STScI 2010 Calibration Workshop

The NICMOS Legacy Archival

Recalibration Project

Anton M. Koekemoer

and the STScI NICMOS Team (E. Barker, E. Bergeron, T. Dahlen, R. de Jong, D.

Grumm, V. Laidler, N. Pirzkal, D. Thatte, A. Viana, T. Wiklind)

Overall Context

Anton Koekemoer - STScI 2010 Calibration Workshop

•NICMOS has provided a unique NIR capability in HST since 1997 until installation of WFC3:

– 32 filters (7 wide, 12 medium, 13 narrow) from 0.9 to 2.4 micron– 3 grisms (J, H, K)– 3 cameras (pixels @ 43 mas, 75 mas, 200 mas)– coronagraphy– polarimetry

•Approximately 100,000 science exposures in the archive

•Extensive time baseline covering more than a decade

•Current operations suspended (pending revival of NCS), with instrument remaining fully capable

The Challenge

Anton Koekemoer - STScI 2010 Calibration Workshop

•NICMOS on HST was a completely new paradigm:

– New wavelength regime up to 2.4 micron– A new type of detector (HgCdTe), totally different from CCDs– Two different eras in the life of the instrument:

– 1997-98: “pre-NCS” (instrument cooled by solid N cryostat, which evaporated by start of 1999 and left NICMOS warm)

– 2002-08: “post-NCS” (after SM3B installation of NICMOS Cooling System “NCS” cryocooler)

– Completely different temperature histories in each era

•The HgCdTe detectors are highly susceptible to the following:

– Temperature / bias voltage changes (affecting DQE, dark current rates, bad pixels)

– Persistence effects (from bright astronomical sources, cosmic rays, and bright earth emission)

Motivation for The Legacy Recalibration

Anton Koekemoer - STScI 2010 Calibration Workshop

•Since NICMOS was so different from CCDs, including all the new detector effects, calibrating it was a challenge:

Electronic shading

SAA-impacted CR persistence Electronic crosstalk

“Supershading”Bright-earth persistence

Cleaned imageOriginal imageSAA model

The Legacy Recalibration Project: Observations

Anton Koekemoer - STScI 2010 Calibration Workshop

•Initiated a full suite of extended NICMOS Calibration observing programs on-orbit, starting from Cycle 15:

– Expanded dark monitoring from just a few darks / month to several hundred darks / cycle, for all the different observing modes

– Expanded flatfield programs to cycle through all the filters repeatedly during each cycle, to fully track throughput changes

– Expanded photometric calibration program to include a wider range of stars, also for cross-calibration with WFC3 and JWST

– Improved grism calibration to map wavelength across entire array

•Implement improved scripts for creating new reference files (incl darks, flats) and treatment of hot pixels (Barker, Dahlen, Thatte et al)

•Coupled with development and implementation of software to correct a wide range of detector / calibration issues

NICMOS Legacy Recalibration: SAAclean

Anton Koekemoer - STScI 2010 Calibration Workshop

•Implemented corrections for removing SAA-impacted cosmic rays in exposures (Barker, Bergeron, Laidler et al):

– As HST moves through the South Atlantic Anomaly (SAA), the CR flux increases by orders of magnitude

– Persistence in the NICMOS detectors shows residual flux for several orbits afterwards, which can be very well characterized using post-SAA darks

– The SAAclean software fits and removes these residualsCleaned imageOriginal image

SAA model

NICMOS Legacy Recalibration: Bright Earth

Anton Koekemoer - STScI 2010 Calibration Workshop

•Since NICMOS possesses no shutter, slews across the bright earth can also cause substantial persistence in subsequent images (Bergeron, Riess et al):

– Resulting residuals change in a time-dependent fashion and can’t be corrected using normal background-fitting techniques

– Also affect the noise properties (since the structure is correlated)– Successful implementation of software to remove this effect

Before After

NICMOS Legacy Recalibration: Bias “temp”

Anton Koekemoer - STScI 2010 Calibration Workshop

•The HgCdTe detectors are highly sensitive to variations in both physical detector temperature and bus voltage levels

•This can be tracked using the zeroth read, using the detector as a “diode” (Bergeron et al):

– “TFB temp (“effective temperature” from bias voltage levels) allows an empirical correction to be developed for darks, flats and photometry

– Full set of flats, darks and photometry reference files developed for different values of this quantity

– Archive pipeline determines this quantity for each exposure and implements this correction using the appropriate reference files

•Can be applied to both pre- and post-NCS datasets

Full Archival NICMOS Recalibration

Anton Koekemoer - STScI 2010 Calibration Workshop

•During 2005 - 2009, all these calibration improvements were developed and implemented into the archive / HLA pipelines:

– SAAclean to remove SAA-impacted CR persistence– Bright Eerth persistence removal– Measurement of “TFBtemp” for all datasets– Implementation of new reference files for different values of

“TFBtemp”, for flatfields, darks and photometry files– New photometry / non-linearity corrections– Many improvements to Calnica, including accurate error array

calculation, and improved up-the-ramp slope fitting / CR rejection

•All NICMOS data were then run through the OPUS pipeline (late 2008 through early 2009), resulting in new calibrated *_cal.fits files

Science-Added MultiDrizzle HLA Products

Anton Koekemoer - STScI 2010 Calibration Workshop

•In 2009-2010, recalibrated NICMOS files were then processed through the Hubble Legacy Archive (HLA) pipelines to create additional products:

– MultiDrizzle-combined images for all NICMOS exposures of a given filter, in a given visit

– Pixel-aligned images for visits that contain exposures taken with more than 1 filter

– Improved CR rejection and bad pixel masking (beyond that provided by calnica), using multiple dithered images

– Instant access to all combined / drizzled data products – Astrometric registration of each image onto the best available

GSC2 / SDSS / 2MASS astrometry

Summary

Anton Koekemoer - STScI 2010 Calibration Workshop

•A new lease on life for the entire NICMOS archive!

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