Asteroseismology of a Star Cooled by Neutrino Emission: The Pulsating Pre-White Dwarf PG 0122+200

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. Multisite 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 Virginis 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, because of 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 days. The most likely period spacing supported by the data implies a mass of 0.69±0.03 M☉. 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 dΠ/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.

[1]  R. Ciardullo,et al.  Asteroseismological Observations of the Central Star of the Planetary Nebula NGC 1501 , 1996, astro-ph/9609024.

[2]  S. Kawaler,et al.  The pulsating pre-white dwarf star PG 0122 + 200 , 1996, astro-ph/9603025.

[3]  S. O. Kepler,et al.  Whole Earth Telescope Observations and Seismological Analysis of the Pre--White Dwarf PG 2131+066 , 1995 .

[4]  S. Kawaler,et al.  Thick to Thin: The Evolutionary Connection between PG 1159 Stars and the Thin Helium--enveloped Pulsating White Dwarf GD 358 , 1995, astro-ph/9503099.

[5]  S. Dreizler,et al.  PG 1159 stars and their evolutionary link to DO white dwarfs , 1995 .

[6]  Paul A. Bradley,et al.  Precision Asteroseismology of Pulsating PG 1159 Stars , 1994 .

[7]  S. Kawaler,et al.  An Enormous Planetary Nebula Surrounding the X-Ray Source RXJ 2117+34 , 1993 .

[8]  Brian Warner,et al.  Asteroseismology of the DOV star PG 1159 - 035 with the Whole Earth Telescope , 1991 .

[9]  Carl J. Hansen,et al.  The whole earth telescope - A new astronomical instrument , 1990 .

[10]  H. Bond,et al.  PG 0122+200 - A new member of the GW Virginis (PG 1159-035) class of extremely hot pulsating white dwarfs , 1987 .

[11]  C. Hansen,et al.  Evolution of the pulsation properties of hot pre-white dwarf stars. , 1985 .

[12]  E. L. Robinson,et al.  A measurement of secular evolution in the pre-white-dwarf star PG 1159-035 , 1985 .

[13]  I. Iben,et al.  Cooling of low-mass carbon-oxygen dwarfs from the planetary nucleus stage through the crystallization stage , 1984 .

[14]  C. Hansen,et al.  Do pulsating PG1159–035 stars put constraints on stellar evolution? , 1983, Nature.

[15]  B. Warner,et al.  The Gravity Oscillations of White Dwarfs , 1975 .