The GJ 436 System: Directly Determined Astrophysical Parameters of an M Dwarf and Implications for the Transiting Hot Neptune

Creators: von Braun, Kaspar; Boyajian, Tabetha S.; Kane, Stephen R.; Hebb, Leslie; van Belle, Gerard T.; Farrington, Chris; Ciardi, David R.; Knutson, Heather A.; ten Brummelaar, Theo A.; Lόpez-Morales, Mercedes; McAlister, Harold A.; Schaefer, Gail; Ridgway, Stephen T.; Collier-Cameron, Andrew; Goldfinger, P. J.; Turner, Nils H.; Sturmann, Laszlo; Sturmann, Judit

Abstract

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_* = 0.455 ± 0.018 R_☉) and effective temperature (T_(EFF) = 3416 ± 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_* = 0.507^(+0.071)_(– 0.062) M_☉), stellar density (ρ_* = 5.37^(+0.30)_(–0.27) ρ_☉), planetary radius (R_p = 0.369^(+0.015)_(–0.015)R _(Jupiter)), and planetary mass (M_p = 0.078^(+0.007)_(–0.008) M_(Jupiter)), implying a mean planetary density of ρ_p = 1.55^(+0.12)_(–0.10) ρ_(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 Spitzer monitoring observations.

Additional Information

© 2012 American Astronomical Society. Received 2012 January 31; accepted 2012 May 11; published 2012 June 26. We extend our gratitude to the anonymous referee for very insightful remarks on this paper that improved its quality. We furthermore thank J.-P. Beaulieu, D. Kipping, R. Therien, and S. Mahadevan for useful discussions about GJ 436's astrophysical parameters, and especially F. Pont for sending us HST data from his and collaborators' 2009 study. T.S.B. acknowledges support provided by NASA through the Hubble Fellowship grant HST-HF-51252.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. The CHARA Array is funded by the National Science Foundation through NSF grants AST-0606958 and AST-0908253 and by Georgia State University through the College of Arts and Sciences, as well as the W. M. Keck Foundation. This research made use of the SIMBAD literature database, operated at CDS, Strasbourg, France, and of NASA's Astrophysics Data System. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.

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