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Post Info TOPIC: GJ 1214b
Blobrana


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RE: GJ 1214b
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Title: The atmospheric circulation of the super Earth GJ 1214b: Dependence on composition and metallicity
Author: Tiffany Kataria, Adam P. Showman, Jonathan J. Fortney, Mark S. Marley, Richard S. Freedman

We present three-dimensional atmospheric circulation models of GJ 1214b, a 2.7 Earth-radius, 6.5 Earth-mass super Earth detected by the MEarth survey. Here we explore the planet's circulation as a function of atmospheric metallicity and atmospheric composition, modeling atmospheres with a low mean-molecular weight (i.e., H2-dominated) and a high mean-molecular weight (i.e. water- and CO2-dominated). We find that atmospheres with a low mean-molecular weight have strong day-night temperature variations at pressures above the infrared photosphere that lead to equatorial superrotation. For these atmospheres, the enhancement of atmospheric opacities with increasing metallicity lead to shallower atmospheric heating, larger day-night temperature variations and hence stronger superrotation. In comparison, atmospheres with a high mean-molecular weight have larger day-night and equator-to-pole temperature variations than low mean-molecular weight atmospheres, but differences in opacity structure and energy budget lead to differences in jet structure. The circulation of a water-dominated atmosphere is dominated by equatorial superrotation, while the circulation of a CO2-dominated atmosphere is instead dominated by high-latitude jets. By comparing emergent flux spectra and lightcurves for 50x solar and water-dominated compositions, we show that observations in emission can break the degeneracy in determining the atmospheric composition of GJ 1214b. The variation in opacity with wavelength for the water-dominated atmosphere leads to large phase variations within water bands and small phase variations outside of water bands. The 50x solar atmosphere, however, yields small variations within water bands and large phase variations at other characteristic wavelengths. These observations would be much less sensitive to clouds, condensates, and hazes than transit observations.

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Blobrana


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Title: Multi-Colour Transit Photometry of GJ 1214b through BJHKs-Bands and a Long-Term Monitoring of the Stellar Variability of GJ 1214
Authors: Norio Narita, Akihiko Fukui, Masahiro Ikoma, Yasunori Hori, Kenji Kurosaki, Yui Kawashima, Takahiro Nagayama, Masahiro Onitsuka, Amnart Sukom, Yasushi Nakajima, Motohide Tamura, Daisuke Kuroda, Kenshi Yanagisawa, Teruyuki Hirano, Kiyoe Kawauchi, Masayuki Kuzuhara, Hiroshi Ohnuki, Takuya Suenaga, Yasuhiro H. Takahashi, Hideyuki Izumiura, Nobuyuki Kawai, Michitoshi Yoshida

We present 5 new transit light curves of GJ 1214b taken in BJHKs-bands. Two transits were observed in B-band using the Suprime-Cam and the FOCAS instruments onboard the Subaru 8.2m telescope, and one transit was done in JHKs-bands simultaneously with the SIRIUS camera on the IRSF 1.4m telescope. MCMC analyses show that the planet-to-star radius ratios are, Rp/Rs = 0.11651 ± 0.00065 (B-band, Subaru/Suprime-Cam), Rp/Rs = 0.11601 ± 0.00117 (B-band, Subaru/FOCAS), Rp/Rs = 0.11654 ± 0.00080 (J-band, IRSF/SIRIUS), Rp/Rs = 0.11550 ^{+0.00142}_{-0.00153} (H-band, IRSF/SIRIUS), and Rp/Rs = 0.11547 ± 0.00127 (Ks-band, IRSF/SIRIUS). The Subaru Suprime-Cam transit photometry shows a possible spot-crossing feature. Provided that this is truly a spot-crossing and if the feature is removed, the radius ratio rises to Rp/Rs = 0.11882 ± 0.00070. Comparisons of the new transit depths and those from previous studies with the theoretical models by Howe & Burrows (2012) suggest that the high molecular weight atmosphere (e.g., 1% H_2O + 99% N_2) models are most likely, however, the low molecular weight (hydrogen dominated) atmospheres with extensive clouds are still not excluded. We also report a long-term monitoring of the stellar brightness variability of GJ 1214 observed with the MITSuME 50cm telescope in g'-, Rc-, and Ic-bands simultaneously. The monitoring was conducted for 32 nights spanning 78 nights in 2012, and we find a periodic brightness variation with a period of Ps = 44.3 ± 1.2 days and semi-amplitudes of 2.1% ± 0.4% in g'-band, 0.56% ± 0.08% in Rc-band, and 0.32% ± 0.04% in Ic-band.

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Blobrana


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Title: Optical Observations of the Transiting Exoplanet GJ 1214b
Authors: Johanna K. Teske, Jake D. Turner, Matthias Mueller, Caitlin A. Griffith

We observed nine primary transits of the super-Earth exoplanet GJ 1214b in several optical photometric bands from March to August 2012, with the goal of constraining the short-wavelength slope of the spectrum of GJ 1214b. Our observations were conducted on the Kuiper 1.55 m telescope in Arizona and the STELLA-I robotic 1.2 m telescope in Tenerife, Spain. From the derived light curves we extracted transit depths in R (0.65 µm), V (0.55 µm), and g' (0.475 µm) bands. Most previous observations of this exoplanet suggest a flat spectrum varying little with wavelength from the near-infrared to the optical, corresponding to a low-scale-height, high-molecular-weight atmosphere. However, a handful of observations around Ks band (~2.15 µm) and g-band (~0.46 µm) are inconsistent with this scenario and suggest a variation on a hydrogen- or water-dominated atmosphere that also contains a haze layer of small particles. In particular, the g-band observations of de Mooij et al. (2012), consistent with Rayleigh scattering, limit the potential atmosphere compositions of GJ 1214b due to the increasing slope at optical wavelengths (Howe & Burrows 2012). We find that our results overlap within errors the short-wavelength observations of de Mooij et al. (2012), but are also consistent with a spectral slope of zero in GJ 1214b in the optical wavelength region. Our observations thus allow for a larger suite of possible atmosphere compositions, including those with a high-molecular-weight and/or hazes.

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Blobrana


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Title: Spitzer Transits of the Super-Earth GJ1214b and Implications for Its Atmosphere
Authors: Jonathan D. Fraine, Drake Deming, Michaėl Gillon, Emmanuėl Jehin, Brice-Olivier Demory, Bjoern Benneke, Sara Seager, Nikole K. Lewis, Heather Knutson, Jean-Michel Desert

We observed the transiting super-Earth exoplanet GJ1214b using Warm Spitzer at 4.5 microns wavelength during a 20-day quasi-continuous sequence in May 2011. The goals of our long observation were to accurately define the infrared transit radius of this nearby super-Earth, to search for the secondary eclipse, and to search for other transiting planets in the habitable zone of GJ1214. We here report results from the transit monitoring of GJ1214b, including a re-analysis of previous transit observations by Desert et al. (2011). In total, we analyse 14 transits of GJ1214b at 4.5 microns, 3 transits at 3.6 microns, and 7 new ground-based transits in the I+z band. Our new Spitzer data by themselves eliminate cloudless solar composition atmospheres for GJ1214b, and methane-rich models from Howe & Burrows (2012). Using our new Spitzer measurements to anchor the observed transit radii of GJ1214b at long wavelengths, and adding new measurements in I+z, we evaluate models from Benneke & Seager (2012) and Howe & Burrows (2012) using a chi-squared analysis. We find that the best-fit model exhibits an increase in transit radius at short wavelengths due to Rayleigh scattering. Pure water atmospheres are also possible. However, a flat line (no atmosphere detected) remains among the best of the statistically acceptable models, and better than pure water atmospheres. We explore the effect of systematic differences among results from different observational groups, and we find that the Howe & Burrows (2012) tholin-haze model remains the best fit, even when systematic differences among observers are considered.

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Blobrana


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Title: GJ 1214 reviewed : Trigonometric parallax, stellar parameters, new orbital solution and updated bulk properties for the super-Earth GJ 1214b
Authors: Guillem Anglada-Escudé, Bįrbara Rojas-Ayala, Alan P. Boss, Alicya J. Weinberger, James P. Lloyd

GJ 1214 is orbited by a super-Earth-mass planet that transits in front of it. It is a primary target for the ongoing efforts to understand the emerging population of super-Earth-mass planets around M dwarfs, some of them detected within the habitable zone of their host stars. We present precision astrometric measurements, a re-analysis of HARPS radial velocity measurements, and medium resolution infrared spectroscopy of GJ 1214. We combine these measurements with recent transit measurements and new catalogue photometry to provide a comprehensive update of the star-planet properties. The distance is obtained at 1.5% precision using CAPSCam astrometry. The new value increases the distance to the star by 10% and is significantly more precise than the previous measurement. New radial velocity measurements were obtained re-analysing public HARPS spectra using the HARPS-TERRA software. The Doppler data combined with recent transit observations significantly update the orbital solution (especially the planet's eccentricity). The analysis of the infrared spectrum and photometry confirm that the star is enriched in metals compared to the Sun. Using all this information, combined only with empirical mass--luminosity relations for low mass stars, we derive updated values for the bulk properties of the star--planet system. Our analysis shows that the updated expected value for the planet mean density is 1.6±0.6 g cm^{-3}, and that a density comparable to the Earth is now completely ruled out. This study illustrates how the fundamental properties of M dwarfs are of paramount importance in the proper characterisation of the low mass planetary candidates orbiting them. Additional Doppler observations, and/or or detection of the secondary transit, are necessary to improve the constraints on the planet properties.

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Blobrana


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GJ1214
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Title: The Transiting System GJ1214: High-Precision Defocused Transit Observations and a Search for Evidence of Transit Timing Variation
Authors: K. B. W. Harpsųe, S. Hardis, T. C. Hinse, U. G. Jųrgensen, L. Mancini, J. Southworth, K. A. Alsubai, V. Bozza, P. Browne, M. J. Burgdorf, S. Calchi Novati, P. Dodds, M. Dominik, F. Finet, T. Gerner, M. Hundertmark, N. Kains, E. Kerins, C. Liebig, M. Mathiasen, D. Nesvornż, N. Nikolov, M. T. Penny, S. Proft, S. Rahvar, D. Ricci, K. C. Sahu, G. Scarpetta, S. Schäfer, F. Schönebeck, C. Snodgrass, J. Skottfelt, J. Surdej, J. Tregloan-Reed, O. Wertz

Aims: We present 11 high-precision photometric transit observations of the transiting super-Earth planet GJ1214b. Combining these data with observations from other authors, we investigate the ephemeris for possible signs of transit timing variations (TTVs) using a Bayesian approach.
Methods: The observations were obtained using telescope-defocusing techniques, and achieve a high precision with random errors in the photometry as low as 1mmag per point. To investigate the possibility of TTVs in the light curve, we calculate the overall probability of a TTV signal using Bayesian methods.
Results: The observations are used to determine the photometric parameters and the physical properties of the GJ1214 system. Our results are in good agreement with published values. Individual times of mid-transit are measured with uncertainties as low as 10s, allowing us to reduce the uncertainty in the orbital period by a factor of two.
Conclusions: A Bayesian analysis reveals that it is highly improbable that the observed transit times show a TTV, when compared with the simpler alternative of a linear ephemeris.

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Blobrana


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RE: GJ 1214b
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Title: An investigation of a GJ 1214b-like exoplanet with a water vapour atmosphere using a simple general circulation model
Authors: Angela M. Zalucha, Timothy I. Michaels, Nikku Madhusudhan

We present results from a simple general circulation model (GCM) of a GJ 1214b-like super-Earth exoplanet. The dynamical core of our model is a scaled-up version of a shallow atmosphere, terrestrial planet GCM that has previously been used for Mars and therefore employs different boundary conditions and physical processes than downsized gas giant models. We assume the planet is tidally locked and has the observed characteristics of GJ-1214b [Charbonneau et al. 2009] for surface mass, surface radius, orbital period, and surface gravitational acceleration. We assume the atmosphere is composed entirely of water vapour. We assume the planet has a surface (i.e., a density discontinuity at depth), which will provide a mechanical drag and affect the radiative balance at the bottom boundary. We assume a grey atmosphere in the IR. We find that a westerly jet is present aloft at the equator and that the longitude of maximum temperature is shifted eastward of the substellar point. A wavenumber-1 feature is present in the equatorial vertical velocity field, indicative of a standing Kelvin and/or Rossby wave. As such, the circulation does not exhibit a cellular structure as on terrestrial Solar System planets; rather, air parcels move up and down on closed horizontal circuits and always return to the same location. The flow at the midlatitudes and poles has both an easterly component and a component that flows poleward along the evening terminator and equatorward along the morning terminator. Temperature inversions exist in the boundary layer and aloft, which are a result of variations in horizontal heat transport. The flow within the boundary layer is more convergent than in the atmosphere aloft. The surface pressure is higher at the poles than the equator.

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Blobrana


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Gliese 1214b
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Gliese 1214 b was discovered in data taken between June and August 2009. The discovery observations were made by the eight identical 40-cm telescopes that form the MEarth Project and follow up observations were taken with the F. L. Whipple Observatory (FLWO) 1.2-meter telescope. The discovery was announced on 16 December 2009.
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Blobrana


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RE: GJ 1214b
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Distant 'waterworld' is confirmed

Astronomers have confirmed the existence of a new class of planet: a waterworld with a thick, steamy atmosphere.
The exoplanet GJ 1214b is a so-called "Super Earth" - bigger than our planet, but smaller than gas giants such as Jupiter.
Observations using the Hubble telescope now seem to confirm that a large fraction of its mass is water.
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Blobrana


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NASA's Hubble Reveals a New Class of Extrasolar Planet

Observations of the extrasolar planet GJ1214b by NASA's Hubble Space Telescope have come up with a new class of planet, a waterworld enshrouded by a thick, steamy atmosphere. It's smaller than Uranus but larger than Earth. A paper reporting these results has been accepted for publication in The Astrophysical Journal and is available online.
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Position (J2000):     R.A. 17 15 18.94  |  Dec. +04° 57' 49.72"



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