Abstract
Aims. The purpose of this paper is to detect and investigate the nature of long-term radial velocity (RV) variations of K-type giants and to confirm planetary companions around the stars. Methods. We have conducted two planet search programs by precise RV measurement using the 1.8 m telescope at Bohyunsan Optical Astronomy Observatory (BOAO) and the 1.88 m telescope at Okayama Astrophysical Observatory (OAO). The BOAO program searches for planets around 55 early K giants. The OAO program is looking for 190 G–K type giants. Results. In this paper, we report the detection of long-period RV variations of three K giant stars, HD 40956, HD 111591, and HD 113996. We investigated the cause of the observed RV variations and conclude the substellar companions are most likely the cause of the RV variations. The orbital analyses yield P = 578.6 ± 3.3 d, m sin i = 2.7 ± 0.6 MJ, a = 1.4 ± 0.1 AU for HD 40956; P = 1056.4 ± 14.3 d, m sin i = 4.4 ± 0.4 MJ, a = 2.5 ± 0.1 AU for HD 111591; P = 610.2 ± 3.8 d, m sin i = 6.3 ± 1.0 MJ, a = 1.6 ± 0.1 AU for HD 113996.
Highlights
Planetary formation around normal stars involves complex processes that depend on various stellar properties: stellar mass, metallicity, radiation flow of central stars, the host star’s environment, binarity, and so on
Based on a Doppler survey of 373 G- and K-type giants, Reffert et al (2015) found that the planet occurrence rate of intermediate-mass stars depends on stellar masses, and the rate reaches its maximum at a stellar mass of 1.9 M and drops off at stellar masses of more than 2.7 M
In order to confirm the nature of these periodic radial velocity (RV) variations, we checked Hipparcos photometeric data, chromospheric activity, line-shape variations, and rotational period
Summary
Planetary formation around normal stars involves complex processes that depend on various stellar properties: stellar mass, metallicity, radiation flow of central stars, the host star’s environment, binarity, and so on. Based on a Doppler survey of 373 G- and K-type giants, Reffert et al (2015) found that the planet occurrence rate of intermediate-mass stars depends on stellar masses, and the rate reaches its maximum at a stellar mass of 1.9 M and drops off at stellar masses of more than 2.7 M. They concluded that no giant planet has been found around stars more massive than 2.7 M and suggested that the giant planet formation and/or inward migration in protoplanetary disks are suppressed for more massive stars because of. We use a pure high-resolution spectrum taken without the I2 cell by BOES to determine stellar parameters
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