The Hyades distance and white dwarf constraints.

Abstract

It is demonstrated how recent determinations of surface gravity and gravitational red shifts for the Hyades white dwarfs constrain the distance of the cluster for which very discrepant values between trigonometric and kinematic results are presently discussed. If the surface gravity data are correct, the Hyades modulus must be close to m - M = 3.35 with = 0.62 M_sun. The more uncertain redshift data would admit m - M = 3.25, or <M(redshift)> = O.66M_sun, whereas (M(R) , determined from the radius, would be incompatibly higher, 0.70 M_sun, for m - M = 3. t6 and currently preferred white dwarf models with thin outer envelopes. If instead amass- radius relation for models with thick outer envelopes is used, redshift, surface gravity and radii for a modulus of 3.35 agree better, at 0.67 M_sun, but for a modulus of 3. t6 the corresponding mass, 0.73 M_sun, would remain incompatible. HIPPARCOS results should finally settle the Hyades distance problem and thereby help also to decide on the outer structure of white dwarfs and their mass scale.