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 and Ralph 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 radius NIC pix NIC2 6.5 pix NIC3 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

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: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 For latest news check NICMOS website Subscribe to the NICMOS STAN newsletter