Related papers: The slowly variable star FY Lacertae
In 2021 BL Lacertae underwent an extraordinary activity phase, which was intensively followed by the Whole Earth Blazar Telescope (WEBT) Collaboration. We present the WEBT optical data in the BVRI bands acquired at 36 observatories around…
We present the results of a spectral variability study of two very luminous stars in the M33 galaxy -- LBV V532 and late WN star (possibly, dormant LBV) FSZ35. We studied spectral variability of V532, derived its atmosphere parameters and…
Several late-type stars present activity cycles resembling the Solar one. This fact has been observed mostly in stars ranging from F to K, i.e., in stars with a radiative core and an outer convective layer. This work aims at studying…
Spectroscopic and photometric variability is widespread among O-type supergiants. It is linked to various phenomena affecting the star and its circumstellar environment, thereby providing direct information concerning them. To investigate…
In this publication we present a study of the general physical, chemical properties and radial velocity monitoring of young active stars. We derive temperatures, log g, [Fe/H], v sin i, and R_{spec} values for eight stars. The detailed…
S5 0716+714 is a typical BL Lacertae object. In this paper we present the analysis and results of long term simultaneous observations in the radio, near-infrared, optical, X-ray and $\gamma$-ray bands, together with our own photometric…
Based on a new and large sample of optical and near-infrared spectra obtained at the Mount Stromlo and Siding Spring Observatories (Lancon & Wood 1998; Lancon & Wood, in preparation), spectrophotometric properties of cool oxygen- and…
We present the optical (V, R, and I) photometry for BL Lacertae, which was observed from 1997 through 1999, with the 1.56-m telescope at the Shanghai astronomical observatory (SHAO). After the 1997 outburst, it dimmed to a low state and…
Random changes in pulsation period are well established in cool pulsating stars, in particular the red giant variables: Miras, semi-regulars of types A and B, and RV Tau variables. Such effects are also observed in a handful of Cepheids,…
The high-frequency peaked BL Lac object 1ES 0229+200 (z = 0.14) was first detected in very high energy (VHE, E > 100 GeV) $\gamma$-rays by the H.E.S.S. (High Energy Stereoscopic System) collaboration in 2006. No flux variability was…
Do some Wolf-Rayet stars owe their strong winds to something else besides radiation pressure? The answer to this question is still not entirely obvious, especially in certain Wolf-Rayet subclasses, mainly WN8 and WC9. Both of these types of…
Among active galactic nuclei, blazars show extreme variability properties. We here investigate the case of the BL Lac object S4 0954+65 with data acquired in 2019-2020 by the Transiting Exoplanet Survey Satellite (TESS) and by the Whole…
Spectral variability is the main tool for constraining emission models of BL Lac objects. By means of systematic observations of the BL Lac prototype PKS 2155-304 in the infrared-optical band, we explore variability on the scales of months,…
Optical surveys, such as the MACHO project, often uncover variable stars whose classification requires followup observations by other instruments. We performed X-ray spectroscopy and photometry of the unusual variable star MACHO…
We present the results of photometric observations of three TeV blazars, 3C 66A, S5 0954+658 and BL Lacertae, during the period 2013--2017. Our extensive observations were performed in a total of 360 nights which produced $\sim$6820 image…
We call attention to the fact that one of the brightest red supergiants in the SMC has recently changed its spectral type from K0-1 I (December 2004) to M4 I (December 2005) and back to K0-1 I (September 2006). An archival spectrum from the…
We present a long (150 ks elapsed time) ASCA X-ray observation of the dM3.5e star EV Lac, during which an exceptionally intense flaring event (lasting approximately 12 ks) was observed: at the flare's peak, the X-ray count rate in the ASCA…
We presented photometric observations for the one UV Ceti type and three W Ursae Majoris-type variable stars. The flare of the UV Ceti type star lasted about two hours, and the star changed magnitude to 3.9 within about two minutes. The…
Using the Southeastern Association for Research in Astronomy 0.6 meter telescope located at Cerro Tololo, we searched for variable stars in the southern globular cluster NGC 6584. We obtained images during 8 nights between 28 May and 6 July…
The polarized and total flux of the BL Lac object PKS 2155-304 were monitored intensively and simultaneously in the optical UBVRI bands with the Turin photopolarimeter at the CASLEO 2.15 m telescope during 4 campaigns in June, August,…