nicmos status roelof de jong (stsci) and the nicmos team: santiago arribas, elizabeth barker, eddie...
TRANSCRIPT
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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
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Overview
• Instrument• Pipeline• Photometry• (Non-)Linearity & Zeropoint• Calibration plans
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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
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Instrument: dark current
• Dark current stable
(near day 600 persistence of Mars observation)
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Instrument: focus
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Instrument: 2-gyro mode
PSF nominal Coronographic rejection identical (no second roll angle in same orbit)
Poster P3-7 Malhotra
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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
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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
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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
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Photometry: sensitivity change
• Detector sensitivity improved going from 66 K to 77.1 K after NCS installation
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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
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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)
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Photometry: count rate standards
• Other HST spectro-photometric standards consistent
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Photometry: time evolution
• Some sensitivity loss in NIC2
• Data in other two cameras too noisy
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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.
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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
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Non-linearity: NICMOS vs ACS
• Similar effect when comparing NICMOS grism to ACS photometry
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Non-linearity: wavelength dependence
• Compare observed NICMOS spectra to white dwarf models extended to IR from STIS optical
• Effect strongly reduced at longer wavelengths
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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
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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)
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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
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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
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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
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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!
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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
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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
• For latest news check NICMOS website• Subscribe to the NICMOS STAN newsletter