Mon. Not. R. Astron. Soc., 416, 2593-2599 (2011/October-1)
A lower mass for the exoplanet WASP-21b.
BARROS S.C.C., POLLACCO D.L., GIBSON N.P., HOWARTH I.D., KEENAN F.P., SIMPSON E.K., SKILLEN I. and STEELE I.A.
Abstract (from CDS):
We present high-precision transit observations of the exoplanet WASP-21b, obtained with the Rapid Imager to Search for Exoplanets instrument mounted on the 2.0-m Liverpool Telescope. A transit model is fitted, coupled with a Markov chain Monte Carlo routine, to derive accurate system parameters. The two new high-precision transits allow us to estimate the stellar density directly from the light curve. Our analysis suggests that WASP-21 is evolving off the main sequence which led to a previous overestimation of the stellar density. Using isochrone interpolation, we find a stellar mass of 0.86 ± 0.04 M☉, which is significantly lower than previously reported (1.01 ±0.03 M☉). Consequently, we find a lower planetary mass of 0.27 ±0.01 MJup. A lower inclination (87°4±0°3) is also found for the system than previously reported, resulting in a slightly larger stellar (R*= 1.10±0.03 R☉) and planetary radius (Rp= 1.14±0.04 RJup). The planet radius suggests a hydrogen/helium composition with no core which strengthens the correlation between planetary density and host star metallicity. A new ephemeris is determined for the system, i.e. T0= 245 5084.519 74±0.000 20 (HJD) and P= 4.322 5060±0.000 0031 d. We found no transit timing variations in WASP-21b.
2011 The Authors Monthly Notices of the Royal Astronomical Society2011 RAS
methods: data analysis - methods: observational - techniques: photometric - stars: individual: WASP-21 - planetary systems
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