GD 66

GD 66 or V361 Aurigae is a 0.64 solar mass (M☉)[3] pulsating white dwarf star located 170 light years from Earth[2] in the Auriga constellation. The estimated cooling age of the white dwarf is 500 million years.[3] Models of the relationship between the initial mass of a star and its final mass as a white dwarf star suggest that when the star was on the main sequence it had a mass of approximately 2.5 M☉, which implies its lifetime was around 830 million years.[3] The total age of the star is thus estimated to be in the range 1.2 to 1.7 billion years.[3]

GD 66
Observation data
Epoch J2000      Equinox J2000
Constellation Auriga
Right ascension  05h 20m 38.31s[1]
Declination +30° 48′ 24.1″[1]
Apparent magnitude (V) 15.56[1]
Characteristics
Spectral type DA[1]
U−B color index -0.59
B−V color index 0.22[1]
Variable type Pulsating white dwarf
Astrometry
Proper motion (μ) RA: 54[1] mas/yr
Dec.: −120[1] mas/yr
Distance170[2] ly
(51 pc)
Absolute magnitude (MV)12
Details
Mass0.64 ± 0.03[3] M☉
Surface gravity (log g)8.05[4] cgs
Temperature11980[4] K
Age1.2–1.7 billion[3] years
Other designations
V361 Aurigae, GD 66, 2MASS J05203829+3048239, WD 0517+30, EGGR 572, WD 0517+307
Database references
SIMBADdata

The star is a pulsating white dwarf of type DAV, with an extremely stable period. Small variations in the phase of pulsation led to the suggestion that the star was being orbited by a giant planet which caused the pulsations to be delayed due to the varying distance to the star caused by the reflex motion about the system's centre-of-mass.[2] Observations with the Spitzer Space Telescope failed to directly detect the planet, which put an upper limit on the mass of 5–6 Jupiter masses.[3] Investigation of a separate pulsation mode revealed timing variations in antiphase with the variations in the originally-analysed pulsation mode.[5] This would not be the case if the variations were caused by an orbiting planet, and thus the timing variations must have a different cause. This illustrates the potential dangers of attempting to detect planets by white dwarf pulsation timing.[6]

References
  1. "V* V361 Aur". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2008-12-19.
  2. Mullally, F.; et al. (2008). "Limits on Planets around Pulsating White Dwarf Stars". The Astrophysical Journal. 676 (1): 573–583. arXiv:0801.3104. Bibcode:2008ApJ...676..573M. doi:10.1086/528672.
  3. Mullally, F.; et al. (2008). "Spitzer Planet Limits around the Pulsating White Dwarf GD66". The Astrophysical Journal. 694: 327. arXiv:0812.2951. Bibcode:2009ApJ...694..327M. doi:10.1088/0004-637X/694/1/327.
  4. Bergeron, P.; et al. (2004). "On the Purity of the ZZ Ceti Instability Strip: Discovery of More Pulsating DA White Dwarfs on the Basis of Optical Spectroscopy". The Astrophysical Journal. 600 (1): 404–408. arXiv:astro-ph/0309483. Bibcode:2004ApJ...600..404B. doi:10.1086/379808.
  5. Hermes, James J. (2013). Complications to the Planetary Hypothesis for GD 66. AAS Meeting #221. American Astronomical Society. Bibcode:2013AAS...22142404H.
  6. Hermes, J. J. (2012). 8 Years On: A Search for Planets Around Isolated White Dwarfs (PDF). Planets around Stellar Remnants. Archived from the original (PDF) on 2014-12-27.
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