August 11-15, 2014


Wide Stellar Binaries as Laboratories: Revisiting the White Dwarf Mass–Radius Relationship Using Gravitational Redshifts

Saurav Dhital (Embry-Riddle Aeronautical University)

Terry D. Oswalt (Embry-Riddle Aeronautical University), Jay B. Holberg (LPL/Univ. of Arizona), Trisha Mizusawa (Florida Tech), Jingkun Zhao (National Astronomical Observatories, China)

We present gravitational redshifts (GRs) and masses for over 20 white dwarfs that have distant, non-interacting main-sequence companions. These are the first results from our ongoing NOAO programs at the KPNO 4-m and SOAR 4.1-m telescopes. We have obtained R~10,000 spectra over three or more epochs for each WD+MS binary and measured precise radial velocities and, thus, gravitational redshifts using the template-matching technique. This removes the subjectivity involved in previous GR studies. Our sample is already the largest set of GRs measured in a single study, thus, eliminating the systematic differences between different studies and telescopes. We have obtained independent radius constraints from extant parallax measurements and surface gravity determinations from Balmer series fits to our spectra. By combining our precise GR measurements with those values, we obtained improved estimates of WD masses and radii. While the WD mass-radius relation underlies much of stellar and galactic astrophysics, only one empirical measurement matches the predicted value within 3%. Furthermore, the current published sample covers a small range of WD masses. Our program provides more precise measurements of GRs for a larger range of WD mass, spanning 0.5-1.2 Msun.

Mode of presentation: poster