The Pan-Pacific Planet Search III: five companions orbiting giant stars

Abstract

We report a new giant planet orbiting the K giant HD 155233, as well as four stellar-mass companions from the Pan-Pacific Planet Search, a Southern hemisphere radial velocity survey for planets orbiting nearby giants and sub-giants. We also present updated velocities and a refined orbit for HD 47205b (7 CMa b), the first planet discovered by this survey. HD 155233b has a period of 885 ± 63 d, eccentricity e = 0.03 ± 0.20, and m sin i = 2.0 ± 0.5 M Jup . The stellar-mass companions range in m sin i from 0.066 to 0.33 M . Whilst HD 104358B falls slightly below the traditional 0.08 M hydrogen-burning mass limit, and is hence a browndwarf candidate, we estimate only a 50 per cent a priori probability of a truly sub-stellar mass.Key words: techniques: radial velocities -planetary systems -planets and satellites: detection. I N T RO D U C T I O NRadial velocity planet search efforts have been underway for more than 20 yr, discovering hundreds of new planetary companions. However, brown-dwarf and stellar-mass companions tend to be largely ignored in these surveys: limited telescope time means that targets showing large amplitude variations ( 500 m s −1 ) are usually dropped from the observing queue. Only limited results on such massive companions have been published (Patel et al. 2007), with many objects featuring incomplete orbits. However, such objects remain valuable for exploring the lower end of the mass function and the properties of stellar systems in the Solar neighbourhood. The observed deficit of companions between 13 and 80 M Jup is known as the 'brown-dwarf desert' (Marcy & Butler 2000;Mazeh et al. 2003), and became evident in the earliest days of radial velocity planet searches (Campbell, Walker & Yang 1988;Murdoch, Hearnshaw & Clark 1993). A comprehensive, self-consistent study by Grether & Lineweaver (2006) confirmed the presence of a 'valley' in the brown-dwarf mass range at M = 31 +25 −18 M Jup . Stellar companions are also not to be ignored, since any binary system with a well-characterized orbit is useful for a range of follow-up science. Most obviously, a precisely determined binary orbit permits the search for E-mail: rob@phys.unsw.edu.au additional Doppler velocity signals due to planets orbiting one or both stars. Binary systems compose ∼50 per cent of nearby star systems (Duquennoy & Mayor 1991;Raghavan et al. 2010), yet are hosts to only ∼5 per cent of known extrasolar planets. The mechanisms and outcomes of planet formation in close binary systems remain significant questions virtually unexplored by observations.At the 3.9 m Anglo-Australian Telescope (AAT), we carried out a five-year survey for planets orbiting intermediate-mass evolved stars in an effort to characterize the dependence of planetary system properties on stellar mass Reffert et al. 2015). The initial sample was selected according to these criteria: 1.0 < (B − V) < 1.2, 1.8 < M V < 3.0, and V < 8.0. Of those stars meeting these criteria, 18 were discarded as binaries by their Hipparcos multiple systems flag. From the 167...

Four new planets around giant stars and the mass-metallicity correlation of planet-hosting stars

“…The full orbital elements solution are listed in Table 2. This planet was independently detected by the PPPS (Wittenmyer et al 2016). Based on 21 RV epochs, they obtained an orbital period of 885 ± 63 days, a minimum mass of 2.0 ± 0.5 M J , and an eccentricity of 0.03 ± 0.2, which is in good agreement with our results.…”

“…In addition, using combined data of the EXPRESS and PPPS surveys, we have detected a two-planet system in a 3:5 mean-motion resonance (Wittenmyer et al 2015) around the giant star HIP 24275. Moreover, Trifonov et al (2014), recently announced the discovery of a two-planet system around HIP 5364 as part of the Lick Survey (Frink et al 2002).…”

Predicting radial-velocity jitter induced by stellar oscillations based on Kepler data

“…Typically, the RV jitter is at the level of ∼ 0.5 m/s in dwarfs, ∼ 1.5 m/s in subgiants, ∼ 4 m/s in low-luminosity red giants (ν max close to 100 µHz) , ∼ 7 m/s in red clump stars (ν max close to 40 µHz), and ∼ 15 m/s in high-luminosity red giants (ν max close to 10 µHz). Encouragingly, these values are consistent with observed jitter values for stars in similar evolutionary states (Johnson et al 2010;Jones et al 2013;Wittenmyer et al 2016Wittenmyer et al , 2017.…”

Precise radial velocities of giant stars

“…The spectral characteristics of solartype main-sequence (MS) stars are favorable for RV measurements, which has made these stars the targets of the majority of the RV planet searches. However, a growing number of research groups are successfully searching for planets around evolved subgiant and giant stars (e.g., Döllinger et al 2009;Johnson et al , 2011Sato et al 2013;Jones et al 2015a,b;Niedzielski et al 2015;Reffert et al 2015;Wittenmyer et al 2016). …”