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1
Content available remote Search for Dormant Black Holes in the OGLE Data
Kapusta M., Mróz P.
Acta Astronomica
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2023
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Vol. 73, No. 3
197--226
EN
Light curves of ellipsoidal variables collected by the Optical Gravitational Lensing Experiment (OGLE) were analyzed, in order to search for dormant black hole candidates. After the preselection based on the amplitude of ellipsoidal modulation, each object was investigated by means of the spectral energy distribution fit, which allowed us to select objects that are in close agreement with the spectrum of a single stellar object. After this final step of the preselection process, we were left with only fourteen objects that were then investigated in detail. For each candidate, we estimated basic physical parameters such as temperature, mass, luminosity, and, in some cases, radial velocity semi-amplitude. One of the objects turned out to be a spotted star while the rest are considered black-hole binary candidates. In the end, we present an alternative explanation for the ellipsoidal modulation in the form of contact binaries, which are not only vast in number, contrary to black-hole binaries, but are also in much better agreement with the radial velocity estimates for some of the systems analyzed. Even if the presented arguments suggest a noncompact character of the companion objects, each of them should be observed spectroscopically in order to verify the compact object hypothesis.
2
Content available remote Variable Star Population in the Open Cluster NGC 6791 Observed by the Kepler Spacecraft
Sanjayan S., Baran A. S., Németh P., Kinemuchi K., Ostrowski J., Sahoo S. K.
Acta Astronomica
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2022
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Vol. 72, No. 2
77--102
EN
We present the list of variable stars we found in the Kepler superstamp data covering approximately 9' from the central region of NGC 6791. We classified the variable stars based on the variability type and we established their cluster membership based on the available Gaia Early Data Release 3 astrometry, by means of the Bayesian Gaussian mixture models. In total we found 278 variable objects, among which 17 binaries, 45 pulsators, 62 rotational and five unclassified variables are cluster members. The remaining 28 binaries, 25 pulsators, 83 rotational, four unclassified and nine unidentified variables are either not members or their membership is not established. In the case of eclipsing binaries we calculated the mid-times of eclipses and derived ephemerides. We searched for eclipse timing variation by means of the observed minus calculated diagrams. Only three objects show significant orbital period variation. Independently of a recently published report, we found 119 new variables. We used isochrones calculated within the MIST project and derived the age (8.91 Gyr), average distance (4134 pc) and iron content [Fe/H] (0.26-0.28), of NGC 6791. Using the cluster members with membership probabilities greater than 0.9, we calculated the distance to the cluster of 4123(31) pc, which agrees with the result from our isochrone fitting.
3
Content available remote Constraints on the Formation of Double Neutron Stars from the Observed Eccentricities and Current Limits on Merger Rates
Chruslinska M., Belczynski K., Bulik T., Gladysz W.
Acta Astronomica
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2017
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Vol. 67, No. 1
37--50
EN
We employ population synthesis method to model the double neutron star (DNS) population and test various possibilities on natal kick velocities gained by neutron stars after their formation. We first choose natal kicks after standard core collapse supernovae (CCSN) from a Maxwellian distribution with velocity dispersion of σ = 265 km/s as proposed by Hobbs and then modify this distribution by changing σ toward smaller and larger kick values. We also take into account the possibility of NS formation through electron capture supernova. In this case we test two scenarios: zero natal kick or small natal kick, drawn from Maxwellian distribution with σ = 26.5 km/s. We calculate the present-day orbital parameters of binaries and compare the resulting eccentricities with those known for observed DNSs. As an additional test we calculate Galactic merger rates for our model populations and confront them with observational limits. We do not find any model unequivocally consistent with both observational constraints simultaneously. The models with low kicks after CCSN for binaries with the second NS forming through core collapse SN are marginally consistent with the observations. This means that either 14 observed DNSs are not representative of the intrinsic Galactic population, or that our modeling of DNS formation needs revision.
4
Content available remote Period-Luminosity Relations for Ellipsoidal Binary Stars in the OGLE-III Fields of the Large Magellanic Cloud
Pawlak M., Soszyński I., Pietrukowicz P., Skowron J., Poleski R., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K., Kozłowski S., Skowron D. M.
Acta Astronomica
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2014
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Vol. 64, No. 4
293--308
EN
We report the discovery of two distinct types of ellipsoidal binary systems occupying, so called, sequence E on the period-luminosity (P-L) diagram. We propose that steeper P-L relation is composed of giant-dwarf binaries, while the other consists of giant-giant binary systems. Analysis is based on a sample of 5334 objects, which we select from the OGLE-III survey data toward the Large Magellanic Cloud. We show that one of the components of ellipsoidal binaries is typically either a Red Clump or a Red Giant Branch star, which leads to clear separation split of the sequence E at P=40 d. In its short-period part, we identify two subsequences corresponding to the two types of binary systems (E2 and E3), while in the longer-period part the two groups merge forming a single subsequence E1.
5
Content available remote Catalog of Binary UV Ceti Type Flare Stars
Tamazian V. S., Malkov O. Yu.
Acta Astronomica
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2014
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Vol. 64, No. 4
359--369
EN
This catalog provides an easy access to the basic astrophysical and dynamical characteristics of nearby (d<25 pc) visual binary systems (pairs) in which at least one component is a UV Cet type flare star. It contains 138 such pairs (111 flare stars) of which 31 pairs have known orbital parameters. Along with parallax mainly (but not only) taken from SIMBAD, apparent and absolute magnitudes of each component, spectral types for all primaries and the vast majority of secondaries are given. On the basis of cataloged data, absolute brightness vs. spectral type and mass vs. spectral type relations for flare and non-flare stars are constructed. It is shown that flare and non-flare stars cannot be distinguished on the absolute brightness vs. spectral type plane. Comparison between photometric and dynamical masses suggests that photometric mass of flare stars can be estimated using the mass vs. absolute brightness relation of non-flare stars.
6
Content available remote Binary Lenses in OGLE-III EWS Database. Seasons 2006-2008
Jaroszyński M., Skowron J., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Soszyński I., Wyrzykowski Ł., Ulaczyk K., Poleski R.
Acta Astronomica
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2010
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Vol. 60, No. 3
197--231
EN
We present 27 binary lens candidates from OGLE-III Early Warning System database for the seasons 2006-2008. The candidates have been selected by visual light curves inspection. Our sample of binary lens events consists now of 78 stellar systems and 7 extrasolar planets of OGLE-III published elsewhere. Examining the distribution of stellar binaries we find that the number of systems per logarithmic mass ratio interval increases with mass ratio q, in contradiction with our previous findings. Stellar binaries belong to the region 0.03
7
Content available remote Binary Source Lensing and the Repeating OGLE EWS Events
Jaroszyński M., Skowron J.
Acta Astronomica
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2008
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Vol. 58, No. 4
345--358
EN
A microlensing event may exhibit a second brightening when the source and/or the lens is a binary star. Previous study revealed 19 such repeating event candidates among 4120 investigated microlensing light curves of the Optical Gravitational Lensing Experiment (OGLE). The same study gave the probability ≈0.0027 for a repeating event caused by a binary lens. We present the simulations of binary source lensing events and calculate the probability of observing a second brightening in the light curve. Applying to simulated light curves the same algorithm as it was used in the analysis of real OGLE data, we find the probability ≈0.0018 of observing a second brightening in a binary source lensing curve. The expected and measured numbers of repeating events are in agreement only if one postulates that all lenses and all sources are binary. Since the fraction of binaries is believed to be ≤50%, there seems to be a discrepancy.
8
Content available remote Binary Lenses in OGLE III EWS Database. Season 2005
Skowron J., Jaroszyński M., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Soszyński I., Szewczyk O., Wyrzykowski Ł., Ulaczyk K.
Acta Astronomica
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2007
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Vol. 57, No. 4
281--299
EN
We present nine new binary lens candidates from OGLE-III Early Warning System database for the season of 2005. We have also found four events interpreted as single mass lensing of double sources. The candidates have been selected by visual light curves inspection. Examining the models of binary lenses in our previous studies (10 caustic crossing events of OGLE-II seasons 1997-1999 and 34 binary lens events of OGLE-III seasons 2002-2004, including one planetary event), in this work and in three publications concerning planetary events of season 2005, we find four cases of extreme mass ratio binaries (q≤0.01), and almost all other models with mass ratios in the range 0.1
9
Content available remote The Recurrent Nova U Scorpii - Evolutionary Consideration
Sarna M. J., Ergma E., Gerškevitš J.
Acta Astronomica
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2006
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Vol. 56, No. 1
65--81
EN
We perform evolutionary calculations of binary stars to find progenitors of systems with parameters similar to the recurrent nova U Sco. We show that a U Sco-type system may be formed starting with an initial binary system which has a low-mass carbon-oxygen white dwarf as an accretor. Since the evolutionary stage of the secondary is not well known, we calculate sequences with hydrogen-rich and helium-rich secondaries. The evolution of the binary may be divided into several observable stages as: classical nova, super soft X-ray source with stable hydrogen shell burning, or strong wind phase. It culminates in the formation of a massive white dwarf near the Chandrasekhar mass limit. We follow the chemical evolution of the secondary as well as of the matter lost from the system, and we show that observed 12C/13C and N/C ratios may give some information about the nature of the binary.
10
Content available remote Binary Lenses in OGLE-III EWS Database. Season 2004
Jaroszyński M., Skowron J., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Soszyński I., Żebruń K., Szewczyk O., Wyrzykowski Ł.
Acta Astronomica
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2006
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Vol. 56, No. 4
307--332
EN
We present 19 binary lens candidates from OGLE-III Early Warning System database for the season of 2004. We have also found five events interpreted as single mass lensing of double sources. The candidates have been selected by visual light curves inspection. Examining the models of binary lenses of this and our previous studies (10 caustic crossing events of OGLE-II seasons 1997-1999 and 15 binary lens events of OGLE-III seasons 2002-2003) we find one case of extreme mass ratio binary (q≈0.005, a known planetary lens OGLE 2003-BLG-235/MOA 2003-BLG-53) and almost all other models with mass ratios in the range 0.1
11
Content available remote Mass Estimates for Some of the Binary Lenses in OGLE-III Database
Jaroszyński M., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Soszyński I., Żebruń K., Szewczyk O., Wyrzykowski Ł.
Acta Astronomica
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2005
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Vol. 55, No. 2
159--175
EN
We model binary microlensing events OGLE 2003-BLG-170, 267, and 291. Source angular sizes are measured for the events 267 and 291. Model fits to the light curves give parallaxes for the events 267 and 291, and relative source sizes for 170 and 267. Selfconsistency arguments provide extra limits on the models of the event 291. As a result we obtain likelihood estimate of the lens mass for the event 170, mass measurement based on angular size and parallax for 267, and narrow limits on mass in the case of 291. Brown dwarfs are most likely candidates for some of the lens components. The influence of the binary lens rotation and the Earth parallax may be important but hard to distinguish when modeling relatively short lasting binary lens events.
12
Content available remote Binary Lenses in OGLE-III EWS Database. Seasons 2002-2003
Jaroszyński M., Udalski A., Kubiak M., Szymański M., Pietrzyński G., Soszyński I., Żebruń K., Szewczyk O., Wyrzykowski Ł.
Acta Astronomica
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2004
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Vol. 54, No. 2
103--128
EN
We present 15 binary lens candidates from OGLE-III Early Warning System database for seasons 2002-2003. We also found 15 events interpreted as single mass lensing of double sources. The candidates were selected by visual light curves inspection. Examining the models of binary lenses of this and our previous study (10 caustic crossing events of OGLE-II seasons 1997-1999) we find one case of extreme mass ratio binary (q≈0.005) and the rest in the range 0.1
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