Related papers: The Globular Cluster Omega Centauri and the Ooster…
We present a new complete Near-Infrared (NIR, $JHK_s$) census of RR Lyrae stars (RRLs) in the globular $\omega$ Cen (NGC 5139). We collected 15,472 $JHK_s$ images with 4-8m class telescopes over 15 years (2000-2015) covering a sky area…
The third Gaia data release provides photometric time series covering 34 months for about 10 million stars. For many of those stars, a characterisation in Fourier space and their variability classification are also provided. This paper…
Because of strong and spatially highly variable interstellar extinction and extreme source crowding, the faint (K>15) stellar population in the Milky Way's nuclear cluster is still poorly studied. RR Lyrae stars provide us with a tool to…
We have frequency analyzed 6391 variables classified earlier as fundamental mode RR Lyrae (RR0) stars in the MACHO database on the Large Magellanic Cloud (LMC). The overwhelming majority of these variables have been proved to be indeed RR0…
The number of stars observed by the Optical Gravitational Lensing Experiment (OGLE) project in the Galactic bulge offers an invaluable chance to study RR Lyrae stars in a statistical manner. We used data of 3141 fundamental-mode RR Lyrae…
We present a new analysis of the stellar population of the Orion Nebula Cluster (ONC) based on multi-band optical photometry and spectroscopy. We study the color-color diagrams in BVI, plus a narrow-band filter centered at 6200A, finding…
We present the OGLE collection of delta Scuti stars in the Large Magellanic Cloud and in its foreground. Our dataset encompasses a total of 15 256 objects, constituting the largest sample of extragalactic delta Sct stars published so far.…
We present a new search for variable stars in the Galactic globular cluster M28 (NGC 6626). The search is based on a series of BVI images obtained with the SMARTS Consortium's 1.3m telescope at Cerro Tololo Inter-American Observatory,…
We present new spectroscopic metal abundances for 74 RR Lyrae stars in omega Cen obtained with FLAMES. The well-known metallicity spread is visible among the RR Lyrae variables. The metal-intermediate (MInt) RR Lyrae stars ([Fe/H] ~ -1.2)…
Multi-wavelength CCD photometry over 21 years has been used to produce deep color-magnitude diagrams together with light curves for the variables in the Galactic globular cluster NGC 5824. Twenty-one new cluster RR Lyrae stars are…
Based on photometric data obtained between 1935 and 2017, $O-C$ diagrams were built for 22 RR Lyrae stars in the globular cluster NGC 6171, leading to the discovery of secular period changes in 4 variables for which we have calculated their…
We present the preliminary results of an image-subtraction analysis of the Galactic globular cluster M79 (NGC 1904), as well as a new investigation of the variable star population in NGC 1851. Both M79 and NGC 1851 have been previously…
We have analyzed the data on 16,836 RR Lyrae (RR Lyr) variables observed toward the Galactic bulge during the third phase of the Optical Gravitational Lensing Experiment (OGLE-III), which took place in 2001-2009. Using these standard…
We report the discovery of 6 SX Phoenicis stars in the southern globular cluster NGC 4833. Images were obtained from January through June 2011 with the Southeastern Association for Research in Astronomy 0.6 meter telescope located at Cerro…
In this letter we investigate the origin of the Oosterhoff dichotomy, considering recent discoveries related to several ancient merging events of external galaxies with the Milky Way (MW). In particular, we aim to clarify if the subdivision…
We report on new B, V and I CCD photometry of the globular cluster M54 that was aimed at the study of its variable stars. With respect to the previous most recent work on M54 we have nearly doubled the number of detected variable stars: M54…
One of the long-standing problems in modern astronomy is the curious division of Galactic globular clusters, the "Oosterhoff dichotomy," according to the properties of their RR Lyrae stars. Here, we find that most of the lowest-metallicity…
We report the discovery of an intriguing triple-mode RR Lyrae star found in the OGLE Galactic bulge collection, OGLE-BLG-RRLYR-24137. In the OGLE catalog the star was identified as RRd star - double-mode pulsator, pulsating simultaneously…
The first catalog of the RR Lyrae stars (RRLS) in the Galactic halo by the QUEST Survey has been searched for significant overdensities that may be debris from disrupted dwarf galaxies or globular clusters. Away from the major…
NGC 6441 is a bulge globular cluster with an unusual horizontal branch morphology and a rich population of RR Lyrae (RRL) and Type II Cepheid (T2C) variables that is unexpected for its relatively high metallicity. We present near-infrared…