HAT-P-18b AND HAT-P-19b: TWO LOW-DENSITY SATURN-MASS PLANETS TRANSITING METAL-RICH K STARS

Journal Article · Sat Jan 01 00:00:00 EST 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/726/1/52· OSTI ID:21567703

Hartman, J D; Bakos, G A; Torres, G; Noyes, R W; Latham, D W; Buchhave, L A; Fueresz, G; Perumpilly, G; Beky, B; Stefanik, R P; Sasselov, D D; Esquerdo, G A; Everett, M; Csubry, Z ^[1]; Sato, B ^[2]; Kovacs, G ^[3]; Fischer, D A ^[4]; Howard, A W; Marcy, G W ^[5]

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1. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
2. Global Edge Institute, Tokyo Institute of Technology, Tokyo (Japan)
3. Konkoly Observatory, Budapest (Hungary)
4. Department of Physics and Astronomy, San Francisco State University, San Francisco, CA (United States)
5. Department of Astronomy, University of California, Berkeley, CA (United States)

We report the discovery of two new transiting extrasolar planets. HAT-P-18b orbits the V = 12.759 K2 dwarf star GSC 2594-00646, with a period P = 5.508023 {+-} 0.000006 days, transit epoch T{sub c} = 2454715.02174 {+-} 0.00020 (BJD), and transit duration 0.1131 {+-} 0.0009 days. The host star has a mass of 0.77 {+-} 0.03 M{sub sun}, radius of 0.75 {+-} 0.04 R{sub sun}, effective temperature 4803 {+-} 80 K, and metallicity [Fe/H] = +0.10 {+-} 0.08. The planetary companion has a mass of 0.197 {+-} 0.013 M{sub J} and radius of 0.995 {+-} 0.052 R{sub J}, yielding a mean density of 0.25 {+-} 0.04 g cm{sup -3}. HAT-P-19b orbits the V = 12.901 K1 dwarf star GSC 2283-00589, with a period P = 4.008778 {+-} 0.000006 days, transit epoch T{sub c} = 2455091.53417 {+-} 0.00034 (BJD), and transit duration 0.1182 {+-} 0.0014 days. The host star has a mass of 0.84 {+-} 0.04 M{sub sun}, radius of 0.82 {+-} 0.05 R{sub sun}, effective temperature 4990 {+-} 130 K, and metallicity [Fe/H] = +0.23 {+-} 0.08. The planetary companion has a mass of 0.292 {+-} 0.018 M{sub J} and radius of 1.132 {+-} 0.072 R{sub J}, yielding a mean density of 0.25 {+-} 0.04 g cm{sup -3}. The radial velocity residuals for HAT-P-19 exhibit a linear trend in time, which indicates the presence of a third body in the system. Comparing these observations with theoretical models, we find that HAT-P-18b and HAT-P-19b are each consistent with a hydrogen-helium-dominated gas giant planet with negligible core mass. HAT-P-18b and HAT-P-19b join HAT-P-12b and WASP-21b in an emerging group of low-density Saturn-mass planets, with negligible inferred core masses. However, unlike HAT-P-12b and WASP-21b, both HAT-P-18b and HAT-P-19b orbit stars with super-solar metallicity. This calls into question the heretofore suggestive correlation between the inferred core mass and host star metallicity for Saturn-mass planets.

• OSTI ID: 21567703
• Journal Information: Astrophysical Journal, Vol. 726, Issue 1; Other Information: DOI: 10.1088/0004-637X/726/1/52; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
DWARF STARS
MASS
METALS
PLANETS
ELEMENTS
STARS