The OGLE Collection of Variable Stars: Nearly 66,000 Mira Stars in the Milky Way

Abstract

We present a collection of 65,981 Mira-type variable stars found in the Optical Gravitational Lensing Experiment (OGLE) project database. Two-thirds of our sample (40,356 objects) are located in the Galactic bulge fields, whereas 25,625 stars are in the Galactic disk. The vast majority of the collection (47,532 objects) comprises new discoveries. We provide basic observational parameters of the Mira variables: equatorial coordinates, pulsation periods, I-band and V-band mean magnitudes, I-band brightness amplitudes, and identifications in other catalogs of variable stars. We also provide the I-band and V-band time-series photometry collected since 1997 during the OGLE-II, OGLE-III, and OGLE-IV phases. The classical selection process, i.e., being mostly based on the visual inspection of light curves by experienced astronomers, has led to the high purity of the catalog. As a result, this collection can be used as a training set for machine-learning classification algorithms. Using overlapping areas of adjacent OGLE fields, we estimate the completeness of the catalog to be about 96%. We compare and discuss the statistical features of Miras located in different regions of the Milky Way. We show examples of stars that change their type over time, from a semiregular variable to Mira and vice versa. This data set is perfectly suited to studying the three-dimensional structure of the Milky Way, and it may help to explain the puzzle of the X-shaped bulge.

Analysing the structure of the bulge with Mira variables

“…The maximum amplitude of the variation within the period for these Mira stars in bulge fields is lower than ≈ 3 magnitudes (Fig. 8, Iwanek et al 2022). The limiting magnitude is m I,max = 19.0 for |b| > 5 • (Udalski et al 2015), although for very crowded fields at lower latitudes it can be lower (for instance, a value of m I,max = 18.5 at = 1 • , b = −2 • was estimated by Udalski et al 2015).…”

“…We used OGLE-IV data of Mira variables (Iwanek et al 2022), carried out with the 1.3 m Warsaw Telescope at the Las Campanas Observatory in Chile. The catalogue covers the whole Galactic bulge area with 40 356 objects, most of them near the plane, and contains an additional 25 625 stars in the Galactic disk, observed in the Johnson V-band (mean wavelength of 0.55 µm) and Cousins I-band (mean wavelength of 0.81 µm) filters.…”

“…We used OGLE-IV data of Mira variables (Iwanek et al 2022) We analysed the bulge using stars far from the plane (700 pc≤ |Z| < 1500 pc) in order to avoid the problems of incompleteness due to extinction, and also because the Xshape features are only notable within this range of Z. The completeness is estimated to be 96% (Iwanek et al 2022); ∼ 4% of Miras are not classified as such due to the small number of epochs.…”

“…Mira variables are pulsating stars, with periods ranging from about 80 to over 1000 days. They are cool giant stars near the tip of the asymptotic giant branch with a high brightness and a well-defined period-luminosity relation, which makes them excellent distance indicators and a useful population for studying Galactic structure (Iwanek et al 2022). In this Letter we repeat the analysis by López-Corredoira (2017) for the density of the bulge with Mira variables, but with a much larger coverage and number of stars provided by the recent data release of the Optical Gravitational Lensing Experiment survey (OGLE-IV).…”

Deep drilling in the time domain with DECam: survey characterization

“…Of the matches, we find 3143 are long period variables (LPV), 1671 are eclipsing binaries (ECL), 511 are RR Lyrae (RRLyr), 12 are short timescale variables, and 4 are Cepheids (CEP). We also cross-matched our good candidates with the variable star catalogs from the Optical Gravitational Lensing Experiment (OGLE) in the Galactic bulge (Udalski et al 2008(Udalski et al , 2015(Udalski et al , 2018Soszyński et al 2014Soszyński et al , 2019Iwanek et al 2022). We found 4480 matches after applying a conservative search radius of 1 for our candidates.…”