Browsing by Author "Parviainen, H."

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    Lower-than-expected flare temperatures for TRAPPIST-1
    (Les Ulis : EDP Sciences, 2022) Maas, A.J.; Ilin, E.; Oshagh, M.; Pallé, E.; Parviainen, H.; Molaverdikhani, K.; Quirrenbach, A.; Esparza-Borges, E.; Murgas, F.; Béjar, V.J.S.; Narita, N.; Fukui, A.; Lin, C.-L.; Mori, M.; Klagyivik, P.
    Aims. Stellar flares emit thermal and nonthermal radiation in the X-ray and ultraviolet (UV) regime. Although high energetic radiation from flares is a potential threat to exoplanet atmospheres and may lead to surface sterilization, it might also provide the extra energy for low-mass stars needed to trigger and sustain prebiotic chemistry. Despite the UV continuum emission being constrained partly by the flare temperature, few efforts have been made to determine the flare temperature for ultra-cool M-dwarfs. We investigate two flares on TRAPPIST-1, an ultra-cool dwarf star that hosts seven exoplanets of which three lie within its habitable zone. The flares are detected in all four passbands of the MuSCAT2 instrument allowing a determination of their temperatures and bolometric energies. Methods. We analyzed the light curves of the MuSCATl (multicolor simultaneous camera for studying atmospheres of transiting exoplanets) and MuSCAT2 instruments obtained between 2016 and 2021 in g, r, i, zs-filters. We conducted an automated flare search and visually confirmed possible flare events. The black body temperatures were inferred directly from the spectral energy distribution (SED) by extrapolating the filter-specific flux. We studied the temperature evolution, the global temperature, and the peak temperature of both flares. Results. White-light M-dwarf flares are frequently described in the literature by a black body with a temperature of 9000- 10 000 K. For the first time we infer effective black body temperatures of flares that occurred on TRAPPIST-1. The black body temperatures for the two TRAPPIST-1 flares derived from the SED are consistent with TSED = 7940- 390+430 K and TSED = 6030- 270+300 K. The flare black body temperatures at the peak are also calculated from the peak SED yielding TSEDp = 13 620- 1220+1520 K and TSEDp = 8290- 550+660 K. We update the flare frequency distribution of TRAPPIST-1 and discuss the impacts of lower black body temperatures on exoplanet habitability. Conclusions. We show that for the ultra-cool M-dwarf TRAPPIST-1 the flare black body temperatures associated with the total continuum emission are lower and not consistent with the usually adopted assumption of 9000- 10 000 K in the context of exoplanet research. For the peak emission, both flares seem to be consistent with the typical range from 9000 to 14 000 K, respectively. This could imply different and faster cooling mechanisms. Further multi-color observations are needed to investigate whether or not our observations are a general characteristic of ultra-cool M-dwarfs. This would have significant implications for the habitability of exoplanets around these stars because the UV surface flux is likely to be overestimated by the models with higher flare temperatures.
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    Planets, candidates, and binaries from the CoRoT/Exoplanet programme: The CoRoT transit catalogue
    (Les Ulis : EDP Sciences, 2018) Deleuil, M.; Aigrain, S.; Moutou, C.; Cabrera, J.; Bouchy, F.; Deeg, H. J.; Almenara, J.-M.; Hébrard, G.; Santerne, A.; Alonso, R.; Bonomo, A.S.; Bordé, P.; Csizmadia, S.; Dìaz, R.F.; Erikson, A.; Fridlund, M.; Gandolfi, D.; Guenther, E.; Guillot, T.; Guterman, P.; Grziwa, S.; Hatzes, A.; Léger, A.; Mazeh, T.; Ofir, A.; Ollivier, M.; Pätzold, M.; Parviainen, H.; Rauer, H.; Rouan, D.; Schneider, J.; Titz-Weider, R.; Tingley, B.; Weingrill, J.
    The CoRoT space mission observed 163 665 stars over 26 stellar fields in the faint star channel. The exoplanet teams detected a total of 4123 transit-like features in the 177 454 light curves. We present the complete re-analysis of all these detections carried out with the same softwares so that to ensure their homogeneous analysis. Although the vetting process involves some human evaluation, it also involves a simple binary flag system over basic tests: Detection significance, presence of a secondary, difference between odd and even depths, colour dependence, V-shape transit, and duration of the transit. We also gathered the information from the large accompanying ground-based programme carried out on the planet candidates and checked how useful the flag system could have been at the vetting stage of the candidates. From the initial list of transit-like features, we identified and separated 824 false alarms of various kind, 2269 eclipsing binaries among which 616 are contact binaries and 1653 are detached ones, 37 planets and brown dwarfs, and 557 planet candidates. We provide the catalogue of all these transit-like features, including false alarms. For the planet candidates, the catalogue gives not only their transit parameters but also the products of their light curve modelling: Reduced radius, reduced semi-major axis, and impact parameter, together with a summary of the outcome of follow-up observations when carried out and their current status. For the detached eclipsing binaries, the catalogue provides, in addition to their transit parameters, a simple visual classification. Among the planet candidates whose nature remains unresolved, we estimate that eight (within an error of three) planets are still to be identified. After correcting for geometric and sensitivity biases, we derived planet and brown dwarf occurrences and confirm disagreements with Kepler estimates, as previously reported by other authors from the analysis of the first runs: Small-size planets with orbital period less than ten days are underabundant by a factor of three in the CoRoT fields whereas giant planets are overabundant by a factor of two. These preliminary results would however deserve further investigations using the recently released CoRoT light curves that are corrected of the various instrumental effects and a homogeneous analysis of the stellar populations observed by the two missions.