arXiv subjects

M. K. Szymanski

Publications and source records attributed to M. K. Szymanski.

At least 127 records · Page 7Linked to original sources

arXiv2010

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. V. R Coronae Borealis Stars in the Large Magellanic Cloud

The fifth part of the OGLE-III Catalog of Variable Stars presents 23 R CrB (RCB) stars in the Large Magellanic Cloud (LMC). 17 of these objects have been spectroscopically confirmed by previous studies, while 6 stars are new candidates for RCB variables. We publish the VI multi-epoch OGLE photometry for all objects. We use the sample of carbon-rich long-period variables released in the previous part of this catalog to select objects with severe drops in luminosity, i.e. with the DY-Per-like light curves. DY Per stars are often related to R CrB variables. We detect at least 600 candidates for DY Per stars, mostly among dust enshrouded giants. We notice that our candidate DY Per stars form a continuity with other carbon-rich long-period variables, so it seems that DY Per stars do not constitute a separate group of variable stars.

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arXiv2010

Frequency of Solar-Like Systems and of Ice and Gas Giants Beyond the Snow Line from High-Magnification Microlensing Events in 2005-2008

We present the first measurement of planet frequency beyond the "snow line" for planet/star mass-ratios[-4.5 200) microlensing events during 2005-8. The sample host stars have typical mass M_host 0.5 Msun, and detection is sensitive to planets over a range of projected separations (R_E/s_max,R_E*s_max), where R_E 3.5 AU sqrt(M_host/Msun) is the Einstein radius and s_max (q/5e-5)^{2/3}, corresponding to deprojected separations ~3 times the "snow line". Though frenetic, the observations constitute a "controlled experiment", which permits measurement of absolute planet frequency. High-mag events are rare, but the high-mag channel is efficient: half of high-mag events were successfully monitored and half of these yielded planet detections. The planet frequency derived from microlensing is a factor 7 larger than from RV studies at factor ~25 smaller separations [2<P<2000 days]. However, this difference is basically consistent with the gradient derived from RV studies (when extrapolated well beyond the separations from which it is measured). This suggests a universal separation distribution across 2 dex in semi-major axis, 2 dex in mass ratio, and 0.3 dex in host mass. Finally, if all planetary systems were "analogs" of the Solar System, our sample would have yielded 18.2 planets (11.4 "Jupiters", 6.4 "Saturns", 0.3 "Uranuses", 0.2 "Neptunes") including 6.1 systems with 2 or more planet detections. This compares to 6 planets including one 2-planet system in the actual sample, implying a first estimate of 1/6 for the frequency of solar-like systems.

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arXiv2009

Interpretation of Strong Short-Term Central Perturbations in the Light Curves of Moderate-Magnification Microlensing Events

To improve the planet detection efficiency, current planetary microlensing experiments are focused on high-magnification events searching for planetary signals near the peak of lensing light curves. However, it is known that central perturbations can also be produced by binary companions and thus it is important to distinguish planetary signals from those induced by binary companions. In this paper, we analyze the light curves of microlensing events OGLE-2007-BLG-137/MOA-2007-BLG-091, OGLE-2007-BLG-355/MOA-2007-BLG-278, and MOA-2007-BLG-199/OGLE-2007-BLG-419, for all of which exhibit short-term perturbations near the peaks of the light curves. From detailed modeling of the light curves, we find that the perturbations of the events are caused by binary companions rather than planets. From close examination of the light curves combined with the underlying physical geometry of the lens system obtained from modeling, we find that the short time-scale caustic-crossing feature occurring at a low or a moderate base magnification with an additional secondary perturbation is a typical feature of binary-lens events and thus can be used for the discrimination between the binary and planetary interpretations.

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arXiv2009

Quantifying Quasar Variability As Part of a General Approach To Classifying Continuously Varying Sources

Robust fast methods to classify variable light curves in large sky surveys are becoming increasingly important. While it is relatively straightforward to identify common periodic stars and particular transient events (supernovae, novae, microlensing), there is no equivalent for non-periodic continuously varying sources (quasars, aperiodic stellar variability). In this paper we present a fast method for modeling and classifying such sources. We demonstrate the method using ~ 86,000 variable sources from the OGLE-II survey of the LMC and ~ 2,700 mid-IR selected quasar candidates from the OGLE-III survey of the LMC and SMC. We discuss the location of common variability classes in the parameter space of the model. In particular we show that quasars occupy a distinct region of variability space, providing a simple quantitative approach to the variability selection of quasars.

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arXiv2009

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. IV. Long-Period Variables in the Large Magellanic Cloud

The fourth part of the OGLE-III Catalog of Variable Stars presents 91 995 long-period variables (LPVs) in the Large Magellanic Cloud (LMC). This sample consists of 79 200 OGLE Small Amplitude Red Giants (OSARGs), 11 128 semiregular variables (SRVs) and 1667 Mira stars. The catalog data include basic photometric and astrometric properties of these stars, long-term multi-epoch VI photometry and finding charts. We describe the methods used for the identification and classification of LPVs. The distribution of I-band amplitudes for carbon-rich stars shows two maxima, corresponding to Miras and SRVs. Such a distinction between Miras and SRVs is not obvious for oxygen-rich stars. We notice additional period-luminosity sequence located between Wood's sequences C and C' and populated by SRVs.

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arXiv2009

OGLE-2005-BLG-071Lb, the Most Massive M-Dwarf Planetary Companion?

We combine all available information to constrain the nature of OGLE-2005-BLG-071Lb, the second planet discovered by microlensing and the first in a high-magnification event. These include photometric and astrometric measurements from Hubble Space Telescope, as well as constraints from higher order effects extracted from the ground-based light curve, such as microlens parallax, planetary orbital motion and finite-source effects. Our primary analysis leads to the conclusion that the host of Jovian planet OGLE-2005-BLG-071Lb is an M dwarf in the foreground disk with mass M= 0.46 +/- 0.04 Msun, distance D_l = 3.3 +/- 0.4 kpc, and thick-disk kinematics v_LSR ~ 103 km/s. From the best-fit model, the planet has mass M_p = 3.8 +/- 0.4 M_Jup, lies at a projected separation r_perp = 3.6 +/- 0.2 AU from its host and so has an equilibrium temperature of T ~ 55 K, i.e., similar to Neptune. A degenerate model less favored by Δχ^2 = 2.1 (or 2.2, depending on the sign of the impact parameter) gives similar planetary mass M_p = 3.4 +/- 0.4 M_Jup with a smaller projected separation, r_\perp = 2.1 +/- 0.1 AU, and higher equilibrium temperature T ~ 71 K. These results from the primary analysis suggest that OGLE-2005-BLG-071Lb is likely to be the most massive planet yet discovered that is hosted by an M dwarf. However, the formation of such high-mass planetary companions in the outer regions of M-dwarf planetary systems is predicted to be unlikely within the core-accretion scenario. There are a number of caveats to this primary analysis, which assumes (based on real but limited evidence) that the unlensed light coincident with the source is actually due to the lens, that is, the planetary host. However, these caveats could mostly be resolved by a single astrometric measurement a few years after the event.

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arXiv2009

The OGLE View of Microlensing towards the Magellanic Clouds. I. A Trickle of Events in the OGLE-II LMC data

We present the results from the OGLE-II survey (1996-2000) towards the Large Magellanic Cloud (LMC), which has the aim of detecting the microlensing phenomena caused by dark matter compact objects in the Galactic Halo (Machos). We use high resolution HST images of the OGLE fields and derive the correction for the number of monitored stars in each field. This also yield blending distributions which we use in 'catalogue level' Monte Carlo simulations of the microlensing events in order to calculate the detection efficiency of the events. We detect two candidates for microlensing events in the All Stars Sample, which translates into an optical depth of 0.43+-0.33x 10e-7. If both events were due to Macho the fraction of mass of compact dark matter objects in the Galactic halo would be 8+-6 per cent. This optical depth, however, along with the characteristics of the events, seems to be consistent with the self-lensing scenario, i.e., self-lensing alone is sufficient to explain the observed microlensing signal. Our results indicate a non-detection of Machos lensing towards the LMC with an upper limit on their abundance in the Galactic halo of 19 per cent for M=0.4 Msun and 10 per cent for masses between 0.01 and 0.2 Msun.

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arXiv2009

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. III. RR Lyrae Stars in the Large Magellanic Cloud

The third part of the OGLE-III Catalog of Variable Stars comprises 24906 RR Lyr stars in the Large Magellanic Cloud (LMC). This sample consists of 17693 fundamental-mode (RRab), 4958 first-overtone (RRc), 986 double-mode (RRd) and 1269 suspected second-overtone (RRe) pulsators. 66 objects are foreground Galactic RR Lyr stars. The catalog data include basic photometric and astrometric properties of these RR Lyr stars, multi-epoch VI photometry and finding charts. We detected one new RR Lyr star with additional eclipsing variations. The spatial distribution of RR Lyr stars in the LMC is distinctly non-spherical and it is elongated in the same direction as the LMC bar. The basic statistical features of RR Lyr stars in the LMC are provided. The apparent V-band magnitudes for RRab stars have the modal value at 19.36 mag, and for overtone RR Lyr stars it is about 19.32 mag. The mean periods for RRab, RRc and RRe stars are 0.576, 0.337 and 0.270 days, respectively.

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arXiv2009

The Optical Gravitational Lensing Experiment. OGLE-III Photometric Maps of the Small Magellanic Cloud

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.

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arXiv2009

A systematic fitting scheme for caustic-crossing microlensing events

We outline a method for fitting binary-lens caustic-crossing microlensing events based on the alternative model parameterisation proposed and detailed in Cassan (2008). As an illustration of our methodology, we present an analysis of OGLE-2007-BLG-472, a double-peaked Galactic microlensing event with a source crossing the whole caustic structure in less than three days. In order to identify all possible models we conduct an extensive search of the parameter space, followed by a refinement of the parameters with a Markov Chain-Monte Carlo algorithm. We find a number of low-chi2 regions in the parameter space, which lead to several distinct competitive best models. We examine the parameters for each of them, and estimate their physical properties. We find that our fitting strategy locates several minima that are difficult to find with other modelling strategies and is therefore a more appropriate method to fit this type of events.

astro-ph.GA↗

arXiv2009

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. II. Type II Cepheids and Anomalous Cepheids in the Large Magellanic Cloud

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 adopted at 4 days, both groups differ significantly in (V-I) colors. We identify a group of 16 peculiar W Vir stars with different appearance of the light curves, brighter and bluer than ordinary stars of that type. Four of these peculiar W Vir stars show additional eclipsing modulation superimposed on the pulsation light curves. Four other stars of that type show long-period secondary variations which may be ellipsoidal modulations. It suggests that peculiar W Vir subgroup may be related to binarity. In total, we identified seven type II Cepheids simultaneously exhibiting eclipsing variations which is a very large fraction compared to classical Cepheids in the LMC. We discuss diagrams showing Fourier parameters of the light curve decomposition against periods. Three sharp features interpreted as an effect of resonances between radial modes are detectable in these diagrams for type II Cepheids.

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arXiv2008

The Optical Gravitational Lensing Experiment. Triple-Mode and 1O/3O Double-Mode Cepheids in the Large Magellanic Cloud

We report the discovery of three new triple-mode classical Cepheids in the Large Magellanic Cloud, two of them with the fundamental, first overtone and second overtone excited, and one pulsating simultaneously in the first three overtones. Thus, the number of triple-mode Cepheids in the LMC is increased to five. We also present two objects belonging probably to a new type of double-mode Cepheids having the first and third overtones excited. We measure the rates of period change in these stars and detect decrease of periods in two of them, what is in conflict with theoretical predictions.

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arXiv2008

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. I. Classical Cepheids in the Large Magellanic Cloud

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 amplitude variable stars which may be Cepheids entering or exiting instability strip. The catalog data include VI high-quality photometry collected since 2001, and for some stars supplemented by the OGLE-II photometry obtained between 1997 and 2000. We provide basic parameters of the stars: coordinates, periods, mean magnitudes, amplitudes and parameters of the Fourier light curve decompositions. Individual objects of particular interest are discussed, including single-mode second-overtone Cepheids, multiperiodic pulsators with unusual period ratios or Cepheids in eclipsing binary systems. We discuss the variations of the Fourier coefficients with periods and point out on the sharp feature for periods around 0.35 days of first-overtone Cepheids, which can be explained by the occurrence of 2:1 resonance between the first and fifth overtones. Similar behavior at P=3 days for 1O Cepheids and P=10 days for F Cepheids are also interpreted as an effect of resonances between two radial modes. We fit the period-luminosity relations to our sample of Cepheids and compare these functions with previous determinations.

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arXiv2008

Microlensing Event MOA-2007-BLG-400: Exhuming the Buried Signature of a Cool, Jovian-Mass Planet

We report the detection of the cool, Jovian-mass planet MOA-2007-BLG-400Lb. The planet was detected in a high-magnification microlensing event (with peak magnification A_max = 628) in which the primary lens transited the source, resulting in a dramatic smoothing of the peak of the event. The angular extent of the region of perturbation due to the planet is significantly smaller than the angular size of the source, and as a result the planetary signature is also smoothed out by the finite source size. Thus the deviation from a single-lens fit is broad and relatively weak (~ few percent). Nevertheless, we demonstrate that the planetary nature of the deviation can be unambiguously ascertained from the gross features of the residuals, and detailed analysis yields a fairly precise planet/star mass ratio of q = 0.0026+/-0.0004, in accord with the large significance (Δχ^2=1070) of the detection. The planet/star projected separation is subject to a strong close/wide degeneracy, leading to two indistinguishable solutions that differ in separation by a factor of ~8.5. Upper limits on flux from the lens constrain its mass to be M < 0.75 M_Sun (assuming it is a main-sequence star). A Bayesian analysis that includes all available observational constraints indicates a primary in the Galactic bulge with a mass of ~0.2-0.5 M_Sun and thus a planet mass of ~ 0.5-1.3 M_Jupiter. The separation and equilibrium temperature are ~0.6-1.1AU (~5.3-9.7AU) and ~103K (~34K) for the close (wide) solution. If the primary is a main-sequence star, follow-up observations would enable the detection of its light and so a measurement of its mass and distance.

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arXiv2008

The Optical Gravitational Lensing Experiment. Final Reductions of the OGLE-III Data

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.

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arXiv2008

The Optical Gravitational Lensing Experiment. OGLE-III Photometric Maps of the Large Magellanic Cloud

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.

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arXiv2008

A Low-Mass Planet with a Possible Sub-Stellar-Mass Host in Microlensing Event MOA-2007-BLG-192

We report the detection of an extrasolar planet of mass ratio q ~ 2 x 10^(-4) in microlensing event MOA-2007-BLG-192. The best fit microlensing model shows both the microlensing parallax and finite source effects, and these can be combined to obtain the lens masses of M = 0.060 (+0.028 -0.021) M_sun for the primary and m = 3.3 (+4.9 -1.6) M_earth for the planet. However, the observational coverage of the planetary deviation is sparse and incomplete, and the radius of the source was estimated without the benefit of a source star color measurement. As a result, the 2-sigma limits on the mass ratio and finite source measurements are weak. Nevertheless, the microlensing parallax signal clearly favors a sub-stellar mass planetary host, and the measurement of finite source effects in the light curve supports this conclusion. Adaptive optics images taken with the Very Large Telescope (VLT) NACO instrument are consistent with a lens star that is either a brown dwarf or a star at the bottom of the main sequence. Follow-up VLT and/or Hubble Space Telescope (HST) observations will either confirm that the primary is a brown dwarf or detect the low-mass lens star and enable a precise determination of its mass. In either case, the lens star, MOA-2007-BLG-192L, is the lowest mass primary known to have a companion with a planetary mass ratio, and the planet, MOA-2007-BLG-192Lb, is probably the lowest mass exoplanet found to date, aside from the lowest mass pulsar planet.

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arXiv2008

Discovery of a Jupiter/Saturn Analog with Gravitational Microlensing

Searches for extrasolar planets have uncovered an astonishing diversity of planetary systems, yet the frequency of solar system analogs remains unknown. The gravitational microlensing planet search method is potentially sensitive to multiple-planet systems containing analogs of all the solar system planets except Mercury. We report the detection of a multiple-planet system with microlensing. We identify two planets with masses of ~0.71 and ~0.27 times the mass of Jupiter and orbital separations of ~2.3 and ~4.6 astronomical units orbiting a primary star of mass ~0.50 solar masses at a distance of ~1.5 kiloparsecs. This system resembles a scaled version of our solar system in that the mass ratio, separation ratio, and equilibrium temperatures of the planets are similar to those of Jupiter and Saturn. These planets could not have been detected with other techniques; their discovery from only six confirmed microlensing planet detections suggests that solar system analogs may be common.

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