[[Astronomy:Epoch|Epoch J2000.0 (ICRS)]] Equinox J2000.0 (ICRS)
|Right ascension||09h 24m 16s|
|Apparent magnitude (V)||15.5|
|U−B color index||-0.6|
|B−V color index||0.2|
|Proper motion (μ)|| RA: -136 mas/yr |
Dec.: 22 mas/yr
G117-B15A was found to be variable in 1974 by Richer and Ulrych, and this was confirmed in 1976 by McGraw and Robinson. 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. Its age is estimated at 400 million years. Its light curve has a dominant period of 215.2 seconds, which is estimated to increase by approximately one second each 14 million years. G117-B15A has been claimed to be the most stable optical clock ever found, much more stable than the ticks of an atomic clock. It is also the first pulsating white dwarf to have its main pulsation mode index identified.
- 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.
- "V* RY LMi". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=V%2A+RY+LMi.
- Kepler, S. O. (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. doi:10.1086/312664. Bibcode: 2000ApJ...534L.185K.
- 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". http://www.revistapesquisa.fapesp.br/?art=1620&bd=1&pg=1&lg=en. 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. http://www.spaceref.ca/news/viewpr.html?pid=18424. Retrieved 2007-06-06. [permanent dead link]
- Kepler SO (December 5, 2005). "Astronomers Find Most Stable Optical Clock In Heavens". http://www.physorg.com/news8712.html.
Original source: https://en.wikipedia.org/wiki/ G 117-B15A. Read more