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Register a new userVery 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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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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We report the discovery of a candidate brown dwarf or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 years. Our Keplerian fit using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of $90.2695^{+0.0188}_{-0.0187}$ days, an eccentricity of $0.4375 pm 0.0040$ and a semi-amplitude of $2948.14^{+16.65}_{-16.55}$ m s$^{-1}$. Using additional high-resolution spectroscopy, we find the host star has an effective temperature $T_{rm{eff}}=6004 pm 34$ K, a surface gravity $log g$ [cgs] $=4.55 pm 0.17$ and a metallicity [Fe/H] $=+0.04 pm 0.06$. The stellar mass and radius determined through the empirical relationship of Torres et al. (2010), yields 1.10$pm$0.09 $M_{sun}$ and 0.92$pm$0.19 $R_{sun}$. The minimum mass of MARVELS-5b is $65.0 pm 2.9 M_{Jup}$, indicating that it is likely to be either a brown dwarf or a very low mass star, thus occupying a relatively sparsely-populated region of the mass function of companions to solar-type stars. The distance to this system is 101$pm$10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2$M_{sun}$ at a separation larger than 40 AU.
We present an eccentric, short-period brown dwarf candidate orbiting the active, slightly evolved subgiant star TYC 2087-00255-1, which has effective temperature T_eff = 5903+/-42 K, surface gravity log (g) = 4.07+/-0.16 (cgs), and metallicity [Fe/H] = -0.23+/-0.07. This candidate was discovered using data from the first two years of the Multi-object APO Radial Velocity Exoplanets Large-area Survey (MARVELS), which is part of the third phase of Sloan Digital Sky Survey. From our 38 radial velocity measurements spread over a two-year time baseline, we derive a Keplerian orbital fit with semi-amplitude K=3.571+/-0.041 km/s, period P=9.0090+/-0.0004 days, and eccentricity e=0.226+/-0.011. Adopting a mass of 1.16+/-0.11 Msun for the subgiant host star, we infer that the companion has a minimum mass of 40.0+/-2.5 M_Jup. Assuming an edge-on orbit, the semimajor axis is 0.090+/-0.003 AU. The host star is photometrically variable at the sim1% level with a period of sim13.16+/-0.01 days, indicating that the host star spin and companion orbit are not synchronized. Through adaptive optics imaging we also found a point source 643+/-10 mas away from TYC 2087-00255-1, which would have a mass of 0.13 Msun if it is physically associated with TYC 2087-00255-1 and has the same age. Future proper motion observation should be able to resolve if this tertiary object is physically associated with TYC 2087-00255-1 and make TYC 2087-00255-1 a triple body system. Core Ca II H and K line emission indicate that the host is chromospherically active, at a level that is consistent with the inferred spin period and measured v_{rot}*sin i, but unusual for a subgiant of this T_eff. This activity could be explained by ongoing tidal spin-up of the host star by the companion.
TYC 4110-01037-1 has a low-mass stellar companion, whose small mass ratio and short orbital period are atypical amongst solar-like (Teff ~< 6000 K) binary systems. Our analysis of TYC 4110-01037-1 reveals it to be a moderately aged (~<5 Gyr) solar-like star having a mass of 1.07 +/- 0.08 MSun and radius of 0.99 +/- 0.18 RSun. We analyze 32 radial velocity measurements from the SDSS-III MARVELS survey as well as 6 supporting radial velocity measurements from the SARG spectrograph on the 3.6m TNG telescope obtained over a period of ~2 years. The best Keplerian orbital fit parameters were found to have a period of 78.994 +/- 0.012 days, an eccentricity of 0.1095 +/- 0.0023, and a semi-amplitude of 4199 +/- 11 m/s. We determine the minimum companion mass (if sin i = 1) to be 97.7 +/- 5.8 MJup. The systems companion to host star mass ratio, >0.087 +/- 0.003, places it at the lowest end of observed values for short period stellar companions to solar-like (Teff ~< 6000 K) stars. One possible way to create such a system would be if a triple-component stellar multiple broke up into a short period, low q binary during the cluster dispersal phase of its lifetime. A candidate tertiary body has been identified in the system via single-epoch, high contrast imagery. If this object is confirmed to be co-moving, we estimate it would be a dM4 star. We present these results in the context of our larger-scale effort to constrain the statistics of low mass stellar and brown dwarf companions to FGK-type stars via the MARVELS survey.
We report the discovery via radial velocity of a short-period (P = 2.430420 pm 0.000006 days) companion to the F-type main sequence star TYC 2930-00872-1. A long-term trend in the radial velocities indicates the presence of a tertiary stellar companion with $P > 2000$ days. High-resolution spectroscopy of the host star yields T_eff = 6427 +/- 33 K, log(g) = 4.52 +/- 0.14, and [Fe/H]=-0.04 +/- 0.05. These parameters, combined with the broad-band spectral energy distribution and parallax, allow us to infer a mass and radius of the host star of M_1=1.21 +/- 0.08 M_odot and R_1=1.09_{-0.13}^{+0.15} R_odot. We are able to exclude transits of the inner companion with high confidence. The host stars spectrum exhibits clear Ca H and K core emission indicating stellar activity, but a lack of photometric variability and small v*sin(I) suggest the primarys spin axis is oriented in a pole-on configuration. The rotational period of the primary from an activity-rotation relation matches the orbital period of the inner companion to within 1.5 sigma, suggesting they are tidally locked. If the inner companions orbital angular momentum vector is aligned with the stellar spin axis, as expected through tidal evolution, then it has a stellar mass of M_2 ~ 0.3-0.4 M_odot. Direct imaging limits the existence of stellar companions to projected separations < 30 AU. No set of spectral lines and no significant flux contribution to the spectral energy distribution from either companion are detected, which places individual upper mass limits of M < 1.0 M_odot, provided they are not stellar remnants. If the tertiary is not a stellar remnant, then it likely has a mass of ~0.5-0.6 M_odot, and its orbit is likely significantly inclined from that of the secondary, suggesting that the Kozai-Lidov mechanism may have driven the dynamical evolution of this system.
[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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