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The subtype of hot algol semidetached binaries dubbed Double Periodic Variables (DPVs) are characterized by a photometric cycle longer than the orbital one, whose nature has been related to a magnetic dynamo in the donor component…

The tenth part of the OGLE-III Catalog of Variable Stars contains 125 Double Periodic Variables (DPVs) from the Large Magellanic Cloud. DPVs are semi-detached binaries which show additional variability with a period around 33 times longer…

Double Periodic Variables (DPV) are among the new enigmas of semi-detached eclipsing binaries. These are intermediate-mass binaries characterized by a long photometric period lasting on average 33 times the orbital period. We present a…

We present results from new optical and UV spectroscopy of the unusual binary system SS 433, and we discuss the relationship of the particular spectral components we observe to the properties of the binary. (1) The continuum spectrum which…

We present multiwavelength broadband photometry and V, I time resolved photometry for two variable bright stars in the SMC, OGLE004336.91-732637.7 (SMC-SC3) and OGLE004633.76-731204.3 (SMC-SC4). The light curves span 12 years and show…

To progress in the comprehension of the double periodic variable (DPV) phenomenon, we analyse a series of optical spectra of the DPV system DQ Velorum during much of its long-term cycle. In addition, we investigate the evolutionary history…

One of the most intriguing spectral features of WR binary stars is the presence of time-dependent line profiles. Long term observations of several systems revealed the periodicity of this variability, synchronized with the orbital movement.…

Binary pulsar systems emit potentially detectable components of gamma ray emission due to Comptonization of the optical radiation of the companion star by relativistic electrons of the pulsar wind, both before and after termination of the…

Eclipses in the 14.4-day period double-lined binary SS Lac were observed photographically and visually early in the 20th century, but stopped some 50 or 60 years ago. This has been explained by the presence of a distant third star in the…

Polarimetry of IGR J1401-4306, a long period (12.7 hours), eclipsing intermediate polar and remnant of Nova Scorpii 1437 A.D., reveals periodic variations of optical circular polarization, confirming the system as the longest period…

PSR B1259-63 is a 47ms radio pulsar with a high spin-down luminosity which is in a close, highly eccentric 3.5-year orbit about a bright stellar companion. The binary system may be a detectable source of hard gamma-rays produced by inverse…

V383Sco was discovered to be an eclipsing binary at the beginning of the XX century. This system has one of the longest orbital periods known (13.5yr) and was initially classified as a zet_Aur-type variable. It was then forgotten for…

We present new observations of the cataclysmic variable V523 Lyr, a member of the open cluster NGC 6791. The Kepler Space telescope obtained photometric observations of this source and we examine the nearly 3 year long light curve. The…

V Sagittae shows quasi-periodic optical high (soft X-ray off) and low (soft X-ray on) states with the total period of ~300 days. A binary model is presented to explain orbital light curves both for the high and low states as well as the…

PSR B1259-63 is a 48 ms radio pulsar in a highly eccentric 3.4 year orbit with a Be star SS 2883. Unpulsed gamma-ray, X-ray and radio emission components are observed from the binary system. It is likely that the collision of the pulsar…

Stochastically-triggered photospheric light variations reaching $\sim$$40$ mmag peak-to-valley amplitudes have been detected in the O8Iaf supergiant V973 Scorpii as the outcome of two months of high-precision time-resolved photometric…

We report simultaneous UBVRI photo-polarimetric observations of the long period (7.98 h) AM Her binary V1309 Ori. The length and shape of the eclipse ingress and egress varies from night to night. We suggest this is due to the variation in…

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…

The radio millisecond pulsar PSR J1023+0038 exhibits complex timing and eclipse behavior. Here we analyze four years' worth of radio monitoring observations of this object. We obtain a long-term timing solution, albeit with large residual…

Centaurus X-3 is a persistent high-mass X-ray binary with the long-term light curve from the source exhibiting orbit-to-orbit intensity variations with no apparent superorbital periodicity. We used $\sim$13.5 years of MAXI/GSC data to study…