Richard Smith, NOIRLab
Mining the PHAT survey: variable stars in M31 stellar clusters
Variable stars are valuable objects of study for multiple fields of astronomy. When detected in stellar clusters, the physical parameters of the variable star can be obtained using their host cluster properties, which can in turn provide key constraints on stellar evolution and pulsation models. I will present the first results produced by mining the archival Panchromatic Hubble Andromeda Treasury (PHAT) survey for variable stars using a combination of light curve analysis and difference imaging. We have produced a catalogue of 89 luminous variable stars detected within M31 stellar clusters, using observed and isochrone-derived properties to characterize the type of variable star detected in each case. This work is the first systematic study of variable stars in extragalactic stellar clusters to leverage the superior resolution of the Hubble Space Telescope, highlighting the enormous potential of the upcoming Roman Observatory.

Tod Lauer, NOIRLab
New Synoptic Observations of the Cosmic Optical Background with New Horizons
We obtained New Horizons LORRI images to measure the cosmic optical background (COB) integrated over 0.4 ≲ λ ≲ 0.9μm. The observations were conducted when New Horizons was 57 AU distant from the Sun.  The survey comprises 16 high galactic-latitude fields selected to minimize diffuse scattered light from the Milky Way galaxy (DGL), as well as scattered light from bright stars. Isolating the COB contribution to the raw total sky levels measured in the fields requires subtracting the remaining scattered light from bright stars and galaxies, flux from faint stars within the fields fainter than the photometric detection-limit, and the DGL foregrounds.  I will present the measured flux of the COB and our conclusion on how it is generated.