Related papers: CH Cygni II: Optical Flickering from an Unstable D…

In this article, we proceed to study convection as a possible factor of episodic accretion in protoplanetary disks. Within the model presented in Article~I, the accretion history is analyzed at different rates and areas of matter inflow…

Context. We analyse the line and continuum spectra of the symbiotic system CH Cygni. Aims. To show that the colliding-wind model is valid to explain this symbiotic star at different phases. Methods. Peculiar observed features such as…

The variability of young stellar objects is mostly driven by star-disk interactions. In long-term photometric monitoring of the accreting T Tauri star GI Tau, we detect extinction events with typical depths of $\Delta V \sim 2.5$ mag that…

The role of convection in the gas-dust accretion disk around a young star is studied. The evolution of a Keplerian disk is modeled using the Pringle equation, which describes the time variations of the surface density under the action of…

1ES 1927+654 was known as a type 2 Seyfert galaxy, which exhibited drastic variability recently in ultraviolet (UV)/optical and X-ray bands. An UV/optical outburst was observed in the end of 2017, and it reached the peak luminosity $\sim…

We analyse optical photometric data of short term variability (flickering) of the accreting white dwarf in the jet-ejecting symbiotic star MWC560. The observations are obtained in 17 nights during the period November 2011 - October 2019.…

Activity of the nuclei of galaxies and stellar mass systems involving disk accretion to black holes is thought to be due to (1) a small-scale turbulent magnetic field in the disk (due to the magneto-rotational instability or MRI) which…

Sokoloski et al (2008) have recently reported evidence that the recurrent nova RS Ophiuchi produced a pair of highly collimated radio jets within days of its 2006 outburst. This suggests that an accretion disc must be present during the…

We present an optical (gri) study during quiescence of the accreting millisecond X-ray pulsar IGR J00291+5934 performed with the 10.4m Gran Telescopio Canarias (GTC) in August 2014. Despite the source being in quiescence at the time of our…

Using the disc instability model and a simple but physically reasonable model for the X-ray, extreme UV, UV and optical emission of dwarf novae we investigate the time lags observed between the rise to outburst at different wavelengths. We…

We present simultaneous X-ray and radio observations of the black hole X-ray binary V404 Cygni at the end of its 2015 outburst. From 2015 July 11-August 5 we monitored V404 Cygni with Chandra, Swift, and NuSTAR in the X-ray, and with the…

The black-hole binary, V404 Cygni, went into outburst in June 2015, after 26 years of X-ray quiescence. We observed the outburst with the Neil Gehrels Swift observatory. We present optical/UV observations taken with the Swift Ultra-violet…

Although during the last decade new observations and new theoretical results have brought better understanding of the physics of accretion onto compact objects, many old and several new questions and problems await answers and solutions. I…

We analyze new and published optical photometric data of FU Orionis, an eruptive pre-main sequence star. The outburst consists of a 5.5 mag rise at B with an e-folding timescale of roughly 50 days. The rates of decline at B and V are…

We performed extensive, multi-wavelength observations of the prototypical symbiotic star Z Andromedae between 2000 and 2003, during a large eruption. The rise to optical maximum occurred in three distinct stages. During the first stage, the…

The UV/optical variability of active galactic nuclei and quasars is useful for understanding the physics of the accretion disk and is gradually attributed to the stochastic fluctuations over the accretion disk. Quasars generally appear…

RS Oph has persistently displayed flickering at optical wavelengths when observed away from its repeating nova outbursts. During the 2006 eruption the flickering disappeared, and this repeated during the recent 2021 event. We have been…

Keplerian accretion discs around massive black holes (MBHs) are gravitationally unstable beyond a few hundredths of parsec and should collapse to form stars. Indeed an accretion/star formation episode took place a few millions years ago in…

Quantifying the variability, measured as the root mean square (rms), of accreting systems as a function of energy is a powerful tool for constraining the physical properties of these objects. Here, we present the first application of this…

Between May 2016 and September 2018, the intermediate polar (IP) FO Aquarii exhibited two distinct low states and one failed low state. We present optical spectroscopy of FO Aquarii throughout this period, making this the first detailed…