About This Article
In this STAN, the COS team announces the release of a new Hubble Spectroscopic Legacy Archive that encompasses all publicly available COS and STIS spectra including more than 60,000 datasets and over 6000 individual targets. The COS team has also updated the Instrument Handbook to version 17.1 and the Data Handbook to version 6.0.
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Announcement of the new Hubble Spectroscopic Legacy Archive (HSLA)
The new Hubble Spectroscopic Legacy Archive (HSLA) provides scientifically validated coadded spectra of individual targets that have been observed with the Cosmic Origins Spectrograph (COS) and the Space Telescope Imaging Spectrograph (STIS) over their operating lifetime. HSLA uses data available in the Mikulski Archive for Space Telescopes (MAST) and automatically produces coadds whenever new data become publicly available, or when there is newly recalibrated data.
A key feature of the new HSLA is that it automatically defines individual targets, groups multiple observations of a single target into associations, and produces a classification for each target. Target associations make use of the dataset coordinates accounting for proper motions, and uses SIMBAD, NED and the Phase II observing proposals to determine which datasets should be associated with each unique target. Then, using the SIMBAD, NED, or Phase II keywords, a detailed classification is determined for an object to aid in the spectroscopic study of classes of astrophysical objects. The classifications consist of three tiers of detail, mapped to the Unified Astronomy Thesaurus (UAT) . For example, the HSLA target Markarian 817 is classified at Tier 1 as a Galaxy, Tier 2 as an Active Galaxy, and at Tier 3 as a Seyfert. It corresponds to the UAT object Seyfert Galaxies (1447). The new HSLA facilitates scientific analysis and creation of diagrams similar to that in Figure 1, which shows the galactic coordinates of all COS and STIS spectra of white dwarfs that cover two silicon (Si) lines that can be used to study the local ISM (Si II 1261 Å) or the accretion of rocky material onto white dwarf atmospheres (Si II 1265 Å). In total, the HSLA contains over 800 white dwarfs (WDs). In addition, the HSLA has spectra for over 3000 individual stars and over 2000 individual galaxies.
Coadded spectra with rigorous input criteria are produced for each observing mode, and in the case of COS far-ultraviolet observations for each lifetime position (LP). Additionally a quicklook spectrum spanning the entire wavelength range covered by the observations is produced by abutting the spectra from a selection of individual modes. An example HSLA composite STIS and COS spectrum of Beta Pictoris is shown in Figure 2, covering a wavelength range from 1135-3095 Å and over four orders of magnitude in flux.
For each individual target HSLA also provides a human-readable metadata file with key information that can be used in searches or for further exploration of the data. The metadata file includes the target name and unique identifiers, the target coordinates in J2000, information on the target's name and classification information, and a summary of the programs and instrument modes that are included in the target association.
HSLA data products, including quicklook coadds (_aspec files), coadded single grating products (_cspec files), metadata files (_metadata files), and code output logs (.trl files) are available at the MAST Portal, the HST Mission Search Form or via astroquery. Since the HSLA is fully automated, it will be updated routinely as new HST spectroscopic data are taken or if data are reprocessed with improved calibrations. Data access may change with time and users are encouraged to visit the HSLA Webpage for the latest details on how to access data.
The coadd code and its HASP/HSLA wrapper are available for public use in Space Telescope’s GitHub Organization (coadd: ULLYSES repository, wrapper: HASP repository). Both codes are scripted in Python (compatible with versions 3.9 and above) and are installable using pip. Two notebooks specifically address the HSLA data products and the challenges inherent in combining data from observing programs that are separated in time by many years.
The first notebook, "Introduction to the HSLA Data Products and Tools," explores the standard HSLA data files returned by MAST. It provides a simple example of a custom coadd, demonstrating how to adjust the logic by which the abutting routine decides which coadded spectra (_cspec files) to use for each wavelength region.
The second notebook, "Combining COS Data from Multiple Lifetime Positions and Central Wavelengths," explores how the COS line-spread function (LSF) varies with LP and CENWAVE. Because the HASP/HSLA script sums all of the spectra from a particular grating without regard to LP or CENWAVE, its final products may not have the highest-possible spectral resolution. The notebook presents several techniques for dealing with these effects.
For comprehensive details, please visit the HSLA webpage or the HSLA Summary ISR.
Updates to the COS Instrument Handbook and Data Handbook
Additionally, the COS team has published a new version 6.0 of the COS Data Handbook edited by N. Indriolo. This version of the handbook was updated to include descriptions of the new High Voltage Dependent Sensitivity Correction (HVDSCORR) calibration step and its corresponding reference file (HVDSTAB) and revised descriptions of reference files that were modified (e.g., DGEOFILE: Delta Geometric Correction File; YWLKFILE: Y-Walk File) as part of the recent delivery to provide improved geometric distortion and walk corrections for the FUV detector. The WCPTAB (Wavelength Calibration Parameter Table) description was also updated to include details about the variables that are used to empirically model shifts in the dispersion direction during long exposures made in SPLIT wavecal mode. Finally, the latest version of the data handbook includes a new Appendix that introduces the Hubble Advanced Spectral Products (HASP), providing users with a general overview of this initiative, information on the newly available products, and a description of the methods adopted for coadding spectra.
The COS team has released an updated version of the COS Instrument Handbook for Cycle 33, Version 17.1, incorporating significant changes to reflect the adoption of new detector Lifetime Positions. Specifically, the handbook now documents the commissioning of LP7 and LP10, which are being used for G130M blue modes (1055, 1096, 1222, and 1291) and all G160M modes, respectively. Corresponding updates were made to tables of default lifetime positions, summaries of spectral coverage, and operational overheads. Together, these changes provide users with accurate guidance for planning and executing COS FUV spectroscopy in the upcoming observing cycles.