0 Assigned ID: 5000 ----- Attempting Submission 1 (Tue Mar 19 12:27:54 GMT 2024) ----- Changed one orbit for G203-47 to use the G230LB grating to test the flux calibration of the other observations. -406923822 ----- Attempting Submission 1 (Tue Aug 06 13:17:56 GMT 2024) ----- ----- Attempting Submission 2 (Thu Feb 27 10:47:58 GMT 2025) ----- ----- Attempting Submission 3 (Thu Feb 27 16:40:43 GMT 2025) ----- ----- Attempting Submission 4 (Tue Jul 15 16:02:13 GMT 2025) ----- ----- Attempting Submission 5 (Wed Dec 03 10:24:53 GMT 2025) ----- Revealing the closest hidden white dwarfs in post-common envelope binaries 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. 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. 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). The PI of this proposal (M. W. O'Brien) led the production of the 40 pc volume-limited white dwarf sample, and has experience fitting local STIS white dwarf spectra. Co-I D. J. Wilson has extensive experience in ultraviolet observations of M dwarfs and white dwarfs. Co-I B. T. Gaensicke is an expert in the evolution of compact white dwarf binaries, including cataclysmic variables and other interacting systems. He has extensive experience with ultraviolet observations of white dwarfs. Co-I P. -E. Tremblay is an expert in white dwarf SED modelling and has worked on 3D model atmospheres of white dwarfs, which are essential to model cool white dwarfs in the ultraviolet. Co-I F. E. Lagos is an expert in modelling common envelope evolution. Stellar Populations and the Interstellar Medium Stellar Physics and Stellar Types 6 false true false false false false SUPPORTED STAR M III-I NO Coordinates, proper motions, and parallaxes are from Gaia Data Release 3. J2000 J2000 STAR M III-I NO Coordinates, proper motions, and parallaxes are from Gaia Data Release 3. J2000 J2000 STAR M V-IV NO Coordinates, proper motions, and parallaxes are from Gaia Data Release 3. J2000 J2000 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/CCD Spectroscopic No No G430L 4300 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/CCD Spectroscopic No No G430L 4300 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/CCD Spectroscopic No No G430L 4300 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. 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CASM was run in Phase II mode. 1755123792000 254.41338028100625 (Tic-Visit :proposal-id 17778 :visit-id "02" :proposal-version -1 :trans-version "20250321" :date "15-Jul-2025 16:41:48.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 166048 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17778 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17778 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2625 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3005 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17778 :visit-id "02" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2625 :al-overhead-at-end 0 :internal-dur-at-end 379 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3005 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. 1758676985000 270.64470207193654 (Tic-Visit :proposal-id 17778 :visit-id "03" :proposal-version -1 :trans-version "20250321" :date "15-Jul-2025 16:41:51.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 110832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17778 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17778 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2739 :al-overhead-at-end 0 :internal-dur-at-end 419 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3119 :pcs-gap 0 ) true 1 0