HST WFPC2 Observations of Astrophysically Important Visual Binaries

Details HST WFPC2 Observations of Astrophysically Important Visual Binaries HST WFPC2 Observations of Astrophysically Important Visual Binaries

May 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...194.7510b&link_type=abstract

American Astronomical Society, 194th AAS Meeting, #75.10; Bulletin of the American Astronomical Society, Vol. 31, p.955

Astronomy and Astrophysics

Astronomy

Scientific paper

Only a handful of white dwarfs have directly measured dynamical masses, including those in the well-known visual binaries 40 Eri, Sirius, and Procyon. Using the Wide Field Planetary Camera (WFPC2) on the Hubble Space Telescope, we have begun a long-term program of direct imaging of two visual binaries containing white dwarfs. Procyon. This system consists of an F5 IV-V star and a very faint 8700 K DZ white-dwarf companion. Its separation and position angle are extremely difficult to measure from the ground, due to the large brightness difference of about 8 mag. We combine short (0.12 s) and long (100 s) WFPC2 exposures without moving the telescope, and are monitoring Procyon once a year. Our existing observations already show that the ground-based measurements of the separation are seriously in error, leading to downward revisions of the masses of both components (A: 1.46 M_sun; B: 0.59 M_sun), and removing a long-standing conflict between the observed and theoretically predicted luminosity of Procyon A. G 107-70. G 107-70 consists of two cool DC white dwarfs, whose separation of about 0secpoint7 makes it difficult to measure from the ground. We are monitoring it twice a year, in order eventually to determine dynamical masses for both white dwarfs. The existing observations have already revised the orbital period to a value near 18.67 yr. We are also observing mu Cassiopeiae twice a year. This binary consists of a metal-poor G dwarf and a faint dM companion. Direct WFPC2 imaging at 9500 Angstroms easily reveals the companion. Eventually we will be able to determine the helium content of the system, from the mass-luminosity relation.

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