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We compiled a catalogue of about 4000 SDSS quasars including individual estimators V for the variability strength, virial black hole masses M, and mass accretion rates dM/dt from the Davis-Laor scaling relation. We confirm significant…

We obtained photometric observations of the nova-like cataclysmic variable RW Tri and gathered all available AAVSO and other data from the literature. We determined the system parameters and found their uncertainties using the code…

Using the largest high-resolution spectroscopic sample to date of young, very low mass stars (VLMS) and brown dwarfs (BDs), we investigate disk accretion in objects ranging from just above the hydrogen-burning limit all the way to nearly…

Millimeter very-long baseline interferometry (mm-VLBI) provides the novel capacity to probe the emission region of a handful of supermassive black holes on sub-horizon scales. For Sagittarius A* (Sgr A*), the supermassive black hole at the…

We compare accretion shock models with optical and ultraviolet spectra of pre-main sequence stars to (1) make the first determinations of accretion rates in intermediate mass T Tauri stars from continuum emission, and (2) derive improved…

Using XMM-Newton we have obtained the first X-ray observation covering a complete orbit of the longest period polar, V1309 Ori. The X-ray light curve is dominated by a short, bright phase interval with EPIC pn count rates reaching up to 15…

We have studied numerically the evolution of protostellar disks around intermediate and upper mass T Tauri stars (0.25 M_sun < M_st < 3.0 M_sun) that have formed self-consistently from the collapse of molecular cloud cores. In the T Tauri…

Tidal disruption events (TDEs) are believed to be an ideal laboratory for studying the evolution of accretion flow around a supermassive black hole (BH). In general, the mass feeding rate to the BH is suggested to be super-Eddington…

We present an analysis of the X-ray light curves of the magnetic cataclysmic variable DP Leo using recently performed XMM-Newton EPIC and archival ROSAT PSPC observations. We determine the eclipse length at X-ray wavelengths to be 235 +-5…

This study of SDSS0804 is primarily concerned with the double-hump shape in the light curve and its connection with the accretion disk in this bounce-back system. Time-resolved photometric and spectroscopic observations were obtained to…

We report the results of a synoptic study of the photometric and spectroscopic variability of the classical T Tauri star AA Tau on timescales ranging from a few hours to several weeks. Emission lines show both infall and outflow signatures…

In transiting planetary systems, the angle between the orbital angular momentum and the stellar spin is usually constrained through the Rossiter-McLaughlin effect observed in radial velocity and can be subject to large uncertainties,…

We present a systematic spectral analysis of six ultraluminous X-ray sources (NGC1313 X-1/X-2, IC342 X-1, HoIX X-1, NGC5408 X-1 and NGC3628 X-1) observed with XMM-Newton Observatory. These extra-nuclear X-ray sources in nearby late-type…

For the majority of the tidal disruption event (TDE) candidates, the observed energy in the optical/near-UV bands is of order 10^{51} erg. We show that this observed energy is smaller than the minimum bolometric energy for the radiative…

We have analyzed all the observations of BP Tauri taken by the International Ultraviolet Explorer in the low resolution (6 A), long wavelength (from 1850 to 3350 A) range. This dataset contains 61 spectra. These spectra do not show any…

We have identified more than a hundred close triply eclipsing hierarchical triple star systems from data taken with the space telescope TESS. Many of them have outer periods less than or, close to 100 days, hence, we call them `ultracompact…

This paper presents a comprehensive analysis of four triply eclipsing triple star systems, namely TIC 88206187, TIC 14839347, TIC 298714297, and TIC 66893949. The four systems with third-body eclipses were found in the TESS lightcurves from…

Light curves of young star systems show photometric variability due to different kinematic, and physical processes. One of the main contributors to the photometric variability is the changing mass accretion rate, which regulates the…

We construct a time-dependent relativistic accretion model for tidal disruption events (TDEs) with an $\alpha-$viscosity and the pressure dominated by gas pressure. We also include the mass fallback rate $\dot{M}_f$ for both full and…

Some close binaries of the beta Lyrae type show photometric cycles longer than the orbital one, which are possibly related to changes in their accretion disks. We aim to understand the short- and long-scale changes observed in the light…