Search for stellar companions of exoplanet host stars by exploring the second ESA-Gaia data release

Abstract

A new survey is presented, which explores the second data release of the ESA-Gaia mission, in order to search for stellar companions of exoplanet host stars, located at distances closer than about 500 pc around the Sun. In total, 176 binaries, 27 hierarchical triples, and one hierarchical quadruple system are detected among more than 1300 exoplanet host stars, whose multiplicity is investigated, yielding a multiplicity rate of the exoplanet host stars of at least about 15 per cent. The detected companions and the exoplanet host stars are equidistant and share a common proper motion, as it is expected for gravitationally bound stellar systems, proven with their accurate Gaia astrometry. The companions exhibit masses in the range between about 0.078 and 1.4 M⊙ with a peak in their mass distribution between 0.15 and $0.3\, \mathrm{M}_{\odot }$. The companions are separated from the exoplanet host stars by about 20 up to 9100 au, but are found most frequently within a projected separation of 1000 au. While most of the detected companions are early M dwarfs, eight white dwarf companions of exoplanet host stars are also identified in this survey, whose true nature is revealed with their photometric properties. Hence, these degenerated companions and the exoplanet host stars form evolved stellar systems with exoplanets, which have survived (physically but also dynamically) the post-main-sequence evolution of their former primary star.

Gaia search for stellar companions of TESS Objects of Interest

“…In stellar systems with primary stars brighter than G = 12.8 (about 86% of the targets of this survey), companions are detectable at angular separations larger than about 1 arcsec, very well consistent with the limit found by Mugrauer (2019) among exoplanet host stars. In this multiplicity survey, there is one companion reported at an angular separation of 1.3 arcsec, which exhibits a magnitude difference of 4.2 mag.…”

“…The differential proper motion of most of these companions is consistent with orbital motion. In contrast, for 34 companions, their differential proper motions significantly exceed the expected escape velocities, indicating an increased degree of multiplicity, as discussed in Mugrauer (2019). Indeed, eight of these companions are located in already confirmed or potential hierarchical triple‐star systems, but follow‐up high contrast imaging observations are needed to further explore the multiplicity status of all these particular systems and their companions, which are listed in Table 5.…”

“…The companions of these targets were already characterized in Mugrauer (2019) or will be presented by Michel Michel & Mugrauer (2020). Taking these additional companions into account, the current multiplicity rate of the (C)TOIs is at least about 19 ± 1%, which is consistent with the minimum multiplicity rate of exoplanet host stars of 15 ± 1%, recently determined by Mugrauer (2019), especially considering that for some (C)TOIs the transit‐like signals in their light curves could turn out to be false positive detections.…”

“…Mugrauer et al 2014, 2020; Mugrauer & Ginski 2015; Roell et al 2012). In addition, recently Mugrauer (2019) explored the second data release of the European Space Agency (ESA) Gaia mission (Gaia Collaboration, Brown, Vallenari, et al 2018), which provides manifold, highly accurate astro‐ and photometric data of a huge number of objects, located across the whole sky, making it an excellent database for the search of stellar companions of exoplanet host stars.…”

Identification of young nearby runaway stars based on Gaia data and the lithium test†

“…For this reason, measurements of their V ‐band extinction from the literature, as listed in VizieR (Ochsenbein et al 2000), were collected instead to calculate the median and standard deviation (SD) of the V ‐band extinction for these targets. This average V ‐band extinction was then converted into G ‐band by using the relations from Jordi et al (2010) as explained in Mugrauer (2019).…”