The theory of substellar evolution predicts that there is a sharp mass boundary between lithium and non-lithium brown dwarfs, not far below the substellar-mass limit. The imprint of thermonuclear burning is carved on the surface lithium abundance of substellar-mass objects during the first few hundred million years of their evolution, leading to a

Transiting planets at young ages are key targets for improving our understanding of the evolution of exo-atmospheres. We present results of a new X-ray observation of V 1298 Tau with XMM-Newton, aimed to determine more accurately the high-energy irradiation of the four planets orbiting this pre-main-sequence star, and the possible variability due

Close-in gas giants present a surprising range of stellar obliquity, the angle between a planet's orbital axis and its host star's spin axis. It is unclear whether the obliquities reflect the planets' dynamical history (e.g., aligned for in situ formation or disk migration versus misaligned for high-eccentricity tidal migration) or whether other

We report multiwavelength observations of the gravitationally lensed blazar QSO B0218+357 in 2016-2020. Optical, X-ray, and GeV flares were detected. The contemporaneous MAGIC observations do not show significant very high energy (VHE; ≳100 GeV) gamma-ray emission. The lack of enhancement in radio emission measured by The Owens Valley Radio

A number of precursor-type methods for solar-cycle prediction are based on the use of regression models and confidence-level estimates. A drawback of these methods is that they do not permit one to make probability statements, nor do they offer straightforward ways to propagate the uncertainty from observations to the quantities of interest. We

Deriving metallicities for solar-like stars follows well-established methods, but for cooler stars such as M dwarfs, the determination is much more complicated due to forests of molecular lines that are present. Several methods have been developed in recent years to determine accurate stellar parameters for these cool stars (T eff ≲ 4000 K)