WFC3 STAN Issue 34, January 2021
1. WFC3 at AAS 237!
Three posters will be presented at the upcoming AAS related to WFC3 data reduction as well as recent WFC3 science results. We invite all WFC3 users at the AAS to stop by during scheduled poster sessions to review these projects and their available tools and results. Below we include condensed summaries of the various posters - full abstracts are available through the AAS; we link to individual poster abstracts below.
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.
2. Updates on stsynphot and pysynphot
J. Mack and P.L. Lim.
HST synthetic photometry simulates photometric data and spectra as they are observed with the telescope. The first generation of software was available via the IRAF-based SYNPHOT package (Bushouse & Simon 1998). This was later replaced with the Python equivalent PYSYNPHOT (Lim, Diaz, & Laidler 2015). In order to repurpose the functionality for a wider audience (other than HST users) and to take advantage of Models and Fitting (astropy.modeling) and Units and Quantities (astropy.units), the software was refactored again and separated into synphot and stsynphot (For more details, see the latest Synthetic Photometry documentation). No active development is currently provided for PYSYNPHOT, except for critical bug fixes, and this package will have a final release and be archived sometime in 2022.
We therefore advise users to transition to using stsynphot for computing synthetic photometry with HST, and several useful HST tutorials are provided. The WFC3 team has developed a Jupyter notebook, available from the most recent News item on the Photmetric Calibration Page, and a preview viewable here, which uses stsynphot to calculate the latest UVIS and IR photometric zeropoints 'on-the-fly' for any observation date. This tutorial is particularly helpful for the new UVIS time-dependent calibration, which makes use of the 'MJD' observation date in observing mode 'obsmode' parameter.
3. DASH (Drift And SHift) Data Processing Package and User Tutorial
DASH mode enables large, shallow WFC3/IR mosaics within one orbit by dropping to gyros for guiding on all exposures after the first exposure (see Section 6.11.5 in IHB). WFC3 now has an in-depth Instrument Science Report 2021-02 available that walks users through a new Jupyter Notebook workflow and software package to aid in processing Drift And SHift (DASH) data. While the general process of how to derive science-ready data from DASH observations is described in the paper that introduces DASH (Momcheva, et. al 2016), the resources found at https://github.com/spacetelescope/wfc3_dash are an interactive and adaptable version of instructions and scripted workflow.
Figure 1: Flowchart of the steps of the wfc3_dash package usage workflow demonstrated in the Jupyter notebook tutorial.
The notebook, 'Step_1-Creating_Science_Data_from_single_exposure_IMAs.ipynb', provides an in-depth walk through of using the wfc3_dash package to turn an individual DASH IMA — a calibrated intermediate IR mutliaccum image — into a stacked single image ready for science analysis. Steps 2 and 3 are currently in production and will provide users with workflows to create more complex science products; those steps are discussed further in section 5 of the ISR.
Figure 2: (Left) Example of DASH observation FLT output from the pipeline. The 'smearing' due to the movement of the telescope over the course of the observation is very visible in all sources. (Right) Example of the wfc3_dash package workflow output of the same observation. The sources now appear un-smeared as the IMA diff files have been aligned using the Jupyter notebook workflow.
4. 'Single Visit Mosaics': New MAST Data products
J. Mack (on behalf of the Hubble Advanced Products Team).
On December 17, 2020, MAST began production of new WFC3 and ACS products in the HST data calibration pipeline. Referred to as 'Single Visit Mosaics' (SVMs), data acquired within the same HST visit are all drizzled onto the same north-up pixel grid and have improved relative alignment between filters. When possible, sources in the images have been further aligned to the Gaia source catalog to improve the absolute astrometry in the image world coordinate system (WCS).
This means that grism images will now be offset from their direct image counterparts, since only the later may be aligned to an external reference catalog. In order to preserve relative alignment between grism and direct images, users may wish to back out the updated WCS as described in Section 5 of the notebook, 'Using updated astrometry solutions'.
The new data products were first announced in the December 2020 MAST Newsletter and will be available as they are produced in the pipeline, taking roughly 1-2 months before all archival data have been processed. Approximately half of WFC3 (non-grism) images will have SVM products, and these will contain the string 'FIT_SVM_GAIA' in the 'WCSNAME' keyword of the science image header. More detail on the software used to compute the new data products is provided in the DrizzlePac documentation for Single Visit Mosaic Processing.
5. Introducing ExoCat: Catalogue of WFC3 Transiting Exoplanet Observations
N. Nikolov, C. Martlin, J. Medina, K. Stevenson.
The beta release of a new WFC3 project webpage, ExoCat, is now available; it tabulates the status of competed and planned observations of transiting exoplanets by the WFC3 IR instrument, both proposed and completed. We hope ExoCat will help reduce target duplication and redundant effort in proposal preparation.
The preliminary (beta) version of this tool is currently available as a static table with the following information:
- Target name
- Program ID
- Status of the program
- Filter used
- Phase start - planet orbital phase
- Phase end
- Number of orbits
- Scan direction
- Scan rate
- Alternative target name
Figure 1. Example of the current beta version of the ExoCat project catalogue.
We are in the active development phase and looking to complete the first version of the dynamic tool soon. Future improvements to the webpage include: Expanding program query to WFC3/UVIS as well as other HST instruments, and a user-friendly interface that allows for easier navigation through the table, which includes a search bar feature and ability to sort the table rows. We are open to community input and suggestions either through opening an issue on our github page or through the HST Help Desk — please be sure to specific the WFC3 Help Desk Team.
Further, with the upcoming launch of JWST, we envision many useful updates and expansions of this tool in the future to include similar information for the JWST instruments.
6. New Documentation
ISR 2020-10: Updated WFC3/IR Photometric Calibration - V. Bajaj, A. Calamida, J. Mack
ISR 2020-09: Updated Calibration of the UVIS G280 Grism - N. Pirzkal
ISR 2021-01: WFC3/IR Filter-Dependent Sky Flats - J. Mack, H. Olszewski, N. Pirzkal
ISR 2021-02: Reducing Drift and Shift (DASH) Data Using wfc3_dash and Accompanying Notebook Workflow - C. Martlin, R. O’Brien, I. Momcheva, M. Gennaro
The complete WFC3 ISR archive is available here.
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