Properties of planets in binary systems

Abstract

Aims. The statistical properties of planets in binaries were investigated. Any difference to planets orbiting single stars can shed light on the formation and evolution of planetary systems. As planets were found around components of binaries with very different separation and mass ratio, it is particularly important to study the characteristics of planets as a function of the effective gravitational influence of the companion. Methods. A compilation of planets in binary systems was made; a search for companions orbiting stars recently shown to host planets was performed, resulting in the addition of two further binary planet hosts (HD 20782 and HD 109749). The probable original properties of the three binary planet hosts with white dwarfs companions were also investigated. Using this updated sample of planets in binaries we performed a statistical analysis of the distributions of planet mass, period, and eccentricity, fraction of multiplanet systems, and stellar metallicity for planets orbiting components of tight and wide binaries and single stars. Results. The only highly significant difference revealed by our analysis concerns the mass distribution of short-period planets. Massive planets in short period orbits are found in most cases around the components of rather tight binaries. The properties of exoplanets orbiting the components of wide binaries are compatible with those of planets orbiting single stars, except for a possible greater abundance of high-eccentricity planets. The previously suggested lack of massive planets with P > 100 days in binaries is not confirmed. Conclusions. We conclude that the presence of a stellar companion with separation smaller than 100-300 AU is able to modify the formation and/or migration and/or the dynamical evolution history of giant planets while wide companions play a more limited role.

Binary frequency of planet-host stars at wide separations

“…5), where more massive planets have on average higher mean eccentricities. Overall, we corroborate the conclusions of Desidera & Barbieri (2007) that wide companions seem to have less influence on the properties of planets than closer systems.…”

“…1, where we assumed the planet-host star distance to determine a possible absolute J-band magnitude. We note that the companion to HD 213240 was already published by Mugrauer et al (2005b) and that Desidera & Barbieri (2007) already reported a wide companion to HD 109749 but at a closer separation.…”

“…Eggenberger et al (2004) announced a sample of 15 new wide low-mass companions to planet-host stars and suggested a possible difference in the mass-period and eccentricity-period distributions, trend previously reported in Zucker & Mazeh (2002). These discoveries and potential differences in the properties of planets orbiting single stars and planets orbiting stars in multiple systems triggered dedicated searches by several groups (Butler et al 1997;Mugrauer et al 2004aMugrauer et al ,b, 2005aMugrauer et al ,b, 2006aMugrauer et al , 2007aKonacki 2005;Eggenberger et al 2006;Desidera & Barbieri 2007;Bonavita & Desidera 2007) to confirm (or otherwise) those trends in the properties of exoplanets. These searches also led to the discoveries of the first wide brown dwarf companion to HD 3651 (Mugrauer et al 2006b), a K7 dwarf with a sub-Saturn mass planet (Fischer et al 2004;Santos et al 2005), and the most evolved multiple system with an exoplanet (Butler et al 2001), composed of a K subgiant and a white dwarf (HD 27442; Chauvin et al 2006;Raghavan et al 2006;Mugrauer et al 2007a).…”

“…In Sects. 7-9 we discuss the stability of the widest companions in our sample, derive the frequency of planet-host stars at wide separations, and examine the dynamical properties of the systems with respect to previous studies (Eggenberger et al 2004;Mugrauer et al 2007a;Desidera & Barbieri 2007).…”

The SOPHIE search for northern extrasolar planets

“…However, in the mass-period and eccentricity-period diagrams, HD 16760b is located in a region not populated much by planets in binary systems. The discovery of this long-period, loweccentricity planet thus adds to the growing evidence that, in contrast to short-period planets, long-period ( > ∼ 100 days) planets residing in binaries possess the same statistical properties as their counterparts orbiting single stars (Eggenberger et al 2004;Mugrauer et al 2005;Desidera et al 2007).…”