17778( 6) - 03-Dec-2025 18:17:22 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17778 Version: 6 Check-in Time: 03-Dec-2025 18:17:22 STScI Edit Number: 1 Title Revealing the closest hidden white dwarfs in post-common envelope binaries ------------------------------------------------------------------------------------ Type Cycle GO 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Mairi O'Brien University of Warwick Y CoI: Dr. David John Wilson University of Colorado at Boulder N CoI: Prof. Boris T. Gaensicke University of Warwick N CoI: Prof. Pier-Emmanuel Tremblay University of Warwick N CoI: Dr. Felipe Esteban Lagos-Vilches University of Warwick N ------------------------------------------------------------------------------------ Abstract When a white dwarf is in a close binary with an M dwarf, they will have undergone a common envelope phase, making the system a post-common envelope binary. The common envelope phase of binary evolution is poorly understood, and the numbers of post-common envelope binaries in the local volume need to be constrained to improve predictions of the space density of binary stars. Despite the high spectroscopic completeness of local samples of single white dwarfs, white dwarfs in post-common envelope binaries are notoriously difficult to detect, as the M dwarf dominates the system's optical spectrum and colours. We request to observe the three closest candidate post-common envelope binaries to the Sun, all of which are M dwarfs with close unconfirmed white dwarf companions that were detected via radial velocity measurements. STIS is the only instrument that can confirm the white dwarf companions as they are brighter than the M dwarf in the near-UV. The mass and effective temperature of the white dwarfs will be constrained by fitting the UV spectra with white dwarf models. Confirming three of these systems that are within 17 parsec of the Sun will place vital constraints on the space density of close binary systems. ------------------------------------------------------------------------------------ Observations Description ------------------------ We are observing three M dwarfs with hidden white dwarf binary companions. We will detect the excesses in the SEDs of these systems caused by the white dwarfs using the G230L and G230LB gratings in the near-UV. For G 203-47, we will use the 52x2 aperture for NUV-MAMA G230L as it is the most spectrophotometric, and therefore enables confirmation and characterisation of the white dwarf excess. We will observe G 203-47 in TIME-TAG mode for G230L to reduce the impact of this flaring on our observations. A rare flare event at LHS 1817 and GJ 207.1 would saturate a G230L observation, so the CCD G230LB grating is used for these targets. G203-47: From the ETC, we achieve a S/N of 8.9 at 2250 Angstrom for the shortest observation of the 2 orbits (1902s). The S/N reaches 35 at 3000 Angstrom. 17778( 6) - 03-Dec-2025 18:17:22 - [ 2] GJ207.1: From the ETC, we achieve a S/N of 7.95 at 2375 Angstrom for the shortest observation of the 2 orbits (1997s). The S/N reaches 51 at 3000 Angstrom. LHS 1817: From the ETC, we achieve a S/N of 17.9 at 2375 Angstrom for the single orbit observation (1734s). The S/N reaches 59 at 3000 Angstrom. We will observe each target in the G430L grating as well, in order to calibrate the NUV data to optical/IR models. For the G430L observations we use the 52x2E1 grating to mitigate for CTE loss (as in STIS handbook 7.3.8). We will not perform the ACQ/PEAK exposures as this is not required for slits greater in width than 0.1 arcsecond (as in STIS handbook 8.3). ------------------------------------------------------------------------------------ 17778( 6) - 03-Dec-2025 18:17:22 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 G-203-47 STAR, M III-I RA=17H09M32.0333S +/- J2000 V = 13.671 0.00038272035", DEC=+43D40'48.38" +/- 0.00039826187" Reference Frame: ICRS Extended: NO Comments: Coordinates, proper motions, and parallaxes are from Gaia Data Release 3. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2016.0 0.030607387260278583 -0.27450099472651857 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 GJ-207.1 STAR, M III-I RA=05H33M44.5529S +/- J2000 V = 11.499 0.000037790846", DEC=+01D56'40.99" +/- 0.00003416744" Reference Frame: ICRS Extended: NO Comments: Coordinates, proper motions, and parallaxes are from Gaia Data Release 3. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2016.0 -0.015444849812485228 -0.15398875225290712 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 LHS-1817 STAR, M V-IV RA=06H05M30.0366S +/- J2000 V = 13.69 0.000034616545", DEC=+60D49'9.84" +/- 0.00003535586" Reference Frame: ICRS Extended: NO Comments: Coordinates, proper motions, and parallaxes are from Gaia Data Release 3. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2016.0 0.039678759269538254 -0.788781768640439 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17778( 6) - 03-Dec-2025 18:17:22 - [ 4] Visit: 01 (G-203-47) 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 G-203-47 STIS/CCD ACQ F28X50LP MIRROR 1 0.1 S (0.1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 G-203-47 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=1051 1 2800 S -MAMA G see below (2034 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 G-203-47 STIS/CCD ACCUM 52X0.2 G230LB 2375 1 2500 S see below (2148 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 G-203-47 STIS/CCD ACCUM 52X2E1 G430L 4300 1 100 S see below (0.2 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 | ------------------------------------------------------------------------------------------------------------------------------------ G-203-47 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A G-203-47 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 2034.0 S -MAMA G G-203-47 3 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 1 2 1074.0 S G-203-47 3 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 2 2 1074.0 S G-203-47 4 STIS/CCD ACCUM 52X2E1 G430L 4300 none none none 1 2 0.1 S G-203-47 4 STIS/CCD ACCUM 52X2E1 G430L 4300 none none none 2 2 0.1 S 17778( 6) - 03-Dec-2025 18:17:22 - [ 5] Visit: 02 (GJ-207.1) 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 GJ-207.1 STIS/CCD ACQ F28X50LP MIRROR 1 0.1 S (0.1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 GJ-207.1 STIS/CCD ACCUM 52X0.2 G230LB 2375 1 1000 S see below (2137 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 GJ-207.1 STIS/CCD ACCUM 52X0.2 G230LB 2375 1 1000 S see below (1997 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 GJ-207.1 STIS/CCD ACCUM 52X2E1 G430L 4300 1 50 S see below (100 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 | ------------------------------------------------------------------------------------------------------------------------------------ GJ-207.1 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A GJ-207.1 2 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 1 1 1137.0 S GJ-207.1 2 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 2 1 1000.0 S GJ-207.1 3 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 1 2 997.0 S GJ-207.1 3 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 2 2 1000.0 S GJ-207.1 4 STIS/CCD ACCUM 52X2E1 G430L 4300 none none none 1 2 50.0 S GJ-207.1 4 STIS/CCD ACCUM 52X2E1 G430L 4300 none none none 2 2 50.0 S 17778( 6) - 03-Dec-2025 18:17:22 - [ 6] Visit: 03 (LHS-1817) 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 LHS-1817 STIS/CCD ACQ F28X50LP MIRROR 1 0.1 S (0.1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 LHS-1817 STIS/CCD ACCUM 52X0.2 G230LB 2375 1 5600 S see below (1734 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 LHS-1817 STIS/CCD ACCUM 52X2E1 G430L 4300 1 100 S see below (161 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 | ------------------------------------------------------------------------------------------------------------------------------------ LHS-1817 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A LHS-1817 2 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 1 1 817.0 S LHS-1817 2 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 2 1 917.0 S LHS-1817 3 STIS/CCD ACCUM 52X2E1 G430L 4300 none none none 1 1 67.0 S LHS-1817 3 STIS/CCD ACCUM 52X2E1 G430L 4300 none none none 2 1 94.0 S 17778( 6) - 03-Dec-2025 18:17:22 - [ 7] Summary Form for Proposal 17778 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2, 52X2, 52X2E1, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1051 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G230L, G230LB, G430L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names G-203-47, GJ-207.1, LHS-1817 ------------------------------------------------------------------------------------------------------------------------------------