J/A+A/538/A46 Transit observations of GJ1214b (de Mooij+, 2012)
Optical to near-infrared transit observations of super-Earth GJ1214b:
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.,
van der Werf P.P.
<Astron. Astrophys. 538, A46 (2012)>
=2012A&A...538A..46D 2012A&A...538A..46D
ADC_Keywords: Stars, double and multiple ; Planets ; Photometry, infrared
Keywords: techniques: photometric - stars: individual: GJ1214 -
planetary systems
Abstract:
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 2sigma 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 hoststar'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.
Description:
The lightcurves of GJ1214b for the INT r- and I-band, GROND g-, r-, i-
and z-band, NOTCam Ks-band and LIRIS Kc-band observations. Note that
the date given is the Julian Date, JD, and not the Heliocentric Julian
Date, HJD.
Objects:
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RA (2000) DE Designation(s)
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17 15 18.9 +04 57 50 GJ1214b = GJ 1214 b
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
grond_g.dat 31 277 GROND g-band lightcurves (on 2.2m MPI/ESO telescope)
grond_i.dat 31 280 GROND i-band lightcurves
grond_r.dat 31 279 GROND r-band lightcurves
grond_z.dat 31 265 GROND z-band lightcurves
int_i.dat 31 142 INT I-band lightcurves (Isaac Newton Telescope)
int_r.dat 31 89 INT r-band lightcurves
not_ks.dat 29 493 NOTCam Ks-band lightcurves
(Nordic Optical Telescope)
wht_kc.dat 32 931 LIRIS Kc-band lightcurves (Long-slit Intermediate
Resolution Infrared Spectrograph on
William Herschel Telescope)
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Byte-by-byte Description of file: grond_?.dat int_?.dat not_ks.dat wht_kc.dat
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Bytes Format Units Label Explanations
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1- 13 F13.5 d JD Julian Date of observation
16- 21 F6.4 --- Flux Corrected flux
24- 29 F6.4 --- e_Flux Uncertainty on Flux
31- 32 A2 --- Band [girzI Kc Ks] Band of the flux
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Acknowledgements:
Ernst De Mooij, demooij(at)strw.leidenuniv.nl
(End) Patricia Vannier [CDS] 18-Nov-2011