18090( 2) - 14-Aug-2025 18:40:31 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18090 Version: 2 Check-in Time: 14-Aug-2025 18:40:31 STScI Edit Number: 0 Title Unraveling Common Envelope Evolution with Star Clusters: A new post-common envelope binary in the Alessi 12 open cluster ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Steffani Grondin University of Toronto Y CoI: Maria Drout University of Toronto Y CoI: Dr. Philip Steven Muirhead Boston University N CoI: Dr. Jason Nordhaus Rochester Institute of Technology N CoI: Dr. Kyle Kremer University of California - San Diego N ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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 18090( 2) - 14-Aug-2025 18:40:31 - [ 2] 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. ------------------------------------------------------------------------------------ 18090( 2) - 14-Aug-2025 18:40:31 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ALESSI12-PCE STAR, DA, M V-IV RA=20H46M24.9967S +/- J2000 V = 18.76 Swift AB magnitudes -- UVW2: 0.00009548908", 16.95mag, UVM2: 17.68mag, UVW1: DEC=+24D38'20.16" +/- 17.44mag, U:18.35mag, B: 18.54mag 0.0001103286499999" Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2016 3.3127491007616634E-4 -0.0045174 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 18090( 2) - 14-Aug-2025 18:40:31 - [ 4] Visit: 01 (Alessi12-2orbits-set1) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 ALESSI12-PC COS/NUV ACQ/IMA PSA MIRRORB 1 24 S (24 E GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ALESSI12-PC COS/FUV TIME-TA PSA G130M 1291 FP-POS=3, BUFFER-TIME=3700 1 2120 S E G (2120 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ALESSI12-PC COS/FUV TIME-TA PSA G130M 1291 FP-POS=4, BUFFER-TIME=3700 1 2535 S E G (2535 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ ALESSI12-PCE 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE ALESSI12-PCE 2 COS/FUV TIME-TA PSA G130M 1291 none none none none 1 N/A G ALESSI12-PCE 3 COS/FUV TIME-TA PSA G130M 1291 none none none none 2 N/A G 18090( 2) - 14-Aug-2025 18:40:31 - [ 5] Visit: 02 (Alessi12-2orbits-set2) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 ALESSI12-PC COS/NUV ACQ/IMA PSA MIRRORB 1 24 S (24 E GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ALESSI12-PC COS/FUV TIME-TA PSA G130M 1291 FP-POS=3, BUFFER-TIME=3700 1 2120 S E G (2120 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ALESSI12-PC COS/FUV TIME-TA PSA G130M 1291 FP-POS=4, BUFFER-TIME=3700 1 2535 S E G (2535 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ ALESSI12-PCE 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE ALESSI12-PCE 2 COS/FUV TIME-TA PSA G130M 1291 none none none none 1 N/A G ALESSI12-PCE 3 COS/FUV TIME-TA PSA G130M 1291 none none none none 2 N/A G 18090( 2) - 14-Aug-2025 18:40:31 - [ 6] Summary Form for Proposal 18090 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=3700, FP-POS=3, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G130M, MIRRORB ------------------------------------------------------------------------------------------------------------------------------------ Target Names ALESSI12-PCE ------------------------------------------------------------------------------------------------------------------------------------