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1

Over 24 000 δ Scuti Stars in the Galactic Bulge and Disk from the OGLE Survey

Soszyński I., Pietrukowicz P., Skowron J., Udalski A., Szymański M. K., Skowron D. M., Poleski R., Kozłowski S., Mróz P., Ulaczyk K., Rybicki K., Iwanek P., Wrona M., Gromadzki M.

Acta Astronomica

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2021

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Vol. 71, No. 3

189--204

EN

We present the largest collection of δ Scuti-type stars in the Milky Way. Together with the recently published OGLE collection of δ Sct variables in the inner Galactic bulge, our sample consists of 24 488 objects distributed along the Milky Way plane, over galactic longitudes ranging from about -170° to +60°. The collection data include the I- and V-band time-series photometry collected since 1997 during the OGLE-II, OGLE-III, and OGLE-IV surveys. We show the on-sky distribution of δ Sct stars in the Galactic bulge and disk, discuss their period, luminosity and amplitude distributions, present Petersen diagram for multimode pulsators, distinguish 34 δ Sct stars in eclipsing and ellipsoidal binary systems, and list probable members of globular clusters.

2

Classical Cepheids in the Milky Way

Pietrukowicz P., Soszyński I., Udalski A.

Acta Astronomica

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2021

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Vol. 71, No. 3

205--222

EN

We share the most up-to-date, carefully verified list of classical Cepheids residing in the Galaxy. Based on long-term OGLE experience in the field of variable stars, we have inspected candidates for Cepheids from surveys such as ASAS, ASAS-SN, ATLAS, Gaia, NSVS, VVV, WISE, ZTF, among others, and also known sources from the General Catalogue of Variable Stars. Only objects confirmed in the optical range as classical Cepheids are included in the list. We provide Gaia EDR3 identifications of the stars. Purity of the sample exceeds 97 per cent, while its completeness is of about 88 per cent down to a magnitude G = 18. The list contains 3352 classical Cepheids, of which 2140 stars are fundamental-mode pulsators. Basic statistics and comparison between the classical Cepheids from the Milky Way, Andromeda Galaxy (M31), and Magellanic Clouds are provided. The list is available at the OGLE Internet Data Archive.

3

Properties of the Milky Way's Old Populations Based on Photometric Metallicities of the OGLE RR Lyrae Stars

Pietrukowicz P., Udalski A., Soszyński I., Skowron D. M., Wrona M., Szymański M. K., Poleski R., Ulaczyk K., Kozłowski S., Skowron J., Mróz P., Rybicki K., Iwanek P., Gromadzki M.

Acta Astronomica

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2020

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Vol. 70, No. 2

121--139

EN

We have used photometric data on almost 91 000 fundamental-mode RR Lyr stars (type RRab) detected by the OGLE survey to investigate properties of old populations in the Milky Way. Based on their metallicity distributions, we demonstrate that the Galaxy is built from three distinct old components: halo, bulge, and disk. The distributions reach their maxima at approximately [Fe/H]J95=-1.2 dex, -1.0 dex, and -0.6 dex on the Jurcsik's metallicity scale, respectively. We find that, very likely, the entire halo is formed from infalling dwarf galaxies. It is evident that halo stars penetrate the inner regions of the Galactic bulge. We estimate that about one-third of all RR Lyr stars within the bulge area belong in fact to the halo population. The whole old bulge is dominated by two populations, A and B, represented by a double sequence in the period--amplitude (Bailey) diagram. The boundary in iron abundance between the halo and the disk population is at about [Fe/H]J95=-0.8 dex. Using Gaia DR2 for RRab stars in the disk area, we show that the observed dispersion of proper motions along the Galactic latitude decreases smoothly with the increasing metal content excluding a bump around [Fe/H]J95=-1.0 dex.

4

Additional Galactic Cepheids from the OGLE Survey

Soszyński I., Udalski A., Szymański M. K., Pietrukowicz P., Skowron J., Skowron D. M., Poleski R., Kozłowski S., Mróz P., Ulaczyk K., Rybicki K., Iwanek P., Wrona M., Gromadzki M.

Acta Astronomica

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2020

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Vol. 70, No. 2

101--119

EN

We report on the results of a comprehensive search for Cepheid variable stars in the fields photometrically monitored by the OGLE Galaxy Variability Survey. We identify 742 Cepheids not included in the first release of the OGLE Collection of Galactic Cepheids and reclassify several dozen previously published variables. The upgraded collection comprises 1974 classical, 1625 type II, and 119 anomalous Cepheids located in the area of about 3000 square degrees covering the disk and bulge of the Milky Way. We present the most interesting objects in our sample: an isolated group of long-period double-mode classical Cepheids pulsating in the fundamental mode and first overtone, the first known Galactic double-mode Cepheid with the second and third overtone excited, double-mode type II Cepheids, candidates for single-mode first-overtone BL Her stars, and Cepheids showing simultaneous eclipsing variability. We also discuss type II and anomalous Cepheids that are potential members of globular clusters.

5

Over 78 000 RR Lyrae Stars in the Galactic Bulge and Disk from the OGLE Survey

Soszyński I., Udalski A., Wrona M., Szymański M. K., Pietrukowicz P., Skowron J., Skowron D., Poleski R., Kozłowski S., Mróz P., Ulaczyk K., Rybicki K., Iwanek P., Gromadzki M.

Acta Astronomica

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2019

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Vol. 69, No. 4

321--337

EN

We present an upgrade of the OGLE Collection of RR Lyrae stars in the Galactic bulge and disk. The size of our sample has been doubled and reached 78 350 RR Lyr variables, of which 56 508 are fundamental-mode pulsators (RRab stars), 21 321 pulsate solely in the first-overtone (RRc stars), 458 are classical double-mode pulsators (RRd stars), and 63 are anomalous RRd variables (including six triple-mode pulsators). For all the newly identified RR Lyr stars, we publish time-series photometry obtained during the OGLE Galaxy Variability Survey. We present the spatial distribution of RR Lyr stars on the sky, provide a list of globular clusters hosting RR Lyr variables, and discuss the Petersen diagram for multimode pulsators. We find new RRd stars belonging to a compact group in the Petersen diagram (with period ratios P 1O/PF≈0.74 and fundamental-mode periods P F≈0.44$ d) and we show that their spatial distribution is roughly spherically symmetrical around the Milky Way center.

6

Searching for Potential Mergers among 22 500 Eclipsing Binary Stars in the OGLE-III Galactic Bulge Fields

Pietrukowicz P., Soszyński I., Udalski A., Szymański M. K., Wyrzykowski Ł., Poleski R., Kozłowski S., Skowron J., Mróz P., Pawlak M., Ulaczyk K.

Acta Astronomica

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2017

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Vol. 67, No. 2

115--130

EN

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 selected a sample of 22 462 short-period (Porb˂4 d) eclipsing binary stars observed toward the Galactic bulge by the OGLE-III survey in years 2001-2009. This dataset was extended with photometry from OGLE-II (1997-2000) and the first six years of OGLE-IV (2010--2015). For some stars, the data were supplemented with OGLE-I photometry (1992-1995). After close inspection of the whole sample we have found 56 systems with realistic period decrease and 52 systems with realistic period increase. We have also recognized 35 systems with cyclic period variations. The highest negative period change rate of -1.943×10-4 d/y has been detected in detached eclipsing binary OGLE-BLG-ECL-139622 with Porb=2.817 d, while all other found systems are contact binaries with orbital periods mostly shorter than 1.0 d. For 22 our systems with decreasing orbital period the absolute rate is higher than the value reported recently for eclipsing binary KIC 9832227. Interestingly, there is an excess of systems with high negative period change rate over systems with positive rate. We cannot exclude the possibility that some of the contact binaries with relatively long orbital period and high negative period change rate will merge in the future. However, our results rather point to the presence of tertiary companions in the observed systems and/or spot activity on the surface of the binary components.

7

OGLE-IV: Fourth Phase of the Optical Gravitational Lensing Experiment

Udalski A., Szymański M. K., Szymański G.

Acta Astronomica

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2015

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Vol. 65, No. 1

1--38

EN

We present both the technical overview and main science drivers of the fourth phase of the Optical Gravitational Lensing Experiment (hereafter OGLE-IV). OGLE-IV is currently one of the largest sky variability surveys worldwide, targeting the densest stellar regions of the sky. The survey covers over 3000 square degrees in the sky and monitors regularly over a billion sources. The main targets include the inner Galactic Bulge and the Magellanic System. Their photometry spans the range of 12

8

Principal Component Abundance Analysis of Microlensed Bulge Dwarf and Subgiant Stars

Andrews B. H., Weinberg D. H., Johnson J. A., Bensby T., Feltzing S.

Acta Astronomica

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2012

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Vol. 62, No. 3

269--279

EN

Elemental abundance patterns can provide vital clues to the formation and enrichment history of a stellar population. Here we present an investigation of the Galactic bulge, where we apply principal component abundance analysis (PCAA) - a principal component decomposition of relative abundances [X/Fe] - to a sample of 35 microlensed bulge dwarf and subgiant stars, characterizing their distribution in the 12-dimensional space defined by their measured elemental abundances. The first principal component PC1, which suffices to describe the abundance patterns of most stars in the sample, shows a strong contribution from α-elements, reflecting the relative contributions of Type II and Type Ia supernovae. The second principal component PC2 is characterized by a Na-Ni correlation, the likely product of metallicity-dependent Type II supernova yields. The distribution in PC1 is bimodal, showing that the bimodality previously found in the [Fe/H] values of these stars is robustly and independently recovered by looking at only their relative abundance patterns. The two metal-rich stars that are α-enhanced have outlier values of PC2 and PC3, respectively, further evidence that they have distinctive enrichment histories. Applying PCAA to a sample of local thin and thick disk dwarfs yields a nearly identical PC1. In PC1, the metal-rich and metal-poor bulge dwarfs track kinematically selected thin and thick disk dwarfs, respectively, suggesting broadly similar α-enrichment histories. However, the disk PC2 is dominated by a Y-Ba correlation, likely indicating a contribution of s-process enrichment from long-lived asymptotic giant branch stars that is absent from the bulge PC2 because of its rapid formation.

9

Detached Red Giant Eclipsing Binary Twins: Rosetta Stones to the Galactic Bulge

Nataf D. M., Gould A., Pinsonneault M. H.

Acta Astronomica

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2012

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Vol. 62, No. 1

33--65

EN

We identify 34 highly-probable detached, red giant eclipsing binary pairs among 315 candidates in Devor's catalog of ≈10 000 OGLE-II eclipsing binaries. We estimate that there should be at least 200 such systems in OGLE-III. We show that spectroscopic measurements of the metallicities and radial-velocity-derived masses of these systems would independently constrain both the age-metallicity and helium-metallicity relations of the Galactic bulge, potentially breaking the age-helium degeneracy that currently limits our ability to characterize the bulge stellar population. Mass and metallicity measurements alone would be sufficient to immediately validate or falsify recent claims about the age and helium abundance of the bulge. A spectroscopic survey of these systems would constrain models of Milky Way assembly, as well as provide significant auxiliary science on research questions such as mass loss on the red giant branch. We discuss the theoretical uncertainties in stellar evolution models that would need to be accounted for to maximize the scientific yield.

10

The Optical Gravitational Lensing Experiment. OGLE-III Photometric Maps of the Galactic Bulge Fields

Szymański M. K., Udalski A., Soszyński I., Kubiak M., Pietrzyński G., Poleski R., Wyrzykowski Ł., Ulaczyk K.

Acta Astronomica

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2011

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Vol. 61, No. 2

83--102

EN

We present OGLE-III Photometric Maps of the Galactic bulge fields observed during the third phase of the OGLE project. This paper describes the last, concluding set of maps based on OGLE-III data. The maps contain precise, calibrated VI photometry of about 340 million stars from 267 fields in the Galactic bulge observed during entire OGLE-III phase (2002-2009), covering about 92 square degrees in the sky. Precise astrometry of these objects is also provided. We briefly discuss the photometry procedures and the quality of the data. We also present sample data and color-magnitude diagrams of the observed fields. All photometric data are available to the astronomical community from the OGLE Internet archive.

11

The Optical Gravitational Lensing Experiment. Internet Access to the OGLE Photometry Data Set: OGLE-II BVI maps and I-band data

Szymański M. K.

Acta Astronomica

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2005

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Vol. 55, No. 1

43--57

EN

We present on-line, interactive interface to the whole I-band photometry data set obtained in the second phase of the OGLE project (OGLE-II). The raw photometric database is accessed through an additional database using MySQL engine, allowing to select objects fulfilling any set of criteria including RA/Dec coordinates, mean brightness, error etc. The results of the queries can be browsed on-line, the light curves can be plotted interactively, the photometric data can be downloaded for the total of over 1010 measurements of more than 40 million objects in the Galactic bulge and the Magellanic Clouds collected during OGLE-II. The MySQL database of parameters also includes the complete data set of the previously published photometric BVI maps of OGLE-II targets, allowing to interactively select objects from these maps.

12

Mass Estimates for Some of the Binary Lenses in OGLE-III Database

Jaroszyński M., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Soszyński I., Żebruń K., Szewczyk O., Wyrzykowski Ł.

Acta Astronomica

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2005

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Vol. 55, No. 2

159--175

EN

We model binary microlensing events OGLE 2003-BLG-170, 267, and 291. Source angular sizes are measured for the events 267 and 291. Model fits to the light curves give parallaxes for the events 267 and 291, and relative source sizes for 170 and 267. Selfconsistency arguments provide extra limits on the models of the event 291. As a result we obtain likelihood estimate of the lens mass for the event 170, mass measurement based on angular size and parallax for 267, and narrow limits on mass in the case of 291. Brown dwarfs are most likely candidates for some of the lens components. The influence of the binary lens rotation and the Earth parallax may be important but hard to distinguish when modeling relatively short lasting binary lens events.

13

Multiperiodic RR Lyr Stars in the Center of the Galaxy

Mizerski T.

Acta Astronomica

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2003

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Vol. 56, No. 4

307--320

EN

This paper presents results of a fully automated search for multiperiodic RR Lyr stars in the center of the Galaxy. The search was carried out on OGLE-II database created by means of image subtraction method. I found more than 2700 RR Lyr stars with about 600 showing various kinds of multiperiodic behavior. Previous OGLE-I database contained only about 200 RR Lyr stars in the Galactic bulge, that is twelve times less than the current sample. There are two most interesting outcomes for the Galactic bulge sample: very high percentage of Blazhko stars and very low percentage of RRd stars. Blazhko effect was confirmed in about 25% of all RRab stars. This incidence rate is almost 2.5 times greater than in the Large Magellanic Cloud. On the other hand I discovered only 3 RRd stars which implies that the incidence rate of this type of variables is much smaller in the bulge sample than in the Magellanic Cloud RR Lyr stars.

14

The Optical Gravitational Lensing Experiment. BVI Maps of Dense Stellar Regions. III. The Galactic Bulge

Udalski A., Szymański M., Kubiak M., Pietrzyński G., Soszyński I., Woźniak P., Żebruń K., Szewczyk O., Wyrzykowski Ł.

Acta Astronomica

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2002

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Vol. 52, No. 3

217--240

EN

We present the VI photometric maps of the Galactic bulge. They contain VI photometry and astrometry of about 30 million stars from 49 fields of 0.225 square degree each in the Galactic center region. The data were collected during the second phase of the OGLE microlensing project. We discuss the accuracy of data and present color-magnitude diagrams of selected fields observed by OGLE in the Galactic bulge. The VI maps of the Galactic bulge are accessible electronically for the astronomical community from the OGLE Internet archive.