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Register a new userThe Frequency of Hot Jupiters Orbiting Nearby Solar-Type Stars
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We determine the fraction of F, G, and K dwarfs in the Solar Neighborhood hosting hot jupiters as measured by the California Planet Survey from the Lick and Keck planet searches. We find the rate to be 1.2pm0.38%, which is consistent with the rate reported by Mayor et al. (2011) from the HARPS and CORALIE radial velocity surveys. These numbers are more than double the rate reported by Howard et al. (2011) for Kepler stars and the rate of Gould et al. (2006) from the OGLE-III transit search, however due to small number statistics these differences are of only marginal statistical significance. We explore some of the difficulties in estimating this rate from the existing radial velocity data sets and comparing radial velocity rates to rates from other techniques.
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The existence of hot Jupiters has challenged theories of planetary formation since the first extrasolar planets were detected. Giant planets are generally believed to form far from their host stars, where volatile materials like water exist in their solid phase, making it easier for giant planet cores to accumulate. Several mechanisms have been proposed to explain how giant planets can migrate inward from their birth sites to short-period orbits. One such mechanism, called Kozai-Lidov migration, requires the presence of distant companions in orbits inclined by more than $sim40$ degrees with respect to the plane of the hot Jupiters orbit. The high occurrence rate of wide companions in hot Jupiter systems lends support to this theory for migration. However, the exact orbital inclinations of these detected planetary and stellar companions is not known, so it is not clear whether the mutual inclination of these companions is large enough for the Kozai-Lidov process to operate. This paper shows that in systems orbiting cool stars with convective outer layers, the orbits of most wide planetary companions to hot Jupiters must be well aligned with the orbits of the hot Jupiters and the spins of the host stars. For a variety of possible distributions for the inclination of the companion, the width of the distribution must be less than $sim20$ degrees to recreate the observations with good fidelity. As a result, the companion orbits are likely well-aligned with those of the hot Jupiters, and the Kozai-Lidov mechanism does not enforce migration in these systems.
We report the discovery by WASP of five planets orbiting moderately bright ($V$ = 11.0-12.9) Solar-type stars. WASP-137b, WASP-143b and WASP-146b are typical hot Jupiters in orbits of 3-4 d and with masses in the range 0.68--1.11 $M_{rm Jup}$. WASP-134 is a metal-rich ([Fe/H] = +0.40 $pm$ 0.07]) G4 star orbited by two warm Jupiters: WASP-134b ($M_{rm pl}$ = 1.41 $M_{rm Jup}$; $P = 10.1$ d; $e = 0.15 pm 0.01$; $T_{rm eql}$ = 950 K) and WASP-134c ($M_{rm pl} sin i$ = 0.70 $M_{rm Jup}$; $P = 70.0$ d; $e = 0.17 pm 0.09$; $T_{rm eql}$ = 500 K). From observations of the Rossiter-McLaughlin effect of WASP-134b, we find its orbit to be misaligned with the spin of its star ($lambda = -44 pm 10^circ$). WASP-134 is a rare example of a system with a short-period giant planet and a nearby giant companion. In-situ formation or disc migration seem more likely explanations for such systems than does high-eccentricity migration.
We present initial results from a new high-contrast imaging program dedicated to stars that exhibit long-term Doppler radial velocity accelerations (or trends). The goal of the TRENDS (TaRgetting bENchmark-objects with Doppler Spectroscopy and) imaging survey is to directly detect and study the companions responsible for accelerating their host star. In this first paper of the series, we report the discovery of low-mass stellar companions orbiting HD 53665, HD 68017, and HD 71881 using NIRC2 adaptive optics (AO) observations at Keck. Follow-up imaging demonstrates association through common proper-motion. These co-moving companions have red colors with estimated spectral-types of K7--M0, M5, and M3--M4 respectively. We determine a firm lower-limit to their mass from Doppler and astrometric measurements. In the near future, it will be possible to construct three-dimensional orbits and calculate the dynamical mass of HD 68017 B and possibly HD 71881 B. We already detect astrometric orbital motion of HD 68017 B, which has a projected separation of 13.0 AU. Each companion is amenable to AO-assisted direct spectroscopy. Further, each companion orbits a solar-type star, making it possible to infer metallicity and age from the primary. Such benchmark objects are essential for testing theoretical models of cool dwarf atmospheres.
We report the discovery of four close-in transiting exoplanets, HATS-50 through HATS-53, discovered using the HATSouth three-continent network of homogeneous and automated telescopes. These new exoplanets belong to the class of hot Jupiters and orbit G-type dwarf stars, with brightness in the range V=12.5-14.0 mag. While HATS-53 has many physical characteristics similar to the Sun, the other three stars appear to be metal rich, larger and more massive. Three of the new exoplanets, namely HATS-50, HATS-51 and HATS-53, have low density and similar orbital period. Instead, HATS-52 is more dense and has a shorter orbital period. It also receives an intensive radiation from its parent star and, consequently, presents a high equilibrium temperature. HATS-50 shows a marginal additional transit feature consistent with an ultra-short period hot super Neptune, which will be able to be confirmed with TESS photometry.
Extremely irradiated, close-in planets to early-type stars might be prone to strong atmospheric escape. We review the literature showing that X-ray-to-optical measurements indicate that for intermediate-mass stars (IMS) cooler than $approx$8250 K, the X-ray and EUV (XUV) fluxes are on average significantly higher than those of solar-like stars, while for hotter IMS, because of the lack of surface convection, it is the opposite. We construct spectral energy distributions for prototypical IMS, comparing them to solar. The XUV fluxes relevant for upper planet atmospheric heating are highest for the cooler IMS and lowest for the hotter IMS, while the UV fluxes increase with increasing stellar temperature. We quantify the influence of this characteristic of the stellar fluxes on the mass loss of close-in planets by simulating the atmospheres of planets orbiting EUV-bright (WASP-33) and EUV-faint (KELT-9) A-type stars. For KELT-9b, we find that atmospheric expansion caused by heating due to absorption of the stellar UV and optical light drives mass-loss rates of $approx$10$^{11}$ g s$^{-1}$, while heating caused by absorption of the stellar XUV radiation leads to mass-loss rates of $approx$10$^{10}$ g s$^{-1}$, thus underestimating mass loss. For WASP-33b, the high XUV stellar fluxes lead to mass-loss rates of $approx$10$^{11}$ g s$^{-1}$. Even higher mass-loss rates are possible for less massive planets orbiting EUV-bright IMS. We argue that it is the weak XUV stellar emission, combined with a relatively high planetary mass, which limit planetary mass-loss rates, to allow the prolonged existence of KELT-9-like systems.
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