Planetary companions orbiting M giants HD 208527 and HD 220074

Aims: The purpose of the present study is to research the origin of planetary companions by using a precise radial velocity (RV) survey.
Methods: The high-resolution spectroscopy of the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy Observatory (BOAO) was used from September 2008 to June 2012.
Results: We report the detection of two exoplanets in orbit around HD 208527 and HD 220074 exhibiting periodic variations in RV of 875.5 ± 5.8 and 672.1 ± 3.7 days. The RV variations are not apparently related to the surface inhomogeneities, and a Keplerian motion of the planetary companion is the most likely explanation. Assuming possible stellar masses of 1.6 ± 0.4 and 1.2 ± 0.3 M_⊙, we obtain the minimum masses for the exoplanets at 9.9 ± 1.7 and 11.1 ± 1.8 M_Jup around HD 208527 and HD 220074 with orbital semi-major axes of 2.1 ± 0.2 and 1.6 ± 0.1 AU and eccentricities of 0.08 and 0.14, respectively. We also find that the previously known spectral classification of HD 208527 and HD 220074 was in error. Our new estimation of stellar parameters suggests that both HD 208527 and HD 220074 are M giants. Therefore, HD 208527 and HD 220074 are so far the first candidate M giants found to harbor a planetary companion.

Based on observations made with the BOES instrument on the 1.8-m telescope at the Bohyunsan Optical Astronomy Observatory in Korea.