NICMOS Status

Roelof de Jong(STScI)

and the NICMOS team:

Santiago Arribas, Elizabeth Barker, Eddie Bergeron, Ilana Dashevsky, Anton

Koekemoer, Sangeeta Malhotra, Bahram Mobasher, Keith Noll, Tom Wheeler, Tommy Wiklind, Chun Xu

andRalph Bohlin, Adam Riess

Overview

• Instrument• Pipeline• Photometry• (Non-)Linearity & Zeropoint• Calibration plans

Instrument

• Very stable due to NICMOS Cryo-cooler System (NCS)

• Darks, Focus, Flats, Temperature stable• 2-gyro mode observations successful• New SPARS MULTIACCUMs added

– SPARS4, SPARS16, SPARS32, SPARS128– SPARS sequences preferred for anything

that has no huge dynamic range

Poster P3-4 Xu

Instrument: dark current

• Dark current stable

(near day 600 persistence of Mars observation)

Instrument: focus

Instrument: 2-gyro mode

PSF nominal Coronographic rejection identical (no second roll angle in same orbit)

Poster P3-7 Malhotra

Pipeline/software updates

• MultiDrizzle implemented for NICMOS• Routines available for

– SAA cosmic ray persistence removal– Crosstalk removal (Mr. Stay-puft)

• Improved imaging and new grism Exposure Time Calculator (July 2004)– Continues improvements made, always use

the latest version for you proposals

P3-6 Koekemoer

P3-5 Bergeron

In the pipeline for the Pipeline

• Improved reference files– Better darks for 77.1K

• SAA clean• Mr. Stay-puft (quadrant crosstalk)• Temperature from bias• Amp glow persistence• Improved treatment of Cosmics removal

– Reduces noise in pixels affected by cosmics

Photometry

• New photometry keywords/zeropoints– Delivered July 2004– Main differences with previous values:

• Separate values Cycles 7/7N and Cycles 11+• Wavelength dependent aperture corrections• Improved (latest) data reduction methods• Better tied to ground-based measurements

Photometry: sensitivity change

• Detector sensitivity improved going from 66 K to 77.1 K after NCS installation

Photometry: aperture corrections

• Going from fixed to infinite apertures

• Wavelength dependence determined from TinyTim PSFs

Aperture radiusNIC1 11.5 pixNIC2 6.5 pixNIC3 5.5 pix

Spectro-photometric calibration

• P330E - Solar Analog– Spectrum: measurements

+ model

• G191B2B - White Dwarf– Spectrum: LTE model

• Tied to ground based through Persson et al. Standards (2MASS)(details in forthcoming ISR)

Photometry: count rate standards

• Other HST spectro-photometric standards consistent

Photometry: time evolution

• Some sensitivity loss in NIC2

• Data in other two cameras too noisy

NICMOS non-linearity

• Classic well depth non-linearity well understood

• Dependents on total counts, not count rate

• Corrected in pipeline

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Count Rate Non-linearity• Stellar standards over

a broad magnitude range were observed with the grisms

• Comparison with overlapping STIS spectra revealed an unexpected disagreement between STIS and NICMOS

• ACS data suggested NICMOS as the source of the difference

• Potential for important consequences to key NICMOS science makes this effect important to understand

Non-linearity: NICMOS vs ACS

• Similar effect when comparing NICMOS grism to ACS photometry

Non-linearity: wavelength dependence

• Compare observed NICMOS spectra to white dwarf models extended to IR from STIS optical

• Effect strongly reduced at longer wavelengths

Non-linearity:NICMOS spec vs phot

• Agreement between observed NICMOS spectra and photometry within errors

• Poor agreement when spectra are corrected to STIS flux expectations

Non-linearity: lamp off/on test

• Increase total count rate by adding light of the flatfield lamp to the background

• Count rate increases as predicted by non-linearity

(cycle 7 NIC2 data)

Non-linearity: no trapping signal

• MULTIACCUM sequences nearly stable independent of count rate

• If non-linearity caused by charge traps, time scales have to be longer than 500 seconds

Non-linearity: The evidence

• NICMOS grism vs– STIS & ACS spectra– ACS photometry

• Lamp off/on test• Supernova models ACS -> NICMOS J&H• Narrowband vs Broadband filter

throughputs ground vs. inflight

• UDF inconclusive

Non-linearity: UDF vs. ground

• Use color corrections or template fitting to match F110W to J ground

• Different results depending on reduction (talk Mobasher & Thompson)

• Effect expected to bottom out at sky level, ~23 AB-mag F110W for point sources, earlier extended sources

• Maximum effect ~0.2 mag in F110W, no effect expected in F160W

Non-linearity: Unknowns

Count Rate Flux() or Electrons ()

(F110W)~1.02, (F160W)~1.00

• Only incoming photons or add dark current?• Power law correction full count rate range?• Same exponent in all cameras?• Same wavelength dependence in all cameras?• Temperature dependence (cycle 7 vs 11+)• Pixel-to-pixel dependence?• Persistence?• Physical explanation!

Calibration plan• Usual monitoring: dark, flat, focus, photometry• Lamp off/on/off test: imaging and grism,

different filters and cameras• Persistence tests using bright stars and

flatfields, test wavelength and count rate dependence

• Deeper photometry on faintest standards• Check consistency between 2MASS and NICMOS

in Orion legacy survey field• Low frequency flat measurement in Camera 1;

monitoring data show residuals with position• Non-linearity correction: may be hard to

implement backward compatible with previous reductions

Poster P3-1 Arribas

Conclusions

• Instrument very stable with NCS• Photometry:

– Improved aperture corrections– Possible count rate dependent non-linearity

at <1.6 micron– Test are scheduled in November to quantify

non-linearity

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