Related papers: The Araucaria Project. Binary Classical Cepheids i…

We have performed systematic frequency analysis of the LMC Cepheids observed by OGLE project. Several new types of pulsation behaviour are identified, including triple-mode and amplitude-modulated double-mode pulsations. In ~10% of the…

This paper presents a detailed analysis of the light and radial velocity curves of the semi-detached eclipsing binary system OGLE-LMC-ECL-09937. The system is composed of a hot, massive and luminous primary star of a late-O spectral type,…

Context: It appears that most (if not all) massive stars are born in multiple systems. At the same time, the most massive binaries are hard to find due to their low numbers throughout the Galaxy and the implied large distances and…

Using Campaign 15 data from the K2 mission, we have discovered a triply-eclipsing triple star system: EPIC 249432662. The inner eclipsing binary system has a period of 8.23 days, with shallow $\sim$3% eclipses. During the entire 80-day…

We present the Catalog of Cepheids from the SMC which contains data for 2049 objects detected in the 2.4 square degree area of central parts of the SMC. For each object period, BVI photometry, astrometry, and R_21, \phi_21 parameters of the…

Inspired by the discovery of the red nova V1309 Sco (Nova Scorpii 2008) and the fact that its progenitor was a binary system with a rapidly decreasing orbital period, we have searched for period changes in OGLE binary stars. We have…

We present an analysis of the period distribution of $\sim 1800$ Cepheids in the Large Magellanic Cloud, based on data obtained by the MACHO microlensing experiment and on a previous catalogue by Payne-Gaposchkin. Using stellar evolution…

We employed the {\it VISTA near-infrared $YJK_\mathrm{s}$ survey of the Magellanic System} (VMC), to analyse the $Y,\,J,\,K_\mathrm{s}$ light curves of $\delta$ Cepheid stars (DCEPs) in the Large Magellanic Cloud (LMC). Our sample consists…

We report the discovery of the classical Cepheid OGLE-GD-CEP-1884 (= GDS_J1535467-555656) with the longest pulsation period known in our Galaxy. The period of 78.14 d is nearly 10 d longer than that of the previous record-holding Cepheid, S…

New spectroscopic observations of the LBV/WR multiple system HD5980 in the Small Magellanic Cloud are used to address the question of the masses and evolutionary status of the two very luminous stars in the 19.3d eclipsing binary system.…

We confirm the existence of a second Large Magellanic Cloud (LMC) star cluster, KMHK 1592, with an age that falls in the middle of the so-called LMC star cluster age gap, a long period of time (~ 4 - 11 Gyr) where no star cluster had been…

We present a detailed optical and X-ray study of the 2013 outburst of the Small Magellanic Cloud Be/X-ray binary SXP7.92, as well as an overview of the last 18 years of observations from OGLE, RXTE, Chandra and XMM-Newton. We revise the…

The Small Magellanic Cloud is increasingly an invaluable laboratory for studying accreting and isolated X-ray pulsars. We add to the class of compact SMC objects by reporting the discovery of three new long period X-ray pulsars detected…

We present the discovery of 32 new double periodic variables (DPVs) located toward the Galactic bulge. We found these objects among the nearly half a million binary stars published by the Optical Gravitational Lensing Experiment project.…

In the present study, we continue testing the Primordial Group hypothesis (Casado 2022), which postulates that only sufficiently young open clusters can be binary or multiple, and old clusters are essentially single. To this end, we revisit…

The Optical Gravitational Lensing Experiment (OGLE) continuously monitors hundreds of thousands of eclipsing binaries in the field of galactic bulge and the Magellanic Clouds. These objects have been classified into main morphological…

The period-change rate (PCR) of pulsating variable stars is a useful probe of changes in their interior structure, and thus of their evolutionary stages. So far, the PCRs of Classical Cepheids in the Large Magellanic Cloud (LMC) have been…

The main aim of the present paper is the very first analysis of the binary-orbit precession out of our Galaxy. The light curves of an eclipsing binary MACHO 82.8043.171 in the Large Magellanic cloud (LMC) were studied in order to analyse…

We analyse photometry of $\sim$2000 Galactic Cepheids available in the OGLE Collection of Variable Stars. We analyse both Galactic disk and Galactic bulge fields; stars classified both as single- and multi-periodic. Our goal was to search…

We present the results of a theoretical investigation aimed at testing whether full amplitude, nonlinear, convective models account for the I-band light curves of Bump Cepheids in the Large Magellanic Cloud (LMC). We selected two objects…