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Extreme Universe: Hottest White Dwarf! December 25, 2008

Posted by jcconwell in Astronomy, Extreme Universe, stars.
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Between finals and jury duty the December blog has been a bit neglected. So let’s close out the year with some of the more fun, extreme objects of the year.

Astronomers have found a white dwarf star with a surface temperature of 359,500 degrees Fahrenheit (200,000 Celsius). It’s so hot that “its photosphere exhibits emission lines in the ultraviolet spectrum, a phenomenon that has never been seen before,”

M.S. Sliwinski and L. I. Slivinska of Lunarismaar

Credit: M.S. Sliwinski and L. I. Slivinska of Lunarismaar

Stars from one to eight times the mass of the sun, end their life as an Earth-sized white dwarfs after the exhaustion of their nuclear fuel. During the change from a normal nuclear-burning star to the white dwarf stage, a star becomes very hot.

The white dwarf, named KPD 0005+5106, lives in the globular cluster M4, 7,200 light years away is among the hottest stars ever known.

Discovered in 1985, KPD 0005+5106 attracted  attention because it’s spectrum  suggested that this white dwarf is very hot. It belongs to a class of rare white dwarfs whose atmospheres are dominated by helium. Studies revealed  emission lines from calcium, and detailed stellar  modeling confirmed their origin in the star’s photosphere. The analysis proves that the temperature must be 200,000 Kelvin, for these emission lines to be present.

The measured calcium abundance (1-10 times the solar value) in combination with the helium-rich nature of its atmosphere represents a chemical surface composition that is not predicted by stellar evolution models.

Citation: Discovery of photospheric CaX emission lines in the far-UV spectrum of the hottest known white dwarf (KPD 0005+5106), by K. Werner, T. Rauch, and J. W. Kruk. Astronomy & Astrophysics Letters, 2008, volume 492-3, pp. L43.

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