gnirs instrument update

GNIRS Instrument Update

• New Features• Phase II problem spots• Recent Science

Greg Doppmann

Tucson NGO meeting

29 Nov. 2005

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

Before• Numerous radiation

events impact the detector

• Affected pixels flagged and interpolated

GNIRS before…

After• No radiation hits -

only bad pixels remain

GNIRS after…

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

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)

GNIRS modes: what’s in demand?

• XD 38%

• IFU 22%

• L or M band modes <5%

GNIRS calibrations with GCAL

• Wavelength Calibration

- Arc Lamps (Ar & Xe)• Flatfielding

- IR & QH lamps• Spatial trace along slit

length

- pinhole

GNIRS calibrations with GCAL

• Wavelength Calibration

- Arc Lamps (Ar & Xe)• Flatfielding

- IR & QH lamps• Spatial trace along slit

length

- pinhole

GNIRS calibrations with GCAL

• Wavelength Calibration

- Arc Lamps (Ar & Xe)• Flatfielding

- IR & QH lamps• Spatial trace along slit

length

- pinhole

GNIRS Phase II Arcs, Flats & Pinhole• Use OT library - cut and paste • GNIRS web pages also detail configurations• New “observing class” in OT

Spectrophotometric Standards

• Use 3.0” wide slit.

• Not a baseline calibration.

• Use template flats and arcs for 1” slit.

• See OT library

GNIRS Phase II:Choosing Good Guide Stars

• Use PWFS2 with DSS• Patrol Field:

- min. radius 4.7’

- max. radius 6.9’

GNIRS Phase II:Choosing Good Guide Stars

• Choose V <= 15 mag• Need brighter stars in

poor conditions

- I.e. CC90 = 2 mag. extinction

GNIRS Phase II:Blind Offsetting

• Use for V >= 18 mag. objects

• Define User1 offset star

• Distance from Base< 1 arcmin.

Acquisition Exposure Times

• New H2 and PAH filters

• Better exposure time guide

GNIRS Phase II:Cross-Dispersed Acquisition Sequence

• Image of the slit• Image of acq. Field• Extra lines for centering

object in slit

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)

NIR Atmospheric Transmission

• L and M band affected by H20

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

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.