Whole Earth Telescope Observations of a Star Cooled by Neutrino Emission: the
Pulsating Pre-White Dwarf PG0122+200
by M.S. O'Brien,
G. Vauclair,S.D. Kawaler, T.K. Watson, D.E. Winget,
R.E. Nather, M. Montgomery, A. Nitta,
S.J. Kleinman, D.J. Sullivan, X.J. Jiang, T.M.K. Marar, S. Seetha, B.N. Ashoka, J. Bhattacharya,
E.M. Leibowitz, S. Hemar, P. Ibbetson, B. Warner, L. van Zyl, P. Moskalik, S. Zol a, G. Pajdosz,
J. Krzesinski, N. Dolez, M. Chevreton, J.-E. Solheim, T. Thomassen, S.O. Kepler, O. Giovannini,
J.L. Provencal, M.A. Wood, & J.C. Clemens
The Astrophysical Journal, submitted 13 August, 1997; accepted, 9 September, 1997
Observation of g-mode pulsations in the variable pre-white dwarf
(GW Virginis) stars provides a unique means to probe their interiors
and to study the late stages of stellar evolution. Multi-site campaigns
have in several cases proved highly successful in decoding pre-white
dwarf light curves. Three previous attempts to untangle the pulsation
spectrum of the coolest GW Vir star, PG 0122+200, confirmed the existence
of multiple g-modes but left the fundamental period spacing and
therefore the star's mass and luminosity in doubt. We present an
analysis based on new observations of PG 0122+200 obtained during a
Whole Earth Telescope (WET) campaign conducted in the fall of 1996.
Although our coverage was, due to bad weather, far poorer than in
previous WET campaigns, we confirm the previous result that PG 0122+200
rotates once in 1.6 +/- 0.1 d. The most likely period spacing
supported by the data implies a mass of 0.69 +/- 0.03 Msun.
Based on the best seismology we can currently do, the cooling of
PG 0122+200 is dominated by neutrino losses. This is not true for all
pre-white dwarf stars and makes PG 0122+200 the prime candidate for learning
useful physics. Constraints placed on the cooling rate of PG 0122+200 by
future measurement of dP/dt could provide a unique test of the standard
theory of lepton interactions in the (experimentally unexplored) region
of phase-space appropriate to pre-white dwarf interiors.