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ROSAT – Roentgen Satellite Joint facility: US, Germany, UK Operated 1990 – 1999 All-‐sky survey + pointed observaDons
Chandra X-‐ray Observatory US Mission OperaDng 1999 – present Pointed observaDons
Wolter X-‐ray telescope • What is the collecDng
area (the size) of the telescope?
• How can we improve the collecDng area?
How do you focus X-‐rays?
ROSAT – InstrumentaDon
Posi;on Sensi;ve Propor;onal Counter (PSPC) • 20” resoluDon, 2 degree FOV • Energy range 0.1 – 2.5 keV • EffecDve area ~ 240 cm2 at 1 keV • Conducted all-‐sky survey • Also did pointed observaDons High Resolu;on Imager (HRI) • 5” resoluDon, 38’ FOV • EffecDve area ~ 80 cm2 at 1 keV • Pointed observaDons
Chandra – InstrumentaDon Advanced CCD Imaging Spectrometer (ACIS) • Imaging: 2” spaDal resoluDon, ten 8’x8’
CCDs • Moderate resoluDon spectroscopy • Energy range 0.4 – 10 keV • EffecDve area ~ 600 cm2 at 1 keV High Resolu;on Camera (HRC) • 0.4” resoluDon, 30’ FOV • EffecDve area ~ 200 cm2 at 1 keV High Energy Transmission Gra;ng (HETG) • E/ΔE = 1000 • 0.4 – 10 keV
Low Energy Transmission Gra;ng (LETG) • OpDmized for low energy (0.08-‐0.2 keV)
spectroscopy
But how do you detect X-‐rays?
Propor;onal Counters (ROSAT PSPC) • Pass X-‐rays into a gas-‐filled chamber • X-‐ray enters chamber, ionizes an atom (primary electron) • Primary electrons can have enough energy to ionize other atoms (secondary
electrons) • Electrons accelerate towards anode wire, ionizing more atoms (“gas gain” ~ 2-‐3
orders of magnitude) • MulDple anode wires give posiDonal sensiDvity • Energy informaDon comes from signal strength • Limited by gas supply
Scin;lla;on Detectors • For X-‐ray energies > 50 keV, the gas density needed to stop an X-‐ray becomes
prohibiDve • ScinDllaDon detectors use solid crystal (NaI or CsI for example) which emits light
upon absorpDon of a photon • Detect photons using a photomulDplier tube
X-‐ray CCDs (Chandra ACIS) • Conceptually like opDcal CCDs • OpDcal photon produces 1 electron, X-‐ray photon produces many • OpDcal CCDs integrate to build up charge • X-‐ray CCDs can be read out fast, so charge tells you energy of X-‐ray
Microchannel plates (Chandra HRC) • Material with many pores/channels, with a voltage
applied. • X-‐ray hits side of channel, kicks out electron • Electron accelerates, kicks out more electrons • Signal measured for each channel • Long life-‐Dme (no gas supply issues) • Good spaDal resoluDon, poor energy resoluDon
The Sloan Digital Sky Survey
Imaging: • MulDband ugriz, median seeing ~ 1.4” • 54s exposure Dme by scanning gives glim = 22.2 • ~ 2% photometric uncertainty • 7,500 square degrees in Legacy (~ 15,000 total) • 208M galaxies, 260M stars Fiber spectroscopy (Legacy): • R ~ 2000 spectra from 3800 – 9200 Å • Redshiq accuracy ~ 30 km/s • Galaxies (r<17.77) and Quasars (i<19.1 or 20.2) • ~ 1M (1.9M) galaxy spectra, 120K (300K)
quasar spectra, (270K) stellar spectra
Dedicated 2.5m telescope at Apache Point, NM Main Survey (“Legacy”) operated 2000 – 2008, through Data Release 7 (DR7) AddiDonal projects since then: SEGUE, BOSS, APOGEE, MARVELS (DR10)
SDSS Data Products
Calibrated Images and Spectra: • Quick look format • Reduced fits files
Data Products (Imaging):
• Magnitudes, colors • For galaxies: size, structural informaDon, photo-‐z
Data Products (Spectra): • Redshiq/velocity • Line indices • Spectral classificaDon
Catalogs, for example:
• Luminous Red Galaxies • Quasar catalog • White dwarf catalog • Moving objects