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Post Info TOPIC: Stellar companions
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RE: Stellar companions
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Title: Wide companions to Hipparcos stars within 67 pc of the Sun
Authors: Andrei Tokovinin, Sebastien Lepine

A catalogue of common-proper-motion (CPM) companions to stars within 67 pc of the Sun is constructed based on the SUPERBLINK proper-motion survey. It contains 1392 CPM pairs with angular separations 30" < rho < 1800", relative proper motion between the two components less than 25 mas/yr, magnitudes and colours of the secondaries consistent with those of dwarfs in the (M_V,V-J) diagram. In addition, we list 21 candidate white-dwarf CPM companions with separations under 300", about half of which should be physical. We estimate a 0.31 fraction of pairs with red-dwarf companions to be physical systems (about 425 objects), while the rest (mostly wide pairs) are chance alignments. For each candidate companion, the probability of a physical association is evaluated. The distribution of projected separations s of the physical pairs between 2 kAU and 64 kAU follows f(s) ~ s^{-1.5}, which decreases faster than \"Opik's law. We find that Solar-mass dwarfs have no less than 4.4% ± 0.3% companions with separations larger than 2 kAU, or 3.8% ± 0.3% per decade of orbital separation in the 2 to 16 kAU range. The distribution of mass ratio of those wide companions is approximately uniform in the 0.1<q<1.0 range, although we observe a dip at q=0.5 which, if confirmed, could be evidence of bimodal distribution of companion masses. New physical CPM companions to two exoplanet host stars are discovered.

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Blobrana


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Three new planets and a mystery discovered outside our solar system

Three planets -- each orbiting its own giant, dying star -- have been discovered by an international research team led by a Penn State University astronomer. Using the Hobby-Eberly Telescope, the astronomers observed the planets' parent stars -- called HD 240237, BD +48 738, and HD 96127 -- tens of light years away from our solar system. One of the massive, dying stars has an additional mystery object orbiting it, according to team leader Alexander Wolszczan, Evan Pugh Professor of Astronomy and Astrophysics at Penn State, who, in 1992, became the first astronomer ever to discover planets outside our solar system. The new research is expected to shed light on the evolution of planetary systems around dying stars. It also will help astronomers to understand how metal content influences the behaviour of dying stars.
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Blobrana


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Substellar-Mass Companions
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Title: Substellar-Mass Companions to the K-Giants HD 240237, BD +48 738 and HD 96127
Authors: S. Gettel, A. Wolszczan, A. Niedzielski, G. Nowak, M. Adamów, P. Zieliski, G. Maciejewski

We present the discovery of substellar-mass companions to three giant stars by the ongoing Penn State-Torun Planet Search (PTPS) conducted with the 9.2 m Hobby-Eberly Telescope. The most massive of the three stars, K2-giant HD 240237, has a 5.3 MJ minimum mass companion orbiting the star at a 746-day period. The K0-giant BD +48 738 is orbited by a > 0.91 MJ planet which has a period of 393 days and shows a non-linear, long-term radial velocity trend that indicates a presence of another, more distant companion, which may have a substellar mass or be a low-mass star. The K2-giant HD 96127, has a > 4.0 MJ mass companion in a 647-day orbit around the star. The two K2-giants exhibit a significant RV noise that complicates the detection of low-amplitude, periodic variations in the data. If the noise component of the observed RV variations is due to solar-type oscillations, we show, using all the published data for the substellar companions to giants, that its amplitude is anti-correlated with stellar metallicity.

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Blobrana


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Title: Substellar-mass companions to the K-dwarf BD +14 4559 and the K-giants HD 240210 and BD +20 2457
Authors: A. Niedzielski, G. Nowak, M. Adamów, A. Wolszczan

We present the discovery of substellar-mass companions to three stars by the ongoing Penn State - Torun Planet Search (PTPS) conducted with the 9.2-m Hobby-Eberly Telescope. The K2-dwarf, BD +14 4559, has a 1.5 M_J companion with the orbital period of 269 days and shows a non-linear, long-term radial velocity trend, which indicates a possible presence of another planet-mass body in the system. The K3-giant, HD 240210, exhibits radial velocity variations that require modelling with multiple orbits, but the available data are not yet sufficient to do it unambiguously. A tentative, one-planet model calls for a 6.9 M_J planet in a 502-day orbit around the star. The most massive of the three stars, the K2-giant, BD +20 2457, whose estimated mass is 2.8 ±1.5 solar masses, has two companions with the respective minimum masses of 21.4 M_J and 12.5 M_J and orbital periods of 380 and 622 days. Depending on the unknown inclinations of the orbits, the currently very uncertain mass of the star, and the dynamical properties of the system, it may represent the first detection of two brown dwarf-mass companions orbiting a giant. The existence of such objects will have consequences for the interpretation of the so-called brown dwarf desert known to exist in the case of solar-mass stars.

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Blobrana


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Stellar companions
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Title: The Palomar/Keck Adaptive Optics Survey of Young Solar Analogues: Evidence for a Universal Companion Mass Function
Authors: Stanimir Metchev, Lynne Hillenbrand

We present results from an adaptive optics survey for substellar and stellar companions to Sun-like stars. The survey targeted 266 F5-K5 stars in the 3Myr to 3Gyr age range with distances of 10-190pc. Results from the survey include the discovery of two brown dwarf companions (HD49197B and HD203030B), 24 new stellar binaries, and a triple system. We infer that the frequency of 0.012-0.072Msun brown dwarfs in 28-1590AU orbits around young solar analogues is 3.2% (+3.1%,-2.7%; 2sigma limits). The result demonstrates that the deficiency of substellar companions at wide orbital separations from Sun-like stars is less pronounced than in the radial velocity "brown dwarf desert." We infer that the mass distribution of companions in 28-1590AU orbits around solar-mass stars follows a continuous dN/dM_2 ~ M_2^(-0.4) relation over the 0.01-1.0Msun secondary mass range, and that it differs significantly from the mass function of isolated objects. Based on this conclusion and on similar results from other direct imaging and radial velocity companion surveys in the literature, we argue that the companion mass function follows the same universal form over the entire range between 0-1590AU in orbital semi-major axis and 0.01-20Msun in companion mass. In this context, the relative dearth of brown dwarf with respect to stellar secondaries at all orbital separations arises naturally from the inferred form of the companion mass function.

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