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1

Mapping the Northern Galactic Disk Warp with Classical Cepheids

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

Acta Astronomica

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2019

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Vol. 69, No. 4

305--320

EN

We present an updated three dimensional map of the Milky Way based on a sample of 2431 classical Cepheid variable stars, supplemented with about 200 newly detected classical Cepheids from the OGLE survey. The new objects were discovered as a result of a dedicated observing campaign of the ≈280 square degree extension of the OGLE footprint of the Galactic disk during 2018-2019 observing seasons. These regions cover the main part of the northern Galactic warp that has been deficient in Cepheids so far. We use direct distances to the sample of over 2390 classical Cepheids to model the distribution of the young stellar population in the Milky Way and recalculate the parameters of the Galactic disk warp. Our data show that its northern part is very prominent and its amplitude is ≈10% larger than that of the southern part. By combining Gaia astrometric data with the Galactic rotation curve and distances to Cepheids from our sample, we construct a map of the vertical component of the velocity vector for all Cepheids in the Milky Way disk. We find large-scale vertical motions with amplitudes of 10-20 km/s, such that Cepheids located in the northern warp exhibit large positive vertical velocity (toward the north Galactic pole), whereas those in the southern warp - negative vertical velocity (toward the south Galactic pole).

2

Concerning the Distance to the Center of the Milky Way and Its Structure

Majaess D.

Acta Astronomica

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2010

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Vol. 60, No. 1

55--74

EN

The distance to the Galactic center inferred from OGLE RR Lyr variables observed in the direction of the bulge is R0=8.1±0.6 kpc. An accurate determination of R0 is hindered by countless effects that include an ambiguous extinction law, a bias for smaller values of R0 because of a preferential sampling of variable stars toward the near side of the bulge owing to extinction, and an uncertainty in characterizing how a mean distance to the group of variable stars relates to R0. A VI-based period-reddening relation for RR Lyr variables is derived to map extinction throughout the bulge. The reddening inferred from RR Lyr variables in the Galactic bulge, LMC, SMC, and IC 1613 match that established from OGLE red clump giants and classical Cepheids. RR Lyr variables obey a period-color (VI) relation that is relatively insensitive to metallicity. Edge-on and face-on illustrations of the Milky Way are constructed by mapping the bulge RR Lyr variables in tandem with cataloged red clump giants, globular clusters, planetary nebulae, classical Cepheids, young open clusters, HII regions, and molecular clouds. The sample of RR Lyr variables do not trace a prominent Galactic bar or triaxial bulge oriented at φ≅25°.

3

Binary Source Lensing and the Repeating OGLE EWS Events

Jaroszyński M., Skowron J.

Acta Astronomica

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2008

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Vol. 58, No. 4

345--358

EN

A microlensing event may exhibit a second brightening when the source and/or the lens is a binary star. Previous study revealed 19 such repeating event candidates among 4120 investigated microlensing light curves of the Optical Gravitational Lensing Experiment (OGLE). The same study gave the probability ≈0.0027 for a repeating event caused by a binary lens. We present the simulations of binary source lensing events and calculate the probability of observing a second brightening in the light curve. Applying to simulated light curves the same algorithm as it was used in the analysis of real OGLE data, we find the probability ≈0.0018 of observing a second brightening in a binary source lensing curve. The expected and measured numbers of repeating events are in agreement only if one postulates that all lenses and all sources are binary. Since the fraction of binaries is believed to be ≤50%, there seems to be a discrepancy.

4

Binary Lenses in OGLE-II 1997-1999 Database. A Preliminary Study

Jaroszyński M.

Acta Astronomica

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2002

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Vol. 52, No. 1

39--60

EN

We present 18 binary lens candidates from OGLE-II database for seasons 1997-1999. The candidates have been selected by visual light curves inspection from the subsample of strong transient events; the same procedure gives 215 single lens candidates. Among the double lenses there are 12 cases interpreted as caustic crossing events. We compare the mass ratio and separation distributions obtained for binary lenses with the predictions based on stellar double systems observations. We take into account the selection bias, which causes over-representation of binary lenses of similar mass and separation close to the Einstein radius. There is no strong discrepancy between the expected and observed distributions of the mass ratio or the binary separations. We find one or two cases of binary lens candidates, SC20_1793 and SC20_3525, with extreme mass ratios, which may suggest presence of planets or brown dwarf companions. Unfortunately, neither case is very strong, as alternative solutions provide fits to the data which are only unsubstantially worse. Binary lenses provide a modest contribution to the overall optical depth to microlensing.

5

The Optical Gravitational Lensing Experiment. Catalog of Microlensing Events in the Galactic Bulge

Udalski A., Żebruń K., Szymański M., Kubiak M., Pietrzyński G., Soszyński I., Woźniak P.

Acta Astronomica

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2000

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Vol. 50, No. 1

1--65

EN

We present the Catalog of microlensing events detected toward the Galactic bulge in three observing seasons, 1997-1999, during the OGLE-II microlensing survey. The search for microlensing events was performed using a database of about 4×109 photometric measurements of about 20.5 million stars from the Galactic bulge. The Catalog comprises 214 microlensing events found in the fields covering about 11 square degrees on the sky and distributed in different parts of the Galactic bulge. The sample includes 20 binary microlensing events, 14 of them are caustic crossing. In one case a double star is likely lensed. We present distribution of the basic parameters of microlensing events and show preliminary rate of microlensing in different regions of the Galactic bulge. The latter reveals clear dependence on the Galactic coordinates. The dependence on l indicates that the majority of lenses toward the Galactic bulge are located in the Galactic bar. Models of the Galactic bar seem to reasonably predict the observed spatial distribution of microlensing events in the Galactic bulge. All data presented in the Catalog and photometry of all events are available from the OGLE Internet archive.