arXiv subjects

I. Soszyński

Publications and source records attributed to I. Soszyński.

At least 19 recordsLinked to original sources

arXiv2026

Historic microlensing events in the euclid Galactic Bulge Survey

Microlensing campaigns have a long history of observations covering the Galactic bulge, where thousands of detections have been obtained, including many exoplanetary systems. The Euclid Galactic Bulge Survey represents a unique opportunity to revisit a large number of past events and attempt the lens-source resolution of known events falling in the covered area. As the analysis of individual events requires non-negligible efforts, it is important to establish priorities among all possible targets, identifying those candidates with the higher chance for a successful resolution of the lens from the source and with the highest scientific interest. Drawing from the databases of the three main microlensing surveys (OGLE, MOA and KMTNet), we compile the complete catalog of past microlensing events in the Euclid survey footprint up to year 2023, containing 7801 entries. By re-modeling all events and cross-checking with Galactic models, we estimate the relative lens-source proper motions for all events. Taking into account all uncertainties, for each microlensing event we are able to estimate the probability that the lens is separated from the source by more than a given angular distance threshold. Hence, we rank all events by their resolution probability, providing additional useful information that will guide future analyses on the most promising candidates. A particular attention is dedicated to the 51 known planetary microlensing events.

astro-ph.EP↗

arXiv2026

Thirty Circumbinary Disk Occultation Systems (KH 15D-like stars) from the OGLE Project

We present a catalog of 30 stars that are candidates for KH 15D-like binary systems, in which the observed brightness variations are caused by a circumbinary dusty disk that periodically obscures at least one of the stellar components as it moves along its orbit. Thanks to the regular observations conducted within the Optical Gravitational Lensing Experiment (OGLE) project, we provide unique light curves in the I and V bands with very long time baselines, in some cases beginning as early as 1997 and extending to the present day. Such long-term monitoring allows us to identify changes in eclipse widths, amplitudes, and light-curve shapes on timescales of many years. We highlight several circumbinary disk occultation (CBO) systems of particular interest and present spectra for three of them.

astro-ph.SR↗

arXiv2026

Cyclic light variations and accretion disk evolution in the LMC eclipsing binary OGLE-LMC-DPV-062

Many intermediate-mass close binaries exhibit photometric cycles longer than their orbital periods, likely related to accretion-disk variability. Previous studies indicate that historical light curves (LC) provide key constraints on disk evolution and may help trace mass-transfer changes in these systems. We investigate the short- and long-term variability of the eclipsing system OGLE-LMC-DPV-062, with special emphasis on the long cycle. Our aims are to clarify the role of the accretion disk in these modulations, particularly on timescales of hundreds of days, and to determine the evolutionary state of the system in order to better understand its stellar components. We analyzed 32.3 years of photometric time series from OGLE in the I and V bands, and from MACHO in the BM and RM bands. Using data from multiple epochs, we modeled the accretion disk at 20 equally spaced phases of the long cycle. To solve the inverse problem, we applied an optimized simplex algorithm to derive the best-fitting parameters of the stars, orbit, and disk. The MESA code was used to assess the evolutionary stage of the system and predict its past and future evolution. We find an orbital period of 6.904858(15) d and a long cycle of 229.7 d. The orbital solutions reproduce the LC, but the quasi-conservative mass-transfer scenario yields rates too high to be compatible with the observed orbital-period stability. We find consistency with the observed orbital-to-long-period ratio under the magnetic dynamo hypothesis. The normalized mass-transfer rate follows the long cycle, reaching a maximum at minimum brightness. At that phase, the inner disk edge thickens, obscuring a larger fraction of the gainer star. Disk variability occurs mainly in its vertical extent, with a standard deviation of 69% of the mean value at the inner border, whereas changes in outer radius and temperature are smaller, 7% and 5%, respectively.

astro-ph.SR↗

arXiv2026

KMT-2024-BLG-0816/OGLE-2024-BLG-0519 -- A Microlensing Event with Candidate Free-Floating Planet Lens and Blended Light

We present the discovery of a free-floating planet microlensing event KMT-2024-BLG-0816. The event shows finite-source effect, significant blending light, and no microlensing signal from a putative planet host. Among the free-floating planet events with finite source effects, this is the only event with unresolved blending light. We discuss how follow-up observations can be used to determine whether the blending light originates from a putative planet host.

astro-ph.EP↗

arXiv2025

Bright Long Secondary Period Stars for Follow-up Observations

Long secondary period (LSP) variable stars are a subclass of long-period variables (LPV) that exhibit additional long-term variability alongside pulsations. Despite being observed in over 30% of LPVs, the reason behind the LSP phenomenon is still debated. The most favoured explanation, supported by recent growing evidence, is binarity, where the pulsating giant star has a substellar-mass companion. To further test this hypothesis, it is important to identify bright LSP variables, for which high-quality spectroscopic and interferometric observations can be obtained more easily. Motivated by the absence of a catalog of bright nearby LSPs, we searched the All Sky Automated Survey (ASAS) data in the $V$-band magnitude range 5.5-14 mag, and for declinations $< +28^\circ$. The resulting catalog contains 23 LSPs, 13 of which are new discoveries. We compare our catalog with the LSP lists available in the literature.

astro-ph.SR↗

arXiv2025

Doubling the Number of Blue Large-Amplitude Pulsators: Final Results of Searches for BLAPs in the OGLE Inner Galactic Bulge Fields

Blue Large-Amplitude Pulsators (BLAPs) are rare short-period ($\lesssim$80 min) pulsating variable stars exhibiting large-amplitude brightness variations (typically between 0.1 and 0.4 mag). As a recently discovered class of radial-mode pulsators, the origin and nature of these variables remain the subject of ongoing investigations. Here, we present a comprehensive summary of all BLAPs identified in the data of the Optical Gravitational Lensing Experiment (OGLE), including the discovery of 88 new BLAPs in the inner Galactic bulge fields. We performed a systematic search for periodic signals in the $I$-band light curves of more than 400 million stars with magnitudes down to $I = 21$. Our search effectively doubles the number of these variables to almost 200. The detected BLAPs exhibit pulsation periods between roughly 5 and 76 minutes. The analyzed dataset covers a timespan from 2001 to 2024, with some stars observed up to 20,000 times, providing the temporal coverage needed to study period and amplitude variations. We report on three objects that show enormous period changes, at a rate of $10^{-5}$ yr$^{-1}$, which could provide important clues to the evolutionary status of BLAPs. Full dataset is incorporated into the publicly available OGLE Collection of Variable Stars (OCVS), enabling future studies of these enigmatic objects.

astro-ph.SR↗

arXiv2025

Eppur non si trovano: Comments on the Primordial Black Hole Limits in the Galactic Halo

In a recent arXiv post, Hawkins & Garcia-Bellido raised doubts on the results of 20-yr long OGLE photometric monitoring, which did not find a large number of gravitational microlensing events in the direction of the Magellanic Clouds. These results implied that primordial black holes and other compact objects with masses from 10^{-8} to 10^3 M_solar cannot comprise a substantial fraction of the Milky Way dark matter halo. Unfortunately, the Hawkins & Garcia-Bellido post contained a number of scientific misrepresentations of our work. Here, we demonstrate that their arguments lack a solid basis or are simply incorrect. As we show below, "and yet they are not found" - compact objects (including primordial black holes) in the dark halo of the Milky Way remain undetected, despite extensive searches.

astro-ph.CO↗

arXiv2025

Microlensing optical depth, event rate, and limits on compact objects in dark matter based on 20 yr of OGLE observations of the Small Magellanic Cloud

Some previous studies have suggested that massive and intermediate-mass primordial black holes (PBHs) could comprise a substantial fraction of dark matter in the Universe. Such black holes, if they existed in the Milky Way halo, would give rise to long-duration microlensing events that may potentially last for years. However, earlier searches were not sufficiently sensitive to detect such events. Here, we present the results of searches for long-timescale gravitational microlensing events toward the Small Magellanic Cloud (SMC) using nearly 20 years of photometric observations collected by the Optical Gravitational Lensing Experiment (OGLE) from 2001 to 2020. We found six events, three of which are new discoveries. We use a sample of five events to measure the microlensing optical depth toward the SMC $τ= (0.32 \pm 0.18) \times 10^{-7}$ and the event rate $Γ= (1.18 \pm 0.57) \times 10^{-7}\,\mathrm{yr}^{-1}\,\mathrm{star}^{-1}$. The properties of the detected events are consistent with lenses originating from known stellar populations within the SMC or in the Milky Way disk. No events with timescales longer than 1 yr were detected, which provides competitive limits on the fraction of massive compact objects, including PBHs, in the Milky Way dark matter halo. Together with the earlier OGLE studies of microlensing events in the direction of the Large Magellanic Cloud, these observations rule out PBHs and other compact objects with masses ranging from $10^{-8}$ to $10^3\,M_{\odot}$ as dominant components of dark matter.

astro-ph.GA↗

arXiv2025

Photometric study of hot Algol-type binaries with long cycles

Double periodic variables (DPVs) are hot Algol-type interacting binary systems with an orbital and a long photometric cycle. The origin of the latter may be related to cyclic structural changes in the accretion disc that surrounds the gainer star that are driven by a variable mass-transfer rate. If this is the case, changes in the orbital light curve would be expected throughout the long cycle. We conducted a detailed photometric analysis of the light curves of 134 Large Magellanic Cloud (LMC) DPVs to investigate variations in the morphology of the orbital light curves as a function of the long-cycle phase. We separated the two photometric cycles from the Optical Gravitational Lensing Experiment (OGLE) I band light curves for the systems. We thus compared the orbital light curves at opposite long-cycle phases, investigated the stability of the long period, and analysed the residuals of the separation process to search for significant frequencies above a 1% false-alarm probability threshold. We confirm that the DPVs OGLE-LMC-DPV-097 and OGLE-BLG-ECL-157529 change most strongly in their orbital light curves throughout the long cycle. By comparison, about 50% of the sample exhibits moderate morphological variations, in particular, around orbital phase 0.5. This is likely associated with structural changes in the accretion discs. In addition, we identified 18 DPVs with variable long periods, including 10 new cases. In some of them, the long period either increases or decreases continuously over time. For the first time, we found DPV systems that alternate between the two behaviours at different epochs. Moreover, we detected frequencies in the residuals that might be directly related to changes in the morphology of the orbital curves. Finally, some previously reported frequencies disappear when a variable long period is taken into account.

astro-ph.SR↗

arXiv2025

The Ultimate I-band Calibration of the TRGB Standard Candle

We present the ultimate I-band calibration of the tip of the red giant branch (TRGB) standard candle. Our calibration is based on photometry from the outer parts of the Large Magellanic Cloud, 2.75<r<6.5 degs from the center, collected during the OGLE-IV phase of the Optical Gravitational Lensing Experiment. Outer regions of the LMC have large advantages compared to the previous attempts of the TRGB calibrations using the red giants from the central parts of this galaxy. The interstellar reddening in these regions is much lower and more uniform, stellar crowding is lower and the outer parts of the LMC can be accurately described as a flat disk within the reasonable distance from the LMC center. The number of red giants in the upper part of the red giant branch in our LMC region is large, ~140 000, making it possible to determine of the tip magnitude with high accuracy. Our ultimate I-band calibration of the TRGB is: M_{I,TRGB}=-4.022 +- 0.006 (stat.) +- 0.033 (syst.) mag. We also provide its values for different techniques of the determination of the tip magnitude. The accuracy of our calibration is mostly limited by the accuracy of the distance to the LMC (~1%) and can be improved in the future. We test our calibration by comparing it with the TRGB in the Small Magellanic Cloud and NGC 4258, i.e., the galaxies with precise geometric distance determination, and find excellent agreement. Finally, we refine the main determinations of the Hubble constant, H_0, with the TRGB using our new calibration of the I-band TRGB brightness.

astro-ph.SR↗

arXiv2025

Automated detection and modeling of binary microlensing events in OGLE-IV data. I. Events with well-separated bumps

Gravitational microlensing depends primarily on the lens mass and presents a larger occurrence rate in crowded regions, which makes it the best tool to uncover the initial mass function (IMF) of low-mass stars in the Galactic bulge. The bulge IMF can be obtained from the luminosity function measured with the Hubble Space Telescope if one knows the statistics of binary stellar systems in the bulge. We aim to analyse a statistically significant number of binary-lens/single-source and single-lens/binary-source events, in order to explore the lower-mass end of the bulge IMF even in unresolved binary systems. This paper deals with events with clearly separated bumps and no caustic crossing or approach, whereas other types will be analysed in following works. A fully-automated approach in the search and modeling of binary events was implemented. Event detection was carried out with a modified version of the algorithm used in previous studies. Model fitting was carried out with Markov chain Monte Carlo and nested sampling methods, in order to find the most probable solution among binary lens or binary source models. We retrieved 107 binary events in Optical Gravitational Lensing Experiment (OGLE) light curves spanning ten years in 9 high-cadence and 112 low-cadence fields towards the bulge. Several criteria were applied to reduce false positives, resulting in 59 most likely binary lenses and 48 binary sources. The tools were effective in detecting a bona-fide sample of binary events, with a distribution of Einstein timescales around 35-40 days and flat distributions for mass ratio and source flux ratio. After proper consideration of detection efficiency, the statistics for binary fraction and mass ratio will provide valuable constraints for the bulge IMF.

astro-ph.GA↗

arXiv2025

Be star demographics: a comprehensive study of thousands of lightcurves in the Magellanic Clouds

Multi-color OGLE survey light curves of about 20 years duration are analyzed for about 3000 classical Be stars in the Large and Small Magellanic Clouds (LMC, SMC) in order to study the properties and variability. Each light curve was manually analyzed to distinguish between different scenarios, such as photospheric baseline levels, and disk build-up and dissipation phases. This analysis was aided by dynamical disk models and photospheric models to coarsely determine inclination angle and mass. Measured quantities such as the fraction of time spent actively ejecting mass (the duty cycle), the fraction of time spent with a detectable disk (the disk duty cycle), the build-up and dissipation time of isolated disk events, and the number of mass outbursts per year allow us to characterize and compare the behavior of the two populations. There is a wide spread in the duty cycle, with median values of 0.44 (LMC) and 0.60 (SMC). The disk duty cycle is high for both populations, with median values of 0.99 (LMC) and 1.0 (SMC), indicating that disks are almost always present for these stars. The occurrence rate of outbursts ranges from zero to about two per year, with median values of 0.31 (LMC) and 0.26 (SMC). There are strong statistical differences in the behavior of the LMC and SMC populations, with the lower metallicity stars being more active in terms of their duty cycle and disk duty cycle, and with less frequent but longer lasting outbursts.

astro-ph.SR↗

arXiv2025

Asteroseismology of Long-Period Variables with OGLE-IV data: Using Global Seismic Parameters as Luminosity Indicators

Long-period variables (LPVs) are high-luminosity red giants or supergiants with pulsation periods ranging from days to years. Many LPVs in the Large Magellanic Cloud (LMC) and Galactic Bulge (BLG) have been continuously observed over a time span of 26 years by the Optical Gravitational Lensing Experiment (OGLE) survey. Using OGLE-IV data, we applied Gaussian Processes with kernels tailored for solar-like oscillations to extract two global asteroseismic parameters: the frequency of maximum power (numax) and the large frequency separation (Dnu), for LPVs with primary mode periods (P1) between 10 and 100 days in the LMC and BLG. We found that the numax-Dnu relation for LPVs in this work aligns with that of lower-luminosity Kepler red giants, confirming that the pulsations of these LPVs are likely solar-like. We found that numax and Dnu can serve as luminosity indicators. Compared to P1, numax and Dnu exhibit significantly tighter correlations with the absolute magnitude in the 2MASS K_s band (M_{K}), with corresponding scatter of 0.27 mag and 0.21 mag, respectively. Using the calibrated numax-mk and Dnu-mk relations for LPVs in the LMC, we determined the M_{K} values for individual stars in the BLG. By accounting for extinction, we further calculated the distances to 4,948 BLG stars. The peak of the resulting distance distribution corresponds to an estimated distance to the Galactic center of approximately 9.1 kpc, which appears to be overestimated, suggesting that the seismic luminosity relation calibrated from the LMC may not be directly applicable to BLG stars.

astro-ph.SR↗

arXiv2025

The OGLE Collection of Variable Stars. Over 75 000 Eclipsing and Ellipsoidal Binary Systems in the Magellanic Clouds

We present an updated collection of eclipsing and ellipsoidal binary systems in the Large and Small Magellanic Clouds (LMC and SMC), as observed by the Optical Gravitational Lensing Experiment (OGLE) survey. The catalog comprises a total of 75 400 binary systems, including 63 252 in the LMC and 12 148 in the SMC. The sample is categorized into 67 971 eclipsing and 7429 ellipsoidal variables. For all stars, we provide I-band and V-band photometric time series collected between 2010 and 2024 during the fourth phase of the OGLE project (OGLE-IV). We discuss methods used to identify binary systems in the OGLE data and present objects of particular interest, including double periodic variables, transient eclipsing binaries, double eclipsing binaries, and binary systems with pulsating stars. We present a comparative analysis based on the most comprehensive catalogs of variable stars in the Magellanic System, compiled from surveys like Gaia, ASAS-SN, and EROS-2, and included in the International Variable Star Index.

astro-ph.SR↗

arXiv2025

Non-evolutionary effects on period change in Magellanic Cepheids

Classical Cepheids are a cornerstone class of pulsators, fundamental to testing stellar evolution and pulsation theories. Their secular period changes, characterized through $O-C$ (Observed minus Calculated) diagrams, offer valuable insights into their evolution. While evolutionary period changes are well understood from both observational and theoretical perspectives, shorter timescale period changes (on the order of ($\sim$ 10$^{2}$-10$^{4}$ days) - known as non-evolutionary period changes are yet to be systematically explored. In this work, we present a detailed and comprehensive search for non-evolutionary period changes using $O-C$ analysis of Magellanic Cloud (MC) Cepheids, based on 20+ years of OGLE photometry data. Our sample includes both the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) Cepheids, focusing on single radial mode Cepheids (both fundamental (FU) and first overtone (FO) modes). The results are grouped into two phenomena: (a) Cepheids in binary systems (b) Non-linear period changes.

astro-ph.SR↗

arXiv2024

OGLE-2015-BLG-1609Lb: Sub-jovian planet orbiting a low-mass stellar or brown dwarf host

We present a comprehensive analysis of a planetary microlensing event OGLE-2015-BLG-1609. The planetary anomaly was detected by two survey telescopes, OGLE and MOA. Each of these surveys collected enough data over the planetary anomaly to allow for an unambiguous planet detection. Such survey detections of planetary anomalies are needed to build a robust sample of planets that could improve studies on the microlensing planetary occurrence rate by reducing biases and statistical uncertainties. In this work, we examined different methods for modeling microlensing events using individual datasets, particularly we incorporated a Galactic model prior to better constrain poorly defined microlensing parallax. Ultimately, we fitted a comprehensive model to all available data, identifying three potential typologies, with two showing comparably high Bayesian evidence. Our analysis indicates that the host of the planet is a brown dwarf with a probability of 34%, or a low-mass stellar object (M-dwarf) with the probability of 66%.

astro-ph.EP↗

arXiv2024

Examining the brightness variability, accretion disk, and evolutionary stage of the binary OGLE-LMC-ECL-14413

Our study aims to elucidate both short-term and long-term variations in the light curve of the eclipsing system OGLE-LMC-ECL-14413, with a particular focus on the unusual reversals in eclipse depth. We aim to clarify the role of the accretion disk in these fluctuations, especially in long-cycle changes spanning hundreds of days. Additionally, we seek to determine the evolutionary stage of the system and gain insights into the internal structure of its stellar components. We analyzed photometric time series from the Optical Gravitational Lensing Experiment (OGLE) project in the I and V bands, and from the MAssive Compact Halo Objects project in the BM and RM bands, covering a period of 30.85 years. Using light curve data from 27 epochs, we constructed models of the accretion disk. An optimized simplex algorithm was employed to solve the inverse problem, deriving the best-fit parameters for the stars, orbit, and disk. We also utilized the Modules for Experiments in Stellar Astrophysics software to assess the evolutionary stage of the binary system, investigating the progenitors and potential future developments. We found an orbital period of 38.15917(54) d and a long-term cycle of approximately 780 d. Temperature, mass, radius, and surface gravity values were determined for both stars. The photometric orbital cycle and the long-term cycle are consistent with a disk containing variable physical properties, including two shock regions. The disk encircles the more massive star and the system brightness variations align with the long-term cycle at orbital phase 0.25. Our mass transfer rate calculations correspond to these brightness changes. \texttt{MESA} simulations indicate weak magnetic fields in the donor star's subsurface, which are insufficient to influence mass transfer rates significantly.

astro-ph.SR↗

arXiv2024

Precise physical parameters of three late-type eclipsing binary giant stars in the Large Magellanic Cloud

Detached eclipsing binaries (DEBs) allow for the possibility of precise characterization of its stellar components. They offer a unique opportunity to derive their physical parameters in a near-model-independent way for a number of systems consisting of late-type giant stars. Here we aim to expand the sample of low-metallicity late-type giant stars with precise parameters determined. We aim to determine the fundamental parameters like the mass, radius, or effective temperature for three long-period late-type eclipsing binaries from the Large Magellanic Cloud: OGLE-LMC-ECL-25304, OGLE-LMC-ECL-28283, and OGLE-IV LMC554.19.81. Subsequently we aim to determine the evolutionary stages of the systems. We fit the light curves from the OGLE project and radial velocity curves from high resolution spectrographs using the Wilson-Devinney code. The spectral analysis was performed with the GSSP code and resulted in the determination of atmospheric parameters such as effective temperatures and metallicities. We used isochrones provided by the MIST models based on the MESA code to derive evolutionary status of the stars. We present the first analysis of three DEBs composed of similar He-burning late-type stars passing through the blue loop. Estimated masses for OGLE-LMC-ECL-29293 (G4III + G4III) are $M_1=2.898\pm0.031$ and $M_2=3.153\pm0.038$ $M_\odot$, stellar radii are $R_1=19.43\pm0.31$ and $R_2=19.30\pm0.31$ $R_\odot$. OGLE-LMC-ECL-25304 (G4III + G5III) has stellar masses of $M_1=3.267\pm0.028$ and $M_2=3.229\pm0.029$ $M_\odot$, radii of $R_1=23.62\pm0.42$ and $R_2=25.10\pm0.43$ $R_\odot$. OGLE-IV LMC554.19.81 (G2III + G2III) have masses of $M_1=3.165\pm0.020$ and $M_2=3.184\pm0.020$ $M_\odot$, radii of $R_1=18.86\pm0.26$ and $R_2=19.64\pm0.26$ $R_\odot$. All masses were determined with a precision better than 2\% and radii better than 1.5\%. The ages of the stars are in the range of 270-341 Myr.

astro-ph.SR↗