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Register a new userKELT-21b: A Hot Jupiter Transiting the Rapidly-Rotating Metal-Poor Late-A Primary of a Likely Hierarchical Triple System
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We present the discovery of KELT-21b, a hot Jupiter transiting the $V=10.5$ A8V star HD 332124. The planet has an orbital period of $P=3.6127647pm0.0000033$ days and a radius of $1.586_{-0.040}^{+0.039}$ $R_J$. We set an upper limit on the planetary mass of $M_P<3.91$ $M_J$ at $3sigma$ confidence. We confirmed the planetary nature of the transiting companion using this mass limit and Doppler tomographic observations to verify that the companion transits HD 332124. These data also demonstrate that the planetary orbit is well-aligned with the stellar spin, with a sky-projected spin-orbit misalignment of $lambda=-5.6_{-1.9}^{+1.7 circ}$. The star has $T_{mathrm{eff}}=7598_{-84}^{+81}$ K, $M_*=1.458_{-0.028}^{+0.029}$ $M_{odot}$, $R_*=1.638pm0.034$ $R_{odot}$, and $vsin I_*=146$ km s$^{-1}$, the highest projected rotation velocity of any star known to host a transiting hot Jupiter. The star also appears to be somewhat metal-poor and $alpha$-enhanced, with [Fe/H]$=-0.405_{-0.033}^{+0.032}$ and [$alpha$/Fe]$=0.145 pm 0.053$; these abundances are unusual, but not extraordinary, for a young star with thin-disk kinematics like KELT-21. High-resolution imaging observations revealed the presence of a pair of stellar companions to KELT-21, located at a separation of 1.2 and with a combined contrast of $Delta K_S=6.39 pm 0.06$ with respect to the primary. Although these companions are most likely physically associated with KELT-21, we cannot confirm this with our current data. If associated, the candidate companions KELT-21 B and C would each have masses of $sim0.12$ $M_{odot}$, a projected mutual separation of $sim20$ AU, and a projected separation of $sim500$ AU from KELT-21. KELT-21b may be one of only a handful of known transiting planets in hierarchical triple stellar systems.
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We report the discovery of KELT-7b, a transiting hot Jupiter with a mass of $1.28 pm 0.18$ MJ, radius of $1.53_{-0.047}^{+0.046}$ RJ, and an orbital period of $2.7347749 pm 0.0000039$ days. The bright host star (HD33643; KELT-7) is an F-star with $V=8.54$, Teff $=6789_{-49}^{+50}$ K, [Fe/H] $=0.139_{-0.081}^{+0.075}$, and $log{g}=4.149 pm 0.019$. It has a mass of $1.535_{-0.054}^{+0.066}$ Msun, a radius of $1.732_{-0.045}^{+0.043}$ Rsun, and is the fifth most massive, fifth hottest, and the ninth brightest star known to host a transiting planet. It is also the brightest star around which KELT has discovered a transiting planet. Thus, KELT-7b is an ideal target for detailed characterization given its relatively low surface gravity, high equilibrium temperature, and bright host star. The rapid rotation of the star ($73 pm 0.5$ km/s) results in a Rossiter-McLaughlin effect with an unusually large amplitude of several hundred m/s. We find that the orbit normal of the planet is likely to be well-aligned with the stellar spin axis, with a projected spin-orbit alignment of $lambda=9.7 pm 5.2$ degrees. This is currently the second most rapidly rotating star to have a reflex signal (and thus mass determination) due to a planetary companion measured.
We report the discovery of KELT-2Ab, a hot Jupiter transiting the bright (V=8.77) primary star of the HD 42176 binary system. The host is a slightly evolved late F-star likely in the very short-lived blue-hook stage of evolution, with $teff=6148pm48{rm K}$, $log{g}=4.030_{-0.026}^{+0.015}$ and $feh=0.034pm0.78$. The inferred stellar mass is $M_*=1.314_{-0.060}^{+0.063}$msun and the star has a relatively large radius of $R_*=1.836_{-0.046}^{+0.066}$rsun. The planet is a typical hot Jupiter with period $4.11379pm0.00001$ days and a mass of $M_P=1.524pm0.088$mj and radius of $R_P=1.290_{-0.050}^{+0.064}$rj. This is mildly inflated as compared to models of irradiated giant planets at the $sim$4 Gyr age of the system. KELT-2A is the third brightest star with a transiting planet identified by ground-based transit surveys, and the ninth brightest star overall with a transiting planet. KELT-2Abs mass and radius are unique among the subset of planets with $V<9$ host stars, and therefore increases the diversity of bright benchmark systems. We also measure the relative motion of KELT-2A and -2B over a baseline of 38 years, robustly demonstrating for the first time that the stars are bound. This allows us to infer that KELT-2B is an early K-dwarf. We hypothesize that through the eccentric Kozai mechanism KELT-2B may have emplaced KELT-2Ab in its current orbit. This scenario is potentially testable with Rossiter-McLaughlin measurements, which should have an amplitude of $sim$44 m s$^{-1}$.
We report the discovery of KELT-4Ab, an inflated, transiting Hot Jupiter orbiting the brightest component of a hierarchical triple stellar system. The host star is an F star with $T_{rm eff}=6206pm75$ K, $log g=4.108pm0.014$, $left[{rm Fe}/{rm H}right]=-0.116_{-0.069}^{+0.065}$, ${rm M_*}=1.201_{-0.061}^{+0.067} {rm M}_{odot}$, and ${rm R_*}=1.610_{-0.068}^{+0.078} {rm R}_{odot}$. The best-fit linear ephemeris is $rm {BJD_{TDB}} = 2456193.29157 pm 0.00021 + Eleft(2.9895936 pm 0.0000048right)$. With a magnitude of $Vsim10$, a planetary radius of $1.699_{-0.045}^{+0.046} {rm R_J}$, and a mass of $0.902_{-0.059}^{+0.060} {rm M_J}$, it is the brightest host among the population of inflated Hot Jupiters ($R_P > 1.5R_J$), making it a valuable discovery for probing the nature of inflated planets. In addition, its existence within a hierarchical triple and its proximity to Earth ($210$ pc) provides a unique opportunity for dynamical studies with continued monitoring with high resolution imaging and precision radial velocities. In particular, the motion of the binary stars around each other and of both stars around the primary star relative to the measured epoch in this work should be detectable when it rises in October 2015.
We report the discovery of a transiting planet orbiting the star TYC 6446-326-1. The star, WASP-22, is a moderately bright (V=12.0) solar-type star (Teff = 6000 +/- 100 K, [Fe/H] = -0.05 +/- 0.08). The lightcurve of the star obtained with the WASP-South instrument shows periodic transit-like features with a depth of about 1 and a duration of 0.14 days. The presence of a transit-like feature in the lightcurve is confirmed using z-band photometry obtained with Faulkes Telescope South. High resolution spectroscopy obtained with the CORALIE and HARPS spectrographs confirm the presence of a planetary mass companion with an orbital period of 3.533 days in a near-circular orbit. From a combined analysis of the spectroscopic and photometric data assuming that the star is a typical main-sequence star we estimate that the planet has a mass M_p = 0.56 +/- 0.02 M_Jup and a radius R_p = 1.12 +/- 0.04 R_Jup. In addition, there is a linear trend of 40 m/s/yr in the radial velocities measured over 16 months, from which we infer the presence of a third body with a long period orbit in this system. The companion may be a low mass M-dwarf, a white dwarf or a second planet.
We report the discovery of KELT-3b, a moderately inflated transiting hot Jupiter with a mass of 1.477 (-0.067, +0.066) M_J, and radius of 1.345 +/- 0.072 R_J, with an orbital period of 2.7033904 +/- 0.000010 days. The host star, KELT-3, is a V=9.8 late F star with M_* = 1.278 (-0.061, +0.063) M_sun, R_* = 1.472 (-0.067, +0.065) R_sun, T_eff = 6306 (-49, +50) K, log(g) = 4.209 (-0.031, +0.033), and [Fe/H] = 0.044 (-0.082, +0.080), and has a likely proper motion companion. KELT-3b is the third transiting exoplanet discovered by the KELT survey, and is orbiting one of the 20 brightest known transiting planet host stars, making it a promising candidate for detailed characterization studies. Although we infer that KELT-3 is significantly evolved, a preliminary analysis of the stellar and orbital evolution of the system suggests that the planet has likely always received a level of incident flux above the empirically-identified threshold for radius inflation suggested by Demory & Seager (2011).
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