At the heart of the Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) UVIS channel is a 4096x4096 pixel e2v
CCD array. While these detectors continue to perform extremely well after more than 7 years in low-earth orbit, the
cumulative effects of radiation damage are becoming increasingly evident. The result is a continual increase of the hotpixel
population and the progressive loss in charge-transfer efficiency (CTE) over time. The decline in CTE has two
effects: (1) it reduces the detected source flux as the defects trap charge during readout and (2) it systematically shifts
source centroids as the trapped charge is later released. The flux losses can be significant, particularly for faint sources in
low background images. In this report, we summarize the radiation damage effects seen in WFC3/UVIS and the
evolution of the CTE losses as a function of time, source brightness, and image-background level. In addition, we
discuss the available mitigation options, including target placement within the field of view, empirical stellar
photometric corrections, post-flash mode and an empirical pixel-based CTE correction. The application of a post-flash
has been remarkably effective in WFC3 at reducing CTE losses in low-background images for a relatively small noise
penalty. Currently, all WFC3 observers are encouraged to consider post-flash for images with low backgrounds. Finally,
a pixel-based CTE correction is available for use after the images have been acquired. Similar to the software in use in
the HST Advanced Camera for Surveys (ACS) pipeline, the algorithm employs an observationally-defined model of how
much charge is captured and released in order to reconstruct the image. As of Feb 2016, the pixel-based CTE correction
is part of the automated WFC3 calibration pipeline. Observers with pre-existing data may request their images from
MAST (Mikulski Archive for Space Telescopes) to obtain the improved products.
Temperature variations in the NICMOS detectors arise from a variety of
thermal sources. These thermal variations lead to several image
artifacts which must be removed before making quantitative scientific
measurements from NICMOS data. Future instruments would do well to
minimize sources of thermal instabilities in their detectors. A related problem is the inability to directly measure detector temperature from bias due to the instability of the low-voltage power supply in NICMOS. Identifying ways to directly monitor detector temperatures would be an important benefit for future missions.
The overall temperature environment of the NICMOS detectors onboard the Hubble Space Telescope (HST) has changed since initial operation in 1997. These changes include an increased detector operating temperature and increases of the temperatures at the aft end of HST and the NICMOS enclosure. The aft shroud of HST is warmer due to on-going degredation of the MultiLayer Insullation (MLI) and increased power from the instruments installed during Servicing Mission 3B (The Advanced Camera for Surveys (ACS) and the NICMOS Cryocooling System (NCS)). This warms the NICMOS fore-optics, affecting the thermal background in long wavelength camera 2 and camera 3 filters. These trends are well described by both direct engineering data from the telescope and thermal emission models which are able to estimate the total thermal contribution to an exposure by knowing the etendue, reflectance, emissivity and temperature of each of the optics. This work reflects the first evidence of spacecraft heating directly affecting science observations onboard HST.
We summarize the current detector performance of the NearInfrared and MultiObject Spectrometer (NICMOS) on board the Hubble Space Telescope. After a three-year hiatus following the exhaustion of its solid nitrogen coolant, NICMOS was revived with the installation of the NICMOS Cooling System during the HST Servicing Mission 3B in March 2002. In this paper, we briefly describe the timeline of the NICMOS cooldown, present the results from the cooldown monitoring program to characterize the NICMOS detectors at their current operating temperature, and summarize the scientific performance of the "new" NICMOS.
We describe the on-orbit performance of the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) aboard the Hubble Space Telescope (HST) following the installation of the NICMOS Cooling System (NCS). NICMOS is operated at a higher temperature (~77 K) than in the previous observing 1997-1998 period (~62 K). Due to the higher operating temperature, the detector QE is higher, while the well depth is less. The spatial structure of the flat field response remained essentially unchanged. We will show the effects of operating at the higher temperature and present current NICMOS calibration images. In addition, we present an overview of on-orbit testing and report on the re-enabling of NICMOS.