J. D. Hartman et al. 2009 ApJ 706 785 doi:10.1088/0004-637X/706/1/785
HAT-P-12b: A LOW-DENSITY SUB-SATURN MASS PLANET TRANSITING A METAL-POOR K DWARF*
FREE ISSUEJ. D. Hartman1, G. Á. Bakos1,10, G. Torres1, Géza Kovács2, R. W. Noyes1, A. Pál1,2,3, D. W. Latham1, B. Sipőcz1,3, D. A. Fischer4, J. A. Johnson5,11, G. W. Marcy6, R. P. Butler7, A. W. Howard6, G. A. Esquerdo1, D. D. Sasselov1, Gábor Kovács1, R. P. Stefanik1, J. M. Fernandez1,8, J. Lázár9, I. Papp9 and P. Sári9
Show affiliationsWe 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 ± 0.0000021 d, transit epoch Tc = 2454419.19556 ± 0.00020 (BJD), and transit duration 0.0974 ± 0.0006 d. The host star has a mass of 0.73 ± 0.02 M ☉, radius of 0.70+0.02 –0.01 R ☉, effective temperature 4650 ± 60 K, 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 ± 0.012 M J and radius of 0.959+0.029 –0.021 R J yielding a mean density of 0.295 ± 0.025 g 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.
- Footnote
- Keywords
planetary systems; stars: individual (HAT-P-12, GSC 03033 – 00706); techniques: photometric; techniques: spectroscopic
- Dates
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Issue 1 (2009 November 20)
Received 2009 April 29, accepted for publication 2009 October 13
Published 2009 November 5
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