Related papers: Rotational and Cyclical Variability in gamma Cassi…
We present the results of an intensive photometric and spectroscopic monitoring campaign of the WN4 Wolf-Rayet (WR) star WR1=HD4004. Our broadband V photometry covering a timespan of 91 days shows variability with a period of…
We report the identification of cyclical changes in the orbital period of the eclipsing dwarf nova Z Cha. We used times of mid-eclipse collected from the literature and our new eclipse timings to construct an observed-minus-calculated…
Long-term measurements of the radio flux density of Cassiopeia A relative to Cygnus A have been carried out at 927 and 151.5 MHz. It was found the following mean secular decrease rates of the radio emission of Cassiopeia A: $(0.72\pm 0.03)%…
We report the results of 24 years of photometric and spectroscopic monitoring of CI Cam since its outburst in 1998. In the early years of our research, we identified a system component responsible for the emission of the He II 4686 line,…
By using six new determined mid-eclipse times together with those collected from the literature, we found that the Observed-Calculated (O-C) curve of RR Cae shows a cyclic change with a period of 11.9 years and an amplitude of 14.3s, while…
The gamma-ray binary LS I +61 303 is composed of a Be star and a compact companion orbiting in an eccentric orbit. Variable flux modulated with the orbital period of ~26.5 d has been detected from radio to very high-energy gamma rays. In…
We present the results of an intensive ground-based spectrophotometric monitoring campaign of the Seyfert galaxy NGC~4151 for a period of over two months, with a typical temporal resolution of one day. Light curves for four optical…
We present an analysis of new Johnson and Stromgren photometric and medium-resolution spectroscopic observations of the delta Scuti type variable star V784 Cassiopeae. The data were obtained in three consecutive years between 1999 and 2001.…
The gamma-ray binary LS I+61 303 has been widely monitored at different wavelengths since its discovery more than sixty years ago. However, the nature of the compact object and the peculiar behavior of the system are still largely debated.…
Be/X-ray binaries are the most populous class of High Mass X-ray Binaries. Their X-ray duty cycle is tightly related to the optical companion wind activity, which in turn can be studied through optical spectroscopical dedicated…
Cassiopeia A (Cas A) as the nearby young remnant of a core-collapse supernova is the best candidate for astrophysical studies in supernova explosion and its environment. We studied hard X-ray emissions from Cas A using the ten-year data of…
A 2.1-year periodic oscillation of the gamma-ray flux from the blazar PG 1553+113 has previously been tentatively identified in almost 7 year of data from the Fermi Large Area Telescope. After 15 years of Fermi sky-survey observations,…
V1022 Cas has been known as a spectroscopic binary for a century. It was found to be eclipsing based on photometry from the Hipparcos satellite, and an astrometric orbit was recently obtained from near-infrared interferometry. We present…
We analyse optical and X-ray spectroscopy of the Of?p star HD108, known for its strong dipolar magnetic field and its optical line profile variability with a timescale of $54 \pm 3$ yrs, interpreted as the stellar rotation period. Optical…
The very massive star system $\eta$ Carinae exhibits regular 5.54-year (2024-day) period disruptive events in wavebands ranging from the radio to X-ray. There is a growing consensus that these events likely stem from periastron passage of…
Broadband optical and narrowband Si XIII X-ray images of the young Galactic supernova remnant Cas A obtained over several decades are used to investigate spatial and temporal correlations on both large and small scales. The data consist of…
Analysis of over 36 years of time series data from the NSO/AFRL/Sac Peak K-line monitoring program elucidates five components of the variation of the seven measured chromospheric parameters: (a) the solar cycle (period ~ 11 years), (b)…
High-dispersion spectroscopic monitoring of HESS J0632+057 has been carried out over four orbital cycles in order to search for orbital modulation, covering the entire orbital phase. We have measured radial velocity of H$\alpha$ emission…
In photometry of $\gamma$ Cas (B0.5 IVe) from the SMEI and BRITE-Constellation satellites, indications of low-order non-radial pulsation have recently been found, which would establish an important commonality with the class of classical Be…
We present the results of our monitoring program to study the long-term variability of the Halpha line in high-mass X-ray binaries. We have carried out the most complete optical spectroscopic study of the global properties of high-mass…