M. Mugrauer

Evidence for a co-moving sub-stellar companion of GQ Lup

We present a companion of the ≤2 Myr young classical T Tauri star GQ Lup in the Lupus star forming region at 140 ± 50 pc from imaging, astrometry, and spectroscopy. With direct K-band imaging using VLT/NACO, we detected an object 6 mag fainter than GQ Lup located 0.7 �� west of it. Compared to images obtained 2 to 5 years earlier with Subaru/CIAO and HST/PC, this object shares the proper motion of GQ Lup by 5 and 7σ, respectively, hence it is a co-moving companion. Its K −Lcolor is consistent with a spectral type early to mid L. Our NACO K-band spectrum yields spectral type M9−L4 with H2O and CO absorption, consistent with the new GAIA-Dusty template spectrum for log g � 2t o 3a ndTeff � 2000 K with ∼2 Rjup radius at ∼140 pc, hence few Jupiter masses. Using the theoretical models from Wuchterl & Tscharnuter (2003), Burrows et al. (1997), and Baraffe et al. (2002), the mass lies between 1 and 42 Jupiter masses.

Extrasolar planets in stellar multiple systems

Aims. Analyzing exoplanets detected by radial velocity (RV) or transit observations, we determine the multiplicity of exoplanet host stars in order to study the influence of a stellar companion on the properties of planet candidates. Methods. Matching the host stars of exoplanet candidates detected by radial velocity or transit observations with online multiplicity catalogs in addition to a literature search, 57 exoplanet host stars are identified having a stellar companion. Results. The resulting multiplicity rate of at least 12% for exoplanet host stars is about four times smaller than the multiplicity of solar like stars in general. The mass and the number of planets in stellar multiple systems depend on the separation between their host star and its nearest stellar companion, e.g. the planetary mass decreases with an increasing stellar separation. We present an updated overview of exoplanet candidates in stellar multiple systems, including 15 new systems (compared to the latest summary from 2009).

Direct detection of exoplanet host star companion γ Cep B and revised masses for both stars and the sub-stellar object

Context. The star γ Cep is known as a single-lined spectroscopic triple system at a distance of 13.8 pc, composed of a K1 III-IV primary star with V = 3.2 mag, a stellar-mass companion in a 66-67 year orbit (Torres 2007, ApJ, 654, 1095), and a substellar companion with M_p sin i = 1.7 M_(Jup) that is most likely a planet (Hatzes et al. 2003, ApJ, 599, 1383). Aims. We aim to obtain a first direct detection of the stellar companion, to determine its current orbital position (for comparison with the spectroscopic and astrometric data), its infrared magnitude and, hence, mass. Methods. We use the Adaptive Optics camera CIAO at the Japanese 8 m telescope Subaru on Mauna Kea, Hawaii, with the semi-transparent coronograph to block most of the light from the bright primary γ Cep A, and to detect at the same time the faint companion B. In addition, we also used the IR camera Ω Cass at the Calar Alto 3.5 m telescope, Spain, to image γ Cep A and B by adding up many very short integrations (without AO). Results. γ Cep B is clearly detected on our CIAO and Ω Cass images. We use a photometric standard star to determine the magnitude of B after PSF subtraction in the Subaru image, and the magnitude difference between A and B in the Calar Alto images, and find an average value of K = 7.3 ± 0.2 mag. The separations and position angles between A and B are measured on 15 July 2006 and 11 and 12 Sept. 2006, B is slightly south of west of A. Conclusions. By combining the radial velocity, astrometric, and imaging data, we have refined the binary orbit and determined the dynamical masses of the two stars in the γ Cep system, namely 1.40 ± 0.12 M_☉ for the primary and 0.409 ± 0.018 M_☉ for the secondary (consistent with being a M4 dwarf). We also determine the minimum mass of the sub-stellar companion to be M_p sin i = 1.60 ± 0.13 M_(Jup).

Transit timing variation in exoplanet WASP-3b★

Photometric follow-ups of transiting exoplanets may lead to discoveries of additional, less massive bodies in extrasolar systems. This is possible by detecting and then analysing variations in transit timing of transiting exoplanets. We present photometric observations gathered in 2009 and 2010 for exoplanet WASP-3b during the dedicated transit-timing-variation campaign. The observed transit timing cannot be explained by a constant period but by a periodic variation in the observations minus calculations diagram. Simplified models assuming the existence of a perturbing planet in the system and reproducing the observed variations of timing residuals were identified by three-body simulations. We found that the configuration with the hypothetical second planet of the mass of ∼15 M⊕, located close to the outer 2:1 mean motion resonance is the most likely scenario reproducing observed transit timing. We emphasize, however, that more observations are required to constrain better the parameters of the hypothetical second planet in WASP-3 system. For final interpretation not only transit timing but also photometric observations of the transit of the predicted second planet and the high precision radial-velocity data are needed.

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 

The multiplicity of exoplanet host stars : Spectroscopic confirmation of the companions GJ 3021 B and HD 27442 B, one new planet host triple-star system, and global statistics

M_{\odot}

Transit timing variation and activity in the WASP-10 planetary system★

. Our first and second epoch observations can rule out additional stellar companions around the primaries from ~200 up to ~2400 AU (

The Dwarf project: Eclipsing binaries – precise clocks to discover exoplanets

{\it S/N}=10

The Hercules-Lyra association revisited - New age estimation and multiplicity study

). 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.

The Young Exoplanet Transit Initiative (YETI)

We present new results from our ongoing multiplicity study of exoplanet host stars and present a list of 29 confirmed planet host multiple-star systems. Furthermore, we discuss the properties of these stellar systems and compare the properties of exoplanets detected in these systems with those of planets orbiting single stars.Aims. We present new results from our ongoing multiplicity study of exoplanet host stars and present a list of 29 confirmed planet host multiple-star systems. Furthermore, we discuss the properties of these stellar systems and compare the properties of exoplanets detected in these systems with those of planets orbiting single stars. Methods. We used direct imaging to search for wide stellar and substellar companions of exoplanet host stars. With infrared and/or optical spectroscopy, we determined the spectral properties of the newly-found co-moving companions. Results. We obtained infrared H -a ndK-band spectra of the co-moving companion GJ 3021 B. The infrared spectra and the apparent H-band photometry of the companion is consistent with an M3–M5 dwarf at the distance of the exoplanet host star. HD 40979 AB is a wide planet host stellar system, with a separation of ∼ 6400 AU. The companion to the exoplanet host star turned out to be a close stellar pair with a projected separation of ∼130 AU, hence, this system is a new member of those rare planet host triple-star systems of which only three other systems are presently known. HD 27442 AB is a wide binary system listed in the Washington Double Star Catalogue, whose common proper motion was recently confirmed. This system is composed of the subgiant HD 27442 A hosting the exoplanet, and its faint companion HD 27442 B. The visible and infrared J-, H-, and KS-band photometry of HD 27442 B at the distance of the primary star shows that the companion is probably a white dwarf. Our multi-epochs SofI imaging observations confirm this result and even refine the suggested physical characteristics of HD 27442 B. This companion should be a relatively young, hot white dwarf with an effective temperature of ∼14 400 K, and cooling age of ∼220 Myr. Finally, we could unambiguously confirm the white dwarf nature of HD 27442 B with follow-up optical and infrared spectroscopy. The spectra of the companion show Hydrogen absorption features of the Balmer, Paschen, and Bracket series. With its subgiant primary and the white-dwarf companion, the HD 27442 AB system is the most evolved planet host stellar system known today. The mass-period and eccentricity-period correlation of planets around single stars and those residing in multiple-star systems seem different for the short-period planets. The distribution functions of planet orbital elements (P, e) are identical, while the mass-distribution (m sin(i)) exhibits one difference. While both planet populations exhibit a peak in their mass-distribution at about 1 MJup, the frequency of more massive planets continually decreases in single-star systems, whereas the mass-distribution of planets residing in multiple-star systems exhibits a further peak at about 4 MJup. This indicates that the mass-distributions of the two planet populations might differ in the intermediate mass-range between 2 and 6 MJup.