HAT-P-12b: A LOW-DENSITY SUB-SATURN MASS PLANET TRANSITING A METAL-POOR K DWARF

Journal Article · Fri Nov 20 00:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/706/1/785· OSTI ID:21378141

Hartman, J D; Bakos, G A; Torres, G; Noyes, R W; Pal, A; Latham, D W; Sipocz, B; Esquerdo, G A; Sasselov, D D; Kovacs, Gabor; Stefanik, R P; Fernandez, J M ^[1]; Kovacs, Geza ^[2]; Fischer, D A ^[3]; Johnson, J A ^[4]; Marcy, G W; Howard, A W ^[5]; Butler, R P ^[6]; Lazar, J; Papp, I ^[7]

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1. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
2. Konkoly Observatory, Budapest (Hungary)
3. Department of Physics and Astronomy, San Francisco State University, San Francisco, CA (United States)
4. Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)
5. Department of Astronomy, University of California, Berkeley, CA (United States)
6. Department of Terrestrial Magnetism, Carnegie Institute of Washington, DC (United States)
7. Hungarian Astronomical Association, Budapest (Hungary)

We report on the discovery of HAT-P-12b, a transiting extrasolar planet orbiting the moderately bright V approx 12.8 K4 dwarf GSC 03033 - 00706, with a period P = 3.2130598 +- 0.0000021 d, transit epoch T{sub c} = 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{sub sun}, radius of 0.70{sup +0.02}{sub -0.01} R{sub sun}, 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{sub J} and radius of 0.959{sup +0.029}{sub -0.021} R{sub J} yielding a mean density of 0.295 +- 0.025 g cm{sup -3}. Comparing these observations with recent theoretical models, we find that HAT-P-12b is consistent with a approx1-4.5 Gyr, mildly irradiated, H/He-dominated planet with a core mass M{sub C} approx< 10 M {sub +}. HAT-P-12b is thus the least massive H/He-dominated gas giant planet found to date. This record was previously held by Saturn.

• OSTI ID: 21378141
• Journal Information: Astrophysical Journal, Vol. 706, Issue 1; Other Information: DOI: 10.1088/0004-637X/706/1/785; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
MASS
METALS
RADIAL VELOCITY
SATURN PLANET
STARS
ELEMENTS
PLANETS
VELOCITY