Data from the newly-commissioned Transiting Exoplanet Survey Satellite (TESS) has revealed a "hot Earth" around LHS 3844, an M dwarf located 15 pc away. The planet has a radius of 1.32 ± 0.02 R ⊕ and orbits the star every 11 hours. Although the existence of an atmosphere around such a strongly irradiated planet is questionable, the star is bright enough (I = 11.9, K = 9.1) for this possibility to be investigated with transit and occultation spectroscopy. The star's brightness and the planet's short period will also facilitate the measurement of the planet's mass through Doppler spectroscopy.
Context. Lithium is extensively known to be a good tracer of non-standard mixing processes occurring in stellar interiors. Aims. We present the results of a new large Lithium survey in red giant stars and combine it with surveys from the literature to probe the impact of rotation-induced mixing and thermohaline double-diffusive instability along stellar evolution. Methods. We determined the surface Li abundance for a sample of 829 giant stars with accurate Gaia parallaxes for a large subsample (810 stars) complemented with accurate Hipparcos parallaxes (19 stars). The spectra of our sample of northern and southern giant stars were obtained in three ground-based observatories (Observatoire de Haute-Provence, ESO-La Silla, and the Mc Donald Observatory). We determined the atmospheric parameters (T eff , log(g) and [Fe/H]), and the Li abundance. We used Gaia parallaxes and photometry to determine the luminosity of our objects and we estimated the mass and evolution status of each sample star with a maximum-likelihood technique using stellar evolution models computed with the STAREVOL code. We compared the observed Li behaviour with predictions from stellar models, including rotation and thermohaline mixing. The same approach was used for stars from selected Li surveys from the literature. Results. Rotation-induced mixing accounts nicely for the lithium behaviour in stars warmer than about 4200K, independently of the mass domain. For stars with masses lower than 2M thermohaline mixing leads to further Li depletion below the T eff of the RGB bump (about 4000K), and on the early AGB, as observed. Depending on the definition we adopt, we find between 0.8 and 2.2% of Li-rich giants in our new sample. Conclusions. Gaia puts a new spin on the understanding of mixing processes in stars, and our study confirms the importance of rotation-induced processes and of thermohaline mixing. However asteroseismology is required to definitively pinpoint the actual evolution status of Li-rich giants.
Context. Since 1998, a planet-search around main sequence stars within 50 pc in the southern hemisphere has been underway with the CORALIE spectrograph at La Silla Observatory. Aims. With an observing time span of more than 20 yr, the CORALIE survey is able to detect long-term trends in data with masses and separations large enough to select ideal targets for direct imaging. Detecting these giant companion candidates will allow us to start bridging the gap between radial-velocity-detected exoplanets and directly imaged planets and brown dwarfs. Methods. Long-term precise Doppler measurements with the CORALIE spectrograph reveal radial-velocity signatures of massive planetary companions and brown dwarfs on long-period orbits. Results. In this paper, we report the discovery of new companions orbiting HD 181234, HD 13724, HD 25015, HD 92987 and HD 50499. We also report updated orbital parameters for HD 50499b, HD 92788b and HD 98649b. In addition, we confirm the recent detection of HD 92788c. The newly reported companions span a period range of 15.6–40.4 yr and a mass domain of 2.93–26.77 MJup, the latter of which straddles the nominal boundary between planets and brown dwarfs. Conclusions. We report the detection of five new companions and updated parameters of four known extrasolar planets. We identify at least some of these companions to be promising candidates for imaging and further characterisation.
We report the Transiting Exoplanet Survey Satellite (TESS) detection of a multi-planet system orbiting the V = 10.9 K0 dwarf TOI 125. We find evidence for up to five planets, with varying confidence. Three high signal-to-noise transit signals correspond to sub-Neptune-sized planets (2.76, 2.79, and 2.94 R ⊕ ), and we statistically validate the planetary nature of the two inner planets (P b = 4.65 days, P c = 9.15 days). With only two transits observed, we report the outer object (P .03 = 19.98 days) as a high signal-to-noise ratio planet candidate. We also detect a candidate transiting super-Earth (1.4 R ⊕ ) with an orbital period of only 12.7 hours and a candidate Neptune-sized planet (4.2 R ⊕ ) with a period of 13.28 days, both at low signal-to-noise. This system is amenable to mass determination via radial velocities and transit timing variations, and provides an opportunity to study planets of similar size while controlling for age and environment. The ratio of orbital periods between TOI 125 b and c (P c /P b = 1.97) is slightly smaller than an exact 2:1 commensurability and is atypical of multiple planet systems from Kepler, which show a preference for period ratios just wide of first-order period ratios. A dynamical analysis refines the allowed parameter space through stability arguments and suggests that, despite the nearly commensurate periods, the system is unlikely to be in resonance.
The Transiting Exoplanet Survey Satellite TESS has begun a new age of exoplanet discoveries around bright host stars. We present the discovery of HD 1397b (TOI-120.01), a giant planet in an 11.54-day eccentric orbit around a bright (V=7.9) G-type subgiant. We estimate both host star and planetary parameters consistently using EXOFASTv2 based on TESS time-series photometry of transits and radial velocity measurements from CORALIE and MINERVA-Australis. We also present high angular resolution imaging with NaCo to rule out any nearby eclipsing binaries. We find that HD 1397b is a Jovian planet, with a mass of 0.415±0.020 M J and a radius of 1.026 ± 0.026 R J . Characterising giant planets in short-period eccentric orbits, such as HD 1397b, is important for understanding and testing theories for the formation and migration of giant planets as well as planet-star interactions.
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