NICMOS Status

1. 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

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

3. 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

4. Instrument: dark current • Dark current stable (near day 600 persistence of Mars observation)

5. Instrument: focus

6. Instrument: 2-gyro mode PSF nominal Coronographic rejection identical (no second roll angle in same orbit) Poster P3-7 Malhotra

7. 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 P3-5 Bergeron P3-6 Koekemoer

8. 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

9. 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

10. Photometry: sensitivity change • Detector sensitivity improved going from 66 K to 77.1 K after NCS installation

11. Photometry: aperture corrections • Going from fixed to infinite apertures • Wavelength dependence determined from TinyTim PSFs Aperture radius NIC1 11.5 pix NIC2 6.5 pix NIC3 5.5 pix

12. 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)

13. Photometry: count rate standards • Other HST spectro-photometric standards consistent

14. Photometry: time evolution • Some sensitivity loss in NIC2 • Data in other two cameras too noisy

15. NICMOS non-linearity • Classic well depth non-linearity well understood • Dependents on total counts, not count rate • Corrected in pipeline

16. 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

17. Non-linearity: NICMOS vs ACS • Similar effect when comparing NICMOS grism to ACS photometry

18. Non-linearity: wavelength dependence • Compare observed NICMOS spectra to white dwarf models extended to IR from STIS optical • Effect strongly reduced at longer wavelengths

19. 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

20. 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)

21. 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

22. 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

23. 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

24. 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!

25. 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

26. 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