Kaspar von Braun, Tabetha S. Boyajian, Stephen R. Kane, Leslie Hebb, Gerard T. van Belle, Chris Farrington, David R. Ciardi, Heather A. Knutson, Theo A. ten Brummelaar, Mercedes Lopez-Morales, Harold A. McAlister, Gail Schaefer, Stephen Ridgway, Andrew Collier Cameron, P. J. Goldfinger, Nils H. Turner, Laszlo Sturmann, Judit Sturmann
The late-type dwarf GJ 436 is known to host a transiting Neptune-mass planet
in a 2.6-day orbit. We present results of our interferometric measurements to
directly determine the stellar diameter ($R_{\star} = 0.455 \pm 0.018
R_{\odot}$) and effective temperature ($T_{\rm EFF} = 3416 \pm 54$ K). We
combine our stellar parameters with literature time-series data, which allows
us to calculate physical and orbital system parameters, including GJ 436's
stellar mass ($M_{\star} = 0.472^{+ 0.0636}_{- 0.0566} M_{\odot}$), planetary
radius ($R_{p} = 0.370^{+ 0.0149}_{- 0.0145} R_{Jupiter}$), planetary mass
($M_{p} = 0.075^{+ 0.0076}_{- 0.0072} M_{Jupiter}$), implying a mean planetary
density of $\rho_{p} = 1.48^{+ 0.116}_{- 0.103} \rho_{Jupiter}$. These values
are generally in good agreement with previous literature estimates based on
assumed stellar mass and photometric light curve fitting. Finally, we examine
the expected phase curves of the hot Neptune GJ 436b, based on various
assumptions concerning the efficiency of energy redistribution in the planetary
atmosphere, and find that it could be constrained with {\it Spitzer} monitoring
observations.
View original:
http://arxiv.org/abs/1202.0083
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