About This Article
In this STAN, we discuss upcoming COS posters at the 245th Meeting of the American Astronomical Society and announce the release of two new notebooks for the Hubble Advanced Spectral Products (HASP) that help users conduct data diagnostics on HASP coadds and apply custom wavelength shifts. Additionally, a new COS notebook is available to assess observing exception reports.
Contents
End calloutCOS Posters at the 245th Meeting of the American Astronomical Society
Two COS posters will be presented at the 245th AAS meeting in the National Harbor, MD. We invite all COS users to review them to learn about the latest developments for COS. Additionally, all COS posters are archived on the COS poster page.
Updated Status and Performance of the Cosmic Origins Spectrograph
Authors: Leonardo Dos Santos1, Andrews Damoah2, John Debes1, Travis Fischer1, David French1, Sten Hasselquist1, Jacqueline Hernandez1, Svea Hernandez1, Nick Indriolo1, Christian Johnson1, Lauren Miller1, Anna Payne1, Marc Rafelski1, David Sahnow1, Ravi Sankrit1, Debopam Som1, Thomas Wevers1
1Space Telescope Science Institute, Baltimore, MD, 2University of Maryland, College Park, College Park, MD
Abstract: After 15 years of operations, the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope remains scientifically productive and continues to provide a high-quality spectroscopic view of the ultraviolet universe through the far-ultraviolet (FUV) and near-ultraviolet (NUV) channels. The FUV channel is currently operating at five different lifetime positions (LPs), with each LP being used for a subset of observing modes. Here we present updates on the current status and performance of COS and summarize recent calibration and user support work of interest to all COS users. We updated the geometric and walk distortion corrections of the FUV detector, which results in improved wavelength calibration and flux accuracy, especially near the detector edges. As the Sun remains at peak magnetic activity, we show that the COS FUV detector continues to experience faster sensitivity decrease. We discuss tips for clearing M dwarf observations with COS, as these have specific rules regarding bright-object protection. We present the Hubble Advanced Spectral Product (HASP) program, whose high-level data products are readily available to the community. Finally, we discuss the forward plan for enabling and calibrating two new lifetime positions LP7 and LP10 covering, respectively, the gratings G130M and G160M, which will allow the continued use of the FUV detector over the next years.
Rectifying Poor Flux Calibration of COS Data due to Bad Time Intervals
Authors: Andrews Damoah1, Sten Hasselquist2, the COS Team
1University of Maryland, College Park, College Park, MD, 2Space Telescope Science Institute, Baltimore, MD,
Abstract: A small but undetermined fraction of observations from the Cosmic Origins Spectrograph (COS) exhibit unexpected fluctuations in count rate across the duration of an exposure, sometimes resulting in poor flux calibration. These changes in count rate can be due to a variety of reasons, including situations where the target has partially or entirely drifted out of the aperture. We have analyzed the count rate as a function of time for all COS TIME-TAG exposures and identified exposures with problematic count rates that can be fixed by defining “bad” time intervals using the BADTTAB reference files, improving the flux calibration for these exposures. In total, we have identified and corrected several dozen exposures, as well as compiled a catalog of intrinsically and rapidly variable objects that have been observed by COS. We have also explored automating this procedure by running Principal Component Analysis (PCA) on the count rates for COS exposures and then utilizing a clustering algorithm to classify exposures into various types based on the inherent patterns in their count rates. We use these classifications to determine exposure inputs to train a simple Convolutional Neural Network (CNN) and plan to use this CNN to automatically identify the bad time intervals for existing and future COS exposures that have problematic count rates.
New HASP Jupyter Notebooks for Data Diagnostics and Wavelength Adjustments
The Hubble Advanced Spectral Products (HASP) program provides the MAST community with high-quality, automated coadded and combined spectra from the Hubble Space Telescope's Cosmic Origins Spectrograph (COS) and Space Telescope Imaging Spectrograph (STIS). HASP products are continually updated with the latest data and calibrations, offering reliable and up-to-date resources for scientific analysis.
To support users in maximizing the utility of these products, two new Jupyter Notebooks are now available:
- Wavelength Adjustment Notebook: This notebook guides users through applying custom wavelength shifts to COS and STIS spectra when running the HASP coadd script.
- Data Diagnostics Notebook: This notebook helps users inspect input spectra and assess what data were included or excluded in the coadded product output.
These tools provide enhanced flexibility for data diagnostics and customization, ensuring users can tailor HASP outputs to their specific scientific needs.
New COS Jupyter Notebook for Assessing a COS Exception Report
Occasionally an observation is marked as failed due to an observatory level issue such as a failed guide star acquisition. In this case, the PI will receive a notification that part or all of the observations associated with a visit is impacted. It is highly recommended to look in detail at the quality of the observations to assess whether a Hubble Observing Problem Report (HOPR) is required. A new COS Jupyter notebook is available that can help the user to assess any possible problems. The notebook goes over how to examine FITS header keywords to determine more specifics about a potential problem and to inspect COS datasets to look for anomalies or degradation in performance. Accurate and timely reporting of problems, even if the data is acceptable for the original science program helps ensure the quality of legacy archive products. The notebook can be found on the COS Jupyter Notebooks Github page.