Browsing by Author "Albrecht, Simon"

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    Gaia-4b and 5b: Radial Velocity Confirmation of Gaia Astrometric Orbital Solutions Reveal a Massive Planet and a Brown Dwarf Orbiting Low-mass Stars
    (IOP Publishing Ltd, 2025) Stefansson, Gudmundur; Mahadevan, Suvrath; Winn, Joshua N.; Marcussen, Marcus L.; Kanodia, Shubham; Albrecht, Simon; Fitzmaurice, Evan; Mikulskyte, One; Canas, Caleb I.; Espinoza Retamal, Juan Ignacio; Zwart, Yiri; Krolikowski, Daniel M.; Hotnisky, Andrew; Robertson, Paul; Alvarado-Montes, Jaime A.; Bender, Chad F.; Blake, Cullen H.; Callingham, J. R.; Cochran, William D.; Delamer, Megan; Diddams, Scott A.; Dong, Jiayin; Fernandes, Rachel B.; Giovinazzi, Mark R.; Halverson, Samuel; Libby-Roberts, Jessica; Logsdon, Sarah E.; Mcelwain, Michael W.; Ninan, Joe P.; Rajagopal, Jayadev; Reji, Varghese; Roy, Arpita; Schwab, Christian; Wright, Jason T.
    Gaia astrometry of nearby stars is precise enough to detect the tiny displacements induced by substellar companions, but radial velocity (RV) data are needed for definitive confirmation. Here we present RV follow-up observations of 28 M and K stars with candidate astrometric substellar companions, which led to the confirmation of two systems, Gaia-4b and Gaia-5b, identification of five systems that are single lined but require additional data to confirm as substellar companions, and the refutation of 21 systems as stellar binaries. Gaia-4b is a massive planet (M = 11.8 +/- 0.7 MJ) in a P = 571.3 +/- 1.4 day orbit with a projected semimajor axis a0 = 0.312 +/- 0.040 mas orbiting a 0.644 +/- 0.02M circle dot star. Gaia-5b is a brown dwarf (M = 20.9 +/- 0.5MJ) in a P = 358.62 +/- 0.20 days eccentric e = 0.6423 +/- 0.0026 orbit with a projected angular semimajor axis of a0 = 0.947 +/- 0.038 mas around a 0.34 +/- 0.03M circle dot star. Gaia-4b is one of the first exoplanets discovered via the astrometric technique, and is one of the most massive planets known to orbit a low-mass star.
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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.