August 11-15, 2014


Dynamical Masses of Cool White Dwarfs in Double Degenerate Visual Binaries

Edmund Nelan (STScI)

Dr. Howard E. Bond, Penn State University Dr. Gail Schaefer, Georgia State University

The cool white dwarfs WD 1639+153 and WD 1818+126 were originally resolved as close, visual double-degenerate binaries in an HST survery using the Fine Guidance Sensor (FGS) in its high angular resolution Transfer mode. 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 in Position mode, 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 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 obtain constraints on the initial-mass/final-mass relation for WD stars.

Mode of presentation: oral