Browsing by Author "Hirano, Teruyuki"

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    K2-280 b - a low density warm sub-Saturn around a mildly evolved star
    (2020) Nowak, Grzegorz; Palle, Enric; Gandolfi, Davide; Deeg, Hans J.; Hirano, Teruyuki; Barragan, Oscar; Kuzuhara, Masayuki; Dai, Fei; Luque, Rafael; Persson, Carina M.; Fridlund, Malcolm; Johnson, Marshall C.; Korth, Judith; Livingston, John H.; Grziwa, Sascha; Mathur, Savita; Hatzes, Artie P.; Prieto-Arranz, Jorge; Nespral, David; Hidalgo, Diego; Hjorth, Maria; Albrecht, Simon; Van Eylen, Vincent; Lam, Kristine W. F.; Cochran, William D.; Esposito, Massimiliano; Csizmadia, Szilard; Guenther, Eike W.; Kabath, Petr; Blay, Pere; Brahm, Rafael; Jordan, Andres; Espinoza, Nestor; Rojas, Felipe; Casasayas Barris, Nuria; Rodler, Florian; Alonso Sobrino, Roi; Cabrera, Juan; Carleo, Ilaria; Chaushev, Alexander; de Leon, Jerome; Eigmueller, Philipp; Endl, Michael; Erikson, Anders; Fukui, Akihiko; Georgieva, Iskra; Gonzalez-Cuesta, Lucia; Knudstrup, Emil; Lund, Mikkel N.; Montanes Rodriguez, Pilar; Murgas, Felipe; Narita, Norio; Niraula, Prajwal; Paetzold, Martin; Rauer, Heike; Redfield, Seth; Ribas, Ignasi; Skarka, Marek; Smith, Alexis M. S.; Subjak, Jano
    We present an independent discovery and detailed characterization of K2-280 b, a transiting low density warm sub-Saturn in a 19.9-d moderately eccentric orbit (e = 0.35(-0.04)(+0.05)) from K2 campaign 7. A joint analysis of high precision HARPS, HARPS-N, and FIES radial velocity measurements and K2 photometric data indicates that K2-280 b has a radius of R-b = 7.50 +/- 0.44 R-circle plus and a mass of M-b = 37.1 +/- 5.6 M-circle plus, yielding a mean density of rho(b) = 0.48(-0.10)(+0.13) g cm(-3). The host star is a mildly evolved G7 star with an effective temperature of T-eff = 5500 +/- 100 K, a surface gravity of log g(star) = 4.21 +/- 0.05 (cgs), and an iron abundance of [Fe/H] = 0.33 +/- 0.08 dex, and with an inferred mass of M-star = 1.03 +/- 0.03 M-circle dot and a radius of R-star = 1.28 +/- 0.07 R-circle dot. We discuss the importance of K2-280 b for testing formation scenarios of sub-Saturn planets and the current sample of this intriguing group of planets that are absent in the Solar system.
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    The Warm Neptune GJ 3470b Has a Polar Orbit
    (2022) Stefansson, Gudmundur; Mahadevan, Suvrath; Petrovich, Cristobal; Winn, Joshua N.; Kanodia, Shubham; Millholland, Sarah C.; Maney, Marissa; Canas, Caleb, I; Wisniewski, John; Robertson, Paul; Ninan, Joe P.; Ford, Eric B.; Bender, Chad F.; Blake, Cullen H.; Cegla, Heather; Cochran, William D.; Diddams, Scott A.; Dong, Jiayin; Endl, Michael; Fredrick, Connor; Halverson, Samuel; Hearty, Fred; Hebb, Leslie; Hirano, Teruyuki; Lin, Andrea S. J.; Logsdon, Sarah E.; Lubar, Emily; McElwain, Michael W.; Metcalf, Andrew J.; Monson, Andrew; Rajagopal, Jayadev; Ramsey, Lawrence W.; Roy, Arpita; Schwab, Christian; Schweiker, Heidi; Terrien, Ryan C.; Wright, Jason T.
    The warm Neptune GJ 3470b transits a nearby (d = 29 pc) bright slowly rotating M1.5-dwarf star. Using spectroscopic observations during two transits with the newly commissioned NEID spectrometer on the WIYN 3.5 m Telescope at Kitt Peak Observatory, we model the classical Rossiter-McLaughlin effect, yielding a sky-projected obliquity of lambda = 98(-12)(+15)degrees and a v sin i = 0.85(-033)(+0.27) km s(-1). Leveraging information about the rotation period and size of the host star, our analysis yields a true obliquity of psi = 95(-8)(+9)degrees, revealing that GJ 3470b is on a polar orbit. Using radial velocities from HIRES, HARPS, and the Habitable-zone Planet Finder, we show that the data are compatible with a long-term radial velocity (RV) slope of gamma = -0.0022 +/- 0.0011 m s(-1) day(-1) over a baseline of 12.9 yr. If the RV slope is due to acceleration from another companion in the system, we show that such a companion is capable of explaining the polar and mildly eccentric orbit of GJ 3470b using two different secular excitation models. The existence of an outer companion can be further constrained with additional RV observations, Gaia astrometry, and future high-contrast imaging observations. Lastly, we show that tidal heating from GJ 3470b's mild eccentricity has most likely inflated the radius of GJ 3470b by a factor of similar to 1.5-1.7, which could help account for its evaporating atmosphere.