coe 2009).

Continuedpage 30

Requirements and technologies for future UVOIR space astronomy missionsThe table below summarizes the range of high-level scientific requirements that we will need to address

the many fundamental questions identified during the course of the workshop. A consensus appeared to emerge amongst the workshop participants for a) continued access to UV wavelengths, b) high angular resolution coupled with high spectral resolution in the UV, c) moderately wide-field (4–8 arcminutes), high angular resolution imaging over the full UVOIR wavelength window with a very stable point-spread function, d) high-contrast (10-10) optical and NIR imaging to within ~50 mas of nearby stars to conduct direct detection and characterization of exoplanets.

SummaryUVOIR astronomy has a promising future if astronomers

think boldly about where the next frontiers lie in this rich field. The most exciting of these frontiers involve resolving sources on or below angular scales of 20 milli-arcseconds, obtaining very high-resolution UV and blue optical spectra on similarly small angular scales, and obtaining photometry and modest resolution spectroscopy of nano-Jansky sources at signal-to-noise ratios of ~10 across the 0.1−2.5 micron wavelength range.

Many of these challenging requirements demand large apertures in space—apertures of at least 8 meters in diameter and, by the end of the 2020 decade, up to 20 meters. Incremental progress in telescope aperture is not compelling, so radical advance is needed. Fortunately, the technology needs of several communities are aligning to make large space-based optical systems affordable.

As we have seen with the Hubble, Chandra, and Spitzer Space Telescopes, NASA’s Great Observatories have the ability to deliver much more than unique forefront science to

a broad community of scientists. They also have the demonstrated capability to captivate the public and inspire school children across this nation. Our community, in partnership with NASA and industry, once again needs to step up to the challenge of inspiring the nation as we seek to understand the origins of life and the cosmos.

Beyond JWSTfrom page 29

Figure 22: Mass map of cluster CL0024+16 at z = 0.40 based on a sparse-sampled survey using WFPC2 on the Hubble Space Telescope (Treu et al. 2003).

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Science Case Field of ViewWavelength Coverage (microns)

Sensitivity Angular Resol.Spectral Resol.

(R = λ / λ ∆)Technologies

Atmospheric chemistry & dynamics of outer solar system bodies

50” 0.11–2.40SNR = 20–50 at

R = 104 in FUV for 20 AB mag

<0.02”R = 10,000 adequate, R = 30,000 desired

High-efficiency solar-blind detectors, large-aperture UV optics

Characterization of Earth-mass exoplan-ets in Habitable Zone

<10”0.65–1.10 adequate,0.30–2.40 desired

SNR = 10 at R = 70 for V = 30

point source<0.03”

R = 5 toR = 100

Very high-contrast coronagraph or exter-nal occulter, stable wavefront control with large aperture, photon counting detectors

Properties of Local interstellar medium and astrospheres

<20”0.11–0.90 adequate,0.10–1.70 desired

Need high dynamic range plus SNR = 100

for R = 105, V = 14 ~0.1” Up to R = 50,000

High-efficiency UV detectors and coat-ings, high-resolution spectrograph

Star formation in the full range of galactic environments

4–8 arcmin0.35–1.00 adequate,0.11–1.70 desired

SNR = 5 for broad-band imaging of

V = 35 point source<0.016” R = 5 for imaging

Large-aperture space telescope that is diffraction limited at 0.5 microns

The role of the IGM in galaxy evolution

1–2 arcmin0.10–0.30 adequate, 0.10–1.20 desired

SNR = 10 at R = 20,000 in FUV,24 AB mag source

0.01”– 0.10” R = 20,000 to 50,000

High-efficiency UV detectors and coat-ings, photon-counting detectors

The Space Telescope–European Coordinating Facility publishes a newsletter which, although aimed prin-cipally at European Space Telescope users, contains articles of general interest to the HST community. If you wish to be included in the mailing list, please contact

the editor and state your affiliation and specific involvement in the Space Telescope Project.

Richard Hook (Editor)

Space Telescope–European Coordinating FacilityKarl Schwarzschild Str. 2D-85748 Garching bei MünchenGermanyE-Mail: rhook@eso.org

ST-ECF Newsletter

The Institute’s website is: http://www.stsci.eduAssistance is available at help@stsci.edu or 800-544-8125. International callers can use 1-410-338-1082.

For current Hubble users, program information is available at:http://www.stsci.edu/hst/scheduling/program_information.

The current members of the Space Telescope Users Committee (STUC) are:

Mario Mateo (chair), U. of Michigan, mmateo@umich.edu

The Space Telescope Science Institute Newsletter is edited by Robert Brown, rbrown@stsci.edu, who invites comments and suggestions.

Contents Manager: Sharon Toolan, toolan@stsci.eduDesign: Melissa Martin, mmartin@stsci.edu

To record a change of address or to request receipt of the Newsletter, please send a message to address-change@stsci.edu.

Mark Dickinson, NOAO

Sarah Gallagher, U. of W. Ontario

Jim Green, U. of Colorado

William Grundy, Lowell Obs.

David Koo, UCSC

Lori Lubin, UC Davis

Robert O’Connell, U. of Virginia

Goran Ostlin, Stockholm U.

Elina Tolstoy, Kapteyn Astr. Inst.

Tommaso Treu, UCSB

Todd Tripp, U. of Massachusetts

31

Contact STScI:

AcknowledgementsThis summary was prepared with significant contributions from the following workshop participants:

Alessandra Aloisi, Daniel Apai, Tom Brown, Dan Coe, Julianne Dalcanton, Mauro Giavalisco, Heidi Hammel, Jason Kalirai, Matt Mountain, Priya Natarajan, Marc Postman, Seth Redfield, David Schiminovich, Mike Shull, Ken Sembach, Dave Soderblom, Jason Tumlinson, Ed Turner.

The organizing committee wishes to thank the Association of Universities for Research in Astronomy (AURA) Inc. and NASA’s Goddard Space Flight Center for providing funding to support this workshop.

Contents:Servicing Hubble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

The Master of Hubble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

ACS Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

COS Delivers Sensitive Ultraviolet Spectroscopy . . . . . . . . . . 7

STIS Performance after Servicing Mission 4 . . . . . . . . . . . . . . 9

WFC3 Commissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Webb Flight Structure Delivered. . . . . . . . . . . . . . . . . . . . . . 12

News from the Multi-mission Archive at Space Telescope . . . . 13

The Hubble Metrics and Bibliographic Database . . . . . . . . . 17

Hubble Fellow Program News . . . . . . . . . . . . . . . . . . . . . . 19

Institute Participation in the Astro2010 Decadal Survey Process . 20

Observational Signatures of Black-Hole Mergers . . . . . . 22

Beyond JWST: the Next Steps in Ultraviolet–Optical–Near-IR Space Astronomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Contact STScI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Calendar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

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Cycle 17 STUC (STScI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–13 November 2009Multi-cycle Treasury deadline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 November 2009Release of Cycle 18 Call for Proposals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 December 2009Multi-cycle TAC (STScI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7–8 January 2010AURA Board (La Serena, Chile) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1–4 February 2010STIC (STScI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–10 February 2010JWST SWG (Washington) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17–18 February 2010Cycle 18 Proposal deadline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 February 2010Young Women Science Forum for Middle and High School Girls (STScI) . . . . . . . . March 6, 2010AURA Board (Annapolis) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21–22 April 2010Cycle 18 Panel and TAC Meetings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17–21 May 2010STIC (Paris, France). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21–22 June 2010JWST SWG (Edinburgh, Scotland) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14–15 July 2010Science with Hubble III (Venice, Italy) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11–14 October 2010

Calendar