0 Assigned ID: 6847 ----- Attempting Submission 1 (Thu Apr 10 23:36:54 GMT 2025) ----- HST Phase I Proposal 6847 successfully submitted. Receipt: # 6847-1 ----- Attempting Submission 2 (Thu Apr 10 23:42:22 GMT 2025) ----- HST Phase I Proposal 6847 successfully submitted. Receipt: # 6847-2 ----- Attempting Submission 3 (Thu Apr 10 23:49:03 GMT 2025) ----- 0 ----- Attempting Submission 1 (Thu Aug 14 18:16:54 GMT 2025) ----- The progenitor systems of type Ia supernovae and gravitational wave sources are believed to arise from a mass transfer process known as common envelope (CE) evolution. Although a large fraction of binary systems will undergo CE evolution, the detailed physics remains poorly understood, largely due to the lack of observed benchmark systems where both the pre-CE and post-CE conditions are known. While post-CE systems containing a white dwarf (WD) and main-sequence (MS) star have been observed, they are located in the field, making it difficult to gain insights into their pre-CE parameters. Finding post-CE systems in star clusters can provide an independent constraint on the binary's age, but only two WD+MS post-CE systems in a star cluster have ever been found. Recently, a new WD+MS post-CE system was discovered in the Alessi 12 cluster. Alessi12-PCE is an ideal candidate to study CE evolution as it (i) is a cluster member, (ii) is a confirmed short-period binary and (iii) has clear spectral features of both a WD and a MS star in an optical spectrum. However, while spectral features at optical wavelengths can measure a WD's temperature and surface gravity (and thus its mass), there are systematic uncertainties that can have a significant impact on the inferred pre-CE conditions. Thus, we request 4 orbits with HST COS to obtain an ultraviolet spectrum to measure the effective temperature and surface gravity of Alessi12-PCE from its Lyman-alpha feature and use this measurement to refine the precision on the WD's mass. Alessi12-PCE will be just the third WD+MS post-CE binary ever identified in a star cluster, highlighting the necessity of this data. This proposal will obtain a UV spectrum for a recently discovered post-common envelope WD+MS binary in the Alessi12 cluster. These measurements will allow for an independent constraint on the mass of the WD via modelling of the Lyman Alpha feature. Observations will be obtained in the G130M grism and a central wavelength of 1291 AA. As the Lyman Alpha feature is in Segment B, observations will be obtained in FP-POS 3 and 4. The impacts of a reduced gyro operations on this program would primarily be reduced schedualability due to the smaller field of regard. Slightly longer acquisition times would have only a small effect on the S/N of our observations. Steffani Grondin will act as team lead of this project as these observations will (i) be used to complete her PhD thesis (producing a catalogue of WD+MS post-CE binaries in stellar clusters to constrain CE evolution) and (ii) be a key component of her upcoming postdoctoral fellowship appointment in Fall 2025. Dr. Maria Drout is an expert in identification and characterization of evolved stellar systems in the Milky Way and Local Group Galaxies, with an emphasis on supernova and gravitational wave progenitor systems. Dr. Philip Muirhead is expert on low-mass stars and eclipsing binary systems, including work on post common envelope eclipsing binary systems. Dr. Jason Nordhaus is an expert in the theory of common envelope and binary evolution having proposed CE scenarios for the formation of highly-magnetized white dwarfs and for shaping outflows in bipolar post-AGB stars and planetary nebulae. Dr. Kyle Kremer is an expert in compact object binaries in stellar clusters and has familiarty with HST through X. Stellar Physics and Stellar Types 6 false true false false false false false SUPPORTED STAR DA M V-IV NO J2000 J2000 Swift AB magnitudes -- UVW2: 16.95mag, UVM2: 17.68mag, UVW1: 17.44mag, U:18.35mag, B: 18.54mag COS/FUV Spectroscopic No No G130M 1291 1783963241482 /System/Volumes/Data/solaris/user1/crodriguez/work/hst/OP-cache/18090-v01.xml The scheduling data was generated by CASM 33.1. 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