We describe methods applied to the final photometric reductions and calibrations to the standard system of the images collected during the third phase of the Optical Gravitational Lensing Experiment survey - OGLE-III. Astrometric reduction methods are also presented.
The OGLE-III data constitute a unique data set covering the Magellanic Clouds, Galactic bulge and Galactic disk fields monitored regularly every clear night since 2001 and being significant extension and continuation of the earlier OGLE observations. With the earlier OGLE-II and OGLE-I photometry some of the observed fields have now 16-year long photometric coverage.
We describe a new 1.3 m Warsaw telescope located at Las Campanas Observatory and new instruments of the second phase of the Optical Gravitational Lensing Experiment - OGLE-2. Results of first observations are also presented.
We present the OGLE-III Photometric Maps of the Large Magellanic Cloud. They cover about 40 square degrees of the LMC and contain mean, calibrated VI photometry and astrometry of about 35 million stars observed during seven observing seasons of the third phase of the Optical Gravitational Lensing Experiment - OGLE-III. We discuss the quality of data and present color-magnitude diagrams of selected fields. The OGLE-III Photometric Maps of the LMC are available to the astronomical community from the OGLE Internet archive.
We describe three real time data analysis systems implemented during the third phase of the OGLE survey (OGLE-III). The EWS system is designed to detect on-going microlensing events. The EEWS system monitors the microlensing phenomena for anomalies from the single mass microlensing. The NOOS system detects transient objects in the OGLE-III fields (SNe, microlensing events, variable stars) that normally are below the detection threshold. Information on objects detected by each of these systems is distributed to the astronomical community for follow up observations. Also a short description of t…
This paper presents the first part of the Optical Gravitational Lensing Experiment (OGLE) General Catalog of Stars in the Galactic bulge. The Catalog is based on observations collected during the OGLE microlensing search. This part contains 33196 stars brighter than I=18mag identified in the Baade's Window BWC field. Stars from remaining 20 OGLE fields will be presented in similar form in the next parts of the Catalog. The Catalog is available to the astronomical community over the Internet network.
We present results of the long term monitoring of the gravitational lens QSO 2237+0305 conducted during the OGLE survey. Light curves of all four components of the lens obtained during the second phase of the OGLE project (OGLE-II; 1997-2000) are supplemented with the data collected in the OGLE-III phase in the observing seasons 2001-2006. Calibration procedures to tie the new OGLE-III data with already calibrated OGLE-II light curves are described. The resulting homogeneous OGLE data set is the most extensive photometric coverage of the gravitational lens QSO 2237+0305, spanning now one decad…
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 10^10 measurements of more than 40 million objects in the Galactic bulge and the Magellanic…
We present the light curve of an unusual variable object, OGLE #7, detected during the OGLE search for microlensing events. After one season of being in a low, normal state, the star brightened by more than 2~mag with a characteristic double-maximum shape, and returned to normal brightness after 60 days. We consider possible explanations of the photometric behavior of OGLE #7. The binary microlens model seems to be the most likely explanation -- it reproduces well the observed light curve and explains the observed colors of OGLE #7. The characteristic time scale of the OGLE #7 event, $t_E$, is…
The photometric data collected by OGLE-III during the 2001 and 2002 observational campaigns aiming at detection of planetary or low-luminosity object transits were corrected for small scale systematic effects using the data pipeline by Kruszewski and Semeniuk and searched again for low amplitude transits. Sixteen new objects with small transiting companions, additional to previously found samples, were discovered. Most of them are small amplitude cases which remained undetected in the original data. Several new objects seem to be very promising candidates for systems containing substellar obje…
We describe two new OGLE-III real time data analysis systems: XROM and RCOM. The XROM system has been designed to provide continuous real time photometric monitoring of the optical counterparts of X-ray sources while RCOM system provides real time photometry of R Coronae Borealis variable stars located in the OGLE-III fields. Both systems can be used for triggering follow-up observations in crucial phases of variability episodes of monitored objects.
We present a proper motion (μ) catalogue of 5,080,236 stars in 49 Optical Gravitational Lensing Experiment II (OGLE-II) Galactic bulge (GB) fields, covering a range of -11 deg. <l< 11 deg. and -6 deg. <b<3 deg., the total area close to 11 square degrees. The proper motion measurements are based on 138 - 555 I-band images taken during four observing seasons: 1997-2000. The catalogue stars are in the magnitude range 11 < I < 18 mag. In particular, the catalogue includes Red Clump Giants (RCGs) and Red Giants in the GB, and main sequence stars in the Galactic disc. The proper motions up to μ= 500…
In 1998 The Optical Gravitational Lensing Experiment (OGLE) successfully implemented automated data reductions for QSO 2237+0305. Using a new image subtraction method we achieved a differential photometry scatter of 1-5 % for images A-D respectively. Combined with a time sampling of 1-2 times a week this is sufficient for early detection of caustic crossings. Nearly real time photometry of QSO 2237+0305 is available from the OGLE web site http://www.astro.princeton.edu/~ogle/ogle2/huchra.html . During the 1999 observing season, the apparent V magnitude of the A, B, C and D images changed by 0.…
We have studied five seasons of OGLE-III data for eight SMC Be/X-ray pulsars for which no other survey data were available. We have determined orbital periods for four of these binary systems, one of which also shows nonradial pulsations. Optical identification of SMC X-2 is reconsidered, but no periods were found for either of the two possible candidates.
The analysis of the first three years of the OGLE data revealed 12 microlensing events of the Galactic bulge stars, with the characteristic time scales in the range $ 8.6 < t_0 < 80 $ days, where $ t_0 = R_E / V $. A complete sample of nine events gave the optical depth to gravitational microlensing larger than $(3.3 \pm 1.2) \times 10^{-6}$, in excess of current theoretical estimates, indicating a much higher efficiency for microlensing by either bulge or disk lenses. The lenses are likely to be ordinary stars in the Galactic bar, which has its long axis elongated towards us. At this time we …
We present 19 binary lens candidates from OGLE-III Early Warning System database for the season of 2004. We have also found five events interpreted as single mass lensing of double sources. The candidates have been selected by visual light curves inspection. Examining the models of binary lenses of this and our previous studies (10 caustic crossing events of OGLE-II seasons 1997--1999 and 15 binary lens events of OGLE-III seasons 2002--2003) we find one case of extreme mass ratio binary (q ~ 0.005, a known planetary lens OGLE 2003-BLG-235/MOA 2003-BLG-53) and almost all other models with mass …
We present nine new binary lens candidates from OGLE-III Early Warning System database for the season of 2005. We have also found four events interpreted as single mass lensing of double sources. The candidates have been selected by visual light curves inspection. Examining the models of binary lenses in our previous studies (10 caustic crossing events of OGLE-II seasons 1997--1999 and 34 binary lens events of OGLE-III seasons 2002--2004, including one planetary event), in this work and in three publications concerning planetary events of season 2005, we find four cases of extreme mass ratio b…
In this Paper, we have derived Cepheid period-luminosity (P-L) relations for the Large Magellanic Cloud (LMC) fundamental mode Cepheids, based on the data released from OGLE-III. We have applied an extinction map to correct for the extinction of these Cepheids. In addition to the VIW band P-L relations, we also include JHK and four Spitzer IRAC band P-L relations, derived by matching the OGLE-III Cepheids to the 2MASS and SAGE datasets, respectively. We also test the non-linearity of the Cepheid P-L relations based on extinction-corrected data. Our results (again) show that the LMC P-L relatio…
We describe the discovery of the longest microlensing event ever observed, OGLE-1999-BUL-32, also independently identified by the MACHO collaboration as MACHO-99-BLG-22. This unique event has an Einstein radius crossing time of 641 days. The high quality data obtained with difference image analysis shows a small but significant parallax signature. This parallax effect allows one to determine the Einstein radius projected onto the observer plane as rE^hat ~ 29.2AU. The transverse velocity projected onto the observer plane is about 79km/s. We argue that the lens is likely to be have a mass of at…
We present the photometry and theoretical models for a Galactic bulge microlensing event OGLE-2000-BUL-43. The event is very bright with I=13.54 mag, and has a very long time scale, t_E=156 days. The long time scale and its light curve deviation from the standard shape strongly suggest that it may be affected by the parallax effect. We show that OGLE-2000-BUL-43 is the first discovered microlensing event, in which the parallax distortion is observed over a period of 2 years. Difference Image Analysis (DIA) using the PSF matching algorithm of Alard & Lupton enabled photometry accurate to 0.5%. …
We present Cepheids located in the close neighborhood of star clusters from the Magellanic Clouds. 204 and 132 such stars were found in the LMC and SMC, respectively. The lists of objects were constructed based on catalogs of Cepheids and star clusters, recently published by the OGLE-II collaboration. Location of selected Cepheids on the sky indicates that many of them are very likely cluster members. Photometric data of Cepheids and clusters are available from the OGLE archive.
We present 15 binary lens candidates from OGLE-III Early Warning System database for seasons 2002-2003. We also found 15 events interpreted as single mass lensing of double sources. The candidates were selected by visual light curves inspection. Examining the models of binary lenses of this and our previous study (10 caustic crossing events of OGLE-II seasons 1997-1999) we find one case of extreme mass ratio binary (q ~ 0.005) and the rest in the range 0.1<q<1.0, which may indicate the division between planetary systems and binary stars. There is no strong discrepancy between the expected and …
The Optical Gravitational Lensing Experiment project has recently provided the OGLE III list of low-luminosity object transits from campaigns #3 and #4, reporting 40 new objects exhibiting the low-amplitude photometric eclipses expected for exoplanets. Compared to previous OGLE targets, these OGLE III candidates have been more restrictively selected and may contain low-mass planets. We have secured follow-up low-resolution spectroscopy for 28 candidates out of this list (and one from the OGLE Carina fields) to obtain an independent characterization of the primary stars by spectral classificati…
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.
We present the BVI photometric maps of the Large Magellanic Cloud. They contain BVI photometry and astrometry of more than 7 million stars from the central parts of the LMC. The data were collected during the second phase of the OGLE microlensing project. We discuss the accuracy of the data and present color-magnitude diagrams of all 26 fields observed by OGLE in the LMC. The BVI maps of the LMC are accessible electronically for the astronomical community from the OGLE Internet archive.
We present results of two observing campaigns conducted by the OGLE-III survey in the 2003 observing season aiming at the detection of new objects with planetary transiting companions. Six fields of 35'x35' each located in the Galactic disk were monitored with high frequency for several weeks in February - July 2003. Additional observations of three of these fields were also collected in the 2004 season. Altogether about 800 and 1500 epochs were collected for the fields of both campaigns, respectively. The search for low depth transits was conducted on about 230000 stars with photometry better…
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.
We present the first part of a new catalog of variable stars (OIII-CVS) compiled from the data collected in the course of the third phase of the Optical Gravitational Lensing Experiment (OGLE-III). In this paper we describe the catalog of 3361 classical Cepheids detected in the ~40 square degrees area in the Large Magellanic Cloud. The sample consists of 1848 fundamental-mode (F), 1228 first-overtone (1O), 14 second-overtone (2O), 61 double-mode F/1O, 203 double-mode 1O/2O, 2 double-mode 1O/3O, and 5 triple-mode classical Cepheids. This sample is supplemented by the list of 23 ultra-low amplit…
We present results of the long term monitoring of the gravitationally lensed quasar HE1104-1805. The photometric data were collected between August 1997 and January 2002 as a subproject of the OGLE survey. We determine the time delay in the light curves of images A and B of HE1104-1805 to be equal to 157+/-21 days with the variability in the image B light curve leading variability of the image A. The result is in excellent agreement with the earlier determination by Ofek and Maoz. OGLE photometry of HE1104-1805 is available to the astronomical community from the OGLE Internet archive.
We present the first edition of a catalog of variable stars from OGLE-II Galactic Bulge data covering 3 years: 1997-1999. Typically 200-300 I band data points are available in 49 fields between -11 and 11 degrees in galactic longitude, totaling roughly 11 square degrees in sky coverage. Photometry was obtained using the Difference Image Analysis (DIA) software and tied to the OGLE data base with the DoPhot package. The present version of the catalog comprises 221,801 light curves. In this preliminary work the level of contamination by spurious detections is still about 10%. Parts of the catalo…
We present accurate V-band photometry for a planetary transit of OGLE-TR-111 acquired with VIMOS at the ESO Very Large Telescope. The measurement of this transit allows to refine the planetary radius, obtaining R_p= 1.01 +/- 0.06 R_J. Given the mass of M_p = 0.53 M_J previously measured from radial velocities, we confirm that the density is rho_p= 0.6 +/- 0.2 g/cm^3. We also revise the ephemeris for OGLE-TR-111-b, obtaining an accurate orbital period P= 4.014484 +/- 0.000014 days, and predicting that the next observable transits would occur around December 2006, and after that only in mid-2008…
We describe a highly unusual microlensing event, OGLE-1999-BUL-19, which exhibits multiple peaks in its light curve. The Einstein radius crossing time for this event is approximately one year, which is unusually long. We show that the motion of the Earth induces these multiple peaks in the light curve, since the relative transverse velocity of the lens projected into the observer plane is very small (v = 12.5 km/s). This is the lowest velocity so far published and we believe that this is the first multiple-peak parallax event ever observed. We also believe that this event may be exhibiting sli…
The photometric data collected during 2001 season OGLE-III planetary/low luminosity object transit campaign were reanalyzed with the new transit search technique -- the BLS method by Kovacs, Zucker and Mazeh. In addition to all presented in our original paper transits, additional 13 objects with transiting low-luminosity companions were discovered. We present here a supplement to our original catalog -- the photometric data, light curves and finding charts of all 13 new objects. The model fits to the transit light curves indicate that a few new objects may be Jupiter-sized (R<1.6 R_Jup). OGLE-…
The list of 127 eclipsing stars in optical coincidence with star clusters from the SMC is presented. It was prepared using the catalogs of eclipsing systems and star clusters from the SMC based on observations collected during the OGLE-II microlensing project. Location of 12 eclipsing stars in the color-magnitude diagram of clusters allows to exclude their membership. Photometric data of 73 systems support their membership. The remaining 42 objects were found in loose, faint clusters and therefore no conclusive statement about their membership can be made. All presented data are available from…
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 …
In the second part of the OGLE-III Catalog of Variable Stars (OIII-CVS) we present 197 type II Cepheids and 83 anomalous Cepheids in the Large Magellanic Cloud (LMC). The sample of type II Cepheids consists of 64 BL Her stars, 96 W Vir stars and 37 RV Tau stars. Anomalous Cepheids are divided into 62 fundamental-mode and 21 first-overtone pulsators. These are the largest samples of such types of variable stars detected anywhere outside the Galaxy. We present the period-luminosity and color-magnitude diagrams of stars in the sample. If the boundary period between BL Her and W Vir stars is adopt…
We present an analysis of the 3-D structure of the Magellanic Clouds, using period-luminosity (P-L) relations of pulsating red giants in the OGLE-II sample. By interpreting deviations from the mean P-L relations as distance modulus variations, we examine the three-dimensional distributions of the sample. The results for the Large Magellanic Cloud, based solely on stars below the tip of the Red Giant Branch, confirm previous results on the inclined and possibly warped bar of the LMC. The depth variation across the OGLE-II field is about 2.4 kpc, interpreted as the distance range of a thin but i…
We present the second part of the OGLE Catalog of Periodic Variable Stars in the Galactic bulge. 800 variable stars found in four Baade's Window fields BW1, BW2, BW3 and BW4 are presented. Among them 71 are classified as pulsating, 465 as eclipsing and 264 as miscellaneous type. The Catalog and individual observations are available in digital form from the OGLE Internet archive.
From the 389 2002 OGLE-III observations of Galactic Bulge microlensing events we select 321 that are well described by a point-source point-lens lightcurve model. From this sample we identify n=1 event, 2002-BLG-055, which we regard as a strong planetary lensing candidate, and another, 2002-BLG-140, which is a possible candidate. If each of the 321 lens stars has 1 planet with a mass ratio q=m/M=10^{-3} and orbit radius a=R_E, the Einstein ring radius, analysis of detection efficiencies indicates that 14 planets should have been detectable with Δχ^2 > 25. Assuming our candidate is due to plane…
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.
A sample of contact binaries discovered by the OGLE project in Baade's Window, with orbital periods longer than one day and with available color and light-curve data, has been analyzed. It consists of only 32 systems, in contrast to 388 WUMa-type systems with shorter periods which were analyzed before. Most systems are very distant and are probably located close to or in the galactic Bulge. Two groups of contact binaries are seen in the sample: (1) a continuation of the WUMa-type sequence, extending up to the orbital periods of 1.3 - 1.5 day, but rather sharply ending in this period range; (2)…
Previous calculations of the rates and optical depths due to microlensing only considered resolved stars. However, if a faint unresolved star lens is close enough to a resolved star, the event will be seen by the microlensing experiments and attributed to the bighter star. The blending biases the duration, making the contribution of the unresolved stars very significant for short events. This contribution is confused with lensing by brown dwarfs. The exact rates of these blended events are extremly sensitive to the limiting magnitude achieved in the microlensing search. Appropriate calculation…
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 fi…
We derive the frequencies of hot Jupiters (HJs) with 3--5 day periods and very hot Jupiters (VHJs) with 1-3 day periods by comparing the planets actually detected in the OGLE-III survey with those predicted by our models. The models are constructed following Gould & Morgan (2003) by populating the line of sight with stars drawn from the Hipparcos catalog. Using these, we demonstrate that the number of stars with sensitivity to HJs and VHJs is only 4--16% of those in the OGLE-III fields satisfying the spectroscopic-followup limit of V_max<17.5. Hence, the frequencies we derive are much higher t…
We present an analysis of OGLE 2004-BLG-254, a high-magnification and relatively short duration microlensing event in which the source star, a Bulge K3-giant, has been spatially resolved by a point-like lens. We have obtained dense photometric coverage of the event light curve with OGLE and PLANET telescopes, as well as a high signal-to-noise ratio spectrum taken while the source was still magnified by 20, using the UVES/VLT spectrograph. Our dense coverage of this event allows us to measure limb darkening of the source star in the I and R bands. We also compare previous measurements of linear…
We present results of the second planetary and low-luminosity object transit campaign conducted by the OGLE-III survey. Three fields (35'x35' each) located in the Carina regions of the Galactic disk (l~290) were monitored continuously in February-May 2002. About 1150 epochs were collected for each field. The search for low depth transits was conducted on about 103000 stars with photometry better than 15 mmag. In total, we discovered 62 objects with shallow depth (<0.08 mag) flat-bottomed transits. For each of these objects several individual transits were detected and photometric elements were…
We used the OGLE-II and OGLE-III photometry of red giants in the Large Magellanic Cloud to select and study objects revealing ellipsoidal variability. We detected 1546 candidates for long period ellipsoidal variables and 121 eclipsing binary systems with clear ellipsoidal modulation. The ellipsoidal red giants follow a period-luminosity (PL) relationship (sequence E), and the scatter of the relation is correlated with the amplitude of variability: the larger the amplitude, the smaller the scatter. We note that some of the ellipsoidal candidates exhibit simultaneously OGLE Small Amplitude Red G…
We present new version of the OGLE-II catalog of eclipsing binary stars detected in the Small Magellanic Cloud, based on Difference Image Analysis catalog of variable stars in the Magellanic Clouds containing data collected from 1997 to 2000. We found 1351 eclipsing binary stars in the central 2.4 square degree area of the SMC. 455 stars are newly discovered objects, not found in the previous release of the catalog. The eclipsing objects were selected with the automatic search algorithm based on the artificial neural network. The full catalog is accessible from the OGLE Internet archive.
Two years ago, the OGLE-III survey (Optical Gravitational Lensing Experiment) announced the detection of 54 short period multi-transiting objects in the Galactic bulge (Udalski et al., 2002a, 2002b). Some of these objects were considered to be potential hot Jupiters. In order to determine the true nature of these objects and to characterize their actual mass, we conducted a radial velocity follow-up of 18 of the smallest transiting candidates. We describe here our procedure and report the characterization of 8 low mass star transiting companions, 2 grazing eclipsing binaries, 2 triple systems,…
We present results of an extensive photometric search for planetary and low-luminosity object transits in the Galactic disk stars commencing the third phase of the Optical Gravitational Lensing Experiment -- OGLE-III. Photometric observations of three fields in the direction of the Galactic center (800 epochs per field) were collected on 32 nights during time interval of 45 days. Out of the total of 5 million stars monitored, about 52~000 Galactic disk stars with photometry better than 1.5% were analyzed for flat-bottomed eclipses with the depth smaller than 0.08 mag. Altogether 46 stars with …
We present the fifth part of the OGLE Catalog of Periodic Variable Stars in the Galactic bulge. 574 variable stars: 44 pulsating, 369 eclipsing and 161 miscellaneous type were detected in four fields located symmetrically in galactic lattitude around the Galactic center: MM5-A, MM5-B, MM7-A and MM7-B. The Catalog and individual observations are available in digital form from the OGLE Internet archive.
The discoveries of 17 microlensing event candidates have been reported over the last year by three teams conducting unprecedented mass photometric searches in the direction of the Galactic bulge and the Magellanic Clouds. These include 10 events found by the OGLE collaboration, 5 by the MACHO team and 2 by the EROS team. All searches have the main goal to detect dark matter in our Galaxy. The detection of 17 event candidates proves that the microlensing is a powerful tool in the search for dark matter, and it may be used for reliable mass determination when the geometry of the event is known. …
OGLE and other projects are likely to discover first stellar mass black holes and the first planets through gravitational lensing in the next year or two. It is important to have follow-up projects ready, using diverse observing methods. The best for black hole detection would be a measurement of image splitting with VLTI, or any other optical interferometer. Alternative approach is to measure non-linear motion of the light centroid with the HST, or even with a ground based telescope. Every year OGLE detects several very long duration microlensing events brighter than I = 16 mag and K = 14 mag…
We present the catalog of 2580 eclipsing binary stars detected in 4.6 square degree area of the central parts of the Large Magellanic Cloud. The photometric data were collected during the second phase of the OGLE microlensing search from 1997 to 2000. The eclipsing objects were selected with the automatic search algorithm based on an artificial neural network. Basic statistics of eclipsing stars are presented. Also, the list of 36 candidates of detached eclipsing binaries for spectroscopic study and for precise LMC distance determination is provided. The full catalog is accessible from the OGL…
BVI photometry of the Magellanic Clouds collected during the OGLE-II microlensing experiment makes it possible to study in detail photometric properties of the "major" stellar distance indicators in the Magellanic Clouds. In addition to Cepheids, RR Lyr and red clump stars, which photometry was presented in the earlier OGLE papers, we present the so far most accurate determination of brightness of the tip of the red giant branch in the LMC and SMC. We analyze the ratios of brightness of all four distance indicators in the LMC and SMC. Additionally, we include in our analysis, when possible, ph…
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 presente…
We describe the Difference Image Analysis (DIA) algorithms and software used to analyze four years (1997-2000) of OGLE-II photometric monitoring of the Magellanic Clouds, the calibration, the photometric error analysis, and the search for variable stars. A preliminary analysis of photometric errors is based on the field LMC_SC2. A full catalog of about 70,000 variable stars will be presented in a separate publication.
We present 97 QSO candidates in 48 Galactic Bulge fields of the Optical Gravitational Lensing Experiment II (OGLE-II) covering about 11 square degrees, which are selected via their variability. We extend light curves of variable objects which were detected in 3-year baseline in the OGLE-II variable star catalog to 4th year. We search for objects which are faint (16<I_0<18.5) and slowly variable during 4 years in this catalog by using the variogram/structure function. Finding the QSOs in such stellar-crowded and high extinction fields is challenging, but should be useful for the astrometric ref…
In the late 1990s, the Optical Gravitational Lensing Experiment (OGLE) team conducted the second phase of their long-term monitoring programme, OGLE-II, which since has been superseded by OGLE-III. All the monitoring data of this second phase, which was primarily aimed at finding microlensing events, have recently been made public. Fields in the OGLE-II survey have typically been observed with a cadence of once per night, over a period of a few months per year. We investigated whether these radically differently sampled data can also be used to search for transiting extrasolar planets, in part…
We present I-band light curves of 54 Population II Cepheids identified in the OGLE-II catalog of variable objects in the Galactic bulge fields. Their periods range from a fraction of a day to several days. Their light curves show very close similarity to the light curves of classical Cepheids with periods a few times longer. We analyze location of the newly identified Population II Cepheids in the color--magnitude diagram. The position of these objects confirms recent discovery that the interstellar extinction toward the Galactic bulge might be anomalous. The slope of the reddening line obtain…
Microlensing events are usually selected among single-peaked non-repeating light curves in order to avoid confusion with variable stars. However, a microlensing event may exhibit a second microlensing brightening episode when the source or/and the lens is a binary system. A careful analysis of these repeating events provides an independent way to study the statistics of wide binary stars and to detect extrasolar planets. Previous theoretical studies predicted that 0.5 - 2 % of events should repeat due to wide binary lenses. We present a systematic search for such events in about 4000 light cur…
We present the first edition of a catalog of variable stars found in the Magellanic Clouds using OGLE-II data obtained during four years: 1997-2000. The catalog covers about 7 square degrees of the sky - 21 fields in the Large Magellanic Cloud and 11 fields in the Small Magellanic Cloud. All variables were found with the Difference Image Analysis (DIA) software. The catalog is divided into two sections. The DC section contains FITS reference images (obtained by co-adding 20 best frames for each field) and profile photometry (DoPHOT) of all variable stars on those images. The AC section contain…
