Related papers: The Be Star HD 215227: A Candidate Gamma-ray Binar…
The rapidly rotating B1 IV:nn star HD3191 lies within the error box of a flaring Fermi gamma-ray source. Although the counterpart of the Fermi source is likely an active galaxy, HD3191 has nevertheless been suggested to be a high-mass X-ray…
PSR B1259-63/LS 2883 is a very high energy (VHE; E > 100 GeV) gamma-ray emitting binary consisting of a 48 ms pulsar orbiting around a Be star with a period of 3.4 years. The Be star features a circumstellar disk which is inclined with…
FF Cam is a variable star near the North celestial pole with hydrogen lines in emission. Its optical variability of ~0.3 mag was discovered by HIPPARCOS. The spectral type assigned to the star in SIMBAD is B9, but its position coincides…
Mass transfer between stars in binary systems profoundly impacts their evolution, yet many aspects of this process (especially the stability, mass loss, and eventual fate of such systems) remain poorly understood. One promising avenue to…
The prototype of the Beta Cep class of pulsating stars, Beta Cep, rotates relatively slowly, and yet displays episodic Halpha emission. Such behaviour is typical of a classical Be star. For some time this posed a contradiction to our…
Gamma-ray binaries are variable sources of GeV-to-TeV photons with the peak in their spectral energy distributions above 100 MeV. There are only five Galactic gamma-ray binaries known and the processes which govern particle acceleration,…
A growing number of early Be stars discovered in X-ray surveys exhibit X-ray luminosities intermediate between those of normal stars and those of most Be/X-ray binaries in quiescence. Their X-ray spectra are also much harder than those of…
We report on a newly detected point-like source, HESS J1943+213 located in the Galactic plane. This source coincides with an unidentified hard X-ray source IGR J19443+2117, which was proposed to have radio and infrared counterparts. HESS…
A correlation of X-ray source and Halpha emission-line object catalogues in the Small Magellanic Cloud (SMC) shows that more than two thirds of the optically identified Be stars in Be/X-ray binaries are found as emission-line objects in the…
The three objects have been identified as members of the recently recognized class of Gamma Doradus stars, which exhibit multi-periodic photometric variations that are thought to arise from non-radial pulsation. The particular objects…
We report the discovery of a new unidentified extended $\gamma$-ray source in the Galactic plane named LHAASO J0341+5258 with a pre-trial significance of 8.2 standard deviations above 25 TeV. The best fit position is…
We report the discovery of a new emission-line object, named SPH4-South = (GAIA EDR3 5616553300192230272), towards the dark cloud LDN 1667. This object came to our attention after inspecting public images that show a faint diffuse nebula a…
We report the discovery of a candidate binary system consisting of a black hole (BH) and a red giant branch star from the Gaia DR3. This binary system is discovered from 64108 binary solutions for which both astrometric and spectroscopic…
4FGL J0822.8-4207 is a point source found in the 4FGL-DR2 catalog by the gamma-ray observatory Fermi-LAT and has no known association. We carry out X-ray observations of 4FGL J0822.8-4207 to help understand its nature. We explore two…
The peculiar QSO J0927+2943 shows multiple sets of emission lines in its optical spectrum. This signature has been interpreted as the relative motion between a black hole, either recoiling or bound in a binary system, and its host galaxy,…
We present the results of a variable stars search in the field of the old open cluster NGC 2204. Five new variables were found, four of them being eclipsing binaries. The sample includes a detached binary located at the turnoff, a W UMa -…
X-ray and gamma-ray binaries are systems consisting of a compact object and normally a non-degenerate companion star. Most of these sources have been shown to emit radiation in a broad frequency range, from radio up to X-rays and sometimes…
We search for LBV stars in galaxies outside the Local Group. Here we present a study of two bright $H\alpha$ sources in the NGC 247 galaxy. Object j004703.27-204708.4 ($M_V=-9.08 \pm 0.15^m$) shows the spectral lines typical for…
Context. HD 110432 was classified as a "\gamma Cas X-ray analog" since it has similar peculiar X-ray and optical characteristics, i.e. a hard-thermal X-ray variable emission and an optical spectrum affected by an extensive disk. Lopes de…
We present results of a decade of X-ray observations of the gamma-ray loud binary HESS J0632+057, and interpret the available broadband data in view of the system geometry and emission mechanisms. We have performed an analysis of all X-ray…