An observational limit to the evolutionary time scale of the 13,000 K white dwarf G117 - B15A

Details An observational limit to the evolutionary time scale of the 13,000 K white dwarf G117 - B15A An observational limit to the evolutionary time scale of the 13,000 K white dwarf G117 - B15A

Jul 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990apj...357..204k&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 357, July 1, 1990, p. 204-207. Research supported by CNPQ, NSF, CNRS, SERC,

Astronomy and Astrophysics

Astrophysics

8

Light Curve, Stellar Evolution, Stellar Interiors, Stellar Oscillations, White Dwarf Stars, Energy Transfer, Iue, Pulsars, Stellar Structure

Scientific paper

Using 204 hr of high-speed photometric observations of the DAV star G117 - B15A during the last 14 yr, an observational limit has been obtained to the rate of period change for its dominant pulsation at 215.2 sec of (8.3 + or - 5.0) x 10 to the -15th sec/sec. This rate of period change corresponds to an evolutionary time scale of (8.2 + or - 5.0) x 10 to the 8th yr, consistent with the change expected due to cooling of the white dwarf undergoing nonradial g-mode pulsations. The observed limit on the rate of period change makes G117 - B15A the most accurate optical clock known, with a stability comparable to that of the atomic clocks used by the National Bureau of Standards, and exceeded only by a few msec radio pulsars. Since all DA white dwarfs are thought to cool through the DAV instability strip, and there are no known differences between the properties of variables and nonvariables white dwarfs, the measurement of an evolutionary time scale, suitably scaled by mass and surface temperature, should apply to all DA white dwarfs.

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