On November 23, 2021, MAST began producing source catalogs as part of the SVM data products.
ASTROMETRY WATCHES SOFTWARE
The software used to compute these new data products is described in the DrizzlePac documentation for Single Visit Mosaic Processing. SVM data products with both relative alignment (by filter) and absolute alignment to Gaia will contain the string 'FIT_SVM_GAIA' in the 'WCSNAME' keyword in the science extension of the image header.
When possible, sources in the images have been aligned directly to the Gaia catalog to improve the WCS. The data products are all drizzled onto the same north-up pixel grid and may include improved relative alignment across filters for datasets acquired within the same visit, enabling easy comparison of the images through multiple filters. These new 'Hubble Advanced Products' (HAP) are referred to as 'Single Visit Mosaics' (SVMs) and are described in a MAST Newsletter article from December 2020.
ASTROMETRY WATCHES ARCHIVE
These Hubble Legacy Archive (HLA)-style mosaics comprise the data from a single HST visit which are aligned to a common astrometric reference frame. On December 17, 2020, the MAST began production of new ACS and WFC3 products in the HST data calibration pipeline (see the following MAST Newsletter article. The software used to produce these drizzled products is described on the Pipeline Astrometric Calibration page. For these data products, the typical pointing uncertainty is reduced to ~10 mas, although the uncertainties increase for observations further in time from the Gaia reference epoch (2015.0 for DR1, 2015.5 for DR2). grism and moving target observations) or the alignment may fail due to a lack of sources in either the HST image or the Gaia catalog, approximately 80% of ACS/WFC and 50% of WFC3/IR frames have been directly aligned. While some observing modes cannot be aligned to Gaia (e.g. When possible, an additional correction was applied by aligning sources in each HST image directly to the Gaia catalog, referred to as an a posteriori correction. Combining this with knowledge of the instrument distortions, an a prioricorrection was made. This reduces the typical uncertainties in the positions of the guide stars to ~200 mas over the entire sky. The first makes use of a new version of the Hubble Guide Star Catalog (GSC version 2.4.0) which updates the coordinates of the guide stars with the positions from Gaia DR1. The World Coordinate System (WCS) in the image header of all WFC3 and ACS datasets were updated and may include one or more corrections. On December 3, 2019, the first set of improved astrometry data were released in MAST. We therefore recommend these to be used as ‘discovery images’ for comparing observations in different detectors and passbands and not for precise photometry. When combining observations over a large date range, MVMs may have photometric errors of several percent or systematic alignment errors when combining visits with different catalog solutions.
The MVM data products combine all ACS/WFC, WFC3/UVIS, or WFC3/IR images falling within a pre-defined 0.2° x 0.2° 'sky cell' for each detector+filter, which are drizzled to a common all-sky pixel grid. These catalogs supersede those produced by the Hubble Legacy Archive and will be the basis of the next version of the Hubble Source Catalog. The SVM products include an additional relative alignment across filters in a visit, and the drizzled images are used to generate point source and segment catalogs during pipeline processing. We describe two new types of Hubble Advanced Products (HAP), referred to as Single Visit Mosaics (SVMs) and Multi Visit Mosaics (MVM), which began production in MAST in late-2020 and mid-2022, respectively. We compute statistics on the alignment fraction for each detector and estimate the uncertainties in the WCS solutions when aligning to different reference catalogs. The updated WCS solutions are computed during pipeline processing by aligning sources in the HST images to a select set of reference catalogs (e.g. This ISR describes updated WCS solutions in MAST data as well two new types of Hubble Advanced Products.Ībstract: As of late-2019, MAST data products for ACS and WFC3 include improved absolute astrometry in the image header World Coordinate System (WCS). In August 2022, a new ACS/WFC3 instrument science report ( ACS ISR 2022-03 WFC-06) titled ' Improved Absolute Astrometry for ACS and WFC3 Data Products' was published.
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