Dr. Astudillo-Defru, Nicola

2020, Hara, N. C., Bouchy, F., Stalport, M., Boisse, I., Rodrigues, J., Delisle, J.-B., Santerne, A., Henry, G. W., Arnold, L., Astudillo-Defru, Nicola, Borgniet, S., Bonfils, X., Bourrier, V., Brugger, B., Courcol, B., Dalal, S., Deleuil, M., Delfosse, X., Demangeon, O., Díaz, R. F., Dumusque, X., Forveille, T., Hébrard, G., Hobson, M. J., Kiefer, F., López, T., Mignon, L., Mousis, O., Moutou, C., Pepe, F., Rey, J., Santos, N. C., Ségransan, D., Udry, S., Wilson, P. A.

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.

2021, Dr. Astudillo-Defru, Nicola, Van Eylen, V., Bonfils, X., Livingston, J., Hirano, T., Luque, R., Lam, K., Justesen, A., Winn, J., Gandolfi, D., Nowak, G., Palle, E., Albrecht, S., Dai, F., Campos-Estrada, B., Owen, J., Foreman-Mackey, D., Fridlund, M., Korth, J., Mathur, S., Forveille, T., Mikal-Evans, T., Osborne, H., Ho, C., Almenara, J., Artigau, E., Barragán, O., Barros, S., Bouchy, F., Cabrera, J., Caldwell, D., Charbonneau, D., Chaturvedi, P., Cochran, W., Csizmadia, S., Damasso, M., Delfosse, X., De Medeiros, J., Díaz, R., Doyon, R., Esposito, M., Fűrész, G., Figueira, P., Georgieva, I., Goffo, E., Grziwa, S., Guenther, E., Hatzes, A., Jenkins, J., Kabath, P., Knudstrup, E., Latham, D., Lavie, B., Lovis, C., Mennickent, R., Mullally, S., Murgas, F., Narita, N., Pepe, F., Persson, C., Redfield, S., Ricker, G., Santos, N., Seager, S., Serrano, L., Smith, A., Suárez-Mascareño, A., Subjak, J., Twicken, J., Udry, S., Vanderspek, R., Zapatero-Osorio, M.

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.