An exoplanet that orbits the blue subdwarf star V391 Pegasi Jadwiga Daszyńska-Daszkiewicz Instytut Astronomiczny, UWr. 12 September 2007, Journal Club.

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An exoplanet that orbits the blue subdwarf star V391 Pegasi Jadwiga Daszyńska-Daszkiewicz Instytut Astronomiczny, UWr. 12 September 2007, Journal Club

S. Undry, N. Santos 2007, ARA&A, 45, 397

Picture courtesy of HELAS, the European Helio- and Asteroseismology Network

V391 Peg – extreme horizontal branch star progenitor – a star with M=0.8 – 0.9 M  at least 10 Gyr old 2 % white dwarfs are formed through this channel Strong mass loss during the red giant phase a hot subdwarf B (sdB)

4 or 5 short period p–mode pulsations very stable in time !

OBSERVATION data from 7 years 151 runs of time-series photometry 18 telescopes (1-3 m) O-C diagram

Second order polonomial → not a satisfactory fit

an oscillating dP/dt would requires that the star expands and contracts every 3 years not compatible with any evolutionary or pulsational model,  dyn  500 s

Wobble of the star’s barycentre by a low-mass companion V391 Peg is closer or more distant by 5.3 light seconds

Two competing processes determine the orbital evolution Mass loss  the orbit of a planet expands tidal effects  spiralling-in V391 Peg b never entered the stellar envelope

Jonathan Fortney, Nature 449, , 13 September 2007

V391 Peg b is the oldest known planet in the Universe O-C – the best method to detect brown dwarfs or planets around sdBs or WDs Effects of the red giant phase on a planetary system The fate of the Earth is still a matter of debate CONCLUSIONS

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