Dissecting The Quadruple Binary Hyad Va 351 Masses For Three M Dwarfs And A White Dwarf

We extend results first announced by Franz et al., that identified vA 351 = H346 in the Hyades as a multiple star system containing a white dwarf. With Hubble Space Telescope Fine Guidance Sensor fringe tracking and scanning, and more recent speckle observations, all spanning 20.7 years, we establish a parallax, relative orbit, and mass fraction for two components, with a period, P = 2.70 yr and total mass 2.1 M-circle dot. With ground-based radial velocities from the McDonald Observatory Otto Struve 2.1 m Telescope Sandiford Spectrograph, and Center for Astrophysics Digital Speedometers, spanning 37 years, we find that component B consists of BC, two M dwarf stars orbiting with a very short period (P-BC = 0.749 days), having a mass ratio M-C/M-B = 0.95. We confirm that the total mass of the system can only be reconciled with the distance and component photometry by including a fainter, higher-mass component. The quadruple system consists of three M dwarfs (A, B, C) and one white dwarf (D). We determine individual M dwarf masses M-A = 0.53 +/- 0.10 M-circle dot, M-B = 0.43 +/- 0.04 M-circle dot, and M-C = 0.41 +/- 0.04 M-circle dot. The white dwarf mass, 0.54 +/- 0.04 M-circle dot, comes from cooling models, an assumed Hyades age of 670 Myr, and consistency with all previous and derived astrometric, photometric, and radial velocity results. Velocities from H alpha and He I emission lines confirm the BC period derived from absorption lines, with similar (He I) and higher (H alpha) velocity amplitudes. We ascribe the larger H alpha amplitude to emission from a region each component shadows from the other, depending on the line of sight.