G 117-B15A
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Leo Minor |
| Right ascension | 09h 24m 16s[1] |
| Declination | +35° 16.9′[1] |
| Apparent magnitude (V) | 15.5[1] |
| Characteristics | |
| Spectral type | DAV4[1] |
| U−B color index | -0.6[1] |
| B−V color index | 0.2[1] |
| Variable type | DAV[1] |
| Astrometry | |
| Proper motion (μ) | RA: -136[2] mas/yr Dec.: 22[2] mas/yr |
| Other designations | |
RY LMi, RY Leonis Minoris, EGGR 65, PG 0921+355, WD 0921+354. | |
G117-B15A[3] is a small, well-observed variable white dwarf star of the DAV, or ZZ Ceti, type in the constellation of Leo Minor.
G117-B15A was found to be variable in 1974 by Richer and Ulrych,[4] and this was confirmed in 1976 by McGraw and Robinson.[5] In 1984 it was demonstrated that the star's variability is due to nonradial gravity wave pulsations. As a consequence, its timescale for period change is directly proportional to its cooling timescale, allowing its cooling rate to be measured using astroseismological techniques.[3] Its age is estimated at 400 million years.[6] Its light curve has a dominant period of 215.2 seconds,[3] which is estimated to increase by approximately one second each 14 million years.[7] G117-B15A has been claimed to be the most stable optical clock ever found, much more stable than the ticks of an atomic clock.[8] It is also the first pulsating white dwarf to have its main pulsation mode index identified.[3]
X-ray source
An X-ray source in the constellation Leo Minor is the white dwarf G117-B15A.[9]
Notes
- 1 2 3 4 5 6 7 A Catalog of Spectroscopically Identified White Dwarfs, George P. McCook and Edward M. Sion, Astrophysical Journal Supplement 121, #1 (March 1999), pp. 1–130. CDS ID III/210. Astrometric data updated to J2000.0.
- 1 2 SIMBAD. Accessed June 14, 2007.
- 1 2 3 4 Kepler, S. O.; et al. (2000-05-10). "Evolutionary Timescale of the Pulsating White Dwarf G117-B15A: The Most Stable Optical Clock Known". The Astrophysical Journal Letters. 534 (2): L185–L188. arXiv:astro-ph/0003478
. Bibcode:2000ApJ...534L.185K. doi:10.1086/312664. - ↑ High-frequency optical variables. II. Luminosity-variable white dwarfs and maximum entropy spectral analysis, H. B. Richer and T. J. Ulrych, Astrophysical Journal 192 (September 1974), pp. 719–730.
- ↑ High-speed photometry of luminosity-variable DA dwarfs: R808, GD 99, and G 117-B15A, J. T. McGraw and E. L. Robinson, Astrophysical Journal 205 (May 1976), pp. L155–L158.
- ↑ Pivetta, Marcos (January 2006). "The star of the moment". Retrieved 2007-06-06.
- ↑ From Ṗ=2.3·10−15 in Kepler et al.
- ↑ McDonald Observatory. "Astronomers Find Most Stable Optical Clock in Heavens; Aids Understanding of Stars' Lives". McDonald Observatory. Retrieved 2007-06-06.
- ↑ Kepler SO (December 5, 2005). "Astronomers Find Most Stable Optical Clock In Heavens".