Companions Of Exoplanet Host Stars Research Articles

Search for Stellar Companions of Exoplanet Host Stars with AstraLux/CAHA 2.2 m

ABSTRACT Stellar multiplicity is a key aspect of exoplanet diversity, as the presence of more than one star in a planetary system can have both devastating and positive effects on its formation and evolution. In this paper, we present the results of a Lucky Imaging survey of 212 exoplanet host stars performed with AstraLux at the 2.2 m telescope of the Centro Astronómico Hispano en Andalucía. The survey includes data from seven observing epochs between August 2015 and September 2020, and data for individual targets from four earlier observing epochs. The targets of this survey are nearby, bright, solar-like stars with high proper motions. In total, we detected 46 co-moving companions of 43 exoplanet host stars. Accordingly, this survey shows that the minimum multiplicity rate of exoplanet host stars is $20 \pm 3~{\rm per\ cent}$. In total, 33 binary and 10 hierarchical triple star systems with exoplanets have been identified. All companions were found to have a common proper motion with the observed exoplanet host stars, and with our astrometry we even find evidence of orbital motion for 28 companions. For all targets, we determine the detection limit and explore the detection space for possible additional companions of these stars. Based on the reached detection limit, additional co-moving companions beyond the detected ones can be excluded around all observed exoplanet host stars. The increasing number of exoplanets discovered in multiple stellar systems suggests that the formation of planets in such systems is by no means rare, but common. Therefore, our study highlights the need to consider stellar multiplicity in future studies of exoplanet habitability.

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.

How many suns are in the sky? Multiplicity surveys of exoplanet host stars

AbstractIn order to determine the true impact of stellar multiplicity on the formation and evolution of planets, we initiated direct imaging surveys to search for (sub)stellar companions of exoplanet host stars on close orbits, as their gravitational impact on the planet bearing disk at first and on formed planets afterwards is expected to be maximal. According to theory these are the most challenging environments for planet formation and evolution but might occur quite frequently in the milky way, due to the large number of multiple stars within our galaxy. On this poster we showed results, obtained so far in the course of our AO and Lucky-imaging campaigns of exoplanet host stars, conducted with NACO/ESO-VLT for southern and with AstraLux/CAHA2.2m for northern targets, respectively. In addition, we introduced our new high contrast imaging survey with SPHERE/ESO-VLT to search for close companions of southern exoplanet host stars, and presented some first results.

Stellar Companions of Exoplanet Host Stars in K2

Abstract It is well established that roughly half of all nearby solar-type stars have at least one companion. Stellar companions can have significant implications for the detection and characterization of exoplanets, including triggering false positives and masking the true radii of planets. Determining the fraction of exoplanet host stars that are also binaries allows us to better determine planetary characteristics as well as establish the relationship between binarity and planet formation. Using high angular resolution speckle imaging, we detect stellar companions within ∼1 arcsec of K2 planet-candidate host stars. Comparing our detected companion rate to TRILEGAL star count simulations and known detection limits of speckle imaging, we estimate the binary fraction of K2 planet host stars to be 40%–50%, similar to that of Kepler exoplanet hosts and field stars.

High-contrast imaging search for stellar and substellar companions of exoplanet host stars

We present the results of our high-contrast imaging survey of close stellar and substellar companions of exoplanet host stars, carried out with the adaptive optics imager NACO at the ESO Paranal observatory, in Chile. In total, 33 exoplanet host stars were observed with NACO in the Ks-band. New comoving companions could be identified close to the stars HD 9578, HD 96167, and HD 142245. The newly detected companions exhibit masses between 0.21 and 0.56 M⊙ and are located at projected separations from their primaries between about 190 and 510 au. In the case of HD 142245, we found evidence that the detected companion is actually a close binary itself with a projected separation of only about 4 au, i.e. HD 142245 might be a hierarchical triple stellar system, which hosts an exoplanet, a new member in the short list of such systems, presently known. In our imaging campaign, a limiting magnitude of Ks = 18.5 mag is reached in average in the background noise limited region around our targets at projected separations beyond about 100 au, which allows the detection of substellar companions with masses down to about 60 MJup. With our NACO observations we can rule out additional stellar companions at projected separations between about 30 and 370 au around the observed exoplanet host stars.

New wide stellar companions of exoplanet host stars

New wide stellar companions of exoplanet host stars

Planetary systems in close binary stars: the case of HD 196885

Context. More than fifty candidate planets are presently known to orbit one component of a binary or a multiple star system. Planets can therefore form and survive in such an environment, although recent observing surveys indicate that short-separation binaries do not favour the presence of a planetary system around one of the components. Dynamical interactions with the secondary component can actually affect the giant planet formation and evolution significantly. For this reason, rare close binaries hosting giant planets offer an ideal laboratory for exploring the properties and the stability of such extreme planetary systems. Aims. In the course of our CFHT and VLT coronographic imaging survey dedicated to the search for faint companions of exoplanet host stars, a close (∼20 AU) secondary stellar companion to the exoplanet host HD 196885 A was discovered. In this study, our aim is to monitor the orbital motion of the binary companion. Combining radial velocity and high-contrast imaging observations, we aim to derive the orbital properties of the complete system and to test its dynamical stability to reveal its formation. Methods. For more than 4 years, we used the NaCo near-infrared adaptive optics instrument to monitor the astrometric position of HD 196885 B relative to A. The system was observed at five different epochs from August 2005 to August 2009 and accurate relative positions were determined. Results. Our observations fully reject the stationary background hypothesis for HD 196885 B. The two components are found to be comoving. The orbital motion of HD 196885 B is resolved well the orbital curvature is even detected. From our imaging data combined with published radial velocity measurements, we refine the complete orbital parameters of the stellar component. We derive for the first time its orbital inclination and its accurate mass. We also find solutions for the inner giant planet HD 196885 Ab that are compatible with previous independent radial velocity studies. Finally, we investigate the stability of the inner giant planet HD 196885 Ab with the binary companion proximity. Our dynamical simulations show that the system is currently and surprisingly more stable in a high mutual inclination configuration that falls in the Kozai resonance regime. If confirmed, this system would constitute one of the most compact non-coplanar systems known so far. It would raise several questions about its formation and stability.

Characterization of the long-period companions of the exoplanet host stars: HD 196885, HD 1237 and HD 27442

Aims. We present the results of near-infrared, follow-up imaging and spectroscopic observations at VLT, aimed at characterizing the long-period companions of the exoplanet host stars HD 196885, HD 1237 and HD 27442. The three companions were previously discovered in the course of our CFHT and VLT coronographic imaging survey dedicated to the search for faint companions of exoplanet host stars. Methods. We used the NACO near-infrared adaptive optics instrument to obtain astrometric follow-up observations of HD 196885 A and B. The long-slit spectroscopic mode of NACO and the integral field spectrograph SINFONI were used to carry out a low-resolution spectral characterization of the three companions HD 196885 B, HD 1237 B and HD 27442 B between 1.4 and 2.5 µm. Results. We can now confirm that the companion HD 196885 B is comoving with its primary exoplanet host star, as previously shown for HD 1237 B and HD 27442 B. We find that both companions HD 196885 B and HD 1237 B are low-mass stars of spectral type M1 ± 1V and M4 ± 1V respectively. HD 196885 AB is one of the closer (∼23 AU) resolved binaries known to host an exoplanet. This system is then ideal for carrying out a combined radial velocity and astrometric investigation of the possible impact of the binary companion on the planetary system formation and evolution. Finally, we confirm via spectroscopy that HD 27442 B is a white dwarf companion, the third one to be discovered orbiting an exoplanet host star, following HD 147513 and Gliese 86. The detection of the broad Brγ line of hydrogen indicates a white dwarf atmosphere dominated by hydrogen.

A search for wide visual companions of exoplanet host stars: The Calar Alto Survey

We have carried out a search for co-moving stellar and substellar companions around 18 exoplanet host stars with the infrared camera MAGIC at the 2.2 m Calar Alto telescope, by comparing our images with images from the all sky surveys 2MASS, POSS I and II. Four stars of the sample namely HD80606, 55 Cnc, HD46375 and BD–10°3166, are listed as binaries in the Washington Visual Double Star Catalogue (WDS). The binary nature of HD80606, 55 Cnc, and HD46375 is confirmed with both astrometry as well as photometry, thereby the proper motion of the companion of HD46375 was determined here for the first time.We derived the companion masses as well as the longterm stability regions for additional companions in these three binary systems. We can rule out further stellar companions around all stars in the sample with projected separations between 270AU and 2500AU, being sensitive to substellar companions with masses down to ∼60 MJup (S /N = 3). Furthermore we present evidence that the two components of the WDS binary BD–10°3166 are unrelated stars, i.e this system is a visual pair. The spectrophotometric distance of the primary (a K0 dwarf) is ∼67 pc, whereas the presumable secondary BD–10°3166B (a M4 to M5 dwarf) is located at a distance of 13 pc in the foreground. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Four new wide binaries among exoplanet host stars

In our ongoing survey for wide (sub)stellar companions of exoplanet host stars we have found 4 new co-moving stellar companions of the stars HD 114729, HD 16141, HD 196050 and HD 213240 with projected separations from 223 up to 3898 AU. The companionship of HD 114729 B, HD 196050 B and HD 213240 C is confirmed by photometry and spectroscopy, all being early M dwarfs. The masses of the detected companions are derived from their infrared JHK magnitudes and range between 0.146 and 0.363 . Our first and second epoch observations can rule out additional stellar companions around the primaries from ~200 up to ~2400 AU (). In our survey we have found so far 6 new binaries among the exoplanet host stars. According to these new detections, the reported differences between single-star and binary-star planets with orbital periods short than 40 days remain significant in both the mass-period and eccentricity-period distribution. In contrast, all exoplanets with orbital periods longer than 100 days tend to display similar distributions.