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Published February 10, 2007 | Published
Journal Article Open

HAT-P-1b: A Large-Radius, Low-Density Exoplanet Transiting One Member of a Stellar Binary


Using small automated telescopes in Arizona and Hawaii, the HATNet project has detected an object transiting one member of the double star system ADS 16402. This system is a pair of G0 main-sequence stars with age about 3 Gyr at a distance of ~139 pc and projected separation of ~1550 AU. The transit signal has a period of 4.46529 days and depth of 0.015 mag. From follow-up photometry and spectroscopy, we find that the object is a "hot Jupiter" planet with mass about 0.53M_J and radius ~1.36R_J traveling in an orbit with semimajor axis 0.055 AU and inclination about 85.9°, thus transiting the star at impact parameter 0.74 of the stellar radius. Based on a data set spanning 3 yr, ephemerides for the transit center are T_C = 2453984.397 + N_(tr) × 4.46529. The planet, designated HAT-P-1b, appears to be at least as large in radius, and smaller in mean density, than any previously known planet.

Additional Information

© 2007 American Astronomical Society. Received 2006 August 12; accepted 2006 September 21. Based in part on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Based in part on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology. Keck time has been granted by NASA. Operation of the HATNet project is funded in part by NASA grant NNG04GN74G. Support for program number HST-HF-01170.01-A to G.Á.B. was provided by NASA through a Hubble Fellowship grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. G. K. wishes to thank support from Hungarian Scientific Research Foundation (OTKA) grant K-60750. We acknowledge partial support from the Kepler Mission under NASA Cooperative Agreement NCC2-1390 (D. W. L., Principal Investigator). G. T. acknowledges partial support from NASA Origins grant NNG04LG89G. We thank Akito Tajitsu for his expertise and support of the Subaru HDS observations. We thank graduate students M. Ohmiya, S. Robinson, and K. Peek for help collecting data at Subaru and Keck. The Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation. D. A. F is a Cottrell Science Scholar of Research Corporation. We acknowledge support from NASA grant NNG05G164G to D. A. F. We would like to thank Carl Akerlof and the decommissioned ROTSE-I project for the generous loan of some of the lenses and CCDs that we use for operating HATNet. We owe special thanks to Emilio Falco, Dan Fabricant, James Moran, and Antony Schinckel for their help in establishing and operating the HATNet stations at FLWO and SMA. G. Á. B. wishes to thank the support given by telescope operators Mike Calkins and Perry Berlind in the operation of the FLWO HATNet station. We also thank Gergely Gálfi for useful discussions. This publication made use of the VizieR interactive catalog (Ochsenbein et al. 2000) at CDS, Strasbourg, and the 2MASS catalog.

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August 19, 2023
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