Download - GNIRS Instrument Update
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GNIRS Instrument Update
• New Features• Phase II problem spots• Recent Science
Greg Doppmann
Tucson NGO meeting
29 Nov. 2005
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Instrument Upgrade - July 2005
• Short Red and Blue Camera Lenses Replaced– No more radiation events due to Thorium AR
coating• H2 and PAH narrowband filters added
– Non saturating for bright acquisitions– Faint acquisitions for emission line objects
• New XD filter installed– Increased throughput at J and X bands
(~30% at 1 micron)• Cold Heads Replaced/Rebuilt
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Before• Numerous radiation
events impact the detector
• Affected pixels flagged and interpolated
GNIRS before…
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After• No radiation hits -
only bad pixels remain
GNIRS after…
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2.54
1.881.41
GNIRS Cross-Dispersed Coverage
1.90
1.13
1.52
0.94
1.09
0.81
0.95
0.70
0.85
0.63
1.27
KH
JX
I
• XD 32 case shown• New XD filter installed• Better transmission at shorter wavelengths
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GNIRS Phase II: Telluric Standards
• Baseline calibration. One allowed per science target w/o charge to program.
• Choose a “before” and “after” case for for longer observation (>20 minutes) science targets.
• Exposure times scaled from integration time calculator on web (or see GNIRS page for K=5 case)
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GNIRS modes: what’s in demand?
• XD 38%
• IFU 22%
• L or M band modes <5%
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GNIRS calibrations with GCAL
• Wavelength Calibration
- Arc Lamps (Ar & Xe)• Flatfielding
- IR & QH lamps• Spatial trace along slit
length
- pinhole
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GNIRS calibrations with GCAL
• Wavelength Calibration
- Arc Lamps (Ar & Xe)• Flatfielding
- IR & QH lamps• Spatial trace along slit
length
- pinhole
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GNIRS calibrations with GCAL
• Wavelength Calibration
- Arc Lamps (Ar & Xe)• Flatfielding
- IR & QH lamps• Spatial trace along slit
length
- pinhole
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GNIRS Phase II Arcs, Flats & Pinhole• Use OT library - cut and paste • GNIRS web pages also detail configurations• New “observing class” in OT
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Spectrophotometric Standards
• Use 3.0” wide slit.
• Not a baseline calibration.
• Use template flats and arcs for 1” slit.
• See OT library
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GNIRS Phase II:Choosing Good Guide Stars
• Use PWFS2 with DSS• Patrol Field:
- min. radius 4.7’
- max. radius 6.9’
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GNIRS Phase II:Choosing Good Guide Stars
• Choose V <= 15 mag• Need brighter stars in
poor conditions
- I.e. CC90 = 2 mag. extinction
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GNIRS Phase II:Blind Offsetting
• Use for V >= 18 mag. objects
• Define User1 offset star
• Distance from Base< 1 arcmin.
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Acquisition Exposure Times
• New H2 and PAH filters
• Better exposure time guide
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GNIRS Phase II:Cross-Dispersed Acquisition Sequence
• Image of the slit• Image of acq. Field• Extra lines for centering
object in slit
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GNIRS Observing Conditions
• SB– Always “any”
• WV
- “any” (J,H,K) or - 50%ile (M or
blue L band)
• CC
- If photometric 50%ile
(20%ile is same)
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NIR Atmospheric Transmission
• L and M band affected by H20
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GNIRS IRAF Package Overview
• Nsprepare- corrects for detector response
• Nsreduce- flat fielding, sky subtraction, trims useful sections on array
• Nswave- arc lines or sky lines for wavelength calibration
• Nstelluric- removes atmospheric lines from science data
• Nscalibrate- flux calibration using a photometric standard
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Recent Science with GNIRS
• Van Dokkum et al., 2005 ApJ, 622L, 13– Z=2.225 galaxy emission lines probe kinematics
and metallicity
• Silge et al., 2005 AJ, 130, 406– dynamical measurements of Centaurus A
characterize the central black hole mass.
• Luhman et al., 2004 ApJ 617, 565– Spectroscopic confirmation of the least massive
brown dwarf known in Chamaeleon.