June 12 - June 16, 2022
Pasadena, California
206.01. hst1pass: One-Pass PSF Photometry for HST Detectors - J. Anderson
We are making public and documenting hst1pass: a software routine that has been used for years to find and measure stars in HST images. The hst1pass routine makes use of empirical models of HST’s effective PSF in order to identify and measure relatively isolated stars in images taken with HST’s primary imaging detectors: ACS/WFC, WFC3/UVIS, WFC3/IR, ACS/HRC---and even WFPC2. The user can specify the finding parameters used to search the images as well as the specific measured parameters to be output for each source. The time-averaged “library” PSFs are generally accurate enough for most projects, but the routine has the ability to use focus-diverse PSFs to tailor the PSF to the particular focus of the exposure. Alternatively, the routine can perturb the PSF in an empirical way to improve the photometry. For S/N ~100 stars, the errors in the measured positions are typically 0.01-0.02 pixel and the photometry is generally good to 0.01-0.02 magnitude, and point-source/resolved-source discrimination is quite accurate. The routine has a flexible output format in order to facilitate subsequent collation of outputs from multiple dithered exposures. Future improvements will depend on demand, but could include PSF-convolved Gaussian or 2-source fitting, or even point-source-plus Gaussian fitting.
215.02. Key Improvements in the HST/WFC3 User Experience - J. Green, F. Dauphin, WFC3 Team.
The Hubble Space Telescope (HST) was launched in 1990, but the user community has evolved greatly since then. In the past few years, the number of new HST users has been higher than ever before. The advent of Jupyter notebooks and identified standards of best practice in notebooks has been adopted by the WFC3 team. Here we present the updated Wide Field Camera 3 (WFC3) software landing page, and the new WFC3 Library github repository. Aimed at newer users, these tools provide clear documentation and should be relied upon to source calibration, throughput, and performance files, as well as other supporting documentation for WFC3. We also preview the integration of the HST exposure time calculator (ETC) into the Pandeia engine, similar to JWST.
302.04. HST's Wide Field Camera 3 in 2022 - D. Som, S. Baggett, WFC3 Team.
Wide Field Camera 3 (WFC3), on board the Hubble Space Telescope (HST), provides coverage from the near-UV to the near-IR with direct (staring) and spatial scanning modes using filters and grisms. Installed in 2009, WFC3 continues to be HST's workhorse instrument and has logged almost 300,000 observations, resulting in exciting scientific discoveries over the past 13 years. Here we review the status of the instrument, including recent adjustments and updates to its performance and technical capabilities. We also present the latest calibrations and observing recommendations, along with some late-breaking science enabled by WFC3.
January, 2021
Virtual Meeting
350.05. Hubble's WFC3 in 2021 - J. Green, S. Baggett, WFC3 Team.
Hubble's Wide Field Camera 3 (WFC3) is the workhorse instrument for HST. We review the status of the instrument, including recent adjustments and updates to its calibration, technical capabilities, and performance, which may be of particular interest to proposers in Cycle 29 as well as observers with data in hand. UVIS zeropoint updates will be useful to GOs using data spread over multiple years.
353.01. Machine Learning Anomaly Detection with PyTorch in WFC3/IR Images - A. Ashraf, J. Medina, H. Olszewski, J. Fraine.
We introduce a method for creating a deep learning algorithm to complement the existing Quicklook software by automatically detecting known and unknown Hubble / WFC3 image anomalies, thus improving detection accuracy and reducing time spent on manual image inspection. The results from our algorithm using a test set of Hubble Ultra Deep Field images show R2 values >= ~0.97, and a reconstructive loss consistently below 10^-3 .
353.03. Updated HST/WFC3 Photometric Calibration - J. Medina, A. Calamida, J. Mack, V. Bajaj, K. Sahu, C. Shanahan, H. Khandrika, C. Martlin.
The WFC3 photometry team presents a new set of UVIS and IR zeropoints that incorporate improvements in the HST CALSPEC models as well as an increase in the Vega reference flux (Bohlin et al. 2020). The new 2020 zeropoints are available on the WFC3 Photometric Calibration webpage, and the team provides a Jupyter Notebook to show how to work with the new UVIS time-dependent solutions.
June, 2020
Virtual Meeting
242.04: Filter-Dependent Sky Flats for WFC3/IR - H. Olszewski, J. Mack, & N. Pirzkal
We present filter-dependent sky flats for Hubble’s WFC3/IR detector, computed by stacking observations of sparse fields (with sources masked) over the instrument lifetime. The new flats replace the current set of P-flat reference files, which were based on ground test data with a single ‘grey’ correction for all filters derived from early inflight data. The sky flats correct for wavelength-dependent residuals ~1% at the center of the detector and ~2% at the detector edges with Poisson errors of 0.2% or better. We also present ‘delta’ flat corrections in six filters for all known ‘blobs’ by stacking observations before and after their individual appearance dates, and these correct for sensitivity residuals of ~5-10%.
341.01: Hubble's WFC3 in 2020- J. Green and WFC3 Team.
Hubble's Wide Field Camera 3 (WFC3) is the workhorse instrument for HST, providing numerous modes in imaging, slitless spectroscopy, covering from the near-IR to near-UV. Installed during the most recent HST servicing mission in 2009, WFC3 has logged numerous observations and exciting scientific discoveries over the past 11 years. We review the status of the instrument, including recent adjustments to its technical capabilities and performance.
A new time-dependent photometric calibration of the WFC3 UVIS detector - A. Calamida, J. Mack, J. Medina, C. Shanahan, V. Bajaj.
January, 2020
Honolulu, Hawaii
109.18: Wide Field Camera 3 (WFC3) Python Data Analysis Tools and Jupyter Notebooks- C. Shanahan
New functionality to aid users in data analysis has been added to the `wfc3tools` Python package which is maintained by the WFC3 team at STScI. In addition, Jupyter notebooks outlining best practice workflows have been created to further guide users in using the tools available in this package.
109.07: A PSF Fitting Workflow for HST/WFC3 - V. Bajaj, J. Anderson
A new Python interface, along with a full workflow within a Jupyter notebook, have been created to aid users in fitting Point Spread Functions (PSF) on HST WFC3 images to generate high precision catalogs of positions and fluxes of stars. Other functionality of the software interface and Jupyter notebook workflow includes matching catalogs, zeropoint correction, as well as input checking.
372.07: WFC3 DASH Reduction Pipeline Development and Launch - R. O'Brien, C. Martlin, I. Momcheva, M. Gennaro
A new Python package has been developed to aid users in reducing the initial data acquired via the DASH (drift-and-shift) observing technique where WFC3/IR images are taken under gyro control. The software creates the partial images and aligns them and includes options for creating mosaics, segmentation maps and association files. We provide documentation and Jupyter notebook tutorials to guide users through the reduction pipeline.
110.12: HST/WFC3/UVIS Survey of Stellar Clusters in the Magellanic Clouds: Search for multiple populations - V. Kozhurina-Platais , N. Bastian, S. Saracino, S. Martocchia, I. Platais
The magic combination of HST/WFC3 UVIS filters from ultraviolet-wide to red-wide along with the narrow F343N is sensitive to C-N-O abundance variations for stars on the Red Giant Branch. Not only for Galactic star clusters, but also for clusters in the Magellanic Clouds. The HST Magellanic Cloud cluster survey shows a strong correlation between the cluster age and the properties of multiple populations (MP) - tracing detailed abundances of N, O, and He as a function of age. The HST observations allowed us to explore in detail the chemical variations and its characterization for large numbers of stars in the cluster, providing fresh constraints on the origin of MPs in the stellar clusters.
January, 2019
Seattle, Washington
157.28 - HST WFC3: Instrument Status and Advice for Proposers and Observers - E. Sabbi, The WFC3 Team
The Wide Field Camera 3 is UV, Visible and near Infrared Camera on boar of the Hubble Space Telescope, that provides astronomers with powerful imaging and slitless spectroscopic capabilities from the near-ultraviolet (200 nm) to the near infrared (1700 nm). We summarize the basic characteristics and performances of WFC3, including our analysis of its stable and time variable calibrations, and summarize the calibration program for Cycle 26. Key recent improvements in our calibrations and instrument characterizations will be discussed including better models for the correction of the degrading Charge Transfer Efficiency, a new tool to derive focus dependent libraries of Point Spread Function, new time dependent dark files for the IR channel, and new IR flat-fields.
158.08: High Precision Photometry with Spatial Scans - WFC3 UVIS - C. Shanahan, S. Baggett, P. McCullough
We provide results on a high precision photometry study with HST/WFC3 using spatial scans. The goal of this study is both to demonstrate the maximum photometric repeatability that can be obtained with WFC3/UVIS, as well as to better characterize the time-dependent trends in photometric throughput. Calibration programs 14878 and 15398 have obtained spatial scans of bright, isolated white dwarf standard stars GD153 and GRW70. The photometric stability of UVIS has historically been continually monitored with staring mode observations of white dwarf standard stars GD153 and GRW70. Based on the excellent results of the first spatial scan program 14878, which achieved ~0.1% repeatability between visits, this monitoring program now incorporates spatial scans for better signal-to noise measurements to characterize any throughput changes with time. We also present analysis tools in Python that will be available to the public for analyzing spatial scan data.
443.11 - WFC3 PSF Database and Analysis Tools - K. Sahu, E. Sabbi, J. Anderson, C. Shanahan, V. Bajaj, L. Dressel
A database of nearly 22 million high signal-to-noise images of non-saturated point sources in WFC3/UVIS observations is accessible from the “WFC3 UVIS PSF advanced search” interface on the MAST portal. The dataset was collected between May 2009 and May 2017, and is updated yearly toinclude new sets of non-proprietary observations. Users can search the database to select sources based on various parameters including filter, telescope focus level, exposure time, as well as by parameters associated with the PSF fit. The online portal allows users to preview and download 21x21 pixel cutouts from the original UVIS files. The images are intended for those projects that would benefit from an accurate understanding of the UVIS point spread function and its dependence on the telescope focus on a specific location, but do not have enough sources to create an accurate model. In the coming year the team will release a similar database for the WFC3/IR channel, along with python-based data analysis tools to assess the focus level of an image and to perform focus dependent PSF fitting analysis in crowded fields. The Python tools provide an interface for running Jay Anderson’s Fortran PSF fitting on individual images, and for matching and averaging the measurements across all of the images.
August, 2018
Vienna, Austria
WFC3/HST photometric calibration: color terms for the UV filters - A. Calamida
The two detectors of the Hubble Space Telescope Wide Field Camera 3 (WFC3) instrument, UVIS1 and UVIS2, have different quantum efficiencies, with the difference being larger in the ultra-violet regime. The two detectors' sensitivities also change differently with time, resulting in different count rate ratios as a function of the observing epoch for UVIS1 and UVIS2. Starting from 2016, a chip-dependent calibration was implemented by the WFC3 calibration pipeline, and new set of values for UVIS1 and UVIS2 inverse sensitivities were provided. The new chip-dependent inverse sensitivities were calculated by using photometry of three CALSPEC standard white dwarfs. However, for cooler (T < 20,000 K) and redder stars, the inverse sensitivities of the two WFC3 detectors are still different. I will present corrections to the inverse sensitivities of UVIS1 and UVIS2 for three ultra-violet filters, namely F218W, F225W, and F275W. These were derived by using multi-band observations of the globular cluster Omega Centauri and synthetic photometry for 72 CALSPEC standards. The corrections are provided as look-up tables as a function of stellar color and are available to WFC3 users.
Comparing Hubble Space Telescope's ACS/WFC and WFC3/UVIS photometry - S. Deustua
A study was undertaken to compare the Hubble Space Telescope's ACS Wide Field Camera (WFC) photometry to that of the WFC3 UVIS imaging channel in eight similarly named passbands corresponding to the broadband filters F435W (ACS/WFC), F438W (WFC3/UVIS), F475W, F555W, F606W, F625W, F775W, F814W and F850LP. We present the results of this study, which may be of interest for science programs that use both ACS and WFC3. The consistency of the photometric calibration of ACS/WFC and WFC3/UVIS is within +/- 1%. Comparing the ACS/WFC to WFC3/UVIS mean flux for stars having a range of spectral types shows a color dependence for all filters except for F814W.
July 2018
Austin, Texas
Sink pixels in the HST wide-field channel 3 CCDs - S. M. Baggett, M. Bourque, J. Anderson, J. Ryon
Isolated pixels with anomalously-low signal in otherwise normal Hubble Space Telescope Wide-Field Channel 3 (HST/WFC3) CCD data have been dubbed 'sink pixels' or SPs. The SPs appear to contain an exceptionally large number of charge traps and thus, they capture a commensurate amount of charge during readout. The effects of the sinks on science data depend on a number of factors including the image background, SP distance from the amplifier, and data epoch. In images with high backgrounds, the sinks act as essentially negative delta-functions, impacting a relatively small number of pixels. In contrast, in images with low backgrounds, the sinks can remove charge from a significant number of trailing pixels generating trough-like profiles. In this paper, we characterize the sink pixels, evaluate their effect on science data, and summarize how the sinks are flagged in the calibration pipeline.
June, 2018
Denver, Colorado
WFC3/UVIS Filter-Distinct and Filter-Dependent Distortion Corrections - C. Martlin, V. Kozhurina-Platais, M. McKay, E. Sabbi
The WFC3/UVIS filter wheel contains 63 filters that cover a large range of wavelengths from near ultraviolet to the near infrared. Previously, analysis was completed on the 14 most used UVIS filters to calibrate geometric distortions. These distortions are due to a combination of the optical assembly of HST as well as the variabilities in the composition of individual filters. We report recent updates to reference files that aid in correcting for these distortions of an additional 21 UVIS filters. They were created following a calibration of the large scale optical distortions and fine scale filter dependent distortions. Furthermore, we present results on a study into a selection of unique polynomial coefficient terms from all solved filters which allows us to better investigate the filter dependent patterns across a large range of wavelengths. These updates will provide important enhancements for HST/WFC3 users as they allow more accurate alignment of images across the range of UVIS filters.
Advances on Hubble Wide Field Camera 3 Grism Calibration and Slitless Spectroscopy Analysis - J. Fowler, G. Brammer, R. Ryan, S. Deustua, & N. Pirzkal
Grisms are spectral elements combining a grating and prism to conduct slitless spectrsocopy; presently they make up approximately 13% of all Wide Field Camera 3 (WFC3) observations on the Hubble Space Telescope (HST). WFC3 contains three grisms, two for the infrared (IR) channel and one for the ultraviolet-visible (UVIS). Here we summarize recent results from an ongoing effort to improve the analysis tools, characterization, and calibration of WFC3 slitless spectroscopic observations. This includes (1) IR linear-reconstruction solving methods that solve for optimal, nonparametric spectra,(2) calibrating the IR wavelength solutions with respect to compact zeroth order images, (3) improved IR throughput curves from modeling grism flux by extending the pixel range of effective point spread functions, (4) calibrating the UVIS +1 and -1 order over the entire field of view of both chips (allowing for spectral extraction from the entire UVIS detector.) With these efforts we continue to improve and advance the science possible with WFC3 grism observations.
Pixel Stability in the Hubble Space Telescope WFC3/UVIS Detector - M. Bourque, S. Baggett, D. Borncamp, T. Desjardins, N. Grogin, and the WFC3 Team (STScI)
The Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Ultraviolet-Visible (UVIS) detector has acquired roughly 12,000 dark images since the installation of WFC3 in 2009 as part of a daily monitoring program to measure the intrinsic dark current of the detector. These images have been reconfigured into “pixel history” images in which detector columns are extracted from each dark and placed into a new time-ordered array, allowing for efficient analysis of a given pixel’s behavior over time. We discuss how we measure each pixel’s stability, as well as plans for a new Data Quality (DQ) flag to be introduced in future deliveries of UVIS bad pixel tables (BPIXTAB) for flagging pixels that are deemed unstable.
March, 2018
Baltimore, Maryland
WFC3/UVIS Filter Dependence of Geometric Distortions - C. Martlin, V. Kozhurina-Platais, M. Mckay, E. Sabbi
WFC3/UVIS filter wheel contains a multitude of filters that cover a large range of wavelengths from far ultraviolet to the infrared. Previously, studies were completed on the most used UVIS filters to examine astrometric irregularities caused by image distortions due to the optical assembly of HST and variabilities in the composition of individual filters due to their manufacturing process. We report recent updates to reference files of an additional 22 UVIS filters following further investigation into the large-scale filter-distinct geometric distortions and fine-scale filter-dependent distortions. Furthermore, we present results on which solutions were created as well as results of a study on a selection of unique polynomial coefficient terms to better investigate these systematic filter-dependent patterns.These updates will provide important enhancements for HST/WFC3 users as they allow more accurate alignment of images to aid in obtaining high precision astrometry results across the range of UVIS filters.
January, 2018
Washington, DC
150.24 – LINEAR - R. Ryan , S. Casertano , N. Pirzkal
We present a new paradigm for extracting one-dimensional spectra from a collection of slitless spectroscopic images obtained at multiple position angles. We compute the optimal spectrum for each object simultaneously by computing all of the transformations from the direct image to each dispersed image at the wavelengths of interest. This approach has several key advantages over standard extraction-based techniques by (1) removing the need for contamination corrections, (2) improving signal-to-noise without loss of spectral resolution, and (3) extracting sources that overlap in the direct image (such as bulge/disk or annular sectors). We present a series of simulated HST/WFC3 data to test the accuracy of our method. We will also show high-redshift sources from various deep fields as illustrations of our technique.
June, 2017
Austin, Texas
117.11 – Using Dark Images to Characterize the Stability of Pixels in the WFC3/UVIS Detector - M. Bourque , D. Borncamp , S. Baggett, N. Grogin, The WFC3 Team
The Ultraviolet-Visible (UVIS) detector on board the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) instrument has been acquiring 'dark' images on a daily basis since its installation in 2009. These dark images are 900 second exposures with the shutter closed as to measure the inherent dark current of the detector. Using these dark exposures, we have constructed ‘pixel history' images in which a specific column of the detector is extracted from each dark and placed into a new time-ordered array. We discuss how the pixel history images are used to characterize the stability of each pixel over time, as well as current trends in the WFC3/UVIS dark current.
117.24 – Long-term Stability of the WFC3 Post-Flash LED Lamp - C. Martlin, S. Baggett
We report the results of a study of the long-term stability of the LED lamp used in post-flashing WFC3/UVIS images (Martlin, C and Baggett, S., 2017). Having analyzed 644 sub-array exposures taken over the course of just over 3 years we find no significant long-term trends in the LED lamp brightness. The average percentage change per year over all FLASH level and shutter combinations is found to be 0.15% per year with an uncertainty of +/- 0.24% per year. The maximum measured percentage change per year was 0.39% for the highest FLASH level of 20 e- on shutter A which would indicate a change of less than 1 e-/pixel over the roughly 3 years since post-flashing began. There are, however, occasional short-term deviations in the LED output. The average minimum and maximum outliers over all FLASH level and shutter combination subsets are 4.1% below and 3.5% above, respectively, the mean of that subset. The maximum outlier over all the sets is 5.8% above the normalized mean value, for FLASH level 3/shutter A. The minimum outlier over all sets is also for FLASH level 3/shutter A and is 8.9% below the normalized mean value. Investigation of these outliers has revealed no systematic cause for the excursions and we recommend that users continue using the post-flash as they would have previously.
216.05 – Optimal Extraction of Contaminated Slitless Spectroscopy - R. Ryan , S. Casertano, N.Pirzkal
We present a new formalism for extracting one dimensional spectra from a collection of slitless spectroscopic images, ideally taken at various position angles and/or dither positions. Our method solves for the spectrum of all the sources simultaneously, hence we inherently correct for contamination from overlapping sources and thereby eliminate the notion of "contamination corrections." Using simulated data, we demonstrate the sensitivity of our algorithm to various instrumental and observational effects, such as astrometric registration, background subtraction, and photometric noise. We also present analysis of HST/WFC3-IR data, which highlights two major advancements over standard extraction-based techniques: (1) increase in spectral resolution without loss in signal-to-noise, and (2) improve spectra for highly contaminated sources. For example, we extract the spectrum of the z~11 galaxy strongly lensed by MACS J0647, and our analysis of this galaxy shows a strong detection of the Lyman break.
January, 2017
Grapevine, Texas
206.04 – Improving HST/WFC3 photometric calibration - S. Deustua, The WFC3 Team
I will discuss improvements in the photometric calibration of the Wide Field Camera 3 (WFC3) imaging channels based on the analisys of 6 years of standard star observations acquired between 2009 and 2015. Observations of the three white dwarf standard stars, GD 153, GD 71, and G191B2B and of the G-type star P330E were obtained at multiple dither positions . Departing from previous practice, chip-dependent inverse sensitivities for the WFC3/UVIS channel are computed at r=10 pixels for the 42 full frame filters (excluding the 20 quad filters); and these data also provide encircled energy fractions as a function of filter. Chip-dependent inverse sensitivities differ on average by 3% from previous computations, primarily due to drizzling effects. I describe the UVIS 2.0 (chip-dependent) philosophy and discuss the esults in the context of prior photometric calculations. Further, I will also discuss the status of the WFC3/IR photometric calibration, in view
238.04 – HST Wide Field Camera 3: Instrument Status and Advice for Cycle 25 Proposers - I. Momcheva, The WFC3 Instrument Team
The Wide Field Camera 3 on-board of the Hubble Space Telescope provides astronomers with powerful imaging and slitless spectroscopic capabilities from the near-ultraviolet (200 nm) to the near-infrared (1700 nm). We summarize the basic characteristics and performances of WFC3, highlight changes in the calibration pipeline, summarize the calibration program for Cycle 24, and provide new information useful for observers planning to apply for
238.05 – Charge transfer efficiency in HST WFC3/UVIS: monitoring and mitigation - S. Baggett , J. Anderson, M. Sosey, M. Bourque, C. Martlin, H. Kurtz, C. Shanahan, V. Kozhurina-Platais, E. Sabbi, The WFC3 Team
The UVIS channel of the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) contains a 4096x4096 pixel e2v CCD array. The detectors have been performing well on-orbit but as expected, are exhibiting the cumulative effects of radiation damage. The result is a growing hot pixel population and declining charge transfer efficiency. We summarize the progression of the CTE losses, their effects on science data, and discuss two of the primary mitigation options: post-flash and a pixel-based CTE correction. The latter is now part of the automated WFC3 calibration pipeline in the Mikulski Archive for Space Telescopes (MAST), providing observers with both standard and CTE-corrected data products.
October, 2016
Sorrento, Italy
The Hubble Space Telescope Wide Field Camera 3 Quicklook Project - M. Bourque, V. Bajaj, A. Bowers, M. Dulude, M. Durbin, C. Gosmeyer, H. Gunning, H. Khandrika, C. Martlin, B. Sunnquist, and A. Viana
The Hubble Space Telescope’s Wide Field Camera 3 (WFC3) instrument has been acquiring ∼50-100 images daily since its installation in 2009. The WFC3 Quicklook project provides a means for WFC3 instrument analysts to store, calibrate, monitor, and interact with these data through the various Quicklook systems: (1) a ∼175 TB filesystem, which stores the entire WFC3 archive on disk, (2) a MySQL database, which stores image header data, (3) a Python-based automation platform, which currently executes 22 unique calibration and monitoring scripts, (4) a Python based code library, which provides system functionality such as logging, downloading tools, database connection objects, and filesystem management, and (5) a Python/Flask based web interface to the Quicklook system. The Quicklook project has enabled large scale WFC3 analyses and calibrations, such as the monitoring of the health and stability of the WFC3 instrument, the measurement of ∼20 million WFC3/UVIS PSFs, the creation of WFC3/IR persistence calibration products, and many others. The Quicklook system may be extended to support the forthcoming James Webb Space Telescope mission.
October, 2016
Trieste, Italy
The Hubble Space Telescope Wide Field Camera 3 Quicklook Project - M. Bourque, V. Bajaj, A. Bowers, M. Dulude, M. Durbin, C. Gosmeyer, H. Gunning, H. Khandrika, C. Martlin, B. Sunnquist, and A. Viana
The Hubble Space Telescope’s Wide Field Camera 3 (WFC3) instrument has been acquiring ∼50-100 images daily since its installation in 2009. The WFC3 Quicklook project provides a means for WFC3 instrument analysts to store, calibrate, monitor, and interact with these data through the various Quicklook systems: (1) a ∼175 TB filesystem, which stores the entire WFC3 archive on disk, (2) a MySQL database, which stores image header data, (3) a Python-based automation platform, which currently executes 22 unique calibration and monitoring scripts, (4) a Python based code library, which provides system functionality such as logging, downloading tools, database connection objects, and filesystem management, and (5) a Python/Flask based web interface to the Quicklook system. The Quicklook project has enabled large scale WFC3 analyses and calibrations, such as the monitoring of the health and stability of the WFC3 instrument, the measurement of ∼20 million WFC3/UVIS PSFs, the creation of WFC3/IR persistence calibration products, and many others. The Quicklook system may be extended to support the forthcoming James Webb Space Telescope mission.
June 2016
Edinburgh, United Kingdom
HST/WFC3: understanding and mitigating radiation damage effects in the CCD detectors - S. M. Baggett, J. Anderson, M. Sosey, C. Gosmeyer, M. Bourque, V. Bajaj, H. Khandrika, C. Martlin
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.
Distortion of the pixel grid in HST WFC3/UVIS and ACS/WFC CCD detectors and its astrometric correction - V. Kozhurina-Platais, J. Mackenty, D. Golimovski, M. Sirianni, D. Borncamp, J. Anderson, N. Grogin
The geometric distortion of the CCD detectors used in the Hubble Space TelescopeWide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) instruments is characterized by both large and fine-scale distortions. The large-scale distortion, due to the complexity of the HST optical assembly, can be modeled by a high-order polynomial. The majority of fine-distortion is inherent to the CCD detectors themselves, which manifests itself as fine-scale, correlated systematic offsets in the residuals from the best-fit polynomial solution. Such systematic offsets across the CCD chip introduce astrometric errors at the level of about 0.1 pix (up to 1.5 μm within the 15 μm pixels). These fine-scale and low-amplitude distortions apparently arise from the spatial irregularities in the pixel grid. For the WFC3/UVIS CCD chips, there is a clear pattern of periodic skew in the lithographic-mask stencil imprinted onto the detector. Similar irregularities in the pixel grid of ACS/WFC CCD chips are even more pronounced by the narrow (68×2048 pixel) lithographic-mask stencil. To remove these distortions, a 2-D correction in the form of a look-up table has been developed using HST images of very dense stellar fields. The post-correction of fine-scale astrometric errors can be removed down to the level of 0.01 pix (0.15 μm) or better.
June, 2016
San Diego, California
216.03 – HST/WFC3: Evolution of the UVIS Channel's Charge Transfer Efficiency - C. Gosmeyer , S. Baggett , J. Anderson, The WFC3 Team
The Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) contains both an IR and a UVIS channel. After more than six years on orbit, the UVIS channel performance remains stable; however, on-orbit radiation damage has caused the charge transfer efficiency (CTE) of UVIS's two CCDs to degrade. This degradation is seen as vertical charge 'bleeding' from sources during readout and its effect evolves as the CCDs age. The WFC3 team has developed software to perform corrections that push the charge back to the sources, although it cannot recover faint sources that have been bled out entirely. Observers can mitigate this effect in various ways such as by placing sources near the amplifiers, observing bright targets, and by increasing the total background to at least 12 electrons, either by using a broader filter, lengthening exposure time, or post-flashing. We present results from six years of calibration data to re-evaluate the best level of total background for mitigating CTE loss and to re-verify that the pixel-based CTE correction software is performing optimally over various background levels. In addition, we alert observers that CTE-corrected products are now available for retrieval from MAST as part of the CALWF3 v3.3 pipeline upgrade.
216.04 – HST/WFC3: Improvements to the UVIS Dark Calibration - M. Bourque , S. Baggett, The WFC3 Team
The Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS detector, comprised of two e2v CCDs, exhibits an inherent dark current (in the absence of any illumination) presently measured at ~7 e-/hr and increasing at ~1 e-/hr/yr. Additionally, detector degradation due to on-orbit radiation damage generates a continuously increasing though small population of hot pixels (dark current exceeding 54 e-/hr, currently ~4% of each chip). We present the results of the WFC3/UVIS dark calibration, which provides calibration files used as a correction for these detector characteristics. We also discuss the impacts that Charge Transfer Efficiency (CTE) losses and detector post-flashing have on the hot pixel population, as well as various improvements to the calibration procedure that were introduced in the CALWF3 v3.3 pipeline.
216.05 – WFC3: Status, Calibrations and Advice for the CY24 Observers - E. Sabbi, The WFC3 Team
The Wide Field Camera 3 is UV, Visible and near Infrared Camera on boar of the Hubble Space Telescope. We report on the current status of the instrument and on the recent significant improvements in the photometric, flat fields, dark current, and CTE calibrations for the UVIS channel. As a result of this effort we obtained the new independent solutions for the two CCD detectors, and have improved the zero points and color terms in the near-UV and visual wavelengths. We report on the improved astrometric solutions and PSF calibrations. We also highlight new observing strategies recently developed to allow efficient observations of very wide fields of view. Finally new tools for the planning and extraction of slittles spectroscopic observations of crowded fields are presented.
216.06 – HST Frontier Fields: WFC3/IR data processing, persistence, time-variable background - H. Khandrika , A. Koekemoer , J. Lotz , J. Mack , M. Robberto , B. Hilbert , E. Sabbi, The Hubble Frontier Fields Pipeline Team, The WFC3 Team
The Hubble Space Telescope Frontier Fields (HFF) pipeline and WFC3 teams discuss the specialized procedures for processing IR data for the Frontier Fields program. Frontier Fields is a Director's Discretionary program that uses ultra-deep imaging to observe lensing galaxy clusters in an effort to search for the most distant observable galaxy. The program uses both the Advanced Camera for Surveys (ACS) and Wide-Field Camera 3 (WFC3/IR) observing the prime and parallel areas of each field simultaneously. The WFC3/IR data are processed through a pipeline which performs calibrations not included in the standard CalWF3 software including persistence correction, Time-Variable-Background (TVB) correction, and scripts used to create satellite trail masks. Here the HFF pipeline team present the individual methods that perform the corrections and showcase the results of these corrections on sample data of Abell 370, Abell S1063 and others.
216.15 – HST/WFC3: IR Channel Photometric Performance and Stability - V. Bajaj , S. Deustua , C. Gosmeyer , P. McCullough, The WFC3 Team
The Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) contains two channels: UVIS and IR. The IR channel makes use of a HgCdTe detector produced by Teledyne. By periodically observing a set of bright white dwarf stars we are able to monitor the photometric performance of the IR detector over the last seven years. We present the results of the photometric measurements over time. In addition we discuss the effects of detector behavior not accounted for by the typical calibration (performed by CALWF3) such as the high order nonlinear response of detector pixels, persistence of previous exposures, and contamination of the channel. The findings of this investigation will have a direct impact on the flux calibration of the channel (and the resulting zeropoints).
August, 2015
Honolulu, Hawaii
P2.051 – HST/WFC3 IR Detector Updates: Photometry, Grisms, and a New SPARS Sequence - C. Gosmeyer, S. Baggett, V. Bajaj, M. Bourque, G. Brammer, M. Durbin, J. MacKenty, P. McCullough, N. Pirzkal, R. Ryan
We discuss new developments to the characterization and monitoring of the IR channel on the Wide Field Camera 3 (WFC3). Installed on the Hubble Space Telescope (HST) in May 2009, WFC3 is a fourthgeneration imaging instrument, comprising a UVIS channel and an IR channel. The IR detector is composed of a low-noise, high-QE 1024×1024 pixel HgCdTe chip and remains stable after 5 years onorbit. We present new measurements of the detector's photometric stability and the high precision photometry that can be achieved through spatial scanning. We give an update on the status and calibrations of the IR grisms. We also report on the IR “blobs” and their effect on photometry, and the evolution and properties of IR "snowballs." Finally, we introduce a new SPARS sequence that is planned for release this fall.
P2.052 – HST/WFC3 UVIS Detector: Dark, Charge Transfer Efficiency, and Point Spread Function Calibrations - M. Bourque, J. Anderson, S. Baggett, A. Bowers, J. MacKenty, K. Sahu
Wide Field Camera 3 (WFC3) is a fourth-generation imaging instrument on board the Hubble Space Telescope (HST) that was installed during Servicing Mission 4 in May 2009. As one of two channels available on WFC3, the UVIS detector is comprised of two e2v CCDs and is sensitive to ultraviolet and visible light. Here we provide updates to the characterization and monitoring of the UVIS performance and stability. We present the long-term growth of the dark current and the hot pixel population, as well as the evolution of Charge Transfer Efficiency (CTE). We also discuss updates to the UVIS dark calibration products, which are used to correct for dark current in science images. We examine the impacts of CTE losses and outline some techniques to mitigate CTE effects during and after observation by use of postflash and pixel-based CTE corrections. Finally, we summarize an investigation of WFC3/UVIS Point Spread Functions (PSFs) and their potential use for characterizing the focus of the instrument.
P2.054 – HST/WFC3 Characteristics: gain, post-flash stability, UVIS low-sensitivity pixels, persistence, IR flats and bad pixel table - H. Gunning, S. Baggett, C. Gosmeyer, K. Long, R. Ryan, J. MacKenty, M. Durbin
The Wide Field Camera 3 (WFC3) is a fourth-generation imaging instrument on the Hubble Space Telescope (HST). Installed in May 2009, WFC3 is comprised of two observational channels covering wavelengths from UV/Visible (UVIS) to infrared (IR); both have been performing well on-orbit. We discuss the gain stability of both WFC3 channel detectors from ground testing through present day. For UVIS, we detail a low-sensitivity pixel population that evolves during the time between anneals, but is largely reset by the annealing procedure. We characterize the post-flash LED lamp stability, used and recommended to mitigate CTE effects for observations with less than 12e-/pixel backgrounds. We present mitigation options for IR persistence during and after observations. Finally, we give an overview on the construction of the IR flats and provide updates on the bad pixel table.
P2.055 – HST/WFC3: UVIS Detector Chip Dependent Photometry, Stability, High Precision Photometry with Spatial Scanning - A. Bowers, J. Mack, S. Deustua
The Wide Field Camera 3 (WFC3) instrument was installed on HST in 2009. The two UVIS CCD chips were constructed on different wafers, making them independent detectors. Motivated by the difference in the quantum efficiency, white dwarf observations were taken in all 42 filters at different positions across each chip to characterize chip-dependent structure of the PSF. We discuss the computation of the average sensitivity ratio per chip for all UVIS filters, which are important for deriving the new chip dependent zeropoints. We also present the new chip dependent zeropoints and encircled energy curves.
January 4 - January 8, 2015
Seattle, Washington
June 1 - June 5, 2014
Boston, Massachusetts
122:06: WFC3 News Regarding IR Backgrounds, Spatial Scans, and Cycle 22 Phase 2 Advice
122.05: HST WFC3: UVIS Charge-Transfer Efficiency Losses: Mitigation and Correction
122.04: HST WFC3: UVIS Dark Calibration
122.03: HST Wide Field Camera 3: Improvements to WFC3/UVIS Photometric Calibration
January 5 - January 8, 2014
Washington, D.C.
149.04 WFC3: Improved WFC3 Calibration Products
149.02 WFC3: Status and Advice for Cycle 22 Proposers
347.21 WFC3: Precision Infrared Spectrophotometry with Spatial Scans of HD 189733b and Vega
149.03 WFC3: Understanding and Mitigating UVIS Charge Transfer Efficiency Losses and IR Persistence Effects
January 6 - January 10, 2013
Long Beach, CA
June 10 - June 14, 2012
Anchorage, AK
Status and Calibration of the HST Wide Field Camera 3
Fitting a Pixel-Based CTE Model to the WFC3/UVIS CCD Detector
January 8th, 2012 - January 12th, 2012
Austin, TX
May 1st, 2011 - May 6th, 2011
Flagstaff, AZ
Spatial Scanning with HST for Exoplanet Transit Spectroscopy and other High Dynamic Range Observations
January 9th, 2011 - January 13th, 2011
Seattle, WA
October 11th, 2010 - October 14th, 2010
Venice, Italy
The WFC3 on-orbit calibration program
January 3rd, 2010 - January 7th, 2010
Washington, D. C.
(463.01) WFC3: Grism Performance
(463.03) WFC3: UVIS and IR Flat Fields
(463.09) WFC3 - Geometric Distortion and Multidrizzle
(463.10) WFC3: UVIS Detectors
(463.12) WFC3: In-Flight Performance Highlights
(463.13) WFC3: The Photometric Performance of the UVIS and IR Cameras
(463.14) WFC3: Calibration Software, Products and Reference Data
(463.18) WFC3: IR Detector Performance in SMOV and Cycle 17
(463.19) WFC3: SMOV and Cycle 17 Calibration Programs
(463.21) WFC3: Correction of UVIS Fringing Effects at Long Wavelengths
(463.22) WFC3: Optical Alignment and Performance