G 117-B15A

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.

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, EGGR 65, WD 0921+354
Database references
SIMBADdata

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. 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.
  2. "V* RY LMi". SIMBAD. Centre de données astronomiques de Strasbourg.
  3. 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.
  4. 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.
  5. 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.
  6. Pivetta, Marcos (January 2006). "The star of the moment". Retrieved 2007-06-06.
  7. From Ṗ=2.3·10−15 in Kepler et al.
  8. McDonald Observatory. "Astronomers Find Most Stable Optical Clock in Heavens; Aids Understanding of Stars' Lives". McDonald Observatory. Retrieved 2007-06-06.
  9. Kepler SO (December 5, 2005). "Astronomers Find Most Stable Optical Clock In Heavens".
gollark: Although I think it would be in python too because... python bad?
gollark: You see, in JS even something like "using an undefined variable" is a *runtime* ReferenceError.
gollark: I actually use TypeScript without even... writing types... the majority of the time, because it means I actually get working autocomplete, and my IÐE will detect errors which for some insane reason JS only notices at runtime.
gollark: TS has compilation anyway, it basically just involves removing the type annotations (this is actually separate from the typechecking).
gollark: Oh, that is JOKE™, `use strict` isn't very big.

See also
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