VA351 - A Quadruple Hyad Containing a White Dwarf?

Details VA351 - A Quadruple Hyad Containing a White Dwarf? VA351 - A Quadruple Hyad Containing a White Dwarf?

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aas...19310207f&link_type=abstract

American Astronomical Society, 193rd AAS Meeting, #102.07; Bulletin of the American Astronomical Society, Vol. 30, p.1402

Astronomy and Astrophysics

Astronomy

Scientific paper

VA351 = H346 = GH7-203 [ V = 13.2, B-V = 1.5, M5V; RA = 04:25:13.2, DEC = 17:16:06 (2000)] is by kinematic, photometric, and spectroscopic evidence a member of the Hyades cluster. It was first resolved with HST-FGS3 into two near-equal components of 51 mas separation in a search for binaries among faint Hyades cluster members (Franz et al. 1994, BAAS 26, 929). Orbital analysis based upon twelve FGS3 measures now available shows compelling evidence of third-body motion with a period p = 0.5692 {+/-} 0.0041 yr and a semimajor axis α = 0.0044 {+/-} 0.0006 arcsec. The dynamical mass derived for the system on the basis of the orbit of its resolved components (P = 5.263 {+/-} 0.112 yr; a = 0.0820 {+/-} 0.0016 arcsec) and the Hipparcos mean cluster distance d = 46.34 pc is 1.98 Msun. Assuming that VA351 lies at the cluster boundary nearest us at a tidal radius of 10pc (Brown et al. 1997, ESA Symp. "Hipparcos", ESA SP-402), we can lower its total dynamic mass to 0.96 Msun. However, the spectroscopic and photometric properties of VA351 are incompatible with such a small distance. Assuming the true mass lies between these two values, we will demonstrate that it cannot be acccounted for by plausible triple systems. A hierarchical quadruple system, on the other hand, consisting of one close pair of unequal M-dwarfs and of a second pair containing an M-dwarf in near-contact with a white dwarf, can readily yield a total mass within the stated range. Each of these two pairs represents one component of the resolved orbital system. We will show that the pair of M-dwarfs easily accounts for the observed perturbation, while the near-contact MD/WD pair is almost certainly responsible for observed Hα emission variability on a time scale of hours. This work is based on observation made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

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