ABSTRACT We present newly derived stellar parameters and the detailed abundances of 19 elements of seven stars with small planets discovered by NASA's Kepler Mission. Each star, save one, has at ...least one planet with a radius ≤1.6 R⊕, suggesting a primarily rocky composition. The stellar parameters and abundances are derived from high signal-to-noise ratio, high-resolution echelle spectroscopy obtained with the 10 m Keck I telescope and High Resolution Echelle Spectrometer using standard spectroscopic techniques. The metallicities of the seven stars range from −0.32 to +0.13 dex, with an average metallicity that is subsolar, supporting previous suggestions that, unlike Jupiter-type giant planets, small planets do not form preferentially around metal-rich stars. The abundances of elements other than iron are in line with a population of Galactic disk stars, and despite our modest sample size, we find hints that the compositions of stars with small planets are similar to stars without known planets and with Neptune-size planets, but not to those of stars with giant planets. This suggests that the formation of small planets does not require exceptional host-star compositions and that small planets may be ubiquitous in the Galaxy. We compare our derived abundances (which have typical uncertainties of 0.04 dex) to the condensation temperature of the elements; a correlation between the two has been suggested as a possible signature of rocky planet formation. None of the stars demonstrate the putative rocky planet signature, despite at least three of the stars having rocky planets estimated to contain enough refractory material to produce the signature, if real. More detailed abundance analyses of stars known to host small planets are needed to verify our results and place ever more stringent constraints on planet formation models.
We have analyzed new and previously published radial velocity (RV) observations of MARVELS-1, known to have an ostensibly substellar companion in a ~6 day orbit. We find significant (~100 m s ...super(-1)) residuals to the best-fit model for the companion, and these residuals are naively consistent with an interior giant planet with a P = 1.965 days in a nearly perfect 3:1 period commensurability (|P sub(b)/P sub(c) - 3| < 10 super(4)). We have performed several tests for the reality of such a companion, including a dynamical analysis, a search for photometric variability, and a hunt for contaminating stellar spectra. We find many reasons to be critical of a planetary interpretation, including the fact that most of the three-body dynamical solutions are unstable. We find no evidence for transits, and no evidence of stellar photometric variability. We have discovered two apparent companions to MARVELS-1 with adaptive optics imaging at Keck; both are M dwarfs, one is likely bound, and the other is likely a foreground object. We explore false-alarm scenarios inspired by various curiosities in the data. Ultimately, a line profile and bisector analysis lead us to conclude that the ~100 m s super(-1) residuals are an artifact of spectral contamination from a stellar companion contributing ~15%-30% of the optical light in the system. We conclude that origin of this contamination is the previously detected RV companion to MARVELS-1, which is not, as previously reported, a brown dwarf, but in fact a G dwarf in a face-on orbit.
We present the fundamental stellar and planetary properties of the transiting planetary system WASP-13 within the framework of the Homogeneous Study of Transiting Systems (HoSTS). HoSTS aims to ...derive the fundamental stellar (T sub(eff), Fe/H, Mlow *, Rlow *) and planetary (M sub(pl), R sub(pl), T sub(eq)) physical properties of known transiting planets using a consistent methodology and homogeneous high-quality data set. Four spectral analysis techniques are independently applied to a Keck+HIRES spectrum of WASP-13 considering two distinct cases: unconstrained parameters and constrained log g from transit light curves. We check the derived stellar temperature against that from a different temperature diagnostic based on an INT+IDS H alpha spectrum. The four unconstrained analyses render results that are in good agreement, and provide an improvement of 50% in the precision of T sub(eff), and of 85% in Fe/H with respect to the WASP-13 discovery paper. The planetary parameters are then derived via the Monte Carlo Markov Chain modeling of the radial velocity and light curves, in iteration with stellar evolutionary models to derive realistic uncertainties. WASP-13 (1.187 + or - 0.065 M sub(middot in circle); 1.574 + or - 0.048 R sub(middot in circle)) hosts a Saturn-mass, transiting planet (0.500 + or - 0.037 M sub(Jup); 1.407 + or - 0.052 R sub(Jup)), and is at the end of its main-sequence lifetime (4-5.5 Gyr). Our analysis of WASP-13 showcases that both a detailed stellar characterization and transit modeling are necessary to well determine the fundamental properties of planetary systems, which are paramount in identifying and determining empirical relationships between transiting planets and their hosts.
We describe the discovery of a likely brown dwarf (BD) companion with a minimum mass of 31.7 + or - 2.0 M sub(Jup) to GSC 03546-01452 from the MARVELS radial velocity survey, which we designate as ...MARVELS-6b. For reasonable priors, our analysis gives a probability of 72% that MARVELS-6b has a mass below the hydrogen-burning limit of 0.072 M sub(odot), and thus it is a high-confidence BD companion. It has a moderately long orbital period of 47.8929 super(+0.0063) sub(-0.0062) days with a low eccentricity of 0.1442 super(+0.0078) sub(-0.0073) and a semi-amplitude of 1644 super(+12) sub(-13) m s super(-1). Moderate resolution spectroscopy of the host star has determined the following parameters: T sub(eff) = 5598 + or - 63, log g = 4.44 + or - 0.17, and Fe/H = +0.40 + or - 0.09. Based upon these measurements, GSC 03546-01452 has a probable mass and radius of M sub(*) = 1.11 + or - 0.11 M sub(odot) and R sub(*) = 1.06 + or - 0.23 Rodot with an age consistent with less than ~6 Gyr at a distance of 219 + or - 21 pc from the Sun. Although MARVELS-6b is not observed to transit, we cannot definitively rule out a transiting configuration based on our observations. There is a visual companion detected with Lucky Imaging at 7".7 from the host star, but our analysis shows that it is not bound to this system. The minimum mass of MARVELS-6b exists at the minimum of the mass functions for both stars and planets, making this a rare object even compared to other BDs. It also exists in an underdense region in both period/eccentricity and metallicity/eccentricity space.
TYC 4110-01037-1 has a low-mass stellar companion, whose small mass ratio and short orbital period are atypical among binary systems with solar-like (T sub(eff) <, ~ 6000 K) primary stars. 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 + or - 0.08 M sub(middot in a circle) and radius of 0.99 + or - 0.18 Re. We analyze 32 radial velocity (RV) measurements from the SDSS-III MARVELS survey as well as 6 supporting RV measurements from the SARG spectrograph on the 3.6 m Telescopio Nazionale Galileo telescope obtained over a period of ~2 years. The best Keplerian orbital fit parameters were found to have a period of 78.994 + or - 0.012 days, an eccentricity of 0.1095 + or - 0.0023, and a semi-amplitude of 4199 + or - 11ms super(-1). We determine the minimum companion mass (if sin i = 1) to be 97.7 + or - 5.8 M sub(Jup). The system's companion to host star mass ratio, > or =0.087 + or - 0.003, places it at the lowest end of observed values for short period stellar companions to solar-like (T sub(eff) <, ~ 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 comoving, 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 (RV) measurements of a short-period (P = 2.430420 + or - 0.000006 days) companion to the F-type main-sequence star TYC 2930-00872-1. We are able to exclude ...transits of the inner companion with high confidence. Further, the host star spectrum exhibits a clear signature of Ca H and K core emission, indicating stellar activity, but a lack of photometric variability and small v sin I suggest that the primary's spin axis is oriented in a pole-on configuration. The rotational period of the primary estimated through an activity-rotation relation matches the orbital period of the inner companion to within 1.5 sigma, suggesting that the primary and inner companion are tidally locked. If the tertiary is not a stellar remnant, then it likely has a mass of ~0.5-0.6 Modot, 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.
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 sub(eff) = 5903 + or - 42 K, ...surface gravity log(g) = 4.07 + or - 0.16 (cgs), and metallicity Fe/H = -0.23 + or - 0.07. 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 + or - 0.041 km s super(-1), period P= 9.0090 + or - 0.0004 days, and eccentricity e = 0.226 + or - 0.011. Through adaptive optics imaging we also found a point source 643 + or - 10 mas away from TYC 2087-00255-1, which would have a mass of 0.13 M sub(middot in circle) if it is physically associated with TYC 2087-00255-1 and has the same age.
We report the discovery of a highly eccentric, double-lined spectroscopic binary star system (TYC 3010-1494-1), comprising two solar-type stars that we had initially identified as a single star with ...a brown dwarf companion. At the moderate resolving power of the MARVELS spectrograph and the spectrographs used for subsequent radial- velocity (RV) measurements (R lap 30,000), this particular stellar binary mimics a single-lined binary with an RV signal that would be induced by a brown dwarf companion (M sin i ~ 50 M sub(JUP)) to a solar-type primary. The discovery of this binary system is an important lesson for RV surveys searching for substellar companions; at a given resolution and observing cadence, a survey will be susceptible to these kinds of astrophysical false positives for a range of orbital parameters.
We present a new short-period brown dwarf (BD) candidate around the star TYC 1240-00945-1. This candidate was discovered in the first year of the Multi-object APO Radial Velocity Exoplanets ...Large-area Survey (MARVELS), which is part of the Sloan Digital Sky Survey (SDSS) III, and we designate the BD as MARVELS-1b. MARVELS uses the technique of dispersed fixed-delay interferometery to simultaneously obtain radial velocity (RV) measurements for 60 objects per field using a single, custom-built instrument that is fiber fed from the SDSS 2.5 m telescope. From our 20 RV measurements spread over a ~370 day time baseline, we derive a Keplerian orbital fit with semi-amplitude K = 2.533 ? 0.025 km s--1, period P = 5.8953 ? 0.0004 days, and eccentricity consistent with circular. Independent follow-up RV data confirm the orbit. Adopting a mass of 1.37 ? 0.11 M for the slightly evolved F9 host star, we infer that the companion has a minimum mass of 28.0 ? 1.5 M Jup, a semimajor axis 0.071 ? 0.002 AU assuming an edge-on orbit, and is probably tidally synchronized. We find no evidence for coherent intrinsic variability of the host star at the period of the companion at levels greater than a few millimagnitudes. The companion has an a priori transit probability of ~14%. Although we find no evidence for transits, we cannot definitively rule them out for companion radii 1 R Jup.
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