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Very Low-Mass Stellar and Substellar Companions to Solar-like Stars From MARVELS VI: A Giant Planet and a Brown Dwarf Candidate in a Close Binary System HD 87646

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 Added by Bo Ma
 Publication date 2016
  fields Physics
and research's language is English




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We report the detections of a giant planet (MARVELS-7b) and a brown dwarf candidate (MARVELS-7c) around the primary star in the close binary system, HD 87646. It is the first close binary system with more than one substellar circum-primary companion discovered to the best of our knowledge. The detection of this giant planet was accomplished using the first multi-object Doppler instrument (KeckET) at the Sloan Digital Sky Survey (SDSS) telescope. Subsequent radial velocity observations using ET at Kitt Peak National Observatory, HRS at HET, the Classic spectrograph at the Automatic Spectroscopic Telescope at Fairborn Observatory, and MARVELS from SDSS-III confirmed this giant planet discovery and revealed the existence of a long-period brown dwarf in this binary. HD 87646 is a close binary with a separation of $sim22$ AU between the two stars, estimated using the Hipparcos catalogue and our newly acquired AO image from PALAO on the 200-inch Hale Telescope at Palomar. The primary star in the binary, HD 87646A, has Teff = 5770$pm$80K, log(g)=4.1$pm$0.1 and [Fe/H] = $-0.17pm0.08$. The derived minimum masses of the two substellar companions of HD 87646A are 12.4$pm$0.7M$_{rm Jup}$ and 57.0$pm3.7$M$_{rm Jup}$. The periods are 13.481$pm$0.001 days and 674$pm$4 days and the measured eccentricities are 0.05$pm$0.02 and 0.50$pm$0.02 respectively. Our dynamical simulations show the system is stable if the binary orbit has a large semi-major axis and a low eccentricity, which can be verified with future astrometry observations.



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128 - Bo Ma , Jian Ge , Rory Barnes 2012
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280 - A. Sozzetti 2009
[abridged] We attempt to improve on the characterization of the properties (orbital elements, masses) of two Doppler-detected sub-stellar companions to the nearby G dwarfs HD 131664 and HD 43848. We carry out orbital fits to the Hipparcos IAD for the two stars, taking advantage of the knowledge of the spectroscopic orbits, and solving for the two orbital elements that can be determined in principle solely by astrometry, the inclination angle $i$ and the longitude of the ascending node $Omega$. A number of checks are carried out in order to assess the reliability of the orbital solutions thus obtained. The best-fit solution for HD 131664 yields $i=55pm33$ deg and $Omega=22pm28$ deg. The resulting inferred true companion mass is then $M_c = 23_{-5}^{+26}$ $M_J$. For object{HD 43848}, we find $i=12pm7$ deg and $Omega=288pm22$ deg, and $M_c = 120_{-43}^{+167}$ $M_J$. Based on the statistical evidence from an $F$-test, the study of the joint confidence intervals of variation of $i$ and $Omega$, and the comparison of the derived orbital semi-major axes with a distribution of false astrometric orbits obtained for single stars observed by Hipparcos, the astrometric signal of the two companions to HD 131664 and HD 43848 is then considered detected in the Hipparcos IAD, with a level of statistical confidence not exceeding 95%. We constrain the true mass of HD 131664b to that of a brown dwarf to within a somewhat statistically significant degree of confidence ($sim2-sigma$). For HD 43848b, a true mass in the brown dwarf regime is ruled out at the $1-sigma$ confidence level. [abridged]
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