IALP   13078
INSTITUTO DE ASTROFISICA LA PLATA
Unidad Ejecutora - UE
artículos
Título:
The pulsation modes of the pre-white dwarf PG 1159-035
Autor/es:
COSTA, J. E. S.; KEPLER, S.O.; WINGET, D. E.; O'BRIEN, M. S.; KAWALER, S. D.; MAS 70 AUTORES; ALTHAUS, L. G.; CORSICO, A. H.; MONTGOMERY, M. H.
Revista:
ASTRONOMY AND ASTROPHYSICS
Editorial:
EDP Sciences
Referencias:
Lugar: Les Ulis; Año: 2008 vol. 477 p. 627 - 640
ISSN:
0004-6361
Resumen:
Context: PG 1159-035, a pre-white dwarf with
Teff=140 000 K, is the prototype of both two classes:
the PG 1159 spectroscopic class and the DOV pulsating class. Previous
studies of PG 1159-035 photometric data obtained with
the Whole Earth Telescope (WET) showed a rich frequency spectrum
allowing the identification of 122 pulsation modes. Analyzing the
periods of pulsation, it is possible to measure the stellar mass, the
rotational period and the inclination of the rotation axis, to estimate
an upper limit for the magnetic field, and even to obtain information
about the inner stratification of the star. Aims: We have three
principal aims: to increase the number of detected and identified
pulsation modes in PG 1159-035, study trapping of the
star's pulsation modes, and to improve or constrain the determination of
stellar parameters. Methods: We used all available WET photometric
data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation
periods. Results: We identified 76 additional pulsation modes,
increasing to 198 the number of known pulsation modes in PG
1159-035, the largest number of modes detected in any star
besides the Sun. From the period spacing we estimated a mass M/M_= 0.59 ± 0.02 for PG 1159-035, with the
uncertainty dominated by the models, not the observation. Deviations in
the regular period spacing suggest that some of the pulsation modes are
trapped, even though the star is a pre-white dwarf and the gravitational
settling is ongoing. The position of the transition zone that causes the
mode trapping was calculated at r_c/R_star = 0.83 ± 0.05. From
the multiplet splitting, we calculated the rotational period P_rot =
1.3920 ± 0.0008 days and an upper limit for the magnetic field, B
< 2000 G. The total power of the pulsation modes at the stellar
surface changed less than 30% for l = 1 modes and less than 50% for l = 2 modes. We find no evidence of linear combinations between the
198 pulsation mode frequencies. PG 1159-035 models
have not significative convection zones, supporting the hypothesis that
nonlinearity arises in the convection zones in cooler pulsating white
dwarf stars.