0 Assigned ID: 6556 ----- Attempting Submission 1 (Thu Apr 10 17:40:53 GMT 2025) ----- Objects flagged with BOT have been analyzed. Model spectra and ETC simulation numbers were sent to the CS via email. -182652029 ----- Attempting Submission 1 (Tue Aug 12 03:39:19 GMT 2025) ----- White dwarfs with inconsistent ages in young open clusters The third data realse of Gaia has unveiled a large population of white dwarfs with main-sequence companions at orbital separations of ~1AU, indicating a history of mass transfer between the two companions. Recently, a subsample of these systems that are located in open clusters was used in order to estimate the mass of the white dwarf's progenitor, and to constrain its evolutionary history. A few of these systems that are located in young open clusters displayed inconsistencies between the cluster and the white dwarf ages, where the estimated white dwarf cooling age appeared older than the cluster. The UV excess and age measurements relied on single-band GALEX photometry alone (mostly NUV), as the optical and infrared are dominated by the main-sequence companion. Here we request ACS/SBC FUV photometry for six of these systems, in order to get a more reliable measurement of the flux of the white dwarf, that will confirm/refute the age inconsistency. The SBC filters will allow us to construct the spectral enetry distribution of the targets in the FUV, constraining their effective temperatures and revealing broad absorption features that could contribute to the age estimate inconsistency. If the system is confirmed to be older than the cluster, it would represent the first evidence of a star captured from the field into an open cluster. For each of our six targets, we request FUV photometry using ACS/SBC long-pass filters: F115LP, F125LP, F140LP, F150LP, and F165LP. As suggested in the ACS instrument handbook, we will subtract the F165LP measurement from each of the other filters, in order to avoid the red flux contamination from the bright MS companion. This will allow us to construct the SED of the system in the FUV. We have verified that exposures of less than 1 min per filter are required in most cases and less than 8 min in the worst case to achieve a minimal signal-to-noise ratio (SNR) of 10 in the F165LP-subtracted bands. We will spend one HST orbit on each target, maximizing the SNR by taking longer exposures. A photometric SNR above 10 in the F165LP-subtracted bands corresponds to a 2.5% error of the WD effective temperature (calculated using a Monte-Carlo experiment covering a wide range of WD masses and compositions, assuming additive and Gaussian white noise and accounts for systematic errors due to the model grids and extinction of 250 K). This error then translates to a WD cooling age precision better than 20%, in most regions of parameter space (also calculated using a Monte-Carlo experiment and represents the typical 5% uncertainty in WD mass and the inherent overlap between models of different internal compositions and atmospheres). In parallel, we are actively pursuing follow-up ground-based spectroscopic observations of these systems and selected cluster members to further confirm their association with the cluster (some of these are already secured on the Magellan telescope) Na'ama Hallakoun is an expert in WD demographics, and is experienced with spectroscopic and photometric analysis of WDs. She participated in a HST UV observing program, in which she was in charge of the obsevation planning and the data analysis. Sahar Shahaf has devised the method to identify astrometric binaries with compact-object companions using Gaia data. He is experienced with spectroscopic and photometric analysis of binary systems. Sagi Ben-Ami is experienced with spectroscopic and photometric analysis, including HST data. He has participated in several HST UV observing programs, in which he was in charge of observation planning. Oren Ironi has led the publication and analysis of the sample presented in this proposal. He has experience in fitting and analyzing open cluster properties and associations. Stellar Physics and Stellar Types 6 false true false false false false SUPPORTED STAR COMPOSITE SPECTRAL TYPE DA F3-F9 Astrometric binary identified by Gaia. NUV magnitude from Galex. Astrometry and photometry suggest this is an MS+WD binary. J2000 J2000 NUV=19.89 STAR COMPOSITE SPECTRAL TYPE DA G V-IV K III-I Astrometric binary identified by Gaia. NUV magnitude from Galex. Astrometry and photometry suggest this is an MS+WD binary. J2000 J2000 NUV=19.61 STAR A4-A9 III-I COMPOSITE SPECTRAL TYPE DA Astrometric binary identified by Gaia. NUV magnitude from Galex. Astrometry and photometry suggest this is an MS+WD binary. J2000 J2000 NUV=17.49 STAR COMPOSITE SPECTRAL TYPE DA F3-F9 Astrometric binary identified by Gaia. NUV magnitude from Galex. Astrometry and photometry suggest this is an MS+WD binary. J2000 J2000 NUV=21.21 STAR A0-A3 III-I COMPOSITE SPECTRAL TYPE DA Astrometric binary identified by Gaia. NUV magnitude from Galex. Astrometry and photometry suggest this is an MS+WD binary. J2000 J2000 NUV=17.43 STAR A4-A9 V-IV COMPOSITE SPECTRAL TYPE DA Astrometric binary identified by Gaia. NUV magnitude from Galex. Astrometry and photometry suggest this is an MS+WD binary. J2000 J2000 FUV=20.06 ACS/SBC Imaging No No F115LP ACS/SBC Imaging No No F125LP ACS/SBC Imaging No No F140LP ACS/SBC Imaging No No F150LP ACS/SBC Imaging No No F165LP ACS/SBC Imaging No No F115LP ACS/SBC Imaging No No F125LP ACS/SBC Imaging No No F140LP ACS/SBC Imaging No No F150LP ACS/SBC Imaging No No F165LP ACS/SBC Imaging No No F115LP ACS/SBC Imaging No No F125LP ACS/SBC Imaging No No F140LP ACS/SBC Imaging No No F150LP ACS/SBC Imaging No No F165LP ACS/SBC Imaging No No F115LP ACS/SBC Imaging No No F125LP ACS/SBC Imaging No No F140LP ACS/SBC Imaging No No F150LP ACS/SBC Imaging No No F165LP ACS/SBC Imaging No No F115LP ACS/SBC Imaging No No F125LP ACS/SBC Imaging No No F140LP ACS/SBC Imaging No No F150LP ACS/SBC Imaging No No F165LP ACS/SBC Imaging No No F115LP ACS/SBC Imaging No No F125LP ACS/SBC Imaging No No F140LP ACS/SBC Imaging No No F150LP ACS/SBC Imaging No No F165LP POS-TARG DITHER 0.472 LINE false false 2 44.4 ACS-SBC-DITHER-LINE 1 false C:\Users\oreni\Documents\OP-cache\phase2_18011-v01.xml The scheduling data was generated by CASM 33.1. 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