Dr. Astudillo-Defru, Nicola

Context. The NASA mission TESS is currently doing an all-sky survey from space to detect transiting planets around bright stars. As part of the validation process, the most promising planet candidates need to be confirmed and characterized using follow-up observations. Aims. In this article, our aim is to confirm the planetary nature of the transiting planet candidate TOI-674b using spectroscopic and photometric observations. Methods. We use TESS, Spitzer, ground-based light curves, and HARPS spectrograph radial velocity measurements to establish the physical properties of the transiting exoplanet candidate TOI-674b. We perform a joint fit of the light curves and radial velocity time series to measure the mass, radius, and orbital parameters of the candidate. Results. We confirm and characterize TOI-674b, a low-density super-Neptune transiting a nearby M dwarf. The host star (TIC 158588995, V = 14.2 mag, J = 10.3 mag) is characterized by its M2V spectral type with M⋆ = 0.420 ± 0.010 M⊙, R⋆ = 0.420 ± 0.013 R⊙, and Teff = 3514 ± 57 K; it is located at a distance d = 46.16 ± 0.03 pc. Combining the available transit light curves plus radial velocity measurements and jointly fitting a circular orbit model, we find an orbital period of 1.977143 ± 3 × 10−6 days, a planetary radius of 5.25 ± 0.17 R⊕, and a mass of 23.6 ± 3.3 M⊕ implying a mean density of ρp =0.91 ± 0.15 g cm−3. A non-circular orbit model fit delivers similar planetary mass and radius values within the uncertainties. Given the measured planetary radius and mass, TOI-674b is one of the largest and most massive super-Neptune class planets discovered around an M-type star to date. It is found in the Neptunian desert, and is a promising candidate for atmospheric characterization using the James Webb Space Telescope.

Distinguishing classes within substellar objects and understanding their formation and evolution need larger samples of substellar companions such as exoplanets, brown dwarfs, and low-mass stars. In this paper, we look for substellar companions using radial velocity surveys of FGK stars with the SOPHIE spectrograph at the Observatoire de Haute-Provence. We assign here the radial velocity variations of 27 stars to their orbital motion induced by low-mass companions. We also constrained their plane-of-the-sky motion using HIPPARCOS and Gaia Data Release 1 measurements, which constrain the true masses of some of these companions. We report the detection and characterization of six cool Jupiters, three brown dwarf candidates, and 16 low-mass stellar companions. We additionally update the orbital parameters of the low-mass star HD 8291 B, and we conclude that the radial velocity variations of HD 204277 are likely due to stellar activity despite resembling the signal of a giant planet. One of the new giant planets, BD+631405 b, adds to the population of highly eccentric cool Jupiters, and it is presently the most massive member. Two of the cool Jupiter systems also exhibit signatures of an additional outer companion. The orbital periods of the new companions span 30 days to 11.5 yr, their masses 0.72 MJ–0.61 M, and their eccentricities 0.04–0.88. These discoveries probe the diversity of substellar objects and low-mass stars, which will help constrain the models of their formation and evolution.

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 RE and a mass of either14.4 ± 1.6 ME or 15.9 ± 1.6 ME 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+0.8−0.7 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 < RE < 4) population. The most likely scenario is that this planet has migrated to its current position.

We present a new algorithm for precision radial velocity (pRV) measurements, a line-by-line (LBL) approach designed to handle outlying spectral information in a simple but efficient manner. The effectiveness of the LBL method is demonstrated on two data sets, one obtained with SPIRou on Barnard’s star, and the other with the High Accuracy Radial velocity Planet Searcher (HARPS) on Proxima Centauri. In the near-infrared, the LBL provides a framework for meters-per-second-level accuracy in pRV measurements despite the challenges associated with telluric absorption and sky emission lines. We confirm with SPIRou measurements spanning 2.7 yr that the candidate super-Earth on a 233 day orbit around Barnard’s star is an artifact due to a combination of time sampling and activity. The LBL analysis of the Proxima Centauri HARPS post-upgrade data alone easily recovers the Proxima b signal and also provides a 2σ detection of the recently confirmed 5 day Proxima d planet, but argues against the presence of the candidate Proximac with a period of 1900 days. We provide evidence that the Proxima c signal is associated with small, unaccounted systematic effects affecting the HARPS-TERRA templatematching radial velocity extraction method for long-period signals. Finally, the LBL framework provides a very 92.1 3.5+ 4.2 effective activity indicator, akin to the FWHM derived from the cross-correlation function, from which we infer a rotation period of days for Proxima.

WASP-121 b is a hot Jupiter that was recently found to possess rich emission (day side) and transmission (limb) spectra, suggestive of the presence of a multitude of chemical species in the atmosphere. Aims. We survey the transmission spectrum of WASP-121 b for line-absorption by metals and molecules at high spectral resolution and elaborate on existing interpretations of the optical transmission spectrum observed with the Hubble Space Telescope (HST). Methods. We applied the cross-correlation technique and direct differential spectroscopy to search for sodium and other neutral and ionised atoms, TiO, VO, and SH in high-resolution transit spectra obtained with the HARPS spectrograph. We injected models assuming chemical and hydrostatic equilibrium with a varying temperature and composition to enable model comparison, and employed two bootstrap methods to test the robustness of our detections. Results. We detect neutral Mg, Na, Ca, Cr, Fe, Ni, and V, which we predict exists in equilibrium with a significant quantity of VO, supporting earlier observations by HST/WFC3. Non-detections of Ti and TiO support the hypothesis that Ti is depleted via a cold-trap mechanism, as has been proposed in the literature. Atomic line depths are under-predicted by hydrostatic models by a factor of 1.5 to 8, confirming recent findings that the atmosphere is extended. We predict the existence of significant concentrations of gas-phase TiO2, VO2, and TiS, which could be important absorbers at optical and near-IR wavelengths in hot Jupiter atmospheres. However, accurate line-list data are not currently available for them. We find no evidence for absorption by SH and find that inflated atomic lines can plausibly explain the slope of the transmission spectrum observed in the near-ultraviolet with HST. The Na I D lines are significantly broadened (FWHM ~50 to 70 km s−1) and show a difference in their respective depths of ~15 scale heights, which is not expected from isothermal hydrostatic theory. If this asymmetry is of astrophysical origin, it may indicate that Na I forms an optically thin envelope, reminiscent of the Na I cloud surrounding Jupiter, or that it is hydrodynamically outflowing.

Context. The HEARTS survey aims to probe the upper layers of the atmosphere by detecting resolved sodium doublet lines, a tracer of the temperature gradient, and atmospheric winds. KELT-10b, one of the targets of HEARTS, is a hot-inflated Jupiter with 1.4 RJup and 0.7 MJup. Recently, there was a report of sodium absorption in the atmosphere of KELT-10b (0.66% ± 0.09% (D2) and 0.43% ± 0.09% (D1); VLT/UVES data from single transit). Aims. We searched for potential atmospheric species in KELT-10b, focusing on sodium doublet lines (Na I; 589 nm) and the Balmer alpha line (H α; 656 nm) in the transmission spectrum. Furthermore, we measured the planet-orbital alignment with the spin of its host star. Methods. We used the Rossiter–McLaughlin Revolutions technique to analyze the local stellar lines occulted by the planet during its transit. We used the standard transmission spectroscopy method to probe the planetary atmosphere, including the correction for telluric lines and the Rossiter–McLaughlin effect on the spectra. We analyzed two new light curves jointly with the public photometry observations. Results. We do not detect signals in the Na I and H α lines within the uncertainty of our measurements. We derive the 3σ upper limit of excess absorption due to the planetary atmosphere corresponding to equivalent height Rp to 1.8Rp (Na I) and 1.9Rp (H α). The analysis of the Rossiter–McLaughlin effect yields the sky-projected spin-orbit angle of the system λ = −5.2 ± 3.4◦ and the stellar projected equatorial velocity veq sin i⋆ = 2.58 ± 0.12 km s−1. Photometry results are compatible within 1σ with previous studies. Conclusions. We found no evidence of Na I and H α, within the precision of our data, in the atmosphere of KELT-10b. Our detection limits allow us to rule out the presence of neutral sodium or excited hydrogen in an escaping extended atmosphere around KELT-10b. We cannot confirm the previous detection of Na I at lower altitudes with VLT/UVES. We note, however, that the Rossiter–McLaughlin effect impacts the transmission spectrum on a smaller scale than the previous detection with UVES. Analysis of the planet-occulted stellar lines shows the sky-projected alignment of the system, which is likely truly aligned due to tidal interactions of the planet with its cool (Teff < 6250 K) host star.

We present the confirmation and characterisation of GJ 3473 b (G 50–16, TOI-488.01), a hot Earth-sized planet orbiting an M4 dwarf star, whose transiting signal (P = 1.198 003 5 ± 0.000 001 8 d) was first detected by the Transiting Exoplanet Survey Satellite (TESS). Through a joint modelling of follow-up radial velocity observations with CARMENES, IRD, and HARPS together with extensive ground-based photometric follow-up observations with LCOGT, MuSCAT, and MuSCAT2, we determined a precise planetary mass, Mb = 1.86 ± 0.30 M⊕, and radius, Rb = 1.264 ± 0.050 R⊕. Additionally, we report the discovery of a second, temperate, non-transiting planet in the system, GJ 3473 c, which has a minimum mass, Mc sin i = 7.41 ± 0.91 M⊕, and orbital period, Pc = 15.509 ± 0.033 d. The inner planet of the system, GJ 3473 b, is one of the hottest transiting Earth-sized planets known thus far, accompanied by a dynamical mass measurement, which makes it a particularly attractive target for thermal emission spectroscopy.

We present the Transiting Exoplanet Survey Satellite (TESS) discovery of the LHS 1678 (TOI-696) exoplanet system, comprised of two approximately Earth-sized transiting planets and a likely astrometric brown dwarf orbiting a bright (V J = 12.5, K s = 8.3) M2 dwarf at 19.9 pc. The two TESS-detected planets are of radius 0.70 ± 0.04 R ⊕ and 0.98 ± 0.06 R ⊕ in 0.86 day and 3.69 day orbits, respectively. Both planets are validated and characterized via ground-based follow-up observations. High Accuracy Radial Velocity Planet Searcher RV monitoring yields 97.7 percentile mass upper limits of 0.35 M ⊕ and 1.4 M ⊕ for planets b and c, respectively. The astrometric companion detected by the Cerro Tololo Inter-American Observatory/Small and Moderate Aperture Telescope System 0.9 m has an orbital period on the order of decades and is undetected by other means. Additional ground-based observations constrain the companion to being a high-mass brown dwarf or smaller. Each planet is of unique interest; the inner planet has an ultra-short period, and the outer planet is in the Venus zone. Both are promising targets for atmospheric characterization with the James Webb Space Telescope and mass measurements via extreme-precision radial velocity. A third planet candidate of radius 0.9 ± 0.1 R ⊕ in a 4.97 day orbit is also identified in multicycle TESS data for validation in future work. The host star is associated with an observed gap in the lower main sequence of the Hertzsprung-Russell diagram. This gap is tied to the transition from partially to fully convective interiors in M dwarfs, and the effect of the associated stellar astrophysics on exoplanet evolution is currently unknown. The culmination of these system properties makes LHS 1678 a unique, compelling playground for comparative exoplanet science and understanding the formation and evolution of small, short-period exoplanets orbiting low-mass stars. © 2022. The Author(s). Published by the American Astronomical Society.

Context. Small planets located at the lower mode of the bimodal radius distribution are generally assumed to be composed of iron and silicates in a proportion similar to that of the Earth. However, recent discoveries are revealing a new group of low-density planets that are inconsistent with that description. Aims. We intend to confirm and characterize the TESS planet candidate TOI-244.01, which orbits the bright (K = 7.97 mag), nearby (d = 22 pc), and early-type (M2.5 V) M-dwarf star GJ 1018 with an orbital period of 7.4 days. Methods. We used Markov chain Monte Carlo methods to model 57 precise radial velocity measurements acquired by the ESPRESSO spectrograph together with TESS photometry and complementary HARPS data. Our model includes a planetary component and Gaussian processes aimed at modeling the correlated stellar and instrumental noise. Results. We find TOI-244 b to be a super-Earth with a radius of Rp = 1.52 ± 0.12 R⊕ and a mass of Mp = 2.68 ± 0.30 M⊕. These values correspond to a density of ρ = 4.2 ± 1.1 g cm−3, which is below what would be expected for an Earth-like composition. We find that atmospheric loss processes may have been efficient to remove a potential primordial hydrogen envelope, but high mean molecular weight volatiles such as water could have been retained. Our internal structure modeling suggests that TOI-244 b has a 479+128 −96 km thick hydrosphere over a 1.17 ± 0.09 R⊕ solid structure composed of a Fe-rich core and a silicate-dominated mantle compatible with that of the Earth. On a population level, we find two tentative trends in the density-metallicity and density-insolation parameter space for the low-density super-Earths, which may hint at their composition. Conclusions. With a 8% precision in radius and 12% precision in mass, TOI-244 b is among the most precisely characterized super-Earths, which, together with the likely presence of an extended hydrosphere, makes it a key target for atmospheric observations

K2-18 b is a transiting mini-Neptune that orbits a nearby (38 pc), cool M3 dwarf and is located inside its region of temperate irradiation. We report on the search for hydrogen escape from the atmosphere K2-18 b using Lyman-α transit spectroscopy with the Space Telescope Imaging Spectrograph instrument installed on the Hubble Space Telescope. We analyzed the time-series of fluxes of the stellar Lyman-α emission of K2-18 in both its blue- and redshifted wings. We found that the average blueshifted emission of K2-18 decreases by 67% ± 18% during the transit of the planet compared to the pre-transit emission, tentatively indicating the presence of H atoms escaping vigorously and being blown away by radiation pressure. This interpretation is not definitive because it relies on one partial transit. Based on the reconstructed Lyman-α emission of K2-18, we estimate an EUV irradiation in the range 101 − 102 erg s−1 cm−2 and a total escape rate on the order of 108 g s−1. The inferred escape rate suggests that the planet will lose only a small fraction (< 1%) of its mass and retain its volatile-rich atmosphere during its lifetime. More observations are needed to rule out stellar variability effects, confirm the in-transit absorption, and better assess the atmospheric escape and high-energy environment of K2-18 b.