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Planets around Red Giant Stars

18 Feb 2015, 22:00 UTC
Planets around Red Giant Stars
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Niedzielski et al. (2015) report the detection of planetary-mass companions around three red giant stars by the ongoing Penn State-Torun Planet Search using the 9.2-meter aperture Hobby-Eberly Telescope (HET) at McDonald Observatory in Texas. The red giant stars are identified as BD+49 828, HD 95127 and HD 216536. All three stars are exhausting the nuclear fuel in their cores and are gradually expanding in size. Their planetary-mass companions were detected with the radial velocity method. It involves a high resolution spectrograph which precisely measures the amount of redshift and blueshift in the star’s spectral lines as the star wobbles back and forth due to gravitational tugging from an orbiting planet.Figure 1: Artist’s impression of a gas-giant planet.BD+49 828 has 30 times the Sun’s luminosity, 1.5 times the Sun’s mass and 7.6 times the Sun’s radius. Its planetary-mass companion, BD+49 828 b, with the added suffix “b” to indicate its planetary nature, is 1.6 times Jupiter’s mass. The planet orbits its host star in a 2590-day orbit at a mean distance of 4.2 AU with eccentricity 0.35.HD 95127 has 190 times the Sun’s luminosity, 1.2 times the Sun’s mass and 20 times the Sun’s radius. Its planetary-mass companion, HD 95127 b, ...

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