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Wilson, CA, United States

Raghavan D.,Georgia State University | McAlister H.A.,Georgia State University | Henry T.J.,Georgia State University | Latham D.W.,Harvard - Smithsonian Center for Astrophysics | And 5 more authors.
Astrophysical Journal, Supplement Series | Year: 2010

We present the results of a comprehensive assessment of companions to solar-type stars. A sample of 454 stars, including the Sun, was selected from the Hipparcos catalog withπ > 40 mas, σπ/π < 0.05, 0.5 ≤ B - V ≤ 1.0 (∼F6-K3), and constrained by absolute magnitude and color to exclude evolved stars. These criteria are equivalent to selecting all dwarf and subdwarf stars within 25 pc with V-band flux between 0.1 and 10 times that of the Sun, giving us a physical basis for the term "solar-type." New observational aspects of this work include surveys for (1) very close companions with long-baseline interferometry at the Center for High Angular Resolution Astronomy Array, (2) close companions with speckle interferometry, and (3) wide proper-motion companions identified by blinking multi-epoch archival images. In addition, we include the results from extensive radial-velocity monitoring programs and evaluate companion information from various catalogs covering many different techniques. The results presented here include four new common proper-motion companions discovered by blinking archival images. Additionally, the spectroscopic data searched reveal five new stellar companions. Our synthesis of results from many methods and sources results in a thorough evaluation of stellar and brown dwarf companions to nearby Sun-like stars. The overall observed fractions of single, double, triple, and higher-order systems are 56% ± 2%, 33% ± 2%, 8% ± 1%, and 3% ± 1%, respectively, counting all confirmed stellar and brown dwarf companions. If all candidate, i.e., unconfirmed, companions identified are found to be real, the percentages would change to 54%±2%, 34%±2%, 9%±2%, and 3%±1%, respectively. Our completeness analysis indicates that only a few undiscovered companions remain in this well-studied sample, implying that the majority (54%±2%) of solar-type stars are single, in contrast to the results of prior multiplicity studies. Our sample is large enough to enable a check of the multiplicity dependence on various physical parameters by analyzing appropriate subsamples. Bluer, more massive stars are seen as more likely to have companions than redder, less massive ones, consistent with the trend seen over the entire spectral range. Systems with larger interaction cross sections, i.e., those with more than two components or long orbital periods, are preferentially younger, suggesting that companions may be stripped over time by dynamical interactions.We confirm the planet-metallicity correlation (i.e., higher metallicity stars are more likely to host planets), but are unable to check it for brown dwarfs due to the paucity of such companions, implying that the brown dwarf desert extends over all separation regimes.We find no correlation between stellar companions and metallicity for B -V < 0.625, but among the redder subset, metal-poor stars ([Fe/H] < -0.3) are more likely to have companions with a 2.4σ significance. The orbital-period distribution of companions is unimodal and roughly log normal with a peak and median of about 300 years. The period-eccentricity relation shows the expected circularization for periods below 12 days, caused by tidal forces over the age of the Galaxy, followed by a roughly flat distribution. The mass-ratio distribution shows a preference for like-mass pairs, which occur more frequently in relatively close pairs. The fraction of planet hosts among single, binary, and multiple systems are statistically indistinguishable, suggesting that planets are as likely to form around single stars as they are around components of binary or multiple systems with sufficiently wide separations. This, along with the preference of long orbital periods among stellar systems, increases the space around stars conducive for planet formation, and perhaps life. © 2010. The American Astronomical Society. All rights reserved.

Ten Brummelaar T.A.,CHARA Array | McAlister H.A.,Georgia State University | Ridgway S.,National Optical Astronomy Observatory
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The CHARA Array has been a PI led, low budget, and low manpower operation, and has followed a fairly unconventional path in its development. In this, the third paper of a series of three, we discuss some of the engineering and design decisions made along the way, some right and some wrong, with a focus on the choice between in-house development and the purchase of pre-built, or sub-contracted, subsystems. Along with these issues we will also address a few parts of the system that we might have done differently given our current knowledge, and those that somehow turned out very well. © 2014 SPIE.

Farrington C.D.,CHARA Array | Ten Brummelaar T.A.,CHARA Array | Mason B.D.,U.S. Naval Observatory | Hartkopf W.I.,U.S. Naval Observatory | And 6 more authors.
Astronomical Journal | Year: 2014

When observed with optical long-baseline interferometers, components of a binary star that are sufficiently separated produce their own interferometric fringe packets; these are referred to as separated fringe packet (SFP) binaries. These SFP binaries can overlap in angular separation with the regime of systems resolvable by speckle interferometry at single, large-aperture telescopes and can provide additional measurements for preliminary orbits lacking good phase coverage, help constrain elements of already established orbits, and locate new binaries in the undersampled regime between the bounds of spectroscopic surveys and speckle interferometry. In this process, a visibility calibration star is not needed, and the SFPs can provide an accurate vector separation. In this paper, we apply the SFP approach to ω Andromeda, HD 178911, and ξ Cephei with the CLIMB three-beam combiner at the CHARA Array. For these systems we determine component masses and parallax of 0.963 ± 0.049 M and 0.860 ± 0.051 M and 39.54 ± 1.85 mas for ω Andromeda, for HD 178911 of 0.802 ± 0.055 M and 0.622 ± 0.053 M with 28.26 ± 1.70 mas, and masses of 1.045 ± 0.031 M and 0.408 ± 0.066 M and 38.10 ± 2.81 mas for ξ Cephei. © 2014. The American Astronomical Society. All rights reserved..

Farrington C.D.,CHARA Array | Ten Brummelaar T.A.,CHARA Array | Mason B.D.,U.S. Naval Observatory | Hartkopf W.I.,U.S. Naval Observatory | And 6 more authors.
Astronomical Journal | Year: 2010

We present the modification of the orbits of χ Draconis and HD 184467, and a completely new orbit for HD 198084, including data taken at the Center for High Angular Resolution Astronomy (CHARA) Array. These data were obtained using a modification of the technique of separated fringe packets (SFPs). The accuracy of the SFP data surpasses that of data taken by speckle, but the technique is much more time and labor intensive. Additionally, using SFPs with the CHARA Array, it is possible to obtain separations below the detection range of speckle interferometry (≥30mas) above the range in "classic" long-baseline interferometry where fringes from a binary overlap are no longer separated (≤10mas). Using spectroscopic binary systems with published speckle orbits, we are able to test our new measurements against their ephemerides to calibrate the method as well as produce entirely new orbits for systems with no current astrometric observations. © 2010. The American Astronomical Society. All rights reserved.

Von Braun K.,California Institute of Technology | Boyajian T.S.,Georgia State University | Kane S.R.,California Institute of Technology | Hebb L.,Vanderbilt University | And 15 more authors.
Astrophysical Journal | Year: 2012

The late-type dwarf GJ436 is known to host a transiting Neptune-mass planet in a 2.6day orbit. We present results of our interferometric measurements to directly determine the stellar diameter (R ⊙ = 0.455 ± 0.018 R ⊙) and effective temperature (T EFF = 3416 ± 54 K). We combine our stellar parameters with literature time-series data, which allows us to calculate physical and orbital system parameters, including GJ436's stellar mass (M ⊙ = 0.507+0.071 - 0.062 M ⊙), stellar density (ρ * = 5.37+0.30 - 0.27 ρ ⊙), planetary radius (Rp = 0.369+0.015 - 0.015 R Jupiter), and planetary mass (Mp = 0.078+0.007 - 0.008 M Jupiter), implying a mean planetary density of ρp = 1.55+0.12 - 0.10 ρJupiter. These values are generally in good agreement with previous literature estimates based on assumed stellar mass and photometric light curve fitting. Finally, we examine the expected phase curves of the hot Neptune GJ436b, based on various assumptions concerning the efficiency of energy redistribution in the planetary atmosphere, and find that it could be constrained with Spitzer monitoring observations. © 2012. The American Astronomical Society. All rights reserved..

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