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, Kevin Bays

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Abstract

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 Rp = 4.31 R ⊕ ± 0.06 R ⊕ and Rs = 0.683 R sun ± 0.009 R sun, 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.
Original languageEnglish
Pages (from-to)33
JournalAstrophysical Journal
Volume740
Issue number1
DOIs
Publication statusPublished - 1 Oct 2011
Externally publishedYes

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Neptune (planet)
Neptune
transit
planet
stars
limb
limb darkening
planets
butterfly
diagram
probe
sun
wavelength
K stars
methodology
dwarf stars
equators
inference
sky
poles

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Deming, D., Sada, P. V., Jackson, B., Peterson, S. W., Agol, E., Knutson, H. A., ... Bays, K. (2011). Kepler and Ground-based Transits of the Exo-Neptune HAT-P-11b. Astrophysical Journal, 740(1), 33. https://doi.org/10.1088/0004-637X/740/1/33
Deming, Drake ; Sada, Pedro V. ; Jackson, Brian ; Peterson, Steven W. ; Agol, Eric ; Knutson, Heather A. ; Jennings, Donald E. ; Haase, Flynn ; Bays, Kevin. / Kepler and Ground-based Transits of the Exo-Neptune HAT-P-11b. In: Astrophysical Journal. 2011 ; Vol. 740, No. 1. pp. 33.
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Deming, D, Sada, PV, Jackson, B, Peterson, SW, Agol, E, Knutson, HA, Jennings, DE, Haase, F & Bays, K 2011, 'Kepler and Ground-based Transits of the Exo-Neptune HAT-P-11b', Astrophysical Journal, vol. 740, no. 1, pp. 33. https://doi.org/10.1088/0004-637X/740/1/33

Kepler and Ground-based Transits of the Exo-Neptune HAT-P-11b. / Deming, Drake; Sada, Pedro V.; Jackson, Brian; Peterson, Steven W.; Agol, Eric; Knutson, Heather A.; Jennings, Donald E.; Haase, Flynn; Bays, Kevin.

In: Astrophysical Journal, Vol. 740, No. 1, 01.10.2011, p. 33.

Research output: Contribution to journalArticle

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T1 - Kepler and Ground-based Transits of the Exo-Neptune HAT-P-11b

AU - Deming, Drake

AU - Sada, Pedro V.

AU - Jackson, Brian

AU - Peterson, Steven W.

AU - Agol, Eric

AU - Knutson, Heather A.

AU - Jennings, Donald E.

AU - Haase, Flynn

AU - Bays, Kevin

PY - 2011/10/1

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N2 - 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 Rp = 4.31 R ⊕ ± 0.06 R ⊕ and Rs = 0.683 R sun ± 0.009 R sun, 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.

AB - 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 Rp = 4.31 R ⊕ ± 0.06 R ⊕ and Rs = 0.683 R sun ± 0.009 R sun, 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.

U2 - 10.1088/0004-637X/740/1/33

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