About This Article
We invite all interested users at the AAS to stop by the WFC3 iPosters at the upcoming AAS meeting, and to reach out to the presenters directly if unable to attend the poster session. Below, we provide abstracts and session information, and link to the presentation listings in the AAS meeting itinerary. Times are given in Mountain Daylight Time (MDT).
102.02 HST/WFC3: Recent Calibration and Machine Learning Updates for 2023 - I. Rivera, C. Martlin, J. Green, F. Dauphin, S. Baggett, and the WFC3 Team
Monday, June 5, 9:00 - 10:00 AM MDT
The Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope (HST) has enabled high-resolution imaging and low-resolving power slitless grism spectroscopy from the ultraviolet (UV) into the near-infrared (NIR) since it was installed in 2009. The WFC3 team works to provide the latest, up-to-date software for calibrating and analyzing WFC3 images to ensure the highest quality data products possible for observers. This poster provides an overview of the available reference files for calibration (e.g. new UVIS post-flash files) as well as new notebook tutorials for WFC3 analysis and machine learning, which are hosted in our “WFC3Library” and “DeepWFC3" GitHub repositories. In the remainder of the poster, we discuss implementation of “stenv”, a software environment developed by Space Telescope Science Institute to replace Astroconda. Stenv provides a common environment for both the HST and the James Webb Space Telescope (JWST) pipelines. Here we will show how to get started with it and highlight the included packages.
102.06 Updates for Slitless Spectroscopy with HST/WFC3 and ACS - A. Pidgeon, D. Som, B. Kuhn, A. Pagul, D. Nguyen, R. O'Steen, N. Hathi
Monday, June 5, 9:00 - 10:00 AM MDT
Wide Field Camera 3 (WFC3) and the Advanced Camera for Surveys (ACS) are primarily used as imaging instruments for the Hubble Space Telescope (HST), but are also capable of slitless spectroscopy using grism and prism elements. HSTaXe is the officially supported software for extracting and calibrating slitless spectroscopic data from WFC3 and ACS. We present recent updates to HSTaXe with major bug fixes and enhanced support for all HST slitless spectroscopy modes. Alongside these updates, we showcase several Jupyter Notebook “cookbooks” designed to improve the experience of new HSTaXe users. These cookbooks serve as tutorials on how to extract spectra from WFC3 and ACS grism data, and include several pre-processing steps that allow for additional functionality and improved output quality. We also discuss the creation of a new master sky image for the WFC3/UVIS G280 grism and the development of new user tools for slitless spectroscopy with HST and JWST.
102.08 HST/WFC3 Photometric Calibration: Recent Results and Tools - M. Marinelli, V. Bajaj
Monday, June 5, 9:00 - 10:00 AM MDT
The Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) is a powerful imager with wavelength coverage from the near-UV to the near-IR. Capable of observing in both direct (staring) and scanning modes, and with 61 total filters and 3 grisms, WFC3 has been the “workhorse” of HST since its installation in 2009. We review the status of the instrument, present results from recent photometric calibration programs, and discuss ongoing work to characterize detector sensitivity for both the WFC3/IR and WFC3/UVIS channels. We also introduce new/newly-public tools for photometric analysis in an effort to increase both accessibility and transparency.
J. Ryon, S. Lockwood, and V. Laidler
STScI has released an alpha version of the Pandeia-based Exposure Time Calculator (ETC) for the Hubble Space Telescope (HST) at hst.etc.stsci.edu. The alpha release is intended for users to familiarize themselves with the new interface and perform example calculations for supported observing modes.
IMPORTANT: The official HST ETC for Cycle 31 proposal submissions is located at etc.stsci.edu. Please do not include results from the Pandeia-based HST ETC in Cycle 31 proposals.
Pandeia is a pixel-based exposure time calculator paired with a modern graphical user interface. While Pandeia was developed for JWST, it is a general framework, data-driven ETC capable of supporting multiple missions, including HST. It includes advanced features that go beyond the capabilities of previous ETCs, such as algorithms that accurately model both data acquisition and post-processing of data, and it provides functionality for users to efficiently explore and compare a large volume of parameter space in their calculations.
The HST implementation of Pandeia supports many HST observing modes. Its graphical user interface allows users to create workbooks to manage related sets of calculations, create complex astronomical scenes with multiple sources, compare the results of multiple calculations, and share their workbooks with other users. Several HST observing modes are not yet available, but will be made available in future releases.
A Migration Guide has been prepared to facilitate the transition to the Pandeia-based ETC for experienced users of the official ETC. Please start there if you are not already experienced with the JWST ETC.
We request feedback from the user community regarding the alpha release via the HST Help Desk, particularly feedback related to the clarity of calculation results. An ETC representative will also attend the summer AAS meeting in Albuquerque to demo the Pandeia-based ETC and answer questions.
Planning to attend AAS? Visit the HST table at the STScI booth to see a demonstration of the new ETC. Isaac Spitzer will be presenting an iPoster on the new ETC on Monday June 5, 9:00 - 10:00 AM, and will also be available for further questions and discussions at the STScI booth Tuesday June 6 (3:00 - 4:00 PM and 5:00 - 6:30 PM) and Wednesday June 7 (10:00 AM - 12:00 PM and 4:00 - 5:30 PM). All times are given in Mountain Daylight Time (MDT).
A. O'Connor, J. Mack, K. Huynh, and F. Dauphin
The WFC3/IR background is a combination of zodiacal light, helium line emission in the Earth's upper atmosphere, and/or scattered light from observing close to the bright Earth limb. Both line emission and scattered light can vary significantly within a
MULTIACCUM exposure, corrupting
calwf3's 'up-the-ramp' fit which is used to identify cosmic-rays. This algorithm assumes that a given pixel sees a constant count rate from both sources and diffuse background (i.e., that the "ramps" are linear). Strong time-variability may compromise the quality of the calibrated 'FLT' image and require manual reprocessing prior to any photometric analysis.
The WFC3 team has developed a new set of Jupyter notebooks to aid the user in identifying images affected by variable background. New visualization tools now make it easier to inspect individual reads and plot the accumulated signal through the exposure. Each notebook illustrates a unique method for correcting the IR images, including: 1) turning off the ramp fitting step, 2) 'flattening' the ramp by subtracting the excess background per read, or 3) excluding reads impacted by scattered light. The notebooks are available in the WFC3Library GitHub repository and summarized in the table below for various use cases.
|Inspect the IMA
Any IR imaging filter.
|Use the final read of the IMA
Any IR imaging filter.
|Subtract the median background per IMA read and re-run the ramp fit with
All filters affected by the helium line emission background.
|Mask specific reads in the RAW image and reprocess with
Removes scattered light present in reads at the beginning or end of an exposure.
|Subtract specific reads from the IMA
Removes scattered light or anomalies present in any read.
Spatial scanning is an observation method in which the telescope moves in a prescribed trajectory after guide star acquisition, trailing flux across the detector. As detailed in WFC3 ISR 2022-04 (Marinelli et al.), spatial scans offer greater photometric precision than standard staring mode observations do. Despite this, spatial scans have never been directly used in the absolute calibration of the WFC3/UVIS detector, since existing software used to generate synthetic observations is unable to model non-circular photometric apertures.
In a new report, we describe our methodology developed to calculate spatial scan aperture corrections, and initial results. As seen in Figure 1, we created scan spread functions (SSFs) to model calibration scans by convolving a point spread function (PSF) with the linear scan trajectory path. Two sets of PSFs were used: one generated from interpolating published encircled energy (EE) curves (top row), and another generated from blending those EE-derived point spread functions (PSFs) with empirically-derived PSFs (bottom row). By applying the same procedure used to calculate the scan photometry to the SSFs, we calculated the fraction of total modeled flux encapsulated within the photometric aperture, and used that as a multiplicative factor to correct synthetic observations.
The ratios of observed-to-synthetic count rates are constant over time (validating the currently-implemented time-dependent zeropoints), but there is a wavelength- and chip-dependent offset, as seen in Figure 2. We also find indications that the UVIS PSF may have 1-2% additional flux beyond a 150-pixel radius, which may be one of the underlying systematic factors contributing to the noted offset. An upcoming calibration program will make deep observations of isolated standard stars to refine our understanding of the UVIS PSF at large radii.
For more details, see WFC3 ISR 2023-02 (Marinelli & Bajaj).
In a new report, we describe an updated procedure for generating WFC3 UVIS superbias reference files. The 2021 and 2022 superbiases created with the updated procedure have been delivered to CRDS; all UVIS data since 2021 has been reprocessed and is available through MAST.
As part of the vetting process, we took a deep dive into the effects of readout dark current on the rising superbias level from 2009-2022. We found that readout dark contributes an appreciable fraction of the gradual increase in superbias level we have observed over the years. Figure 3 shows how the average residual signal in the superbias level is closely correlated with the estimated readout dark current, from 2009 to present. CTE trails from hot pixels and CRs also artificially increase the measured level in the superbias.
For more details see WFC3 ISR 2023-03 (Rivera & Kuhn).
ISR 2023-01: WFC3/UVIS Post-Flash: Stability of the LED and Creation of Time-Dependent Reference Files - C. Martlin & J. Green
ISR 2023-02: Testing Aperture Corrections for WFC3/UVIS Spatial Scans - M. Marinelli & V. Bajaj
ISR 2023-03 : WFC3/UVIS: 2021 and 2022 Superbias Reference File Procedural Updates - I. Rivera & B. Kuhn
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