PG 1159 star Thursday, July 2, 2009

A PG 1159 star, often also called a pre-degenerate^[1], is a star with a hydrogen-deficient atmosphere which is in transition between being the central star of a planetary nebula and being a hot white dwarf. These stars are hot, with surface temperatures between 75,000 K and 200,000 K^[2], and are characterized by atmospheres with little hydrogen and absorption lines for helium, carbon and oxygen. Their surface gravity is typically between 10⁴ and 10⁶ meters per second squared. Some PG 1159 stars are still fusing helium.^{[3], § 2.1.1, 2.1.2, Table 2.} The PG 1159 stars are named after their prototype, PG 1159-035. This star, found in the Palomar-Green survey of ultraviolet-excess stellar objects^[4], was the first PG 1159 star discovered.

It is thought that the atmospheric composition of PG 1159 stars is odd because, after they have left the asymptotic giant branch, they have reignited helium fusion. As a result, a PG 1159 star's atmosphere is a mixture of material which was between the hydrogen- and helium-burning shells of its AGB star progenitor.^{[3], §1.} They are believed to eventually lose mass, cool, and become DO white dwarfs.^{[2]; [5], §4.}

Some PG 1159 stars have varying luminosities. These stars vary slightly (5–10%) in brightness due to non-radial gravity wave pulsations within themselves. They vibrate in a number of modes simultaneously, with typical periods between 300 and 3,000 seconds.^{[6][7], Table 1.} The first known star of this type is also PG 1159-035, which was found to be variable in 1979^[8], and was given the variable star designation GW Vir in 1985.^[9] These stars are called GW Vir stars, after their prototype, or the class may be split into DOV and PNNV stars.^{[7], § 1.1;[10]}

See also

• Planetary nebula
• White dwarf

References

1. ^ Jaschek & Jaschek: CARBON C
2. ^ ^{a b} Observational constraints on the evolutionary connection between PG 1159 stars and DO white dwarfs, S. D. Huegelmeyer, S. Dreizler, K. Werner, J. Krzesinski, A. Nitta, and S. J. Kleinman. arXiv:astro-ph/0610746.
3. ^ ^{a b} The Elemental Abundances in Bare Planetary Nebula Central Stars and the Shell Burning in AGB Stars, Klaus Werner and Falk Herwig, Publications of the Astronomical Society of the Pacific 118, #840 (February 2006), pp. 183–204
4. ^ The Palomar-Green catalog of ultraviolet-excess stellar objects, R. F. Green, M. Schmidt, and J. Liebert, Astrophysical Journal Supplement 61 (June 1986), pp. 305–352. CDS ID II/207.
5. ^ Determination of Mass-Loss Rates of PG 1159 Stars from Far-Ultraviolet Spectroscopy, Lars Koesterke and Klaus Werner, Astrophysical Journal 500 (June 1998), pp. L55–L59.
6. ^ Asteroseismology of white dwarf stars, D. E. Winget, Journal of Physics: Condensed Matter 10, #49 (December 14, 1998), pp. 11247–11261. DOI 10.1088/0953-8984/10/49/014.
7. ^ ^{a b} Mapping the Instability Domains of GW Vir Stars in the Effective Temperature-Surface Gravity Diagram, Quirion, P.-O., Fontaine, G., Brassard, P., Astrophysical Journal Supplement Series 171 (2007), pp. 219–248.
8. ^ PG1159-035: A new, hot, non-DA pulsating degenerate, J. T. McGraw, S. G. Starrfield, J. Liebert, and R. F. Green, pp. 377–381 in White Dwarfs and Variable Degenerate Stars, IAU Colloquium #53, ed. H. M. van Horn and V. Weidemann, Rochester: University of Rochester Press, 1979.
9. ^ The 67th Name-List of Variable Stars, P. N. Kholopov, N. N. Samus, E. V. Kazarovets, and N. B. Perova, Information Bulletin on Variable Stars, #2681, March 8, 1985.
10. ^ §1, Detection of non-radial g-mode pulsations in the newly discovered PG 1159 star HE 1429-1209, T. Nagel and K. Werner, Astronomy and Astrophysics 426 (2004), pp. L45–L48.