HATS-6b: a Warm Saturn

HATS-6b: A Warm Saturn Transiting an Early M Dwarf Star, and a Set of Empirical Relations for Characterizing K and M Dwarf Planet Hosts

Authors:

Hartman et al

Abstract:

We report the discovery by the HATSouth survey of HATS-6b, an extrasolar planet transiting a V=15.2 mag, i=13.7 mag M1V star with a mass of 0.57 Msun and a radius of 0.57 Rsun. HATS-6b has a period of P = 3.3253 d, mass of Mp=0.32 Mjup, radius of Rp=1.00 Rjup, and zero-albedo equilibrium temperature of Teq=712.8+-5.1 K. HATS-6 is one of the lowest mass stars known to host a close-in gas giant planet, and its transits are among the deepest of any known transiting planet system. We discuss the follow-up opportunities afforded by this system, noting that despite the faintness of the host star, it is expected to have the highest K-band S/N transmission spectrum among known gas giant planets with Teq less than 750 K. In order to characterize the star we present a new set of empirical relations between the density, radius, mass, bolometric magnitude, and V, J, H and K-band bolometric corrections for main sequence stars with M less than 0.80 Msun, or spectral types later than K5. These relations are calibrated using eclipsing binary components as well as members of resolved binary systems. We account for intrinsic scatter in the relations in a self-consistent manner. We show that from the transit-based stellar density alone it is possible to measure the mass and radius of a ~0.6 Msun star to ~7% and ~2% precision, respectively. Incorporating additional information, such as the V-K color, or an absolute magnitude, allows the precision to be improved by up to a factor of two.

MOA-2008-BLG-379Lb: ~2 Saturn Gas Giant at 3.3 AU

MOA-2008-BLG-379Lb: A MASSIVE PLANET FROM A HIGH MAGNIFICATION EVENT WITH A FAINT SOURCE

Authors:

Suzuki et al

Abstract:

We report on the analysis of the high microlensing event MOA-2008-BLG-379, which has a strong microlensing anomaly at its peak due to a massive planet with a mass ratio of q = 6.9 × 10–3. Because the faint source star crosses the large resonant caustic, the planetary signal dominates the light curve. This is unusual for planetary microlensing events, and as a result, the planetary nature of this light curve was not immediately noticed. The planetary nature of the event was found when the Microlensing Observations in Astrophysics (MOA) Collaboration conducted a systematic study of binary microlensing events previously identified by the MOA alert system. We have conducted a Bayesian analysis based on a standard Galactic model to estimate the physical parameters of the lens system. This yields a host star mass of $M_{\rm L} = 3.3_{-1.2}^{+1.7}\ M_\odot$ orbited by a planet of mass $m_{\rm P} = 0.56_{-0.27}^{+0.24}\ M_{\rm Jup}$ at an orbital separation of $a = 3.3_{-1.2}^{+1.3}$ AU at a distance of $D_{\rm L} = 4.1^{+1.7}_{-1.9}$ kpc. The faint source magnitude of I S = 21.30 and relatively high lens-source relative proper motion of μrel = 7.6 ± 1.6 mas yr–1 imply that high angular resolution adaptive optics or Hubble Space Telescope observations are likely to be able to detect the source star, which would determine the masses and distance of the planet and its host star.

erratum here.

How EChO Will Characterize Gas Giant Exoplanet Atmospheres

EChO's view on gas giant exoplanets atmospheres

Authors:

Parmentier et al

Abstract:

The last decade has seen the discovery of more than a thousand exoplanets but, more excitingly, probing their atmospheres has become possible. With current data we caught a glimpse of the diversity of exoplanet atmospheres that will be revealed in the next years. However, numerous questions concerning their chemical composition, thermal structure, and atmospheric dynamics remain to be answered. More observations of higher quality are needed. The Exoplanet Characterisation Observatory (EChO) is a space-based observatory dedicated to the characterization of exoplanets atmospheres proposed to the ESA cosmic vision program. With its large spectral coverage (4-16 {\mu}m) and high spectral resolution (\Delta{\lambda}/{\lambda} greater than 300 below 5 {\mu}m and \Delta{\lambda}/{\lambda} greater than 30 above 5 {\mu}m) EChO will provide spectrally resolved transit lightcurves, secondary eclipses lightcurves, and full phase curves of numerous exoplanets with an unprecedented signal to noise ratio. In this technical note we review some of today's main scientific questions about gas giant exoplanets atmospheres, for which EChO will bring a decisive contribution.