Related papers: H$\alpha$ Emission From Active Equal-mass, Wide M …
[Abridged] As part of our on-going investigation of magnetic activity in ultracool dwarfs we present simultaneous radio, X-ray, UV, and optical observations of LSR1835+32 (M8.5), and simultaneous X-ray and UV observations of VB10 (M8), both…
We obtained ultraviolet and optical spectra for 9 M~dwarfs across a range of rotation periods to determine whether they showed stochastic intrinsic variability distinguishable from flares. The ultraviolet spectra were observed during the…
We present results from a high-resolution spectroscopic survey of 45 L dwarfs, which includes both very low-mass stars and brown dwarfs. Our spectra allow us to derive a significant number of new rotational velocities, and discover a slowly…
M dwarfs remain active over longer timescales than their Sunlike counterparts, with potentially devastating implications for the atmospheres of their planets. However, the age at which fully-convective M dwarfs transition from active and…
We present here a continuation of our ongoing project of multiwavelength optical observations aimed at studying the chromosphere of active binary systems using the information provided for several optical spectroscopic features that are…
There are several strong K I lines found in the spectra of M dwarfs, among them the doublet near 7700 AA and another doublet near 12 500 AA. We study these optical and near-infrared doublets in a sample of 324 M dwarfs, observed with…
We present here 55 short period PCEBs containing a hot WD and a low-mass MS. Based on the photometric data from ZTF DR19, the light curves are analyzed for about 200 WDMS binaries with emission line(s) identified from SDSS or LAMOST…
We report multi-wavelength monitoring observations of an M-dwarf flare star AD Leonis with Seimei Telescope (6150--7930 {\AA}), SCAT (Spectroscopic Chuo-university Astronomical Telescope; 3700--7500 {\AA}), NICER (Neutron Star Interior…
We announce the discovery of a new eclipsing hot subdwarf B + M dwarf binary, EC 10246-2707, and present multi-colour photometric and spectroscopic observations of this system. Similar to other HW Vir-type binaries, the light curve shows…
The first detailed photometric and spectroscopic analysis of the G-type eclipsing binary KM UMa is presented, which indicates that the system is a short-period detached eclipsing binary. The radial velocity curves were calculated using the…
Due to their low mass and luminosity, M dwarfs are ideal targets if one hopes to find low-mass planets similar to Earth by using the radial velocity (RV) method. However, stellar magnetic cycles could add noise or even mimic the RV signal…
Use of the highly sensitive Hokupa'a curvature wavefront sensor has allowed for the first time direct adaptive optics (AO) guiding on brown dwarfs and VLM stars (SpT=M7-L2). An initial survey of 9 such objects discovered one 0.15" binary…
Four months of quasi-simultaneous spectroscopic and photometric observations were used to study the variations of the photometric light curve, the evolution of the chromospheric activity from the H$\alpha$ and H$\beta$ lines, and the…
We present a study of the dynamics and magnetic activity of M dwarfs using the largest spectroscopic sample of low-mass stars ever assembled. The age at which strong surface magnetic activity (as traced by H-alpha) ceases in M dwarfs has…
Millimeter (mm) emission from F - M dwarfs (cool stars) primarily traces chromospheric activity, with thermal emission thought to dominate in quiescence. Despite the high chromospheric activity, the quiescent mm spectral fluence…
(abridged) The heating mechanism at high densities during M dwarf flares is poorly understood. Spectra of M dwarf flares in the optical and near-ultraviolet wavelength regimes have revealed three continuum components during the impulsive…
We have obtained a series of high-resolution optical spectra for the brown dwarf 2MASSW J1207334-393254 (2M1207) using the ESO Very Large Telescope with the UVES spectrograph during two consecutive observing nights (time resolution of ~12…
A detailed analysis of more than 800 electronic high-resolution spectra of gamma Cas, which were obtained during a time interval of over 6000 days (16.84 yrs) at several observatories, documents the smooth variations in the density and/or…
We have carried out a search for flares from the analysis of light curves for 12 active G, K, and M dwarfs. As sources of data we used ground-based observations in 2000-2020 from the photometric databases ASAS, SuperWASP, KWS. Events of…
M dwarfs are magnetically active stars that frequently produce flares, which have implications for both stellar evolution and exoplanet studies. Flare occurrence rates and activity levels of M dwarfs correlate with stellar characteristics…