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EX Lupi is the prototype for a class of young, pre-main sequence stars which are observed to undergo irregular, presumably accretion-generated, optical outbursts that result in a several magnitude rise of the optical flux. EX Lupi was…

Swift J1753.5-0127 (J1753) is a candidate black hole low-mass X-ray binary (BH-LMXB) that was discovered in outburst in May 2005. It remained in outburst for $\sim12$ years, exhibiting a wide range of variability on various timescales,…

The Andromeda Galaxy recurrent nova M31N 2008-12a had been caught in eruption eight times. The inter-eruption period of M31N 2008-12a is ~1 year, making it the most rapidly recurring system known, and a strong single-degenerate Type Ia…

We report the analysis of 22 B-band light curves of the dwarf nova V4140 Sgr obtained with SOI/SOAR during two nights along the decline of a superoutburst in 2006 Sep 12-24 and in quiescence over 50 days following the superoutburst.…

We propose that the energetic major outburst of the supernova (SN) impostor SN 2009ip in September 2012 (outburst 2012b) was a mergerburst event, where two massive stars merged. The previous outbursts of 2009 and 2011 might have occurred…

Time-resolved HST UV eclipse spectrophotometry is presented for the magnetic CVs V1309 Ori, MN Hya, V2301 Oph, and V1432 Aql. Separation of the light curves into wavebands allows the multiple emission components to be distinguished.…

In this paper we present and discuss our time-resolved photometry of an eclipsing recurrent nova, U Sco, during an outburst in 1999, which was conducted from immediately after the optical maximum to the final fading toward the quiescence.…

The decade-long Vista Variables in the Via Lactea (VVV) survey has detected numerous highly variable young stellar objects (YSOs). We present a study of 61 highly variable VVV YSOs ($\Delta K_s$ = 1-5 mag), combining near infrared spectra…

We present densely-sampled ultraviolet/optical photometric and low-resolution optical spectroscopic observations of the type IIP supernova 2013ab in the nearby ($\sim$24 Mpc) galaxy NGC 5669, from 2 to 190d after explosion. Continuous…

For the He/N nova M31N 2007-12b, we analyzed XMM-Newton EPIC and Chandra HRC-I observations of our monitoring program performed at intervals of ten days and added results of a XMM-Newton target of opportunity observation and Swift XRT…

Aims. We report the discovery of a strong outburst of the embedded young stellar object (YSO), namely UKIDSS-J185318.36+012454.5, located in the star-forming region associated with IRAS 18507+0121 source and GAL 034.4+00.23 HII region.…

We report photometry and spectroscopy of the outburst of the young stellar object ESO-Halpha 99. The outburst was first noticed in Gaia alert Gaia18dvc and later by ATLAS. We have established the outburst light curve with archival ATLAS…

During the pre-main-sequence (pre-MS) evolution stage of a star, significant amounts of stellar mass are accreted during episodic accretion events, such as multi-decade FUor-type outbursts. Here, we present a near-infrared spectroscopic…

FU Orionis-type objects (FUors) are young low-mass stars undergoing powerful accretion outbursts. The increased accretion is often accompanied by collimated jets and energetic, large-scale molecular outflows. The extra heating during the…

Nova Her 2021 (V1674 Her), which erupted on 2021 June 12, reached naked-eye brightness and has been detected from radio to $\gamma$-rays. An extremely fast optical decline of 2 magnitudes in 1.2 days and strong Ne lines imply a high-mass…

We present a nuclear transient event, PS1-13cbe, that was first discovered in the Pan-STARRS1 survey in 2013. The outburst occurred in the nucleus of the galaxy SDSS J222153.87+003054.2 at $z = 0.12355$, which was classified as a Seyfert 2…

We observed the 2002 October-November outburst of the dwarf nova CW Mon. The outburst showed a clear signature of a premaximum halt, and a more rapid decline after reaching the outburst maximum. On two separate occasions, during the…

Nova Scorpii 2023 was first detected as a luminous supersoft X-ray source (SSS) 93 days after outburst and continued emitting soft X-rays for over two months, until it was too close to the Sun to observe. The nova was monitored with the…

Mid-infrared (mid-IR) variability in young stellar objects (YSOs) is driven by several physical mechanisms, which produce a variety of amplitudes and light curve shapes. One of these mechanisms, variable disk accretion is predicted by…

It is well known that massive stars (M > 8 M_sun) evolve up to the collapse of the stellar core, resulting in most cases as a supernova (SN) explosion. Their heterogeneity is related mainly to different configurations of the progenitor star…