Planetary companions orbiting M giants HD 208527 and HD 220074

Abstract

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.

Search for exoplanet around northern circumpolar stars

“…HD 12648 b becomes the exoplanet detected in the highest declination of 85.7 • so far, and HD 24064 b corresponds to an exoplanet found around one of the largest stars. The planets discovered in five of the six stars larger than HD 24064 were reported in another exoplanet survey program using 1.8 m telescope at BOAO (Lee et al 2013(Lee et al , 2014bHatzes et al 2015).…”

Planetary companions in K giantsβCancri,μ Leonis, andβUrsae Minoris

“…To obtain the stellar spectrum, we used a stellar template spectrum that was obtained by deconvolving a pure stellar spectrum with the spectrograph IP determined from a specrtrum of a tungsten-halogen lamp (THL) observed through the I 2 cell. The long-term stability of the BOES with the I 2 cell was demonstrated by observing the RV standard star τ Ceti, which was constant with an rms scatter (intrinsic uncertainty) of ∼7 m s −1 (Lee et al 2013). The resulting RV measurements are listed as online data (Tables 4-6).…”

“…To search for variations in the spectral line shapes, the BVS was computed for a strong, unblended spectral features with a high flux level, namely Ni I 6643.6 Å as described in Hatzes et al (2005) and Lee et al (2013). The selected line shows a high flux level and is located beyond the I 2 absorption region so contamination should not affect our bisector measurements.…”

Low-amplitude and long-period radial velocity variations in giants HD 3574, 63 Cygni, and HD 216946

“…These results demonstrate that the high rms scatter about the orbital solution can easily be accounted for entirely by stellar oscillations. These increase toward later spectral types and evolved stars (Hatzes et al 2005;Hekker et al 2006;Lee et al 2013). …”

“…To provide precise RV measurements, the spectrograph is equipped with an iodine absorption (I 2 ) cell that produces reference absorption lines in the region of 4900−6000 Å. Observations of an RV standard star, τ Cet, show long-term rms scatter of ∼7 m s −1 (Lee et al 2013).…”