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Post Info TOPIC: HD 97658b
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RE: HD 97658b
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Title: A warm, likely volatile-rich super-Earth: HD 97658b transits, but not quite when expected
Authors: Diana Dragomir, Jaymie M. Matthews, Jason D. Eastman, Chris Cameron, Andrew W. Howard, David B. Guenther, Rainer Kuschnig, Anthony F. J. Moffat, Jason F. Rowe, Slavek M. Rucinski, Dimitar Sasselov, Werner W. Weiss

Through photometric monitoring of the extended transit window of HD 97658b with the MOST space telescope, we have found that this exoplanet transits with an ephemeris consistent with that predicted from radial velocity measurements. The mid-transit times are 6\sigma earlier than those of the unverified transit-like signals reported in 2011, and we find no connection between the two sets of events. The transit depth indicates a 2.34^{+0.18}_{-0.15} Earth radii super-Earth. When combined with the radial velocity determined mass of 7.86 ± 0.73 Earth masses, our radius measure allows us to derive a planet density of 3.44^{+0.91}_{-0.82} g cm^{-3}. Models suggest that a planet with our measured density has a rocky core that is enveloped in an atmosphere composed of lighter elements. The star of the HD 97658 system is the second brightest known to host a transiting super-Earth, facilitating follow-up studies of this not easily daunted, warm and likely volatile-rich exoplanet.

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Title: Detection of a Transiting Low-Density Super-Earth
Authors: Gregory W. Henry, Andrew W. Howard, Geoffrey W. Marcy, Debra A. Fischer, John Asher Johnson

We present evidence for photometric transits of the low-mass planet HD 97658b across the disk of its host star, an early K dwarf. This planet was previously discovered in radial velocities (RVs) from Keck/HIRES as part of the Eta-Earth Survey. Using photometry from the Automated Photometric Telescopes at Fairborn Observatory, we detected four separate planetary egress events at times predicted from the RV orbit. We measured a transit depth of 1470 ±260 ppm, a result that should be confirmed and refined with space-based photometry. We also collected additional Keck-HIRES RV measurements that refined the transit ephemeris and planet mass. With an orbital period of 9.4957 ±0.0022 days, HD 97658b is a close-in planet that had been classified as a 'super-Earth' based on its mass of 6.4 ±0.7 earth masses. However, the planet radius of 2.93 ±0.28 earth radii implies a density of 1.40 g/cc and suggests 'sub-Neptune' status. The low density can be explained by an extended atmosphere of volatiles such as hydrogen, helium, and water. HD 97658b is similar to GJ 1214b in mass, radius, and density, although HD 97658b has a higher equilibrium temperature of 510 - 720 K. The star HD 97658 (V = 7.8, K = 5.7) is among the brightest known to host a transiting planet, which will facilitate detailed follow-up measurements.

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