Monitoring

The WFC3 Team regularly monitors the performance and status of the instrument through a variety of calibration programs. For more details regarding these calibration programs, please see the WFC3 Calibration Plan webpage.

Throughout the lifetime of WFC3, a growing number of ‘blobs’ (small, circular regions with slightly decreased sensitivity) have appeared in WFC3/IR images. The blob monitor allows us to identify and flag new IR blobs that appear and monitor the repeatability of the Channel Select Mechanism (CSM) movements.

In the expandable tab below, we document the history of blob appearance over time.

References:

ISR 2021-10: WFC3/IR Blob Flats
H. Olszewski & J. Mack, 05 July 2021

ISR 2021-08: WFC3 IR Blob Classification with Machine Learning
F. Dauphin et al., 23 June 2021

ISR 2018-06: WFC3/IR Blob Monitoring 
B. Sunnquist, 08 May 2019 (last updated)

HST spectrophotometric standards are routinely observed to monitor throughput stability. Analysis of the high signal-to-noise photometry in W and M bands indicates that the instrument is photometrically stable, with measured variations that are <0.4%. The measure of the photometric throughput of WFC3 as a function of time also checks for the presence of possible contaminants on the optics. See also the Throughputs webpage and the Photometric Calibration webpages.

References:

ISR 2021-04: New time-dependent WFC3 UVIS inverse sensitivities
A. Calamida, J. Mack, J. Medina, C. Shahanan, V. Bajaj, S. Deustua 10 Feb 2021

ISR 2020-10: Updated WFC3/IR Photometric Calibration
V. Bajaj, A. Calamida, J. Mack 03 Dec 2020

ISR 2018-16: WFC3/UVIS - Temporal and Spatial Variations in Photometry
H. Khandrika, S. Deustua, J. Mack 08 Nov 2018

ISR 2017-15: 2017 Update on the WFC3/UVIS Stability and Contamination Monitor
C. E. Shanahan, C. M. Gosmeyer, S. Baggett 12 June 2017

ISR 2014-20: Update on the WFC3/UVIS Stability and Contamination Monitor
C.M. Gosmeyer, S. Baggett, S. Deustua, & D.M. Hammer10 Sep 2014 

ISR 2010-14:The Photometric Performance of WFC3/UVIS:Temporal Stability Through Year 1.
Kalirai et al. 14 Oct 2010 

Charge Transfer Efficiency/Extended Pixel Edge Response

For information on how CTE losses affect science data as well as options for mitigating those losses, please see the CTE webpage.

The EPER (Extended Pixel Edge Response) method can be used to measure CCD detector Charge Transfer Inefficiency (CTI)-induced losses via internal exposures. EPER data consist of short tungsten lamp flat field exposures in several filters in order to obtain a large range of illumination levels (from ~100e- to 4000e-). By measuring the signal profiles as they extend into the trailing overscan region, an assessment can be made of the CTE level.

Tabulated data of EPER CTE levels as a function of signal and time
Columns are filename (date encoded as ddmmyy), Modified Juilan Date, average signal across all four amps at five different levels (cols 3-7), CTE for those average signals (cols 8-12), and the error bars for the EPER CTE measurements (cols 13-17).

CTE-EPER vs. Time Plot

References:

ISR 2016-10: WFC3/UVIS EPER CTE Cycles Aug 2009 - Apr 2016 
H. Khandrika, S. Baggett, A. Bowers 23 May 2016

ISR 2013-03: WFC3/UVIS EPER CTE Measurement: Cycles 19 & 20
M. Bourque & V. Kozhurina-Platais 15 Feb 2013 

ISR 2011-17: WFC3/UVIS CTE-EPER Measurement: Cycle 17 & 18. 
Khozurina-Platais et al. 27 Sept 2011 

2010 HST Calibration Workshop Proceedings: Internal Monitoring of WFC3/UVIS Charge Transfer Efficiency (page 573)
Khozurina-Platais et al. 2010 

ISR 2009-10: WFC3/UVIS CTE-EPER Measurement. 
Khozurina-Platais et al. 21 Jun 2009 

ISR 2007-13: UVIS CCD EPER CTE measurements performed during the April 2007 Ambient Calibration campaign (SMS UV02S01). 
M. Robberto 2007

The WFC3 dark current slowly increases over time and is monitored each cycle. This monitoring enables the creation of superdark reference files for the calibration pipeline and the monitoring of dark current and hot pixels.

References:

ISR 2016-08: WFC3/UVIS Dark Calibration: Monitoring Results and Improvements to Dark Reference Files
M. Bourque and S. Baggett 22 April 2016 

ISR 2014-04: WFC3 Cycle 19 & 20 Dark Calibration: Part I
J. Biretta and M. Bourque 10 April 2014 

ISR 2009-16: WFC3 SMOV Proposals 11419, 11426, 11431, and 11446: On-Orbit Darks.
Borders and Baggett 16 Nov 2009 

Gain is the conversion factor from electronic analog digital units (ADUs) to electrons, and is a fundamental parameter needed to characterize the WFC3 IR and UVIS detectors. In order to ensure that the true value of the gain in each quadrant does not deviate significantly from the nominal gain it is monitored each cycle.

WFC3/UVIS gain: 2010 to 2023 (Cycle 17 to Cycle 30)

WFC3/IR gain: 2010 to 2023 (Cycle 17 to Cycle 30)

Other plots:

SMOV Gain Plot
SMOV mean-variance plot for Quad A, B, C, and D.

TV3 Gain Plot
TV3 mean-variance plot for Quad A, B, C, and D.

References:

ISR 2017-08: Monitoring the WFC3/UVIS Relative Gain with Internal Flatfields
J. Fowler & S. Baggett 15 March 2017

ISR 2013-02: WFC3 Cycle 19 Proposal 12690: UVIS Gain
H. Gunning, C. Pavlovsky, S. Baggett 29 Jan 2013

ISR 2011-13: WFC3 Cycle 17 Proposal 11906: UVIS Gain
Borders, Pavlovsky, and Baggett 23 June 2011