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Paper: Dynamical Masses of Cool White Dwarfs in Double Degenerate Binary Systems
Volume: 493, 19th European Workshop on White Dwarfs
Page: 501
Authors: Nelan, E. P.; Bond, H. E.; Schaefer, G.
Abstract: The cool white dwarfs WD 1639+153 and WD 1818+126 were originally discovered as close, visual double-degenerate (DD) binaries in an HST survey using the Fine Guidance Sensor (FGS). Follow up FGS observations of these two DDs, along with the previously known double-degenerate G 107-70, have yielded the orbital elements of all three systems. We find orbital periods of 3.88 yr, 12.19 yr, and 18.84 yr for WD 1639+153, WD 1818+126, and G 107-70, respectively. We have also been obtaining astrometry of nearby field stars with FGS, from which we obtain the parallax and proper motion of each DD, along with the motion of each WD about system barycenter. In addition, we have spatially resolved, low resolution broad-band STIS observations of the six WDs. Combining the FGS astrometry and STIS spectroscopy leads to a determination of the mass, radius, effective temperature, and WD subclass, providing insight into the cooling age of each star. From the cooling ages and dynamical masses, we will obtain constraints on the initial-mass/final-mass relation for WD stars. Here we report the results of the FGS observations.
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