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Register a new userKepler-77b: a very low albedo, Saturn-mass transiting planet around a metal-rich solar-like star
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We report the discovery of Kepler-77b (alias KOI-127.01), a Saturn-mass transiting planet in a 3.6-day orbit around a metal-rich solar-like star. We combined the publicly available Kepler photometry (quarters 1-13) with high-resolution spectroscopy from the Sandiford@McDonald and FIES@NOT spectrographs. We derived the system parameters via a simultaneous joint fit to the photometric and radial velocity measurements. Our analysis is based on the Bayesian approach and is carried out by sampling the parameter posterior distributions using a Markov chain Monte Carlo simulation. Kepler-77b is a moderately inflated planet with a mass of Mp=0.430+/-0.032 Mjup, a radius of Rp=0.960+/-0.016 Rjup, and a bulk density of 0.603+/-0.055 g/cm^3. It orbits a slowly rotating (P=36+/-6 days) G5V star with M*=0.95+/-0.04 Msun, R*=0.99+/-0.02 Rsun, Teff=5520+/-60 K, [M/H]=0.20+/-0.05, that has an age of 7.5+/-2.0 Gyr. The lack of detectable planetary occultation with a depth higher than about 10 ppm implies a planet geometric and Bond albedo of Ag<0.087+/-0.008 and Ab<0.058+/-0.006, respectively, placing Kepler-77b among the gas-giant planets with the lowest albedo known so far. We found neither additional planetary transit signals nor transit-timing variations at a level of about 0.5 minutes, in accordance with the trend that close-in gas giant planets seem to belong to single-planet systems. The 106 transits observed in short-cadence mode by Kepler for nearly 1.2 years show no detectable signatures of the planets passage in front of starspots. We explored the implications of the absence of detectable spot-crossing events for the inclination of the stellar spin-axis, the sky-projected spin-orbit obliquity, and the latitude of magnetically active regions.
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We report the spectroscopic confirmation of the Kepler object of interest KOI-183.01 (Kepler-423b), a half-Jupiter mass planet transiting an old solar-like star every 2.7 days. Our analysis is the first to combine the full Kepler photometry (quarters 1-17) with high-precision radial velocity measurements taken with the FIES spectrograph at the Nordic Optical Telescope. We simultaneously modelled the photometric and spectroscopic data-sets using Bayesian approach coupled with Markov chain Monte Carlo sampling. We found that the Kepler pre-search data conditioned (PDC) light curve of KOI-183 exhibits quarter-to-quarter systematic variations of the transit depth, with a peak-to-peak amplitude of about 4.3 % and seasonal trends reoccurring every four quarters. We attributed these systematics to an incorrect assessment of the quarterly variation of the crowding metric. The host star KOI-183 is a G4 dwarf with $M_star=0.85pm0.04$ M$_rm{Sun}$, $R_star=0.95pm0.04$ R$_rm{Sun}$, $T_mathrm{eff}=5560pm80$ K, $[M/H]=-0.10pm0.05$ dex, and with an age of $11pm2$ Gyr. The planet KOI-183b has a mass of $M_mathrm{p}=0.595pm0.081$ M$_mathrm{Jup}$ and a radius of $R_mathrm{p}=1.192pm0.052$ R$_mathrm{Jup}$, yielding a planetary bulk density of $rho_mathrm{p}=0.459pm0.083$ g/cm$^{3}$. The radius of KOI-183b is consistent with both theoretical models for irradiated coreless giant planets and expectations based on empirical laws. The inclination of the stellar spin axis suggests that the system is aligned along the line of sight. We detected a tentative secondary eclipse of the planet at a 2-$sigma$ confidence level ($Delta F_{mathrm{ec}}=14.2pm6.6$ ppm) and found that the orbit might have a small non-zero eccentricity of $e=0.019^{+0.028}_{-0.014}$. With a Bond albedo of $A_mathrm{B}=0.037pm0.019$, KOI-183b is one of the gas-giant planets with the lowest albedo known so far.
We report the discovery of HAT-P-38b, a Saturn-mass exoplanet transiting the V=12.56 dwarf star GSC 2314-00559 on a P = 4.6404 d circular orbit. The host star is a 0.89Msun late G-dwarf, with solar metallicity, and a radius of 0.92Rsun. The planetary companion has a mass of 0.27MJ, and radius of 0.82RJ. HAT-P-38b is one of the closest planets in mass and radius to Saturn ever discovered.
M-dwarf stars -- hydrogen-burning stars that are smaller than 60 per cent of the size of the Sun -- are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star. The nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. Here we report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away. Our Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the Earth and precisely measured densities. Receiving 19 times more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. Because the host star is nearby and only 21 per cent the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.
We report on the discovery of HAT-P-12b, a transiting extrasolar planet orbiting the moderately bright V=12.8 K4 dwarf GSC 03033-00706, with a period P = 3.2130598 +- 0.0000021 d, transit epoch Tc = 2454419.19556 +- 0.00020 (BJD) and transit duration 0.0974 +- 0.0006 d. The host star has a mass of 0.73 +- 0.02 Msun, radius of 0.70 +- ^0.02_0.01 Rsun, effective temperature 4650 +- 60 K and metallicity [Fe/H] = -0.29 +- 0.05. We find a slight correlation between the observed spectral line bisector spans and the radial velocity, so we consider, and rule out, various blend configurations including a blend with a background eclipsing binary, and hierarchical triple systems where the eclipsing body is a star or a planet. We conclude that a model consisting of a single star with a transiting planet best fits the observations, and show that a likely explanation for the apparent correlation is contamination from scattered moonlight. Based on this model, the planetary companion has a mass of 0.211 +- 0.012 MJup, and a radius of 0.959 +- ^0.029_0.021 RJup yielding a mean density of 0.295 +- 0.025 g cm^-3. Comparing these observations with recent theoretical models we find that HAT-P-12b is consistent with a ~ 1-4.5 Gyr, mildly irradiated, H/He dominated planet with a core mass Mc <~ 10 Mearth. HAT-P-12b is thus the least massive H/He dominated gas giant planet found to date. This record was previously held by Saturn.
We report the discovery and analysis of a sub-Saturn-mass planet in the microlensing event OGLE-2018-BLG-0799. The planetary signal was observed by several ground-based telescopes, and the planet-host mass ratio is $q = (2.65 pm 0.16) times 10^{-3}$. The ground-based observations yield a constraint on the angular Einstein radius $theta_{rm E}$, and the microlens parallax $pi_{rm E}$ is measured from the joint analysis of the Spitzer and ground-based observations, which suggests that the host star is most likely to be a very low-mass dwarf. A full Bayesian analysis using a Galactic model indicates that the planetary system is composed of an $M_{rm planet} = 0.22_{-0.06}^{+0.19}~M_{J}$ planet orbiting an $M_{rm host} = 0.080_{-0.020}^{+0.080}~M_odot$, at a distance of $D_{rm L} = 4.42_{-1.23}^{+1.73}$ kpc. The projected planet-host separation is $r_perp = 1.27_{-0.29}^{+0.45}$ AU, implying that the planet is located beyond the snowline of the host star. However, because of systematics in the Spitzer photometry, there is ambiguity in the parallax measurement, so the system could be more massive and farther away.
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