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 d. 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 photoevaporation. 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 (T_eff < 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 photoevaporation 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.

LTT 1445 is a hierarchical triple M-dwarf star system located at a distance of 6.86 pc. The primary star LTT 1445A (0.257 M _⊙) is known to host the transiting planet LTT 1445Ab with an orbital period of 5.36 days, making it the second-closest known transiting exoplanet system, and the closest one for which the host is an M dwarf. Using Transiting Exoplanet Survey Satellite data, we present the discovery of a second planet in the LTT 1445 system, with an orbital period of 3.12 days. We combine radial-velocity measurements obtained from the five spectrographs, Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, High Accuracy Radial Velocity Planet Searcher, High-Resolution Echelle Spectrometer, MAROON-X, and Planet Finder Spectrograph to establish that the new world also orbits LTT 1445A. We determine the mass and radius of LTT 1445Ab to be 2.87 ± 0.25 M _⊕ and ${1.304}_{-0.060}^{+0.067}$ R _⊕, consistent with an Earth-like composition. For the newly discovered LTT 1445Ac, we measure a mass of ${1.54}_{-0.19}^{+0.20}$ M _⊕ and a minimum radius of 1.15 R _⊕, but we cannot determine the radius directly as the signal-to-noise ratio of our light curve permits both grazing and nongrazing configurations. Using MEarth photometry and ground-based spectroscopy, we establish that star C (0.161 M _⊙) is likely the source of the 1.4 day rotation period, and star B (0.215 M _⊙) has a likely rotation period of 6.7 days. We estimate a probable rotation period of 85 days for LTT 1445A. Thus, this triple M-dwarf system appears to be in a special evolutionary stage where the most massive M dwarf has spun down, the intermediate mass M dwarf is in the process of spinning down, while the least massive stellar component has not yet begun to spin down.

We present a catalogue with coordinates and photometric data of 2446 Be star candidates in the Large Magellanic Cloud (LMC), based on a search of the OGLE II data base. The I -band light curves of these stars show outbursts in 24 per cent of the sample (Type-1 stars), high and low states in 10 per cent, periodic variations in 6 per cent (Type-3 stars), and stochastic variations in 60 per cent of the cases. We report on the result of the statistical study of light curves of Type-1 and Type-3 stars in the LMC, and the comparison with the previously reported results of the Small Magellanic Cloud (SMC) sample. We find a statistically significant difference between amplitude, duration and asymmetry distributions of outbursts in both galaxies. Outbursts of SMC Type-1 stars are usually brighter, longer and with a slower decline. We find a bimodal distribution of periods of Type-3 stars in both galaxies, probably related to the recently discovered double periodic blue variables. We find also period and amplitude distributions of Type-3 LMC stars statistically different from those of the SMC stars. Our findings above suggest that the mechanisms causing the observed photometric variability of Type-1 and Type-3 stars could depend on metallicity. Moreover, they suggest that the outbursts are not primarily caused by stellar winds.

We modelled the V-band light curve of β Lyrae (Lyr) with two stellar components plus an optically thick accretion disc around the gainer assuming a semidetached configuration. We present the results of this calculation, giving physical parameters for the stars and the disc, along with general system dimensions. We discuss the evolutionary stage of the system finding the best match with one of the evolutionary models of Van Rensbergen et al. According to this model, the system is found at age 2.30 × 10⁷ yr, in the phase of rapid mass transfer, the second one in the life of this binary, in a Case-B mass-exchange stage with $$\dot{M} = 1.58\times 10^{-5}$$ M_⊙ yr⁻¹. This result, along with the reported rate of orbital period change and observational evidence of mass-loss, suggests that the mass transfer in β Lyr is quasi-conservative. The best model indicates that β Lyr finished a relatively large mass-loss episode 31 400 yr ago. The light-curve model that best fit the observations has inclination angle i = 81°, M₁ = 13.2 M_⊙, M₂ = 3.0 M_⊙, R₁ = 6.0 R_⊙ and R₂ = 15.2 R_⊙. The disc contributes 22 per cent to the total V-band light curve at quadrature, has a radius of 28.3 R_⊙ and the outer edge thickness is 11.2 R_⊙. The light-curve model is significantly better with two bright regions in the disc rim with temperatures 10 and 20 per cent higher than the disc outer edge temperature. We compare our results with earlier studies of this interacting binary.

We report on the H-band spectral variability of classical Be stars observed over the course of the Apache Point Galactic Evolution Experiment (APOGEE), one of four subsurveys comprising SDSS-III. As described in the first paper of this series, the APOGEE B-type emission-line (ABE) star sample was culled from the large number of blue stars observed as telluric standards during APOGEE observations. In this paper, we explore the multi-epoch ABE sample, consisting of 1100 spectra for 213 stars. These “snapshots” of the circumstellar disk activity have revealed a wealth of temporal variability including, but not limited to, gradual disappearance of the line emission and vice versa over both short and long timescales. Other forms of variability include variation in emission strength, emission peak intensity ratios, and emission peak separations. We also analyze radial velocities (RVs) of the emission lines for a subsample of 162 stars with sufficiently strong features, and we discuss on a case-by-case basis whether the RV variability exhibited by some stars is caused by binary motion versus dynamical processes in the circumstellar disks. Ten systems are identified as convincing candidates for binary Be stars with as of yet undetected companions.