Asteroseismology of the PG 1159 star PG 0122+200

J. N. Fu, G. Vauclair, J. E. Solheim, M. Chevreton, N. Dolez, M. S. O'Brien, S. L. Kim, B. G. Park, G. Handler, R. Medupe, M. Wood, J. Gonzalez Perez, O. Hashimoto, K. Kinugasa, H. Taguchi, E. Kambe, J. Provencal, S. Dreizler, S. Schuh, E. LeibowitzY. Lipkin, X. B. Zhang, M. Paparo, B. Szeidl, G. Virághalmy, D. Zsuffa

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17 Citations (Scopus)

Abstract

Context. The variable pre-white dwarf PG 1159 stars (GW Vir) are g-mode non-radial pulsators. Asteroseismology puts strong constraints on their global parameters and internal structure. PG 0122+200 defines the red edge of the instability strip and its evolutionary timescale is predicted to be dominated by neutrino emission. Its study offers the opportunity to better understand the instability mechanism and to validate the physics of the neutrino production in dense plasma. Aims. To achieve such a goal requires determining precisely its fundamental parameters. This is the goal of this paper. Methods. We present new multi-site photometric observations obtained in 2001 and 2002. Together with previous data, they allow us to detect 23 frequencies, composed of 7 triplets and 2 single frequencies, which are used to constrain its internal structure and derive its fundamental parameters. Results. All the observed frequencies correspond to ℓ - 1 g-modes. The period distribution shows a signature of mode trapping from which we constrain the He-rich envelope mass fraction to be -6.0 ≤ log(qy) ≤ -5.3. The comparison of the mode trapping amplitudes among GW Vir stars suggests that the mass-loss efficiency must decrease significantly below Teff ≤ 140 kK. We measure an average period spacing of 22.9 s from which we derive a mass of 0.59 ± 0.02 M. From the triplets we measure a mean rotational splitting of 3.74 μHz and a rotational period of 1.55 days. We derive an upper limit to the magnetic field of B ≤ 4 × 103 G. The luminosity (log L/L = 1.3 ± 0.5) and the distance (D = 0.7 -0.4+1.0 kpc) are only weakly constrained due to the large uncertainty on the spectroscopically derived surface gravity and the absence of a measured parallax. Conclusions. From the asteroseismic mass, the ratio of the neutrino luminosity on the photon luminosity is 1.6 ± 0.2 confirming that the PG 0122+200 evolutionary time scale should be dominated by neutrino cooling. A measurement of P for the largest amplitude untrapped modes should verify this prediction.

Original languageEnglish
Pages (from-to)237-248
Number of pages12
JournalAstronomy and Astrophysics
Volume467
Issue number1
DOIs
Publication statusPublished - May 2007

Keywords

  • Stars: evolution
  • Stars: fundamental parameters
  • Stars: individual: PG 0122+200
  • Stars: oscillations
  • Stars: white dwarfs

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Fu, J. N., Vauclair, G., Solheim, J. E., Chevreton, M., Dolez, N., O'Brien, M. S., Kim, S. L., Park, B. G., Handler, G., Medupe, R., Wood, M., Gonzalez Perez, J., Hashimoto, O., Kinugasa, K., Taguchi, H., Kambe, E., Provencal, J., Dreizler, S., Schuh, S., ... Zsuffa, D. (2007). Asteroseismology of the PG 1159 star PG 0122+200. Astronomy and Astrophysics, 467(1), 237-248. https://doi.org/10.1051/0004-6361:20066295