HAT-P-12b: A low-density sub-saturn mass planet transiting a metal-poor K dwarf

J. D. Hartman, G. Á Bakos, G. Torres, Géza Kovcs, R. W. Noyes, A. Pál, D. W. Latham, B. Sipc'z, D. A. Fischer, J. A. Johnson, G. W. Marcy, R. P. Butler, A. W. Howard, G. A. Esquerdo, D. D. Sasselov, Gábor Kovács, R. P. Stefanik, J. M. Fernandez, J. Lázár, I. PappP. Sári

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67 Citations (Scopus)

Abstract

We report on the discovery of HAT-P-12b, a transiting extrasolar planet orbiting the moderately bright V 12.8 K4 dwarf GSC 03033 - 00706, with a period P = 3.2130598±0.0000021d, transit epoch Tc = 2454419.19556± 0.00020 (BJD), and transit duration 0.0974±0.0006d. The host star has a mass of 0.73 0.02M , radius of 0.70 +0.02 -0.01R , effective temperature 4650 60K, and metallicity [Fe/H] = -0.29 0.05. We find a slight correlation between the observed spectral line bisector spans and the radial velocity, so we consider, and rule out, various blend configurations including a blend with a background eclipsing binary, and hierarchical triple systems where the eclipsing body is a star or a planet. We conclude that a model consisting of a single star with a transiting planet best fits the observations, and show that a likely explanation for the apparent correlation is contamination from scattered moonlight. Based on this model, the planetary companion has a mass of 0.211±0.012M J and radius of 0.959+0.029 -0.021R J yielding a mean density of 0.295±0.025g cm-3. Comparing these observations with recent theoretical models, we find that HAT-P-12b is consistent with a ∼1-4.5 Gyr, mildly irradiated, H/He-dominated planet with a core mass MC ≲ 10 M . HAT-P-12b is thus the least massive H/He-dominated gas giant planet found to date. This record was previously held by Saturn.

Original languageEnglish
Pages (from-to)785-796
Number of pages12
JournalAstrophysical Journal
Volume706
Issue number1
DOIs
Publication statusPublished - Jan 1 2009

Keywords

  • Planetary systems
  • Stars: Individual (HAT-P-12, GSC 03033?00706)
  • Techniques: Photometric
  • Techniques: Spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Hartman, J. D., Bakos, G. Á., Torres, G., Kovcs, G., Noyes, R. W., Pál, A., Latham, D. W., Sipc'z, B., Fischer, D. A., Johnson, J. A., Marcy, G. W., Butler, R. P., Howard, A. W., Esquerdo, G. A., Sasselov, D. D., Kovács, G., Stefanik, R. P., Fernandez, J. M., Lázár, J., ... Sári, P. (2009). HAT-P-12b: A low-density sub-saturn mass planet transiting a metal-poor K dwarf. Astrophysical Journal, 706(1), 785-796. https://doi.org/10.1088/0004-637X/706/1/785