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STScI Newsletter
2024 / Volume 41 / Issue 01

About this Article

Travis Fischer (tfischer[at]stsci.edu) and the HASP Team

The Hubble Advanced Spectral Products (HASP) initiative, developed by the Space Telescope Science Institute (STScI), marks a pivotal advancement in archival Hubble Space Telescope (HST) data. This innovative program significantly enhances the utility of data from the Cosmic Origins Spectrograph (COS) and Space Telescope Imaging Spectrograph (STIS), with the ultimate goal of providing easy access to high quality one-dimensional (1-D) spectra that are robustly and flexibly combined at the program and visit level. With data products that are automatically updated as calibrations change or new data comes in, a user can immediately access the latest, up to date spectroscopic data without having to conduct their own spectroscopic coaddition.

The default pipeline products of a given program observing targets with COS and/or STIS do not typically include combinations of different gratings, central wavelengths (CENWAVEs), or apertures. This has historically meant that users were responsible for coadding different spectra for final scientific analyses. The Hubble Spectroscopic Legacy Archive (HSLA) coadds multiple COS modes into single 1-D spectra. The coadd provides the foundation for the UV Legacy Library of Young Stars as Essential Standards (ULLYSES) program in order to create high level science products of spectra from a variety of modes and spectrographic instruments. The HASP coadd algorithm is an evolution of these works, designed to be applied in an automated fashion to nearly every COS and STIS spectrum in the archive, creating robust coadded and combined products for programs and their constituent visits (Figure 1). HASP provides a foundation for automated multi-program coaddition in order to create an updated and improved HSLA in the future.

Eight graphs in two columns of four. The left stack is titled COS Program PID 14910 ; Target WDO308-565 ; G160M Observations. The right stack is titled COS Program PID 14910 ; Target WDO308-565.  On the left, the first graph is colorful bar with jagged edges on the top and bottom and elongated lines on the far left and right and in a portion of the center. The second shows a compressed black bar like a double-ended trumpet with jagged edges on the top and bottom. The bar is slightly tipped diagonally with the left higher and the right lower. The third graph has two plateaus with a dip in the middle, all outlined by a thin, jagged blue line. The fourth looks like a mountain sloping to the right with a dip in the middle, all outline with a thick, jagged blue line. On the right, the top graph shows a red, jagged diagonal line with colorful spikes. The second graph shows a very similar pattern, but the line and spikes are black. The third and fourth graphs show undulating, jagged, blue lines.
Figure 1: The two key techniques from the Hubble Advanced Spectral Products for a white-dwarf star, WD 0308-565. On the left, we see combined data from multiple observations using different G160M settings (CENWAVEs), detailing the coadded spectrum, exposure times, and signal-to-noise ratios. The right shows data from three different gratings abutted together, highlighting the smoothness of the compiled spectrum and the corresponding exposure and signal quality metrics. This visual comparison showcases HASP's ability to refine and enhance astronomical data.

The HASP products are designed to work best for astrophysical sources that have compact angular sizes and are not variable, which ensures flux continuity across different gratings and apertures. In those cases, the coadditions should match each instrument’s requirements for flux and wavelength repeatability and accuracy. However, HASP might not fit all science cases or requirements, so an integral part of the project is to provide user-friendly access to custom coaddition for situations when more individualized approaches might need to be taken.

The HASP project also enables custom coaddition to the community through a publicly available Python script and accompanying Jupyter notebooks (Figure 2). HASP custom coaddition opens the possibility that future archival analysis projects might build on the HASP legacy in order to create high level science products that are consistent with both HASP and ULLYSES.

 The four panels show from left to right a screenshot of the setup: 2 charts that show results from the Coadd Tutorial, a single chart with some code that shows the Flux Scaling Tutorial, and lastly a chart that shows Data Diagnostics.
Figure 2: Users can explore interactive HASP Jupyter Notebooks that provides step-by-step guides on creating custom coadded datasets, enabling users to tailor spectral data combination to fit their unique research needs.
Search functionality in MAST showing HASP result
Figure 3: A snapshot from the Hubble MAST download window showcasing the integration of Hubble Advanced Spectral Products (HASP). Users will now find new cspec.fits (combined spectrum) data as default download products.

HASP will be seamlessly integrated into the Hubble MAST search form as default recommended download products from the archive (Figure 3). Users looking for HASP data can access them through new cspec.fits files, which are becoming a default MAST product. 

The HASP project is the first step of a larger initiative to create a new, automated and updated HSLA. The codes and processes developed as part of HASP will directly inform our approach in the next step of this process: to create cross-program target level coadds in a semi-automated way. HASP will continue as its own project providing combined visit and program level spectra for each target through the archive as new data are obtained or additional calibrations for instruments are enacted in the current and upcoming cycles. There will be continuity and synergy between HASP and the new HSLA as we enhance the legacy value of COS and STIS spectroscopy across the operational lifetime of both instruments for years to come.

For comprehensive details, please refer to the HASP webpage or HASP Instrument Science Report.

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