2012A&A...538A..46D


Query : 2012A&A...538A..46D

2012A&A...538A..46D - Astronomy and Astrophysics, volume 538A, 46-46 (2012/2-1)

Optical to near-infrared transit observations of super-Earth GJ 1214b: water-world or mini-Neptune ?

DE MOOIJ E.J.W., BROGI M., DE KOK R.J., KOPPENHOEFER J., NEFS S.V., SNELLEN I.A.G., GREINER J., HANSE J., HEINSBROEK R.C., LEE C.H. and VAN DER WERF P.P.

Abstract (from CDS):

GJ1214b, the 6.55 Earth-mass transiting planet recently discovered by the MEarth team, has a mean density of ∼35% of that of the Earth. 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. In the case of a hydrogen-rich atmosphere, molecular absorption and scattering processes may result in detectable radius variations as a function of wavelength. The aim of this paper is to measure these variations. We have obtained observations of the transit of GJ1214b in the r- and I-band with the Isaac Newton Telescope (INT), in the g-, r-, i- and z-bands with the 2.2m MPI/ESO telescope, in the Ks-band with the Nordic Optical Telescope (NOT), and in the Kc-band with the William Herschel Telescope (WHT). By comparing the transit depth between the the different bands, which is a measure for the planet-to-star size ratio, the atmosphere is investigated. We do not detect clearly significant variations in the planet-to-star size ratio as function of wavelength. Although the ratio at the shortest measured wavelength, in g-band, is 2σ larger than in the other bands. The uncertainties in the Ks and Kc bands are large, due to systematic features in the light curves. The tentative increase in the planet-to-star size ratio at the shortest wavelength could be a sign of an increase in the effective planet-size due to Rayleigh scattering, which would require GJ1214b to have a hydrogen-rich atmosphere. If true, then the atmosphere has to have both clouds, to suppress planet-size variations at red optical wavelengths, as well as a sub-solar metallicity, to suppress strong molecular features in the near- and mid-infrared. However, star spots, which are known to be present on the host-star's surface, can (partly) cancel out the expected variations in planet-to-star size ratio, because the lower surface temperature of the spots causes the effective size of the star to vary with wavelength. A hypothetical spot-fraction of ∼10%, corresponding to an average stellar dimming of ∼5% in the i-band, would be able to raise the near- and mid-infrared points sufficiently with respect to the optical measurements to be inconsistent with a water-dominated atmosphere. Modulation of the spot fraction due to the stellar rotation would in such case cause the observed flux variations of GJ1214.

Abstract Copyright:

Journal keyword(s): techniques: photometric - stars: individual: GJ1214 - planetary systems

VizieR on-line data: <Available at CDS (J/A+A/538/A46): grond_g.dat grond_i.dat grond_r.dat grond_z.dat int_i.dat int_r.dat not_ks.dat wht_kc.dat>

Simbad objects: 4

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Number of rows : 4
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 NAME G 139-21b Pl 17 15 18.9337265994 +04 57 50.064695682           ~ 581 1
2 G 139-21 PM* 17 15 18.9337265994 +04 57 50.064695682       14.394   M4.5V 259 1
3 HD 189733b Pl 20 00 43.7130382888 +22 42 39.071811263           ~ 1184 1
4 HD 209458b Pl 22 03 10.7729598762 +18 53 03.548248479           ~ 1585 1

    Equat.    Gal    SGal    Ecl

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2021.07.25-15:28:56

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