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Kepler and Ground-based Transits of the Exo-Neptune HAT-P-11b

Deming, Drake and Sada, Pedro V. and Jackson, Brian and Peterson, Steven W. and Agol, Eric and Knutson, Heather A. and Jennings, Donald E. and Haase, Flynn and Bays, Kevin (2011) Kepler and Ground-based Transits of the Exo-Neptune HAT-P-11b. Astrophysical Journal, 740 (1). Art. No. 33. ISSN 0004-637X.

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We analyze 26 archival Kepler transits of the exo-Neptune HAT-P-11b, supplemented by ground-based transits observed in the blue (B band) and near-IR (J band). Both the planet and host star are smaller than previously believed; our analysis yields R_p = 4.31 R_⊕ ± 0.06 R_⊕ and R_s = 0.683 R_☉ ± 0.009 R_☉, both about 3σ smaller than the discovery values. Our ground-based transit data at wavelengths bracketing the Kepler bandpass serve to check the wavelength dependence of stellar limb darkening, and the J-band transit provides a precise and independent constraint on the transit duration. Both the limb darkening and transit duration from our ground-based data are consistent with the new Kepler values for the system parameters. Our smaller radius for the planet implies that its gaseous envelope can be less extensive than previously believed, being very similar to the H-He envelope of GJ 436b and Kepler-4b. HAT-P-11 is an active star, and signatures of star spot crossings are ubiquitous in the Kepler transit data. We develop and apply a methodology to correct the planetary radius for the presence of both crossed and uncrossed star spots. Star spot crossings are concentrated at phases –0.002 and +0.006. This is consistent with inferences from Rossiter-McLaughlin measurements that the planet transits nearly perpendicular to the stellar equator. We identify the dominant phases of star spot crossings with active latitudes on the star, and infer that the stellar rotational pole is inclined at about 12° ± 5° to the plane of the sky. We point out that precise transit measurements over long durations could in principle allow us to construct a stellar Butterfly diagram to probe the cyclic evolution of magnetic activity on this active K-dwarf star.

Item Type:Article
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URLURL TypeDescription Paper
Deming, Drake0000-0001-5727-4094
Agol, Eric0000-0002-0802-9145
Knutson, Heather A.0000-0002-0822-3095
Additional Information:© 2011 American Astronomical Society. Received 2011 April 26; accepted 2011 July 13; published 2011 September 23. We thank Dick Joyce for his expert assistance with FLAMINGOS, and we thank the anonymous referee for insightful comments that allowed us to improve this paper. Eric Agol acknowledges support from NSF Career grant AST-0645416.
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Subject Keywords:planetary systems; planets and satellites: general; stars: activity; starspots
Issue or Number:1
Record Number:CaltechAUTHORS:20130129-153335557
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Official Citation:Kepler and Ground-based Transits of the Exo-Neptune HAT-P-11b Drake Deming, Pedro V. Sada, Brian Jackson, Steven W. Peterson, Eric Agol, Heather A. Knutson, Donald E. Jennings, Flynn Haase, and Kevin Bays doi:10.1088/0004-637X/740/1/33
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36670
Deposited By: Ruth Sustaita
Deposited On:29 Jan 2013 23:50
Last Modified:03 Oct 2019 04:40

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