Science Goals and AO for the TMT

TMT.PSC.PRE.09.031.REL01 1

Jerry NelsonUniversity of California at Santa Cruz

Adaptive Optics for Extremely Large TelescopesParis, 2009June23

Science Goals and AO for the TMT


Outline

Project IntroductionTelescope overviewScience-based metricsTMT key featuresMajor science goalsScience Instruments


Project Introduction

Time line– 2004 project start, design development– 2009 preconstruction phase– 2011 start construction– 2018 complete, first light, start AO science

Partnership– UC– Caltech– Canada– Japan– NSF?– Others?


Telescope Overview

Tensional members

M2 hexagonal ring

M2 support tripod

M2 support columns

Elevation journal

M1 cell Azimuth truss

Azimuth cradle

M2 structural hexapod

LGSF beam transfer

LGSF launch telescope

Nasmyth platform

Laser room


TMT Optical Design:Ritchey Chrétien

M1 Parameters – ø30m, f/1, Hyperboloid

k = -1.000953– Paraxial RoC = 60.0m– Sag = 1.8m– Asphericity = 29.3mm (entire M1)

M2 Parameters– ø3.1m, ~f/1, Convex hyperboloid,

k = -1.31823– Paraxial RoC = -6.228m– Sag = ~650mm– Aspheric departure: 850 m

M3 Parameters– Flat – Elliptical, 2.5 X 3.5m


Segment Size


Primary Mirror Control System (M1CS)

The M1CS, with the Alignment and Phasing System, turn the 492 individual segments into the equivalent of a monolithic 30 meter diameter mirror.TMT control strategy is an evolutionary improvement on the successful strategy used at the two Keck Telescopes.

SSA prototype with dummy segment


M1CS off: 223 nm RMS

M1CS on: 14 nm RMS

M1 surface error from wind disturbance

M1CS OverviewM1CS maintains the overall shape of the primary mirror

– Attenuates gravity, temperature, wind, and vibration disturbancesThe primary mirror is aligned and phased using the Alignment and Phasing System (APS) every 4 weeks or after a segment exchange.

– Look up tables are used in between calibration runsM1CS controls the global shape of the M1 using segment-mounted edge sensors and actuatorsReal time “On-instrument Wavefront Sensors” (OIWFS) measurements or AO system offloads will augment the static look up tables built using APS data


Science-based Metrics

We use the time needed to make an observation as our metric– Generally assume that we are observing point sources– Generally assume the sources are background limited (most

photons come from background, rather than source)– In detail this is based on King’s paper that shows

For these assumptions we get

This is true for seeing-limited or diffraction-limited observations

€

point source sensitivity (PSS) ~ 1/equivalent noise area ~ PSF2∫ (θ)dθ

€

PSS ~ 1t

~ area * throughput(background/solid angle) * (image solid angle)


Science Merit Function

For seeing-limited observations – PSS ~ D2/image diameter2

For diffraction-limited observations– image solid angle varies as 1/area, so we get the well known

PSS~D4 rule– For finite Strehl, the signal strength is reduced by S, but the

background is not reduced, so one gets PSS~S2 where

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Strehl = S = e−σ 2

and σ is the wavefront error in radians


Reflectivity, emissivity, throughput

Clearly we want the highest possible reflectivity of our optics– Obvious, since PSS ~ throughput– In the visible r ~ 0.9, so for 3 mirrors, net throughput ~ 0.73– But, as important, thermal emission from the warm optics can

increase the IR background, particularly in K band– When the IR sky is dark (between OH lines) the telescope

emission can be the dominant background source– Background ~ (# warm mirrors)*(1-reflectivity)

So it can be VERY important to minimize the number of warm mirrors between the target and the IR instrument


Blackbody Flux vs wavelength (various T's)

1.E+06

1.E+07

1.E+08

1.E+09

1.5 1.7 1.9 2.1 2.3 2.5

Wavelength (µm)

Photons/s/arcsec2/µm/TMT

5°C0°C-5°C-10°C-15°C-20°C-25°C


Thermal backgrounds

Previous graph shows the blackbody fluxCooling the optic by ~ 30° reduces the flux in this wavelength region by a factor of ~ 15Below ~ 2µm the flux is lower than natural backgroundsThese fluxes are multiplied by the mirror emissivities and the number of mirrors

Observatory created backgrounds– Three ambient temperature telescope mirrors (M1, M2, M3)– NFIRAOS science path

1 ambient window5 cold mirrors1 cold beam splitter1 cold window


K band thermal background

In the near IR, only K band will see significant thermal flux from telescopeTelescope– 3 mirrors at 1.5% emissivity each– Segment gaps 0.5%– Net background ~ 0.05*ambient blackbody flux

NFIRAOS– Net throughput 85%, so emissivity ~ 0.15– Cooling 30° reduces flux by a factor of ~ 15, so – Net added background ~ 0.01*ambient blackbody flux


Field of View

For many science programs larger field of view is useful– Multiple targets– Complex targets (galaxies, etc)– Astrometry where reference objects are needed

Seeing-limited unvignetted 15 arcmin FoVAtmospheric angular anisoplanatism limits the correctable field of view for AO– One must measure the atmosphere over a sufficient volume to

know what the angle dependent correction needs to be– With lasers, one must do tomography to get this information– One must have multiple deformable mirrors to make the added

correction


Impact of multiple deformable mirrors

More DM’s allow greater 3-d fidelity of atmospheric correction, improving correction over larger field of view

Strehl Ratio

Off axis angle (arcsec)

Wavelength 0” 6” 12” 18”

J 1 DM 0.56 0.42 0.21 0.07J 2 DM 0.60 0.60 0.58 0.51

H 1 DM 0.72 0.61 0.40 0.21H 2 DM 0.75 0.75 0.73 0.70K 1 DM 0.83 0.75 0.60 0.41K 2 DM 0.85 0.85 0.84 0.81


TMT design path

30m diameter telescopeHigh reflectivity opticsOnly 3 reflections to science instruments or NFIRAOSNFIRAOS cooled by 30° to reduce thermal emissionNFIRAOS is initial AO system and can feed 3 instFor AO, two DM’s for increased field of viewFor AO, large sky coverage enabled by using 3 partially corrected natural stars (focus, tip, tilt) with 6 LGS15 arcmin unvignetted field of view for seeing-limitedAll instruments always available in < 10 minutes


Nasmyth Configuration: First Decade Instrument Suite

TMT GCAR, April 2009 18

/IRMS


NFIRAOS MCAO has better performance than current systems

Strehl Ratio Band SRD (120 nm) Baseline (177

nm) Baseline + TT

R 0.313 0.080 0.052 I 0.411 0.145 0.105 Z 0.566 0.290 0.236 J 0.674 0.424 0.366 H 0.801 0.617 0.569 K 0.889 0.774 0.742

Dual conjugate AO system– Order 61x61 DM and TTS at h=0 km– Order 75x75 DM at h=12 km

– Better Strehl than current AO systems (e.g., Keck ~280-300nm WFE)

Completely integrated system Fast (<5 min) switch between targets

>50% sky coverage at galactic poles (w/<2mas TT error)

IRIS

IRMS (NIRES)

(WIRC)

NFIRAOS


• Nature and composition of the Universe• Formation of the first stars and galaxies• Evolution of galaxies and the intergalactic medium• Relationship between black holes and their galaxies• Formation of stars and planets• Nature of extra-solar planets• Presence of life elsewhere in the Universe

TMT: Key Science


Science Drivers for large O/IR Telescopes:3 Basic Types

Science that you know you want to do now, but have discovered to be out of reach through experience on 8-10m telescopes.

– These tend to be what is written in “design reference mission” or “science case” documents

Solving problems we do not even know about yet – Thinking about “capability space”, or “discovery space”, rather than specific

science cases– Some intuition is necessary- where will the surprises be, what will we need to

follow them up?Supporting roles and “complementarity” with other facilities on ground, in space.

– Harder to make such roles sound exciting/compelling… BUT next-generation O/IR telescopes will play key role in supporting ALMA, JWST, CCAT, LSST, IXO (CON-X), ZEUS, etc.

– While many other facilities may not publicly admit that they “need” large O/IR telescopes on the ground (for the same reason), in fact, history suggests that they will.


TMT Detailed Science Case

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•~100 page summary of TMT science case (David Silva, editor), completed and posted publicly in October 2007. (http://tmt.org)•Developed with AURA/NOAO as full partner (US community interests accounted for). •Includes science cases developed by instrument feasibility study teams•From fundamental physics and cosmology, to galaxy and structure formation, to extra-solar planets, to solar system studies.

http://tmt.org/

http://tmt.org/

http://tmt.org/


Key TMT features for Science

30m, f/1 primary, RC telescope, ~20’ field– 30-m is a judgment about the proper balance between science benefit, cost,

technological readiness, and scheduleFilled aperture, 492 1.44m segments– produces a more concentrated point spread function (PSF), improving signal-

to-noise ratios and easing data analysis Integrated AO systems, including Laser Guide Star (LGS) facility– MCAO, MOAO, GLAO, MIRAO, ExAO – Sensitivity: D4 advantage for background-limited point sources with AO

Wavelength range: 0.31 - 28 microns (entire UV-mid-IR)Spatial resolution: 0.007” at 1 micron, 0.014” at 2 micronsInstruments on large Nasmyth platforms, addressed by articulated tertiary– Rapid switching between targets with different instruments (< 10 min)– (Rapid target acquisition: time between targets < 5 min)


SAC Instrument Prioritization

Desire to fund first-light instrument suite out of cost-capped construction budgetDiscovery space: largest gains in broadest range of science in the near-IR (0.8-2.5 microns)@diffraction limit

– IRIS: IFU+diffraction limited imager– IRMS: multiplexed faint object spectroscopy in the near-IR -- leverages investment

in facility MCAO system. Ability to perform guaranteed high-priority science we can think of now

– WFOS– PFI very focused, but very powerful (GPI as a pathfinder...)– HROS workhorse capability, strong science case

Raw gains in sensitivity (D4) over existing or planned facilities, well defined science

– MIRES (mid-IR echelle)– NIRES (near-IR echelle)– WIRC (wider field diff. limited imager)


Instrument Spectral Resolution Science Case

Near-IR DL Spectrometer & Imager(IRIS)

~4000

Assembly of galaxies at large redshift Black holes/AGN/Galactic Center Resolved stellar populations in crowded fields Astrometry

Wide-field Optical Spectrometer

(WFOS)1000-5000

IGM structure and composition 2<z<6 High-quality spectra of z>1.5 galaxies suitable for measuring stellar

pops, chemistry, energeticsNear-field cosmology

Multi-slit near-DL near-IR Spectrometer

(IRMS)2000 - 5000 Near-IR spectroscopic diagnostics of the faintest objects

JWST follow-up

Mid-IR Echelle Spectrometer & Imager

(MIRES)5000 - 100000

Physical structure and kinematics of protostellar envelopes Physical diagnostics of circumstellar/protoplanetary disks: where and

when planets form during the accretion phase

ExAO I(PFI)

50 - 300 Direct detection and spectroscopic characterization of extra-solar planets

High Resolution Optical Spectrograph

(HROS)30000 - 50000

Stellar abundance studies throughout the Local Group ISM abundances/kinematics, IGM characterization to z~6 Extra-solar planets!

MCAO imager(WIRC)

5 - 100 Precision astrometry Stellar populations to 10Mpc

Near-IR, DL Echelle(NIRES)

5000 - 30000 Precision radial velocities of M-stars and detection of low-mass planets IGM characterizations for z>5.5

TMT First Decade Instrument/Capability Suite


Instrument Spectral Resolution Science Case

Near-IR DL Spectrometer & Imager

(IRIS)~4000

Assembly of galaxies at large redshift Black holes/AGN/Galactic Center Resolved stellar populations in crowded fields Astrometry

Wide-field Optical Spectrometer

(WFOS)1000-5000

IGM structure and composition 2<z<6 High-quality spectra of z>1.5 galaxies suitable for measuring

stellar pops, chemistry, energeticsNear-field cosmology

Multi-slit near-DL near-IR Spectrometer

(IRMS)2000 - 5000 Near-IR spectroscopic diagnostics of the faintest objects

JWST followup

Mid-IR Echelle Spectrometer & Imager

(MIRES)

5000 - 100000

Physical structure and kinematics of protostellar envelopes Physical diagnostics of circumstellar/protoplanetary disks: where

and when planets form during the accretion phase

ExAO I(PFI)

50 - 300 Direct detection and spectroscopic characterization of extra-solar planets

High Resolution Optical Spectrograph

(HROS)

30000 - 50000

Stellar abundance studies throughout the Local Group ISM abundances/kinematics, IGM characterization to z~6 Extra-solar planets!

MCAO imager(WIRC)

5 - 100 Galactic center astrometry Stellar populations to 10Mpc

Near-IR, DL Echelle(NIRES)

5000 - 30000 Precision radial velocities of M-stars and detection of low-mass

planets IGM characterizations for z>5.5

TMT Early Light Instrument Suite


TMT Science and “Flow-down”Requirements for early light capabilities have been fine- tuned as a balance between unfettered science-driven desires and technical/fiscal realities (SAC/Project interactions have been crucial). We are proposing to build the most powerful suite of capabilities we can, through close interaction between science and engineering. Currently-envisioned capabilities address a huge range of questions we can formulate now (and complement other powerful facilities)The same capabilities will make new discoveries and will be the primary diagnostic tool for making sense of the discoveries made elsewhere.

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IRIS Conceptual Design Team

James Larkin (UCLA), PI, Lenslet IFSAnna Moore (Caltech), co-I, Slicer IFSRyuji Suzuki, Masahiro Konishi, Tomonori Usuda (NAOJ), ImagerBetsy Barton (UC Irvine), Project ScientistScience Team

– Mate Adamkovics(UCB), Aaron Barth(UCI), Josh Bloom(UCB), Pat Cote(HIA), Tim Davidge(HIA), Andrea Ghez(UCLA), Miwa Goto(MPIA), James Graham(UCB), Shri Kulkarni(Caltech), David Law(UCLA), Jessica Lu(UCLA),Hajime Sugai(Kyoto U), Jonathan Tan(UF), Shelley Wright(UCI)

OIWFS (On Instrument Wavefront Sensor) Team (HIA + Caltech)– Led by David Loop, Anna Moore

NSCU (NFIRAOS Science Calibration Unit) Team (U of Toronto)– Led by Dae-Sik Moon


Motivation for IRIS

Should be the most sensitive astronomical IR spectrograph ever builtUnprecedented ability to investigate objects on small scales. 0.01” @ 5 AU = 36 km (Jovian’s and moons)

5 pc = 0.05 AU (Nearby stars – companions)100 pc = 1 AU (Nearest star forming regions)1 kpc = 10 AU (Typical Galactic Objects)8.5 kpc = 85 AU (Galactic Center or Bulge)1 Mpc = 0.05 pc (Nearest galaxies)20 Mpc = 1 pc (Virgo Cluster)z=0.5 = 0.07 kpc (galaxies at solar formation epoch)z=1.0 = 0.09 kpc (disk evolution, drop in SFR)z=2.5 = 0.09 kpc (QSO epoch, H in K band)z=5.0 = 0.07 kpc (protogalaxies, QSOs, reionization)

Titan with an overlayed 0.05’’ grid (~300 km) (Macintosh et al.)

High redshift galaxy. Pixels are 0.04” scale (0.35 kpc).Barczys et al.)

M31 Bulge with 0.1” grid (Graham et al.)

Keck AO images


WFOS/MOBIE Team

Rebecca Bernstein (UCSC), PIBruce Bigelow (UCSC), PMChuck Steidel (Caltech), PSScience Team: Bob Abraham(U Toronto), Jarle Brinchmann(Leiden), Judy Cohen(Caltech), Sandy Faber(UCSC), Raja Guhathakurta(UCSC), Jason Kalirai(UCSC), Gerry Lupino(UH), Jason Prochaska(UCSC), Connie Rockosi(UCSC), Alice Shapley(UCLA)Some “flagship” science cases, “work horse capability”

– High quality spectra of faint galaxies/AGN/stars– IGM tomography

Great “follow-up” and “discovery” potential - full wavelength coverage with spectral resolutions up to R = 8000

– JWST, ALMA, etc., follow-upSensitivity >14 x current 8m telescopes


IR Multi-Slit Spectrometer(IRMS)

IRMOS (deployable MOAO IFUs) deemed too risky/expensive for first light=> IRMS: clone of Keck MOSFIRE, first step towards IRMOS

– Multi-slit NIR imaging spectro: – 46 slits,W: 160+ mas, L: 2.5”– Deployed behind NFIRAOS

2’ field60mas pixelsEE good (80% in K over 30”)

– Spectral resolution up to 5000– Full Y, J, H, K spectra (one at a time)

Images entire 2’ field

Slit width

Whole 120” field


IRMS Spectra

Configurable Slit Unit originally developed for JWST (slits formed by opposing bars)Full Y, J, H, K spectra with R ~ 5000 with 160mas (2 pix) slits in central ~1/3 of field


Summary

TMT will be a 30-m telescope with AO capabilities from the start – ~ 190 nm rms wavefront error over 10 arcsec– First light 2018

Very large and exciting science case8 instruments planned for the first decade3 instruments planned for first light– IRIS (an AO NIR integral field spectrograph and imager)– IRMS (an AO NIR multi object spectrometer (46 slits)– WFOS (a seeing-limited multiobject spectrometer with R<8000,

and ~ 50 arcmin2coverage)Many papers will elaborate on TMT AO in this conference

Documents

Science Goals and AO for the TMT