Showing papers by "M. Kubiak published in 2002"

Optical Gravitational Lensing Experiment OGLE‐1999‐BUL‐32: the longest ever microlensing event – evidence for a stellar mass black hole?

Abstract: 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 640 d. 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 on to the observer plane as r E 29.1 au. The transverse velocity projected on to the observer plane is about 79 km s - 1 . We argue that the lens is likely to have a mass of at least a few solar masses, i.e. it could be a stellar black hole. The black hole hypothesis can be tested using the astrometric microlensing signature with the soon-to-be installed Advanced Camera for Surveys on board the Hubble Space Telescope. Deep X-ray and radio images may also be useful for revealing the nature of the object.

Microlensing of Relativistic Knots in the Quasar HE1104-1805

Abstract: We present 3 years of photometry of the ``Double Hamburger'' lensed quasar, HE1104-1805, obtained on 102 separate nights using the OGLE 1.3-m telescope. Both the A and B images show variations, but with substantial differences in the lighcurves at all time delays. At the 310 day delay reported by Wisotzki and collaborators the difference lightcurve has an rms amplitude of 0.060 mag. The structure functions for the A and B images are quite different, with image A more than twice as variable as image B (a factor of 4 in structure function) on timescales of less than a month. Adopting microlensing as a working hypothesis for the uncorrelated variability, the short timescale argues for the relativistic motion of one or more components of the source. We argue that the small amplitude of the fluctuations is due to the finite size of the source with respect to the microlenses.

The Optical Gravitational Lensing Experiment. Search for Planetary and Low- Luminosity Object Transits in the Galactic Disk. Results of 2001 Campaign -- Supplement

Abstract: 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-TR-56 is a particularly interesting case. Its transit has only 13 mmag depth, short duration and a period of 1.21190 days. Model fit indicates that the companion may be Saturn-sized if the passage were central. Spectroscopic follow-up observations are encouraged for final classification of the transiting objects as planets, brown dwarfs or late M-type dwarf stars. We also provide the most recent ephemerides of other most promising planetary transits: OGLE-TR-10 and OGLE-TR-40 based on observations collected in June 2002. All photometric data are available to the astronomical community from the OGLE Internet archive.

Optical Gravitational Lensing Experiment. OGLE-1999-BUL-19: The First Multi-Peak Parallax Event

Abstract: 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 slight binary-source signatures in addition to these parallax-induced multiple peaks. With spectroscopic observations it is possible to test this `parallax plus binary-source' hypothesis and (if this hypothesis turns out to be correct) to simultaneously fit both models and obtain a measurement of the lens mass. Furthermore, spectroscopic observations could also supply information regarding the lens properties, possibly providing another avenue for determining the lens mass. We found that most of the I-band blending is probably caused by light from the lens or a binary companion to the source. However, in the V-band, there appears to be a second blended source 0.35" away from the lensed source. HST observations will be very useful for understanding the nature of the blends. We also suggest that a radial velocity survey of all parallax events will be very useful for further constraining the lensing kinematics and understanding the origins of these events and the excess of long events toward the bulge.

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

Abstract: 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.

The Optical Gravitational Lensing Experiment. Search for Planetary and Low-Luminosity Object Transits in the Galactic Disk. Results of 2001 Campaign

Abstract: 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 transiting low-luminosity objects were detected. For 42 of them multiple transits were observed, a total of 185, allowing orbital period determination. Transits in two objects: OGLE-TR-40 and OGLE-TR-10, with the radii ratio of about 0.14 and estimate of the radius of the companion 1.0-1.5R_Jup, resemble the well known planetary transit in HD 209458. The sample was selected by the presence of apparent transits only, with no knowledge on any other properties. Hence, it is very well suited for general study of low-luminosity objects. The transiting objects may be Jupiters, brown dwarfs, or M dwarfs. Future determination of the amplitude of radial velocity changes will establish their masses, and will confirm or refute the reality of the so called ``brown dwarf desert''. The low-mass stellar companions will provide new data needed for the poorly known mass-radius relation for the lower main sequence. All photometric data are available to the astronomical community from the OGLE Internet archive.

The Optical Gravitational Lensing Experiment. Planetary and Low-Luminosity Object Transits in the Carina Fields of the Galactic Disk

Abstract: 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 determined. Also lower limits on radii of the primary and companion were calculated. The 2002 OGLE sample of stars with transiting companions contains considerably more objects that may be Jupiter-sized (R<1.6 R_Jup) compared to our 2001 sample. There is a group of planetary candidates with the orbital periods close to or shorter than one day. If confirmed as planets, they would be the shortest period extrasolar planetary systems. In general, the transiting objects may be extrasolar planets, brown dwarfs, or M-type dwarfs. One should be, however, aware that in some cases unresolved blends of regular eclipsing stars can mimic transits. Future spectral analysis and eventual determination of the amplitude of radial velocity should allow final classification. High resolution spectroscopic follow-up observations are, therefore, strongly encouraged. All photometric data are available from the OGLE Internet archive. Note added for astro-ph version: One of the best planetary candidates from the OGLE 2001 campaign, OGLE-TR-56, has recently been confirmed as a planetary system by Konacki, Torres, Jha and Sasselov [astro-ph/0301052].

Difference Image Analysis of the OGLE-II Bulge Data. III. Catalog of 200,000 Candidate Variable Stars

Abstract: 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 catalog have only crude calibration, insufficient for distance determinations. The next, fully calibrated, edition will include the data collected in year 2000. The data is accessible via FTP. Due to the data volume, we also distribute DAT tapes upon request.