A Close-in Planet Orbiting Giant Star HD 167768

Abstract

We report the detection of a giant planet orbiting a G-type giant star HD 167768 from radial velocity measurements using HIgh Dispersion Echelle Spectrograph (HIDES) at Okayama Astrophysical Observatory (OAO). HD 167768 has a mass of $1.08_{-0.12}^{+0.14}{M}_{\odot }$, a radius of $9.70_{-0.25}^{+0.25}{R}_{\odot }$, a metallicity of $[Fe/H]=-0.67_{-0.08}^{+0.09}$, and a surface gravity of $\log g=2.50_{-0.06}^{+0.06}$. The planet orbiting the star is a warm Jupiter, having a period of $20.6532_{-0.0032}^{+0.0032}\mathrm{d}$, a minimum mass of $0.85_{-0.11}^{+0.12}{M}_{\mathrm{J}}$, and an orbital semimajor axis of $0.1512_{-0.0063}^{+0.0058}\mathrm{au}$. The planet has one of the shortest orbital periods among those ever found around deeply evolved stars ($\log g<3.5$) using radial velocity methods. The equilibrium temperature of the planet is $1874\mathrm{K}$, as high as a hot Jupiter. The radial velocities show two additional regular variations at $41\mathrm{d}$ and $95\mathrm{d}$, suggesting the possibility of outer companions in the system. Follow-up monitoring will enable validation of the periodicity. We also calculated the orbital evolution of HD 167768 b and found that the planet will be engulfed within 0.15\,Gyr.

arXiv commentAccepted by Publications of the Astronomical Society of Japan, 9 pages, 7 figures, 2 tables

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