HST Observations of Astrophysically Important Visual Binaries

Astronomy and Astrophysics – Astrophysics

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Scientific paper

We report on our ongoing HST observations to measure the orbits of four astrophysically important visual binaries. All four are very difficult to resolve from the ground, but can be measured easily at HST resolution. For each binary, we present updated orbital fits, revised dynamical masses, and limits on the presence of third bodies down to planetary mass. The binaries we discuss are as follows:
(1) Procyon (P=40.9 yr) contains a bright F5 IV-V star and its much fainter white-dwarf companion. Combined with ground-based astrometry of the bright star, our initial observation with WFPC2 in 1995 significantly revised downward the derived masses, and brought Procyon A into excellent agreement with theoretical evolutionary tracks. Based on our continued WFPC2 measurements over the past decade, we present an improved orbital solution, revised masses for both components, and tight limits on planetary bodies in the system.
(2) The Sirius system (P=50.1 yr), which contains the nearest and brightest of all white dwarfs, has been followed with HST/WFPC2 imaging since 1997. We revise the dynamical masses of both stars, and are investigating hints of a small perturbation in this system.
(3) G 107-70 (P=18.5 yr) is a close double white dwarf system of nearly equal brightness. We have been following it since 1995 with WFPC2 and FGS, which will enable us also to refine the parallax of the system.
(4) Mu Cassiopeiae (P=20.8 yr) contains a metal-deficient G star and an M dwarf companion. Determining the dynamical mass of the G star would provide the helium content for a metal-poor star. We have observed it since 1997 with WFPC2 and will present an updated orbit. The next few years will be crucial in refining the mass to a level useful for the helium determination.
Supported by STScI grants GO-10990 and GO-10914.

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