- PG 1159 star
A PG 1159 star is a
starwith a hydrogen-deficient atmosphere which is in transition between being the central star of a planetary nebulaand being a hot white dwarf. These stars are hot, with surface temperatures between 75,000 K and 200,000 K [http://arxiv.org/abs/astro-ph/0610746 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.] , and are characterized by atmospheres with little hydrogenand absorption lines for helium, carbonand oxygen. Their surface gravityis typically between 104 and 106 meters per second squared. Some PG 1159 stars are still fusing helium. [http://adsabs.harvard.edu/abs/2006PASP..118..183W 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] , § 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 [http://adsabs.harvard.edu/abs/1986ApJS...61..305G 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 [http://cdsweb.u-strasbg.fr/cgi-bin/Cat?II/207 II/207] .] , 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., §1. They are believed to eventually lose mass, cool, and become DO white dwarfs.; [ [http://adsabs.harvard.edu/abs/1998ApJ...500L..55K 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.] , §4.
Some PG 1159 stars have varying
luminosities. These stars vary slightly (5–10%) in brightness due to non-radial gravity wavepulsations within themselves. They vibrate in a number of modes simultaneously, with typical periods between 300 and 3,000 seconds. [ [http://dx.doi.org/10.1088/0953-8984/10/49/014 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.] [http://adsabs.harvard.edu/abs/2007ApJS..171..219Q 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.] , Table 1. The first known star of this type is also PG 1159-035, which was found to be variable in 1979 [ [http://adsabs.harvard.edu/abs/1979wdvd.coll..377M 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.] , and was given the variable star designation "GW Vir" in 1985. [http://adsabs.harvard.edu/abs/1985IBVS.2681....1K 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.] These stars are called "GW Vir" stars, after their prototype, or the class may be split into "DOV" and " PNNV" stars., § 1.1; [§1, [http://adsabs.harvard.edu/abs/2004A%26A...426L..45N 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.]
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