GD 66 or V361 Aurigae is a 0.64 solar mass (M☉)[4]pulsating white dwarf star located 170 light years from Earth[3] in the Auriga constellation. The estimated cooling age of the white dwarf is 500 million years.[4] 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.[4] The total age of the star is thus estimated to be in the range 1.2 to 1.7 billion years.[4]
In 1983, Noël Dolez et al. discovered that GD 66 is a variable star, from photometric data obtained at Haute-Provence Observatory.[6] It was given its variable star designation, V361 Aurigae, in 1985.[7] 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.[3] 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.[4] Investigation of a separate pulsation mode revealed timing variations in antiphase with the variations in the originally-analysed pulsation mode.[8] 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.[9]
