SEARCH FOR RAYLEIGH SCATTERING IN THE ATMOSPHERE OF GJ1214b

• Published in: The Astrophysical journal 2013-07, Vol.771 (2), p.1-7
• Main Authors: DE MOOIJ, E J W, Brogi, M, De Kok, R J, Snellen, I A G, Croll, B, Jayawardhana, R, Hoekstra, H, OTTEN, G P P L, Bekkers, D H, Haffert, S Y, Van Houdt, J J
• Format: Article
• Language: English
• Subjects: ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ATMOSPHERES; Band spectra; DENSITY; INT; LAYERS; Mathematical models; PLANETS; RAYLEIGH SCATTERING; SCALE HEIGHT; SPECTRA; STARS; TELESCOPES; Transit; TRANSMISSION; WATER; WAVELENGTHS
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/771/2/109

We investigate the atmosphere of GJ1214b, a transiting super-Earth planet with a low mean density, by measuring its transit depth as a function of wavelength in the blue optical portion of the spectrum. It is thought that this planet is either a mini-Neptune, consisting of a rocky core with a thick, hydrogen-rich atmosphere, or a planet with a composition dominated by water. Most observations favor a water-dominated atmosphere with a small scale-height, however, some observations indicate that GJ1214b could have an extended atmosphere with a cloud layer muting the molecular features. In an atmosphere with a large scale-height, Rayleigh scattering at blue wavelengths is likely to cause a measurable increase in the apparent size of the planet toward the blue. We observed the transit of GJ1214b in the B band with the FOcal Reducing Spectrograph at the Very Large Telescope and in the g band with both ACAM on the William Herschel Telescope (WHT) and the Wide Field Camera at the Isaac Newton Telescope (INT). We find a planet-to-star radius ratio in the B band of 0.1162 + or - 0.0017, and in the g band 0.1180 + or - 0.0009 and 0.1174 + or - 0.0017 for the WHT and INT observations, respectively. These optical data do not show significant deviations from previous measurements at longer wavelengths. In fact, a flat transmission spectrum across all wavelengths best describes the combined observations. When atmospheric models are considered, a small scale-height water-dominated model fits the data best.