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 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.

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. Aims. We take advantage of the ongoing radial velocity survey with the SOPHIEhigh-resolution spectrograph, which continues the search started by its predecessor ELODIEto further characterize the cold Jupiter population.Methods.Analyzing the radial velocity data from six bright solar-like stars taken over a period of up to 15 yr, we attempt the detection and confirmation of Keplerian signals. Results. We announce the discovery of six planets, one per system, with minimum masses in the range 4.8–8.3Mjupand orbital periods between 200 days and 10 yr. The data do not provide enough evidence to support the presence of additional planets in any of these systems. The analysis of stellar activity indicators confirms the planetary nature of the detected signals. Conclusions. These six planets belong to the cold and massive Jupiter population, and four of them populate its eccentric tail. In this respect, HD 80869 b stands out as having one of the most eccentric orbits, with an eccentricity of 0.862−0.018+0.028. These planets can thus help to better constrain the migration and evolution processes at play in the gas giant population. Furthermore, recent works presenting the correlation between small planets and cold Jupiters indicate that these systems are good candidates to search for small inner planets.

The Transiting Exoplanet Survey Satellite mission identified a deep and asymmetric transit-like signal with a periodicity of 4.5 days orbiting the M4 dwarf star TOI-3884. The signal has been confirmed by follow-up observations collected by the ExTrA facility and Las Cumbres Observatory Global Telescope, which reveal that the transit is chromatic. The light curves are well modelled by a host star having a large polar spot transited by a 6-RE planet. We validate the planet with seeing-limited photometry, high-resolution imaging, and radial velocities. TOI-3884 b, with a radius of 6.00 ± 0.18 RE, is the first sub-Saturn planet transiting a mid-M dwarf. Owing to the host star’s brightness and small size, it has one of the largest transmission spectroscopy metrics for this planet size and becomes a top target for atmospheric characterisation with the James Webb Space Telescope and ground-based telescopes.

Context. M dwarfs are active stars that exhibit variability in chromospheric emission and photometry at short and long timescales, including long cycles that are related to dynamo processes. This activity also impacts the search for exoplanets because it affects the radial velocities. Aims. We analysed a large sample of 177 M dwarfs observed with HARPS during the period 2003–2020 in order to characterise the long-term variability of these stars. We compared the variability obtained in three chromospheric activity indices (Ca II H & K, the Na D doublet, and Hα) and with ASAS photometry. Methods. We focused on the detailed analysis of the chromospheric emission based on linear, quadratic, and sinusoidal models. We used various tools to estimate the significance of the variability and to quantify the improvement brought by the models. In addition, we analysed complementary photometric time series for the most variable stars to be able to provide a broader view of the long-term variability in M dwarfs. Results. We find that most stars are significantly variable, even the quietest stars. Most stars in our sample (75%) exhibit a long-term variability, which manifests itself mostly through linear or quadratic variability, although the true behaviour may be more complex. We found significant variability with estimated timescales for 24 stars, and estimated the lower limit for a possible cycle period for an additional 9 stars that were not previously published. We found evidence of complex variability because more than one long-term timescale may be present for at least 12 stars, together with significant differences between the behaviour of the three activity indices. This complexity may also be the source of the discrepancies observed between previous publications. Conclusions. We conclude that long-term variability is present for all spectral types and activity level in M dwarfs, without a significant trend with spectral type or mean activity level.

We report the detection of a transiting super-Earth-sized planet (R = 1.39 ± 0.09 R⊕) in a 1.4-day orbit around L 168-9 (TOI-134), a bright M1V dwarf (V = 11, K = 7.1) located at 25.15 ± 0.02 pc. The host star was observed in the first sector of the Transiting Exoplanet Survey Satellite (TESS) mission. For confirmation and planet mass measurement purposes, this was followed up with ground-based photometry, seeing-limited and high-resolution imaging, and precise radial velocity (PRV) observations using the HARPS and Magellan/PFS spectrographs. By combining the TESS data and PRV observations, we find the mass of L 168-9 b to be 4.60 ± 0.56 M⊕ and thus the bulk density to be 1.74−0.33+0.44 times higher than that of the Earth. The orbital eccentricity is smaller than 0.21 (95% confidence). This planet is a level one candidate for the TESS mission’s scientific objective of measuring the masses of 50 small planets, and it is one of the most observationally accessible terrestrial planets for future atmospheric characterization.

Aims. Since 2011, the SOPHIE spectrograph has been used to search for Neptunes and super-Earths in the northern hemisphere. As part of this observational program, 290 radial velocity measurements of the 6.4 V magnitude star HD 158259 were obtained. Additionally, TESS photometric measurements of this target are available. We present an analysis of the SOPHIE data and compare our results with the output of the TESS pipeline. Methods. The radial velocity data, ancillary spectroscopic indices, and ground-based photometric measurements were analyzed with classical and ℓ1 periodograms. The stellar activity was modeled as a correlated Gaussian noise and its impact on the planet detection was measured with a new technique. Results. The SOPHIE data support the detection of five planets, each with m sin i ≈ 6 M⊕, orbiting HD 158259 in 3.4, 5.2, 7.9, 12, and 17.4 days. Though a planetary origin is strongly favored, the 17.4 d signal is classified as a planet candidate due to a slightly lower statistical significance and to its proximity to the expected stellar rotation period. The data also present low frequency variations, most likely originating from a magnetic cycle and instrument systematics. Furthermore, the TESS pipeline reports a significant signal at 2.17 days corresponding to a planet of radius ≈1.2 R⊕. A compatible signal is seen in the radial velocities, which confirms the detection of an additional planet and yields a ≈2 M⊕ mass estimate. Conclusions. We find a system of five planets and a strong candidate near a 3:2 mean motion resonance chain orbiting HD 158259. The planets are found to be outside of the two and three body resonances.

We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf (d = 22 pc, M⋆ = 0.39 M⊙, R⋆ = 0.38 R⊙), which hosts three transiting planets that were recently discovered using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.2, 2.4, and 2.1 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 days. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be 1.58 ± 0.26, 6.15 ± 0.37, and 4.78 ± 0.43 M⊕, respectively. The combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of Earth, while the outer two planets have lower densities. Thus, the inner planet and the outer planets are on opposite sides of the ‘radius valley’ — a region in the radius-period diagram with relatively few members, which has been interpreted as a consequence of atmospheric photo-evaporation. We place these findings into the context of other small close-in planets orbiting M dwarf stars, and use support vector machines to determine the location and slope of the M dwarf (Teff < 4000 K) radius valley as a function of orbital period. We compare the location of the M dwarf radius valley to the radius valley observed for FGK stars, and find that its location is a good match to photo-evaporation and core-powered mass loss models. Finally, we show that planets below the M dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a H-He atmosphere.

We report the discovery of two planetary systems, namely G 264–012, an M 4.0 dwarf with two terrestrial planets (Mb sin i=2.50−0.30+0.29 M⊕ and Mc sin i=3.75−0.47+0.48 M⊕), and Gl 393, a bright M 2.0 dwarf with one terrestrial planet (Mb sini = 1.71 ± 0.24M⊕). Although both stars were proposed to belong to young stellar kinematic groups, we estimate their ages to be older than about 700 Ma. The two planets around G 264–012 were discovered using only radial-velocity (RV) data from the CARMENES exoplanet survey, with estimated orbital periods of 2.30 d and 8.05 d, respectively.Photometric monitoring and analysis of activity indicators reveal a third signal present in the RV measurements, at about 100 d,caused by stellar rotation. The planet Gl 393 b was discovered in the RV data from the HARPS, CARMENES, and HIRES instruments. Its identification was only possible after modelling, with a Gaussian process (GP), the variability produced by the magnetic activity of the star. For the earliest observations, this variability produced a forest of peaks in the periodogram of the RVs at around the 34 d rotation period determined from Kepler data, which disappeared in the latestepochs. After correcting for them with this GP model, a significant signal showed at a period of 7.03 d. No significant signals in any of our spectral activity indicators or contemporaneous photometry were found at any of the planetary periods. Given the orbital and stellar properties, the equilibrium temperatures of the three planets are all higher than that for Earth. Current planet formation theories suggest that these two systems represent a common type of architecture. This is consistent with formation following the core accretion paradigm.