Aims. The main goal of this work is to measure rotation periods of the M-type dwarf stars being observed by the CARMENES exoplanet survey to help distinguish radial-velocity signals produced by magnetic activity from those produced by exoplanets. Rotation periods are also fundamental for a detailed study of the relation between activity and rotation in late-type stars. Methods. We look for significant periodic signals in 622 photometric time series of 337 bright, nearby M dwarfs obtained by long-time baseline, automated surveys (MEarth, ASAS, SuperWASP, NSVS, Catalina, ASAS-SN, K2, and HATNet) and for 20 stars which we obtained with four 0.2–0.8 m telescopes at high geographical latitudes. Results. We present 142 rotation periods (73 new) from 0.12 d to 133 d and ten long-term activity cycles (six new) from 3.0 a to 11.5 a. We compare our determinations with those in the existing literature; we investigate the distribution of Prot in the CARMENES input catalogue, the amplitude of photometric variability, and their relation to v sini and pEW(Hα); and we identify three very active stars with new rotation periods between 0.34 d and 23.6 d.

The Kilodegree Extremely Little Telescope (KELT) project has been conducting a photometric survey of transiting planets orbiting bright stars for over 10 years. The KELT images have a pixel scale of ∼23″ pixel −1-very similar to that of NASA's Transiting Exoplanet Survey Satellite (TESS)-as well as a large point-spread function, and the KELT reduction pipeline uses a weighted photometric aperture with radius 3′. At this angular scale, multiple stars are typically blended in the photometric apertures. In order to identify false positives and confirm transiting exoplanets, we have assembled a follow-up network (KELT-FUN) to conduct imaging with spatial resolution, cadence, and photometric precision higher than the KELT telescopes, as well as spectroscopic observations of the candidate host stars. The KELT-FUN team has followed-up over 1600 planet candidates since 2011, resulting in more than 20 planet discoveries. Excluding ∼450 false alarms of non-astrophysical origin (i.e., instrumental noise or systematics), we present an all-sky catalog of the 1128 bright stars (6<V<13) that show transit-like features in the KELT light curves, but which were subsequently determined to be astrophysical false positives (FPs) after photometric and/or spectroscopic follow-up observations. The KELT-FUN team continues to pursue KELT and other planet candidates and will eventually follow up certain classes of TESS candidates. The KELT FP catalog will help minimize the duplication of follow-up observations by current and future transit surveys such as TESS.

RW Aur is a binary system composed of two young, low-mass stars. The primary, RW Aur A, has undergone visual dimming events (ΔV = 2–3 mag) in 2011, 2014–16, and 2017–2018. Visual and IR observations indicate a gray absorber that moved into the line of sight. This dimming is also associated with changes in the outflow. In 2017, when the optical brightness was almost 2 mag below the long-term average, we triggered a Chandra observation to measure the absorbing column density N H and to constrain dust properties and the gas-to-dust ratio of the absorber. In 2017, the X-ray spectrum is more absorbed than it was in the optically bright state ( ) and shows significantly more hot plasma than in X-ray observations taken before. Furthermore, a new emission feature at 6.63 ± 0.02 keV (statistic) ±0.02 keV (systematic) appeared, indicating an Fe abundance an order of magnitude above solar, in contrast with previous sub-solar Fe abundance measurements. Comparing X-ray absorbing column density N H and optical extinction A V , we find that either the gas-to-dust ratio in the absorber is orders of magnitude higher than in the ISM, or the absorber has undergone significant dust evolution. Given the high column density coupled with changes in the X-ray spectral shape, this absorber is probably located in the inner disk. We speculate that a breakup of planetesimals or a terrestrial planet could supply large grains, causing gray absorption; some of these grains would be accreted and enrich the stellar corona with iron, which could explain the inferred high abundance.

The first stars are known to form in primordial gas, either in minihalos with about 10 6 M or so-called atomic cooling halos of about 10 8 M . Simulations have shown that gravitational collapse and disk formation in primordial gas yield dense stellar clusters. In this paper, we focus particularly on the formation of protostellar binary systems, and aim to quantify their properties during the early stage of their evolution. For this purpose, we combine the smoothed particle hydrodynamics code GRADSPH with the astrochemistry package KROME. The GRADSPH-KROME framework is employed to investigate the collapse of primordial clouds in the high-density regime, exploring the fragmentation process and the formation of binary systems. We observe a strong dependence of fragmentation on the strength of the turbulent Mach number M and the rotational support parameter β. Rotating clouds show significant fragmentation, and have produced several Pop. III proto-binary systems. We report maximum and minimum mass accretion rates of 2.31 × 10 −1 M yr −1 and 2.18 × 10 −4 M yr −1 . The mass spectrum of the individual Pop III proto-binary components ranges from 0.88 M to 31.96 M and has a sensitive dependence on the Mach number M as well as on the rotational parameter β. We also report a range from ∼ 0.01 to ∼ 1 for the mass ratio of our proto-binary systems.

We describe the algorithms implemented in the first version of GRADSPH, a parallel, tree-based, smoothed particle hydrodynamics code for simulating self-gravitating astrophysical systems written in FORTRAN 90. The paper presents details on the implementation of the Smoothed Particle Hydro (SPH) description, where a gridless approach is used to model compressible gas dynamics. This is done in the conventional SPH way by means of 'particles' which sample fluid properties, exploiting interpolating kernels. The equations of self-gravitating hydrodynamics in the SPH framework are derived self-consistently from a Lagrangian and account for variable smoothing lengths ('GRAD-h') terms in both the hydrodynamic and gravitational acceleration equations. A Barnes-Hut tree is used for treating selfgravity and updating the neighbour list of the particles. In addition, the code updates particle properties on their own individual timesteps and uses a basic parallelisation strategy to speed up calculations on a parallel computer system with distributed memory architecture. Extensive tests of the code in one and three dimensions are presented. Finally, we describe the program organisation of the publicly available 3D version of the code, as well as details concerning the structure of the input and output files and the execution of the program. Solution method: Hydrodynamics is described using SPH, self-gravity using the Barnes-Hut tree method. Program summary