A lower mass for the exoplanet WASP-21b

S. C. C. Barros, D. L. Pollacco, N. P. Gibson, I. D. Howarth, F. P. Keenan, E. K. Simpson, I. Skillen, I. A. Steele

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


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 Msun, which is significantly lower than previously reported (1.01 ± 0.03 Msun). 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 Rsun) 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.
Original languageEnglish
Pages (from-to)2593-2599
Number of pages7
JournalMonthly Notices of the Royal Astronomical Society
Publication statusPublished - Oct 2011

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics


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