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M. Szymanski

Publications and source records attributed to M. Szymanski.

At least 55 records · Page 3Linked to original sources
arXiv2000

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

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*10^9 photometric measurements of about 20.5 million stars from the Galactic bulge. The Catalog comprises 214 cases of 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.

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arXiv1999

The Optical Gravitational Lensing Experiment. Catalog of Star Clusters from the Large Magellanic Cloud

We present the catalog of star clusters found in the area of about 5.8 square degree in the central regions of the Large Magellanic Cloud. It contains data for 745 clusters. 126 of them are new objects. For each cluster equatorial coordinates, radius, approximate number of members and cross-identification are provided. Photometric data for all clusters presented in the catalog and Atlas consisting of finding charts and color-magnitude diagrams are available electronically from the OGLE Internet archive.

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arXiv1999

The Optical Gravitational Lensing Experiment. Cepheids in the Magellanic Clouds. V. Catalog of Cepheids from the Small Magellanic Cloud

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, ϕ_21 parameters of the Fourier decomposition of I-band light curve are provided. The Catalog is based on observations collected during the OGLE-II microlensing survey. Tests of completeness performed in overlapping parts of adjacent fields indicate that completeness of the Catalog is very high: about 92%. Statistics and distributions of basic parameters of Cepheids are also presented. All presented data, including individual BVI observations (about 4.7*10^5 BVI measurements), are available from the OGLE Internet archive.

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arXiv1999

The Optical Gravitational Lensing Experiment. Cepheids in the Magellanic Clouds. IV. Catalog of Cepheids from the Large Magellanic Cloud

We present the Catalog of Cepheids from the LMC. The Catalog contains 1333 objects detected in the 4.5 square degree area of central parts of the LMC. About 3.4*10^5 BVI measurements of these stars were collected during the OGLE-II microlensing survey. The Catalog data include period, BVI photometry, astrometry, and R_21, ϕ_21 parameters of the Fourier decomposition of I-band light curve. The vast majority of objects from the Catalog are the classical Cepheids pulsating in the fundamental or first overtone mode. The remaining objects include Population II Cepheids and red giants with pulsation-like light curves. Tests of completeness performed in overlapping parts of adjacent fields indicate that completeness of the Catalog is very high: >96%. Statistics and distributions of basic parameters of Cepheids are also presented. Finally, we show the light curves of three eclipsing systems containing Cepheid detected among objects of the Catalog. All presented data, including individual BVI observations are available from the OGLE Internet archive.

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arXiv1999

The Optical Gravitational Lensing Experiment. Cepheids in the Magellanic Clouds. III. Period-Luminosity-Color and Period-Luminosity Relations of Classical Cepheids

We present Period-Luminosity-Color and Period-Luminosity relations of classical Cepheids constructed for about 1280 Cepheids from the LMC and 2140 from the SMC. High quality BVI observations (120-360 epochs in the I-band and 15-40 in the BV-bands) were collected during the OGLE-II microlensing experiment. The I-band diagrams of the LMC show very small scatter, σ=0.074 mag, indicating that Cepheid variables can potentially be a very good standard candle. We compare relations of fundamental mode Cepheids from the LMC and SMC and we do not find significant differences of slopes of the Period-Luminosity- Color and Period-Luminosity relations in these galaxies. For the first overtone Cepheids a small change of the slope of Period-Luminosity relation is possible. We determine the difference of distance moduli between the SMC and LMC with Cepheid relations and compare the result with difference obtained with other standard candles: RR Lyr and red clump stars. Results are very consistent and indicate that the values of zero points of the fundamental mode Cepheid relations are similar in these galaxies. The mean difference of distance moduli between the SMC and LMC is equal to μ_SMC-μ_LMC=0.51\pm0.03 mag. We calibrate the Period-Luminosity-Color and Period-Luminosity relations for classical, fundamental mode Cepheids using the observed LMC relations and adopting the short LMC distance modulus, μ_LMC=18.22\pm0.05 mag, resulting from the recent determination with eclipsing system HV2274, RR Lyr and red clump stars and consistent with observations of Cepheids in NGC4258 galaxy, to which precise geometric distance is known. Finally, we determine a constraint on the absolute magnitude of Cepheids by comparison of their mean V-band magnitude with that of RR Lyr stars in both Magellanic Clouds.

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arXiv1999

The Optical Gravitational Lensing Experiment. UBVI Photometry of Stars in Baade's Window

We present UBVI photometry for 8530 stars in Baade's Window obtained during the OGLE-II microlensing survey. Among these are over one thousand red clump giants. 1391 of them have photometry with errors smaller than 0.04, 0.06, 0.12, and 0.20 mag in the I, V, B and U-band, respectively. We constructed a map of interstellar reddening. The corrected colors of the red clump giants: (U-B)_0, (B-V)_0, and (V-I)_0 are very well correlated, indicating that a single parameter determines the observed spread of their values, reaching almost 2 mag in the (U-B)_0. It seems most likely that heavy element content is the dominant parameter, but it is possible that another parameter: the age (or mass) of a star moves it along the same trajectory in the color--color diagram as the metallicity. The current ambiguity can be resolved with spectral analysis, and our catalog may be useful as a finding list of red clump giants. We point out that these K giants are more suitable for a fair determination of the distribution of metallicity than brighter M giants. We also present a compilation of UBVI data for 308 red clump giants near the Sun, for which Hipparcos parallaxes are more accurate than 10%. Spectral analysis of their metallicity may provide information about the local metallicity distribution as well as the extent to which mass (age) of these stars affects their colors. It is remarkable that in spite of a number of problems, stellar models agree with observations at the 0.1-0.2 mag level, making red clump giants not only the best calibrated but also the best understood standard candle.

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arXiv1999

The Optical Gravitational Lensing Experiment. Monitoring of QSO 2237+0305

We present results from 2 years of monitoring of Huchra's lens (QSO 2237+0305) with the 1.3 m Warsaw telescope on Las Campanas, Chile. Photometry in the V band was done using a newly developed method for image subtraction. Reliable subtraction without Fourier division removes all complexities associated with the presence of a bright lensing galaxy. With positions of lensed images adopted from HST measurements it is relatively easy to fit the variable part of the flux in this system, as opposed to modeling of the underlying galaxy. For the first time we observed smooth light variation over a period of a few months, which can be naturally attributed to microlensing. We also describe automated software capable of real time analysis of the images of QSO 2237+0305. It is expected that starting from the next observing season in 1999 an alert system will be implemented for high amplification events (HAE) in this object. Time sampling and photometric accuracy achieved should be sufficient for early detection of caustic crossings.

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arXiv1999

The Optical Gravitational Lensing Experiment. Cepheids in the Magellanic Clouds. I. Double-Mode Cepheids in the Small Magellanic Cloud

We present a sample of 93 double-mode Cepheids detected in the 2.4 square degree area in the central part of the SMC. 23 stars from the sample pulsate in the fundamental mode and the first overtone while 70 objects are the first and second overtone pulsators. This is the largest sample of such type Cepheids detected in one environment so far. We analyze period ratio of double-mode Cepheids and Fourier parameters of decomposition of the light curves of these objects. We also present location of different type Cepheids from the SMC in the color-magnitude diagram and show their distribution of V-I color indices. We find one object which is probably a blend, either physical or optical, of two Cepheids pulsating in the fundamental mode.

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arXiv1999

The Optical Gravitational Lensing Experiment. Cepheids in the Magellanic Clouds. II. Single-Mode Second Overtone Cepheids in the Small Magellanic Cloud

We present a sample of 13 candidates for single-mode second overtone Cepheids discovered in the 2.4 square degree area of the SMC bar during the OGLE microlensing search. All candidates passed four photometric tests: analysis of Fourier parameters of the light curve, R_21 and ϕ_21, position in the period-luminosity diagram and location in the color-magnitude diagram. The stars form a very homogeneous group of objects with very similar light curves of low amplitude and almost sinusoidal shape. Their color indices B-V and V-I are also very similar and the objects determine the observational blue edge of the instability strip of the first overtone Cepheids. This is the first firm sample of the single-mode second overtone Cepheids detected so far.

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arXiv1998

The Optical Gravitational Lensing Experiment. Eclipsing Binary Stars in the Small Magellanic Cloud

We present the catalog of 1459 eclipsing binary stars detected in the central 2.4 square degree area of the Small Magellanic Cloud during the OGLE-II microlensing search. The sample includes objects brighter than I=20 mag with periods ranging from about 0.3 to 250 days. The average completeness of the catalog is about 80%. Statistics of the entire sample and well detached systems, suitable for distance determination, are also presented. The catalog, finding charts and BVI photometry data for all objects are available from the OGLE Internet archive.

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arXiv1998

The Optical Gravitational Lensing Experiment. Short Distance Scale to the LMC

We present {\it UBVI} photometry of the eclipsing binary HV2274 - the system which has been recently used for distance determination to the LMC by Guinan et al. (1998). We determine the interstellar reddening to the star, E(B-V)=0.149+/-0.015 mag, based on observed colors of the star. This value is in excellent agreement with the mean reddening towards HV2274 obtained from photometry of the red clump stars in the surrounding field. The reddening is almost twice as large as determined by Guinan et al. (1998). We discuss the consequences of reddening underestimate. Most likely HV2274 is located much closer with the distance modulus to the star and the LMC: m-M = 18.22+/-0.13 mag supporting the short distance scale to the LMC. Such a distance modulus is in excellent agreement with the recent distance determinations with RR Lyr and red clump stars.

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arXiv1998

The Optical Gravitational Lensing Experiment. Photometry of the MACHO-SMC-98-1 Binary Microlensing Event

We present photometry of the unique binary microlensing event MACHO-SMC-98-1 collected by the OGLE group. Particularly interesting observation was made close to the first caustic crossing which was not covered by observations of other groups. It allows to test proposed models of which Model~1 proposed by PLANET group seems to be in the best agreement with the OGLE observations.

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arXiv1998

The Optical Gravitational Lensing Experiment. BVI Maps of Dense Stellar Regions. I. The Small Magellanic Cloud

We present three color, BVI maps of the Small Magellanic Cloud. The maps contain precise photometric and astrometric data for about 2.2 million stars from the central regions of the SMC bar covering ~2.4 square degrees on the sky. Mean brightness of stars is derived from observations collected in the course of the OGLE-II microlensing search from about 130, 30 and 15 measurements in the I, V and B-bands, respectively. Accuracy of the zero points of photometry is about 0.01 mag, and astrometry 0.15 arcsec (with possible systematic error up to 0.7 arcsec). Color-magnitude diagrams of observed fields are also presented. The maps of the SMC are the first from the series of similar maps covering other OGLE fields: LMC, Galactic bulge and Galactic disk. The data are very well suited for many projects, particularly for the SMC which has been neglected photometrically for years. Because of potentially great impact on many astrophysical fields we decided to make the SMC data available to the astronomical community from the OGLE Internet archive.

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arXiv1998

The Optical Gravitational Lensing Experiment. The Catalog of Clusters in the Small Magellanic Cloud

We present the catalog of clusters found in the area of ~2.4 square degree in the central regions of the Small Magellanic Cloud. The catalog contains data for 238 clusters, 72 of them are new objects. For each cluster equatorial coordinates, radii, approximate number of members, cross-identification, finding chart and color magnitude diagrams: V-(B-V) and V-(V-I) are provided. Photometric data for all clusters presented in the catalog are available from the OGLE Internet archive.

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arXiv1998

Optical Gravitational Lensing Experiment. Distance to the Magellanic Clouds with the Red Clump Stars: Are the Magellanic Clouds 15% Closer than Generally Accepted?

We present a new distance determination to the Large and Small Magellanic Clouds using the newly developed red clump stars method (Paczynski and Stanek 1998). This new, single-step, Hipparcos calibrated method seems to be one of the most precise techniques of distance determination with very small statistical error due to large number of red clump stars usually available. The distances were determined independently along four lines-of-sight located at opposite sides of each Magellanic Cloud. The results for each line-of-sight are very consistent. For the SMC we obtain the distance modulus: m-M=18.56+/-0.03+/-0.06 mag (statistical and systematic errors, respectively) and for the LMC: m-M=18.08+/-0.03+/-0.12} mag where systematic errors are mostly due to uncertainty in reddening estimates. Both distances will be refined and systematic errors reduced when accurate reddening maps for our fields are available. Distance moduli to both Magellanic Clouds are ~0.4 mag smaller than generally accepted values. The modulus to the LMC is in good agreement with the recent determinations from RR Lyrae type stars and upper limit resulting from the SN1987A echo. We suspect that the distance to the LMC and SMC is shorter by about 15% than previously assumed: 42 kpc and 52 kpc, respectively. We also present our color-magnitude diagrams around the red clump for the LMC and SMC. We identify vertical red clump, first noted by Zaritsky and Lin (1997), in the color-magnitude diagram of both Magellanic Clouds and we interpret it as an evolutionary feature rather than unknown stellar population between the LMC and our Galaxy.

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arXiv1997

Optical Gravitational Lensing Experiment. Photometry of the MACHO-SMC-1 Microlensing Candidate

We present photometric observations of the MACHO-SMC-1 microlensing candidate collected by the OGLE-2 project. We show light curves of both components of the 1.6 arcsec blend: microlensed star and its optical companion. We find the contribution of the optical companion to the total flux to be 24% and confirm presence of the small amplitude periodic oscillations in the light curve of the lensed star with the period of 5.096 days and amplitude 0.05 mag. The lensed star is probably an ellipsoidal binary system.

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arXiv1997

The Optical Gravitational Lensing Experiment. Variable Stars in Globular Clusters - IV. Fields 104A-E in 47 Tuc

Five fields located close to the center of the globular cluster NGC 104=47 Tuc were surveyed in a search for variable stars. We present V-band light curves for 42 variables. This sample includes 13 RR Lyr stars -- 12 of them belong to the Small Magellanic Cloud (SMC) and 1 is a background object from the galactic halo. Twelve eclipsing binaries were identified -- 9 contact systems and 3 detached/semi-detached systems. Seven eclipsing binaries are located in the blue straggler region on the cluster color-magnitude diagram (CMD) and four binaries can be considered main-sequence systems. One binary is probably a member of the SMC. Eight contact binaries are likely members of the cluster and one is most probably a foreground star. We show that for the surveyed region of 47 Tuc, the relative frequency of contact binaries is very low as compared with other recently surveyed globular clusters. The sample of identified variables also includes 15 red variables with periods ranging from about 2 days to several weeks. A large fraction of these 15 variables probably belong to the SMC but a few stars are likely to be red giants in 47 Tuc. VI photometry for about 50 000 stars from the cluster fields was obtained as a by product of our survey.

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