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 1.0-1.5 R sub(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.
We present results of the photometric campaign for planetary and low- luminosity object transits conducted by the OGLE survey in the 2005 season (Campaign #5). About twenty of the most promising ...candidates discovered in these data were subsequently verified spectroscopically with the VLT/FLAMES spectrograph. One of the candidates, OGLE-TR-211, reveals clear changes of radial velocity with a small amplitude of 82 m/s, varying in phase with photometric transit ephemeris. Further analysis confirms the planetary nature of this system. Follow-up precise photometry of OGLE-TR-211 with VLT/FORS, together with radial velocity spectroscopy, supplemented with high- resolution, high S/N VLT/UVES spectra allowed us to derive parameters of the planet and host star. OGLE-TR-211b is a hot Jupiter orbiting an F7-8 spectral type dwarf star with a period of 3.68 days. The mass of the planet is equal to 1.03\pm0.20 M_{\rm Jup}, while its radius {\rm 1.36} R_{\rm Jup}. The radius is about 20% larger than the typical radius of hot Jupiters of similar mass. OGLE-TR-211b is, then, another example of inflated hot Jupiters-a small group of seven exoplanets with large radii and unusually low densities- objects that are a challenge to the current models of exoplanets.
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Context. An R Coronae Borealis (RCB) star is a rare type of supergiant star that is increasingly suspected to be the evolved merger product of two white dwarfs. Lately, many RCBs have been found ...distributed in a thin disk structure embedded inside the Galactic bulge. This unexpectedly high density may provide additional insight into the nature and age of RCB stars. Aims. We apply and test a new technique to find RCB stars based on their particular infrared emission due to circumstellar shell. We attempt to demonstrate that RCB stars can be identified without performing a light curve analysis, which would simplified the search outside optically monitored fields. Methods. We selected RCB candidates based on their near-infrared excess and on their particular mid-infrared shells emission, using photometric data from the 2MASS and Spitzer/GLIMPSE surveys. Each candidates OGLE light curves were then visually inspected and we selected for spectroscopy follow-up those that underwent large and rapid declines. Results. We discover two new R Coronae Borealis stars, but also indicate four new possible candidates. We emphasize that all of the 7 known RCB stars located in both the Spitzer/GLIMPSE and OGLE-III fields were also re-discovered, which illustrates the high efficiency of our analysis. Conclusions. The proposed new technique to find RCB stars has been successful. It can now be extended to larger areas, in particular where the interstellar extinction is too high to be monitored by optical microlensing surveys, such as the inner part of the Galactic bulge.
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Period-luminosity (PL) relations of variable red giants in the Large (LMC) and Small Magellanic Clouds (SMC) are presented. The PL diagrams are plotted in three planes: log P-K sub(S), log P-W ...sub(JK), and log P-W sub(I), where W sub(JK) and W sub(I) are reddening free Wesenheit indices. Fourteen PL sequences are distinguishable, and some of them consist of three closely spaced ridges. Each of the sequences is fitted with a linear or quadratic function. The similarities and differences between the PL relations in both galaxies are discussed for four types of red giant variability: OGLE Small Amplitude Red Giants (OSARGs), Miras and Semiregular Variables (SRVs), Long Secondary Periods (LSPs) and ellipsoidal variables. We propose a new method of separating OSARGs from non-variable stars and SRVs. The method employs the position in the reddening-free PL diagrams and the characteristic period ratios of these multiperiodic variables. The PL relations for the LMC OSARG are compared with the calculated relations for RGB models along isochrones of relevant ages and metallicities. We also compare measured periods and amplitudes of the OSARGs with predictions based on the relations valid for less luminous solar-like pulsators. Miras and SRVs seem to follow PL relation of the same slopes in the LMC and SMC, while for LSP and ellipsoidal variables slopes in both galaxies are different. The PL sequences defined by LSP variables and binary systems overlap in the whole range of analyzed wavebands. We put forward new arguments for the binary star scenario as an explanation of the LSP variability and elaborate on it further. The measured pulsation to orbital period ratio implies nearly constant ratio of the star radius to orbital distance, R/A approximately 0.4, as we find. Combined effect of tidal friction and mass loss enhanced by the low-mass companion may explain why such a value is preferred.
The sixth part of the OGLE-III catalog of Variable Stars presents delta Sct pulsators in the Large Magellanic Cloud. Altogether 2786 variable stars were found and amongst them 92 are multi-mode ...objects, including 67 stars pulsating in the fundamental mode and the first overtone (F/1O), nine double-mode pulsators with various combinations of the first three overtones excited (10/20, 20/30 and 10/30 pulsators), and two triple mode (F/10/20) delta Sct stars. In total 1490 of stars are marked as uncertain, due to scattered photometry and small amplitudes. For single-mode objects it was not possible to unambiguously identify pulsation mode, however we suggest the most of the single-mode variable stars pulsate in the first overtone.
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 present OGLE-III Photometric Maps of the Small Magellanic Cloud. They contain precise, calibrated VI photometry of about 6.2 million stars from 41 OGLE-III fields in the SMC observed regularly in ...the years 2001-2008 and covering about 14 square degrees in the sky. Also precise astrometry of these objects is provided. One of the fields, SMC140, is centered on the 47 Tucanae Galactic globular cluster providing unique data on this object. We discuss quality of the data and present a few color-magnitude diagrams of the observed fields. All photometric data are available to the astronomical community from the OGLE Internet archive.
By re-processing the data of the second season of the OGLE survey for planetary transits and adding new mesurements on the same fields gathered in subsequent years with the OGLE telescope, we have ...identified 23 new transit candidates, recorded as OGLE-TR-178 to OGLE-TR-200. We studied the nature of these objects with the FLAMES/UVES multi-fiber spectrograph on the VLT. One of the candidates, OGLE-TR-182, was confirmed as a transiting gas giant planet on a 4-day orbit. We characterised it with further observations using the FORS1 camera and UVES spectrograph on the VLT. OGLE-TR-182b is a typical “hot Jupiter” with an orbital period of 3.98 days, a mass of $1.01 \pm 0.15~M_{\rm Jup}$ and a radius of 1.13$^{+0.24}_{-0.08}~R_{\rm Jup}$. Confirming this transiting planet required a large investment in telescope time with the best instruments available, and we comment on the difficulty of the confirmation process for transiting planets in the OGLE survey. We delineate the zone were confirmation is difficult or impossible, and discuss the implications for the CoRoT space mission in its quest for transiting telluric planets.
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ABSTRACT
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° < l < 11° and −6° ...< b < 3°, the total area close to 11 deg2. 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 and red giants in the GB, and main‐sequence stars in the Galactic disc. The proper motions up to μ= 500 mas yr−1 were measured with a mean accuracy of 0.8–3.5 mas yr−1, depending on the brightness of a star. This catalogue may be useful for studying the kinematics of stars in the GB and the Galactic disc.
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