arXiv subjects

I. Soszyński

Publications and source records attributed to I. Soszyński.

At least 91 records · Page 5Linked to original sources

arXiv2018

Structural changes in the hot Algol OGLE-LMC-DPV-097 and its disk related to its long-cycle

Double Periodic Variables (DPVs) are hot Algols showing a long photometric cycle of uncertain origin. We report the discovery of changes in the orbital light curve of OGLE-LMC-DPV-097 which depend on the phase of its long photometric cycle. During the ascending branch of the long-cycle the brightness at the first quadrature is larger than during the second quadrature, during the maximum of the long-cycle the brightness is basically the same at both quadratures, during the descending branch the brightness at the second quadrature is larger than during the first quadrature and during the minimum of the long-cycle the secondary minimum disappears. We model the light curve at different phases of the long-cycle and find that the data are consistent with changes in the properties of the accretion disk and two disk spots. The disk's size and temperature change with the long-cycle period. We find a smaller and hotter disk at minimum and larger and cooler disk at maximum. The spot temperatures, locations and angular sizes also show variability during the long-cycle.

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arXiv2018

OGLE-2017-BLG-0329L: A Microlensing Binary Characterized with Dramatically Enhanced Precision Using Data from Space-based Observations

Mass measurements of gravitational microlenses require one to determine the microlens parallax $\pie$, but precise $\pie$ measurement, in many cases, is hampered due to the subtlety of the microlens-parallax signal combined with the difficulty of distinguishing the signal from those induced by other higher-order effects. In this work, we present the analysis of the binary-lens event OGLE-2017-BLG-0329, for which $\pie$ is measured with a dramatically improved precision using additional data from space-based $Spitzer$ observations. We find that while the parallax model based on the ground-based data cannot be distinguished from a zero-$\pie$ model at 2$σ$ level, the addition of the $Spitzer$ data enables us to identify 2 classes of solutions, each composed of a pair of solutions according to the well-known ecliptic degeneracy. It is found that the space-based data reduce the measurement uncertainties of the north and east components of the microlens-parallax vector $\pivec_{\rm E}$ by factors $\sim 18$ and $\sim 4$, respectively. With the measured microlens parallax combined with the angular Einstein radius measured from the resolved caustic crossings, we find that the lens is composed of a binary with components masses of either $(M_1,M_2)\sim (1.1,0.8)\ M_\odot$ or $\sim (0.4,0.3)\ M_\odot$ according to the two solution classes. The first solution is significantly favored but the second cannot be securely ruled out based on the microlensing data alone. However, the degeneracy can be resolved from adaptive optics observations taken $\sim 10$ years after the event.

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arXiv2018

OGLE-2017-BLG-1434Lb: Eighth q < 1 * 10^-4 Mass-Ratio Microlens Planet Confirms Turnover in Planet Mass-Ratio Function

We report the discovery of a cold Super-Earth planet (m_p=4.4 +/- 0.5 M_Earth) orbiting a low-mass (M=0.23 +/- 0.03 M_Sun) M dwarf at projected separation a_perp = 1.18 +/- 0.10 AU, i.e., about 1.9 times the snow line. The system is quite nearby for a microlensing planet, D_Lens = 0.86 +/- 0.09 kpc. Indeed, it was the large lens-source relative parallax pi_rel=1.0 mas (combined with the low mass M) that gave rise to the large, and thus well-measured, "microlens parallax" that enabled these precise measurements. OGLE-2017-BLG-1434Lb is the eighth microlensing planet with planet-host mass ratio q < 1 * 10^-4. We apply a new planet-detection sensitivity method, which is a variant of "V/V_max", to seven of these eight planets to derive the mass-ratio function in this regime. We find dN/d(ln q) ~ q^p, with p = 1.05 (+0.78,-0.68), which confirms the "turnover" in the mass function found by Suzuki et al. relative to the power law of opposite sign n = -0.93 +/- 0.13 at higher mass ratios q >~ 2 * 10^-4. We combine our result with that of Suzuki et al. to obtain p = 0.73 (+0.42,-0.34).

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arXiv2018

A Gravitationally Lensed Quasar Discovered in OGLE

We report the discovery of a new gravitationally lensed quasar (double) from the Optical Gravitational Lensing Experiment (OGLE) identified inside the $\sim$670 sq. deg area encompassing the Magellanic Clouds. The source was selected as one of $\sim$60 "red W1-W2" mid-IR objects from WISE and having a significant amount of variability in OGLE for both two (or more) nearby sources. This is the first detection of a gravitational lens, where the discovery is made "the other way around", meaning we first measured the time delay between the two lensed quasar images of $-132<t_{\rm AB}<-76$ days (90% CL), with the median $t_{\rm AB}\approx-102$ days (in the observer frame), and where the fainter image B lags image A. The system consists of the two quasar images separated by 1.5" on the sky, with $I\approx20.0$ mag and $I\approx19.6$ mag, respectively, and a lensing galaxy that becomes detectable as $I \approx 21.5$ mag source, 1.0" from image A, after subtracting the two lensed images. Both quasar images show clear AGN broad emission lines at $z=2.16$ in the NTT spectra. The SED fitting with the fixed source redshift provided the estimate of the lensing galaxy redshift of $z \approx 0.9 \pm 0.2$ (90% CL), while its type is more likely to be elliptical (the SED-inferred and lens-model stellar mass is more likely present in ellipticals) than spiral (preferred redshift by the lens model).

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arXiv2018

The OGLE Collection of Variable Stars. Classical, Type II, and Anomalous Cepheids toward the Galactic Center

We present a collection of classical, type II, and anomalous Cepheids detected in the OGLE fields toward the Galactic center. The sample contains 87 classical Cepheids pulsating in one, two or three radial modes, 924 type II Cepheids divided into BL Her, W Vir, peculiar W Vir, and RV Tau stars, and 20 anomalous Cepheids - first such objects found in the Galactic bulge. Additionally, we upgrade the OGLE Collection of RR Lyr stars in the Galactic bulge by adding 828 newly identified variables. For all Cepheids and RR Lyr stars, we publish time-series VI photometry obtained during the OGLE-IV project, from 2010 through 2017. We discuss basic properties of our classical pulsators: their spatial distribution, light curve morphology, period-luminosity relations, and position in the Petersen diagram. We present the most interesting individual objects in our collection: a type II Cepheid with additional eclipsing modulation, W Vir stars with the period doubling effect and the RVb phenomenon, a mode-switching RR Lyr star, and a triple-mode anomalous RRd star.

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arXiv2018

OGLE Collection of Star Clusters. New Objects in the Magellanic Bridge and the Outskirts of the Small Magellanic Cloud

The Magellanic System (MS) encompasses the nearest neighbors of the Milky Way, the Large (LMC) and Small (SMC) Magellanic Clouds, and the Magellanic Bridge (MBR). This system contains a diverse sample of star clusters. Their parameters, such as the spatial distribution, chemical composition and age distribution yield important information about the formation scenario of the whole Magellanic System. Using deep photometric maps compiled in the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV) we present the most complete catalog of star clusters in the Magellanic System ever constructed from homogeneous, long time-scale photometric data. In this second paper of the series, we show the collection of star clusters found in the area of about 360 square degrees in the MBR and in the outer regions of the SMC. Our sample contains 198 visually identified star cluster candidates, 75 of which were not listed in any of the previously published catalogs. The new discoveries are mainly young small open clusters or clusters similar to associations.

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arXiv2018

Spitzer Microlensing Parallax for OGLE-2016-BLG-1067: a sub-Jupiter Orbiting an M-dwarf in the Disk

We report the discovery of a sub-Jupiter mass planet orbiting beyond the snow line of an M-dwarf most likely in the Galactic disk as part of the joint Spitzer and ground-based monitoring of microlensing planetary anomalies toward the Galactic bulge. The microlensing parameters are strongly constrained by the light curve modeling and in particular by the Spitzer-based measurement of the microlens parallax, $π_\mathrm{E}$. However, in contrast to many planetary microlensing events, there are no caustic crossings, so the angular Einstein radius, $θ_\mathrm{E}$ has only an upper limit based on the light curve modeling alone. Additionally, the analysis leads us to identify 8 degenerate configurations: the four-fold microlensing parallax degeneracy being doubled by a degeneracy in the caustic structure present at the level of the ground-based solutions. To pinpoint the physical parameters, and at the same time to break the parallax degeneracy, we make use of a series of arguments: the $χ^2$ hierarchy, the Rich argument, and a prior Galactic model. The preferred configuration is for a host at $D_L=3.73_{-0.67}^{+0.66}~\mathrm{kpc}$ with mass $M_\mathrm{L}=0.30_{-0.12}^{+0.15}~\mathrm{M_\odot}$, orbited by a Saturn-like planet with $M_\mathrm{planet}=0.43_{-0.17}^{+0.21}~\mathrm{M_\mathrm{Jup}}$ at projected separation $a_\perp = 1.70_{-0.39}^{+0.38}~\mathrm{au}$, about 2.1 times beyond the system snow line. Therefore, it adds to the growing population of sub-Jupiter planets orbiting near or beyond the snow line of M-dwarfs discovered by microlensing. Based on the rules of the real-time protocol for the selection of events to be followed up with Spitzer, this planet will not enter the sample for measuring the Galactic distribution of planets.

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arXiv2018

OGLE-2014-BLG-0289: Precise Characterization of a Quintuple-Peak Gravitational Microlensing Event

We present the analysis of the binary-microlensing event OGLE-2014-BLG-0289. The event light curve exhibits very unusual five peaks where four peaks were produced by caustic crossings and the other peak was produced by a cusp approach. It is found that the quintuple-peak features of the light curve provide tight constraints on the source trajectory, enabling us to precisely and accurately measure the microlensing parallax $π_{\rm E}$. Furthermore, the three resolved caustics allow us to measure the angular Einstein radius $\thetae$. From the combination of $π_{\rm E}$ and $\thetae$, the physical lens parameters are uniquely determined. It is found that the lens is a binary composed of two M dwarfs with masses $M_1 = 0.52 \pm 0.04\ M_\odot$ and $M_2=0.42 \pm 0.03\ M_\odot$ separated in projection by $a_\perp = 6.4 \pm 0.5$ au. The lens is located in the disk with a distance of $D_{\rm L} = 3.3 \pm 0.3$~kpc. It turns out that the reason for the absence of a lensing signal in the {\it Spitzer} data is that the time of observation corresponds to the flat region of the light curve.

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arXiv2017

A companion on the planet/brown dwarf mass boundary on a wide orbit discovered by gravitational microlensing

We present the discovery of a substellar companion to the primary host lens in the microlensing event MOA-2012-BLG-006. The companion-to-host mass ratio is 0.016, corresponding to a companion mass of $\approx8~M_{\rm Jup} (M_*/0.5M_\odot)$. Thus, the companion is either a high-mass giant planet or a low-mass brown dwarf, depending on the mass of the primary $M_*$. The companion signal was separated from the peak of the primary event by a time that was as much as four times longer than the event timescale. We therefore infer a relatively large projected separation of the companion from its host of $\approx10~{\rm a.u.}(M_*/0.5M_\odot)^{1/2}$ for a wide range (3-7 kpc) of host star distances from the Earth. We also challenge a previous claim of a planetary companion to the lens star in microlensing event OGLE-2002-BLG-045.

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arXiv2017

The SMC B-type supergiant AzV322: a g-mode pulsator with a circumstellar disc

We present a photometric and spectroscopic study of AzV322, an emission line object located in the Small Magellanic Cloud previously classified between O9 and B0. We analyze 17.5 years of $I$ and $V$ band OGLE-II, III and IV light curves and find four significant frequencies, viz. $f_1$= 0.386549 $\pm$ 0.000003, $f_2$= 0.101177 $\pm$ 0.000005, $f_3$= 0.487726 $\pm$ 0.000015 and $f_4$= 0.874302 $\pm$ 0.000020 c/d. The $f_1$ frequency (period 2.58700 $\pm$ 0.00002 days) provides the stronger periodogram peak and gives a single wave light curve of full amplitude 0.066 mag in the $I$-band. High-resolution optical spectroscopy confirms the early B-type spectral type and reveals prominent double peak Balmer, Paschen, OI 8446 and HeI 5875 emissions. The spectral energy distribution shows significant color excess towards long wavelengths possibly attributed to free-free emission in a disk-like envelope. Our analysis yields $T_{eff}$ = 23000 $\pm$ 1500 K, log g = 3.0 $\pm$ 0.5, $M$ = 16 $\pm$ 1 M$_{\odot}$, $R$ = 31.0 $\pm$ 1.1 R$_{\odot}$, and $L_{bol}$ = 10$^{4.87 \pm 0.06}$ $L_{\odot}$. AzV322 might be a member of the new class of slowly pulsating B supergiants introduced by Saio et al. (2006) and documented by Lefever, Puls & Aerts (2007), however its circumstellar disk make it an hitherto unique object. Furthermore, we notice that a O-C analysis for $f_1$ reveals quasi-cyclic changes for the times of maximum in a time scale of 20 years which might indicate a light-travel time effect in a very wide orbit binary with an undetected stellar component.

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arXiv2017

OGLE-2016-BLG-0613LABb: A Microlensing Planet in a Binary System

We present the analysis of OGLE-2016-BLG-0613, for which the lensing light curve appears to be that of a typical binary-lens event with two caustic spikes but with a discontinuous feature on the trough between the spikes. We find that the discontinuous feature was produced by a planetary companion to the binary lens. We find 4 degenerate triple-lens solution classes, each composed of a pair of solutions according to the well-known wide/close planetary degeneracy. One of these solution classes is excluded due to its relatively poor fit. For the remaining three pairs of solutions, the most-likely primary mass is about $M_1\sim 0.7\,M_\odot$ while the planet is a super-Jupiter. In all cases the system lies in the Galactic disk, about half-way toward the Galactic bulge. However, in one of these three solution classes, the secondary of the binary system is a low-mass brown dwarf, with relative mass ratios (1 : 0.03 : 0.003), while in the two others the masses of the binary components are comparable. These two possibilities can be distinguished in about 2024 when the measured lens-source relative proper motion will permit separate resolution of the lens and source.

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arXiv2017

Hydrogen-rich supernovae beyond the neutrino-driven core-collapse paradigm

We present our study of OGLE-2014-SN-073, one of the brightest Type II SN ever discovered, with an unusually broad lightcurve combined with high ejecta velocities. From our hydrodynamical modelling we infer a remarkable ejecta mass of $60^{+42}_{-16}$~M$_\odot$, and a relatively high explosion energy of $12.4^{+13.0}_{-5.9} \times10^{51}$~erg. We show that this object belongs, with a very small number of other hydrogen-rich SNe, to an energy regime that is not explained by standard core-collapse (CC) neutrino-driven explosions. We compare the quantities inferred by the hydrodynamical modelling with the expectations of various exploding scenarios, trying to explain the high energy and luminosity released. We find some qualitative similarities with pair-instabilities SNe, although a prompt injection of energy by a magnetar seems also a viable alternative to explain such extreme event.

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arXiv2017

Extracting Microlensing Signals from K2 Campaign 9

The reduction of the \emph{K2}'s Campaign 9 (K2C9) microlensing data is challenging mostly because of the very crowded field and the unstable pointing of the spacecraft. In this work, we present the first method that can extract microlensing signals from this K2C9 data product. The raw light curves and the astrometric solutions are first derived, using the techniques from Soares-Furtado et al. and Huang et al. for \emph{K2} dense field photometry. We then minimize and remove the systematic effect by performing simultaneous modeling with the microlensing signal. We also derive precise $(K_p-I)$ vs. $(V-I)$ color-color relations that can predict the microlensing source flux in the \emph{Kepler} bandpass. By implementing the color-color relation in the light curve modeling, we show that the microlensing parameters can be better constrained. In the end, we use two example microlensing events, OGLE-2016-BLG-0980 and OGLE-2016-BLG-0940, to test our method.

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arXiv2017

OGLE-2016-BLG-0263L\lowercase{b}: Microlensing Detection of a Very Low-mass Binary Companion Through a Repeating Event Channel

We report the discovery of a planet-mass companion to the microlens OGLE-2016-BLG-0263L. Unlike most low-mass companions that were detected through perturbations to the smooth and symmetric light curves produced by the primary, the companion was discovered through the channel of a repeating event, in which the companion itself produced its own single-mass light curve after the event produced by the primary had ended. Thanks to the continuous coverage of the second peak by high-cadence surveys, the possibility of the repeating nature due to source binarity is excluded with a $96\%$ confidence level. The mass of the companion estimated by a Bayesian analysis is $M_{\rm p}=4.1_{-2.5}^{+6.5}\ M_{\rm J}$. The projected primary-companion separation is $a_\perp = 6.5^{+1.3}_{-1.9}$ au. The ratio of the separation to the snow-line distance of $a_\perp/a_{\rm sl}\sim 15.4$ corresponds to the region beyond Neptune, the outermost planet of the solar system. We discuss the importance of high-cadence surveys in expanding the range of microlensing detections of low-mass companions and future space-based microlensing surveys.

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arXiv2017

Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. VI. Age and abundance structure of the stellar populations in the central sub-kpc of the Milky Way

We present a detailed elemental abundance study of 90 F and G dwarf, turn-off and subgiant stars in the Galactic bulge. Based on high-resolution spectra acquired during gravitational microlensing events, stellar ages and abundances for 11 elements (Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Zn, Y and Ba) have been determined. We find that the Galactic bulge has a wide metallicity distribution with significant peaks at [Fe/H]=-1.09, -0.63, -0.20, +0.12, +0.41. We also find a high fraction of intermediate-age to young stars: at [Fe/H]>0 more than 35 % are younger than 8 Gyr. For [Fe/H]<-0.5 most stars are 10 Gyr or older. We have also identified several episodes when significant star formation in the bulge happened: 3, 6, 8, and 12 Gyr ago. We further find that the "knee" in the alpha-element abundance trends of the sub-solar metallicity bulge is located at about 0.1 dex higher [Fe/H] than in the local thick disk. The Galactic bulge has complex age and abundance properties that appear to be tightly connected to the main Galactic stellar populations. In particular, the peaks in the metallicity distribution, the star formation episodes, and the abundance trends, show similarities with the properties of the Galactic thin and thick disks. At the same time there are additional components not seen outside the bulge region, and that most likely can be associated with the Galactic bar. For instance, the star formation rate appears to have been slightly faster in the bulge than in the local thick disk, which most likely is an indication of the denser stellar environment closer to the Galactic centre. Our results strengthen the observational evidence that support the idea of a secular origin for the Galactic bulge, formed out of the other main Galactic stellar populations present in the central regions of our Galaxy.

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arXiv2017

OGLE-ing the Magellanic System: Three-Dimensional Structure of the Clouds and the Bridge Using RR Lyrae Stars

We present a three-dimensional analysis of a sample of 22 859 type $ab$ RR Lyrae stars in the Magellanic System from the OGLE-IV Collection of RR Lyrae stars. The distance to each object was calculated based on its photometric metallicity and a theoretical relation between color, absolute magnitude and metallicity. The LMC RR Lyrae distribution is very regular and does not show any substructures. We demonstrate that the bar found in previous studies may be an overdensity caused by blending and crowding effects. The halo is asymmetrical with a higher stellar density in its north-eastern area, which is also located closer to us. Triaxial ellipsoids were fitted to surfaces of a constant number density. Ellipsoids farther from the LMC center are less elongated and slightly rotated toward the SMC. The inclination and position angle change significantly with the $a$ axis size. The median axis ratio is $1:1.23:1.45$. The RR Lyrae distribution in the SMC has a very regular, ellipsoidal shape and does not show any substructures or asymmetries. All triaxial ellipsoids fitted to surfaces of a constant number density have virtually the same shape (axis ratio) and are elongated along the line of sight. The median axis ratio is $1:1.10:2.13$. The inclination angle is very small and thus the position angle is not well defined. We present the distribution of RR Lyrae stars in the Magellanic Bridge area, showing that the Magellanic Clouds' halos overlap. A comparison of the distributions of RR Lyrae stars and Classical Cepheids shows that the former are significantly more spread and distributed regularly, while the latter are very clumped and form several distinct substructures.

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arXiv2017

Concluding Henrietta Leavitt's Work on Classical Cepheids in the Magellanic System and Other Updates of the OGLE Collection of Variable Stars

More than a century ago, Henrietta Leavitt discovered the first Cepheids in the Magellanic Clouds together with the famous period-luminosity relationship revealed by these stars, which soon after revolutionized our view of the Universe. Over the years, the number of known Cepheids in these galaxies has steadily increased with the breakthrough in the last two decades thanks to the new generation of large-scale long-term sky variability surveys. Here we present the final upgrade of the OGLE Collection of Cepheids in the Magellanic System which already contained the vast majority of known Cepheids. The updated collection now comprises 9649 classical and 262 anomalous Cepheids. Type-II Cepheids will be updated shortly. Thanks to high completeness of the OGLE survey the sample of classical Cepheids includes virtually all stars of this type in the Magellanic Clouds. Thus, the OGLE survey concludes the work started by Leavitt. Additionally, the OGLE sample of RR Lyrae stars in the Magellanic System has been updated. It now counts 46 443 variables. A collection of seven anomalous Cepheids in the halo of our Galaxy detected in front of the Magellanic Clouds is also presented. OGLE photometric data are available to the astronomical community from the OGLE Internet Archive. The time-series photometry of all pulsating stars in the OGLE Collection has been supplemented with new observations.

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arXiv2017

OGLE-2016-BLG-0168 Binary Microlensing Event: Prediction and Confirmation of the Micorlens Parallax Effect from Space-based Observation

The microlens parallax is a crucial observable for conclusively identifying the nature of lens systems in microlensing events containing or composed of faint (even dark) astronomical objects such as planets, neutron stars, brown dwarfs, and black holes. With the commencement of a new era of microlensing in collaboration with space-based observations, the microlens parallax can be routinely measured. In addition, space-based observations can provide opportunities to verify the microlens parallax measured from ground-only observations and to find a unique solution of the lensing lightcurve analysis. However, since most space-based observations cannot cover the full lightcurves of lensing events, it is also necessary to verify the reliability of the information extracted from fragmentary space-based lightcurves. We conduct a test based on the microlensing event OGLE-2016-BLG-0168 created by a binary lens system consisting of almost equal mass M-dwarf stars to demonstrate that it is possible to verify the microlens parallax and to resolve degeneracies by using the space-based lightcurve even though the observations are fragmentary. Since space-based observatories will frequently produce fragmentary lightcurves due to their short observing windows, the methodology of this test will be useful for next-generation microlensing experiments that combine space-based and ground-based collaboration.

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