Browsing by Author "Demangeon, O. D. S."

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    HD 207897 b: A dense sub-Neptune transiting a nearby and bright K-type star
    (2022) Heidari, N.; Boisse, I; Orell-Miquel, J.; Hebrard, G.; Acuna, L.; Hara, N. C.; Lillo-Box, J.; Eastman, J. D.; Arnold, L.; Astudillo-Defru, N.; Adibekyan, V; Bieryla, A.; Bonfils, X.; Bouchy, F.; Barclay, T.; Brasseur, C. E.; Borgniet, S.; Bourrier, V; Buchhave, L.; Behmard, A.; Beard, C.; Batalha, N. M.; Courcol, B.; Cortes-Zuleta, P.; Collins, K.; Carmona, A.; Crossfield, I. J. M.; Chontos, A.; Delfosse, X.; Dalal, S.; Deleuil, M.; Demangeon, O. D. S.; Diaz, R. F.; Dumusque, X.; Daylan, T.; Dragomir, D.; Mena, E. Delgado; Dressing, C.; Dai, F.; Dalba, P. A.; Ehrenreich, D.; Forveille, T.; Fulton, B.; Fetherolf, T.; Gaisne, G.; Giacalone, S.; Riazi, N.; Hoyer, S.; Hobson, M. J.; Howard, A. W.; Huber, D.; Hill, M. L.; Hirsch, L. A.; Isaacson, H.; Jenkins, J.; Kane, S. R.; Kiefer, F.; Luque, R.; Latham, D. W.; Lubin, J.; Lopez, T.; Mousis, O.; Moutou, C.; Montagnier, G.; Mignon, L.; Mayo, A.; Mocnik, T.; Murphy, J. M. A.; Palle, E.; Pepe, F.; Petigura, E. A.; Rey, J.; Ricker, G.; Robertson, P.; Roy, A.; Rubenzahl, R. A.; Rosenthal, L. J.; Santerne, A.; Santos, N. C.; Sousa, S. G.; Stassun, K. G.; Stalport, M.; Scarsdale, N.; Strom, P. A.; Seager, S.; Segransan, D.; Tenenbaum, P.; Tronsgaard, R.; Udry, S.; Vanderspek, R.; Vakili, F.; Winn, J.; Weiss, L. M.
    We present the discovery and characterization of a transiting sub-Neptune that orbits the nearby (28 pc) and bright (V = 8.37) K0V star HD 207897 (TOI-1611) with a 16.20-day period. This discovery is based on photometric measurements from the Transiting Exoplanet Survey Satellite mission and radial velocity (RV) observations from the SOPHIE, Automated Planet Finder, and HIRES high-precision spectrographs. We used EXOFASTv2 to model the parameters of the planet and its host star simultaneously, combining photometric and RV data to determine the planetary system parameters. We show that the planet has a radius of 2.50 +/- 0.08 R-E and a mass of either 14.4 +/- 1.6 M-E or 15.9 +/- 1.6 M-E with nearly equal probability. The two solutions correspond to two possibilities for the stellar activity period. The density accordingly is either 5.1 +/- 0.7 g cm(-3) or 5.5(-0.7)(+0.8) g cm(-3), making it one of the relatively rare dense sub-Neptunes. The existence of this dense planet at only 0.12 AU from its host star is unusual in the currently observed sub-Neptune (2 < R-E < 4) population. The most likely scenario is that this planet has migrated to its current position.
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    The EBLM project - VIII. First results for M-dwarf mass, radius, and effective temperature measurements using CHEOPS light curves
    (2021) Swayne, M., I; Maxted, P. F. L.; Triaud, A. H. M. J.; Sousa, S. G.; Broeg, C.; Floren, H-G; Guterman, P.; Simon, A. E.; Boisse, I; Bonfanti, A.; Martin, D.; Santerne, A.; Salmon, S.; Standing, M. R.; Van Grootel, V.; Wilson, T. G.; Alibert, Y.; Alonso, R.; Anglada Escude, G.; Asquier, J.; Barczy, T.; Barrado, D.; Barros, S. C. C.; Battley, M.; Baumjohann, W.; Beck, M.; Beck, T.; Bekkelien, A.; Benz, W.; Billot, N.; Bonfils, X.; Brandeker, A.; Busch, M-D; Cabrera, J.; Charnoz, S.; Cameron, A. Collier; Csizmadia, Sz; Davies, M. B.; Deleuil, M.; Deline, A.; Delrez, L.; Demangeon, O. D. S.; Demory, B-O; Dransfield, G.; Ehrenreich, D.; Erikson, A.; Fortier, A.; Fossati, L.; Fridlund, M.; Futyan, D.; Gandolfi, D.; Gillon, M.; Guedel, M.; Hebrard, G.; Heidari, N.; Hellier, C.; Heng, K.; Hobson, M.; Hoyer, S.; Isaak, K. G.; Kiss, L.; Hodzic, V. Kunovac; Lalitha, S.; Laskar, J.; des Etangs, A. Lecavelier; Lendl, M.; Lovis, C.; Magrin, D.; Marafatto, L.; McCormac, J.; Miller, N.; Nascimbeni, V; Olofsson, G.; Ottensamer, R.; Pagano, I; Palle, E.; Peter, G.; Piotto, G.; Pollacco, D.; Queloz, D.; Ragazzoni, R.; Rando, N.; Rauer, H.; Ribas, I; Santos, N. C.; Scandariato, G.; Segransan, D.; Smith, A. M. S.; Steinberger, M.; Steller, M.; Szabo, Gy M.; Thomas, N.; Udry, S.; Walter, I; Walton, N. A.; Willett, E.
    The accuracy of theoretical mass, radius, and effective temperature values for M-dwarf stars is an active topic of debate. Differences between observed and theoretical values have raised the possibility that current theoretical stellar structure and evolution models are inaccurate towards the low-mass end of the main sequence. To explore this issue, we use the CHEOPS satellite to obtain high-precision light curves of eclipsing binaries with low-mass stellar companions. We use these light curves combined with the spectroscopic orbit for the solar-type companion to measure the mass, radius, and effective temperature of the M-dwarf star. Here, we present the analysis of three eclipsing binaries. We use the pycheops data analysis software to fit the observed transit and eclipse events of each system. Two of our systems were also observed by the TESS satellite - we similarly analyse these light curves for comparison. We find consistent results between CHEOPS and TESS, presenting three stellar radii and two stellar effective temperature values of low-mass stellar objects. These initial results from our on-going observing programme with CHEOPS show that we can expect to have similar to 24 new mass, radius, and effective temperature measurements for very low-mass stars within the next few years.
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    The SOPHIE search for northern extrasolar planets XVIII. Six new cold Jupiters, including one of the most eccentric exoplanet orbits
    (2021) Demangeon, O. D. S.; Dalal, S.; Hebrard, G.; Nsamba, B.; Kiefer, F.; Camacho, J. D.; Sahlmann, J.; Arnold, L.; Astudillo-Defru, N.; Bonfils, X.; Boisse, I; Bouchy, F.; Bourrier, V; Campante, T.; Delfosse, X.; Deleuil, M.; Diaz, R. F.; Faria, J.; Forveille, T.; Hara, N.; Heidari, N.; Hobson, M. J.; Lopez, T.; Moutou, C.; Rey, J.; Santerne, A.; Sousa, S.; Santos, N. C.; Strom, P. A.; Tsantaki, M.; Udry, S.
    Context. Due to their low transit probability, the long-period planets are, as a population, only partially probed by transit surveys. Radial velocity surveys thus have a key role to play, in particular for giant planets. Cold Jupiters induce a typical radial velocity semi-amplitude of 10 m s(-1), which is well within the reach of multiple instruments that have now been in operation for more than a decade.