Wyniki wyszukiwania - BazTech

1

Soczewkowanie grawitacyjne gwiazd bozonowych i fermionowych

Osarczuk Janusz

Postępy Fizyki

|

2023

|

T. 74, z. 2

30--34

PL

Gwiazdy bozonowe oraz gwiazdy fermionowe mogły powstać we wczesnym Wszechświecie podczas grawitacyjnego przejścia fazowego pierwszego rzędu. Być może część z nich zachowała się do dziś. Poszukiwania ich obejmują przede wszystkim centralne części galaktyk. Soczewkowanie grawitacyjne jest jedną z metod obserwacyjnych, która może pomóc je znaleźć.

EN

Boson stars and fermion stars may have formed in the early universe during a first-order gravitational phase transition. Perhaps some of them have survived till now. The search for them covers mainly the central parts of galaxies. Gravitational lensing is one of the observational methods that can help find them.

2

Analysis of Photometric Uncertainties in the OGLE-IV Galactic Bulge Microlensing Survey Data

Skowron J., Udalski A., Kozłowski S., Szymański M. K., Mróz P., Wyrzykowski Ł., Poleski R., Pietrukowicz P., Ulaczyk K., Pawlak M., Soszyński I.

Acta Astronomica

|

2016

|

Vol. 66, No. 1

1--13

EN

We present a statistical assessment of both, observed and reported, photometric uncertainties in the OGLE-IV Galactic bulge microlensing survey data. This dataset is widely used for the detection of variable stars, transient objects, discovery of microlensing events, and characterization of the exo-planetary systems. Large collections of RR Lyr stars and Cepheids discovered by the OGLE project toward the Galactic bulge provide light curves based on this dataset. We describe the method of analysis, and provide the procedure, which can be used to update preliminary photometric uncertainties, provided with the light curves, to the ones reflecting the actual observed scatter at a given magnitude and for a given CCD detector of the OGLE-IV camera. This is of key importance for data modeling, in particular, for the correct estimation of the goodness of fit.

3

Limited Approach to Ray Tracing through the Millennium Simulation: Tangential Shear and Its Peaks

Jaroszyński M., Kostrzewa Z.

Acta Astronomica

|

2010

|

Vol. 60, No. 1

41--54

EN

We employ a hybrid method of modeling matter distribution in space based on the Millennium Simulation, using a coarse grid averaged matter density distribution with overlaid population of gravitationally bound halos. Using Born approximation we simulate the light propagation in such inhomogeneous cosmological model, obtaining shear maps for five ≈3°×3° fields at several redshifts. We analyze the influence of halos and background mass density on the tangential shear component. We show the presence of a weak signal at large separations caused by the large scale structure in matter distribution. We also investigate the relation between the shear peaks and the distribution of halo masses in their foregrounds, obtaining the dependence of mass spectra on the shear value. As other studies show, the top peaks of the shear are always related to the presence of very massive halos (galaxy clusters), but we find that their expected mass decreases with the increasing redshift of a map and with the increasing angular scale of its smoothing.

4

The Optical Gravitational Lensing Experiment. Variable Baseline Microlensing Events in the Galactic Bulge

Wyrzykowski Ł., Udalski A., Mao S., Kubiak M., Szymański M. K., Pietrzyński G., Soszyński I., Szewczyk O.

Acta Astronomica

|

2006

|

Vol. 56, No. 2

145--169

EN

We present the first systematic search for microlensing events with variability in their baselines using data from the third phase of the Optical Gravitational Lensing Experiment (OGLE-III). A total of 137 candidates (88 new) was discovered toward the Galactic bulge. Among these, 21 have periodic oscillations in their baselines, 111 are irregular variables and 5 are potential long period detached eclipsing binaries. This is about 10% of the total number of constant baseline events. They are hence quite common and can be regarded as a new type of exotic events, which allow the determination of extra parameters of the events. We show that microlensing of variable stars may allow us to break the degeneracy between the blending parameter and magnification. We note that in some cases variability hidden in the baseline due to strong blending may be revealed in highly magnified events and resemble other exotic microlensing behavior, including planetary deviation. A new system (VEWS) for detecting ongoing variable baseline microlensing events is presented.

5

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

|

2005

|

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.

6

Cluster AgeS Experiment (CASE): Dwarf Novae and a Probable Microlensing Event in the Globular Cluster M22

Pietrukowicz P., Kaluzny J., Thompson I. B., Jaroszyński M., Schwarzenberg-Czerny A., Krzeminski W., Pych W.

Acta Astronomica

|

2005

|

Vol. 55, No. 3

261--274

EN

We report the identification of a new cataclysmic variable (denoted as CV2) and a probable microlensing event in the field of the globular cluster M22. Two outbursts were observed for CV2. During one of them superhumps with Psh=0.08875 d were present in the light curve. CV2 has an X-ray counterpart detected by XMM-Newton. A very likely microlensing event at a radius of 2.'3 from the cluster center was detected. It had an amplitude of Δ V=0.75 mag and a characteristic time of 15.9 days. Based on model considerations we show that the most likely configuration has the source in the Galactic bulge with the lens in the cluster. Two outbursts were observed for the already known dwarf nova CV1.

7

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

|

2004

|

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

8

The Optical Gravitational Lensing Experiment. Optical Monitoring of the Gravitationally Lensed Quasar HE1104-1805 in 1997-2002

Wyrzykowski Ł., Udalski A., Schechter P. L., Szewczyk O., Szymański M., Kubiak M., Pietrzyński G., Soszyński I., Żebruń K.

Acta Astronomica

|

2003

|

Vol. 56, No. 3

229--240

EN

We present results of the long term monitoring of the gravitationally lensed quasar HE1104-1805. The photometric data were collected between August 1997 and January 2002 as a subproject of the OGLE survey. We determine the time delay in the light curves of images A and B of HE1104-1805 to be equal to 157±21 days with the variability in the image B light curve leading variability of the image A. The result is in excellent agreement with the earlier determination by Ofek and Maoz. OGLE photometry of HE1104-1805 is available to the astronomical community from the OGLE Internet archive.

9

Microlensing and the Structure of X-ray Emitting Regions in QSOs

Jaroszyński M.

Acta Astronomica

|

2002

|

Vol. 52, No. 3

203--215

EN

We simulate microlensing of distant, multiply lensed quasars by stars in an intervening galaxy - lens. The calculations include the influence of the effect on the fluorescence Fe Kα lines. We use standard source models, involving accretion disks and a hot, diffuse component, which explain the presence of the lines as a result of radiation reprocessing in a cold disk. In all calculations we use cosmological and macro-lens parameters relevant to the source MG J0414+0534, a quasar where the iron line has been observed by Chandra. We investigate probability distribution for the line equivalent width of the microlensed source and find its dependence on the source model parameters. We show that the probability of a high strengthening of the line (as measured by the equivalent width) decreases sharply with the size of the emitting region. We apply the results of our simulations to the source MG J0414+0534. We find that the observed behavior of the source is not easy to reproduce with the help of the simplest disk and microlensing models. Of the models considered the best results are obtained with the disks around 107 Msolar black holes with inner edges at ≈10 gravitational radii.

10

Binary Lenses in OGLE-II 1997-1999 Database. A Preliminary Study

Jaroszyński M.

Acta Astronomica

|

2002

|

Vol. 52, No. 1

39--60

EN

We present 18 binary lens candidates from OGLE-II database for seasons 1997-1999. The candidates have been selected by visual light curves inspection from the subsample of strong transient events; the same procedure gives 215 single lens candidates. Among the double lenses there are 12 cases interpreted as caustic crossing events. We compare the mass ratio and separation distributions obtained for binary lenses with the predictions based on stellar double systems observations. We take into account the selection bias, which causes over-representation of binary lenses of similar mass and separation close to the Einstein radius. There is no strong discrepancy between the expected and observed distributions of the mass ratio or the binary separations. We find one or two cases of binary lens candidates, SC20_1793 and SC20_3525, with extreme mass ratios, which may suggest presence of planets or brown dwarf companions. Unfortunately, neither case is very strong, as alternative solutions provide fits to the data which are only unsubstantially worse. Binary lenses provide a modest contribution to the overall optical depth to microlensing.

11

Automatic Variability Analysis of Bulge Stars in OGLE-II Image Subtraction Database

Mizerski T., Bejger M.

Acta Astronomica

|

2002

|

Vol. 52, No. 1

61--80

EN

We present results of star variability analysis in the OGLE-II bulge field BUL_SC1. Photometric database was derived by means of image subtraction method and contains 4597 objects preclassified as variables. We analyzed all the light curves in order to find periodic variables, non periodic but all-time variables and stars showing episodic changes in their brightness, e.g., gravitational lenses. Variability of 3969 stars was confirmed, among them we detected 12 lensing event candidates whose light curves are shown. We found 762 periodic variables. Algorithmic methods allowed us to identify 71 RR Lyr and 110 W UMa stars. Almost all luminous red giants are found to be variable. Most of red clump giants are not variable. Classification of all 4597 objects is presented online.

12

A Possible Planetary Event OGLE-2002-BLG-055

Jaroszyński M., Paczyński B.

Acta Astronomica

|

2002

|

Vol. 52, No. 4

361--367

EN

The microlensing event OGLE-2002-BLG-055 has a single, but very reliable data point, deviating upward from a single source microlensing light curve by 0.6 mag. The simplest interpretation calls for a binary lens with a strong parallax effect and the mass ratio in the range of 0.01-0.001, putting the companion in the Jupiter mass range. Given only a single deviant point it is impossible to fit a unique model. We propose a modification of the OGLE observing strategy: instant verification of reality of future deviant points, followed by frequent time sampling, to make a unique model fit possible.

13

Difference Image Analysis of the OGLE-II Bulge Data. II. Microlensing Events

Woźniak P. R., Udalski A., Szymański M., Kubiak M., Pietrzyński G., Soszyński I., Żebruń K.

Acta Astronomica

|

2001

|

Vol. 51, No. 3

175--219

EN

We present a sample of microlensing events discovered in the Difference Image Analysis (DIA) of the OGLE-II images collected during three observing seasons, 1997-1999. 4424 light curves pass our criteria on the presence of a brightening episode on top of a constant baseline. Among those, 512 candidate microlensing events were selected visually. We designed an automated procedure, which unambiguously selects up to 237 best events. Including eight candidate events recovered by other means, a total of 520 light curves are presented in this work. In addition to microlensing events, the larger sample contains certain types of transients, but is also strongly contaminated by artifacts. All 4424 light curves in the weakly filtered group are available electronically, with the intent of showing the gray zone between microlensing events and variable stars, as well as artifacts, to some extent inevitable in massive data reductions. We welcome suggestions for improving the selection process before the full analysis of complete four seasons of the OGLE-II bulge data. Selection criteria for binary events can also be investigated with our extended sample.

14

The Optical Gravitational Lensing Experiment. Catalog of Microlensing Events in the Galactic Bulge

Udalski A., Żebruń K., Szymański M., Kubiak M., Pietrzyński G., Soszyński I., Woźniak P.

Acta Astronomica

|

2000

|

Vol. 50, No. 1

1--65

EN

We present the Catalog of microlensing events detected toward the Galactic bulge in three observing seasons, 1997-1999, during the OGLE-II microlensing survey. The search for microlensing events was performed using a database of about 4×109 photometric measurements of about 20.5 million stars from the Galactic bulge. The Catalog comprises 214 microlensing events found in the fields covering about 11 square degrees on the sky and distributed in different parts of the Galactic bulge. The sample includes 20 binary microlensing events, 14 of them are caustic crossing. In one case a double star is likely lensed. We present distribution of the basic parameters of microlensing events and show preliminary rate of microlensing in different regions of the Galactic bulge. The latter reveals clear dependence on the Galactic coordinates. The dependence on l indicates that the majority of lenses toward the Galactic bulge are located in the Galactic bar. Models of the Galactic bar seem to reasonably predict the observed spatial distribution of microlensing events in the Galactic bulge. All data presented in the Catalog and photometry of all events are available from the OGLE Internet archive.

15

Erratum: Relativistic Effects in Proper Motions of Stars Surrounding the Galactic Center

Jaroszyński M.

Acta Astronomica

|

1999

|

Vol. 49, No. 1

117

EN

In the paper "Relativistic Effects in Proper Motions of Stars Surrounding the Galactic Center" (Acta Astron., 48, p. 653) the highest astrometric accuracy of the Keck Interferometer (≈ 20 μas) was assumed to objects as faint as K ≈ 22 mag.

16

The Optical Gravitational Lensing Experiment. Photometry of the MACHO-SMC-98-1 Binary Microlensing Event

Udalski A., Kubiak M., Szymański M., Pietrzyński G., Woźniak P., Żebruń K.

Acta Astronomica

|

1998

|

Vol. 48, No. 3

431--438

EN

We present photometry of the unique binary microlensing event MACHO-SMC-98-1 collected by the OGLE group. Particularly interesting observation was made close to the first caustic crossing which was not covered by observations of other groups. It allows to test proposed models of which Model 1 proposed by PLANET group seems to be in the best agreement with the OGLE observations.

17

Stellar Variability Background in OGLE-I Microlensing Search

Woźniak P., Szymański M.

Acta Astronomica

|

1998

|

Vol. 48, No. 2

269--288

EN

We search OGLE-I photometric database for stars which, as defined by formal criteria adopted by OGLE-I microlensing search, showed variability during only one out of 3 or 4 observing seasons. The results include 17 previously reported microlensing events, 2 newly discovered candidate events and 15 intrinsically variable stars that have a potential of contaminating samples of microlensing events. Based on photometry obtained in 1992 and 1993 OGLE #10 was tentatively included in the list of microlensing candidates, however its light curve in 1994 and 1995 shows many characteristics of the variable stars found in our search, and most likely it is not a microlensing event. For all stars which passed our tests, we provide 44×44 arcsec (101×101 pixel) centered subframes from each OGLE-I frame in the I-band. It is the first time when images used to derive photometry of microlensing events are available in convenient format to astronomical community.

18

Relativistic Effects in Proper Motions of Stars Surrounding the Galactic Center

Jaroszyński M.

Acta Astronomica

|

1998

|

Vol. 48, No. 4

653--665

EN

We simulate the astrometric observations of stars moving close to the black hole in the Galactic center. We show that for orbits ≤103 a.u. and position measurements with the accuracy of the Keck Interferometer, the periastron motion of elliptical orbits will be measurable. The models of star trajectories neglecting the periastron motion will be easy to reject with the high confidence level. The measurement of orbital elements and the periastron motion can be effectively used as an independent estimate the distance to the Galactic center. The effects of orbit precession may be visible in some cases. The effects of gravitational radiation are completely negligible as well as influence of the black hole rotation on the propagation of light.

19

Gravitational Lensing and Proper Motions of Stars Surrounding the Galactic Center

Jaroszyński M.

Acta Astronomica

|

1998

|

Vol. 48, No. 3

413--429

EN

We examine lensing by the black hole in the Galactic center. We use the new photometric data in the infrared to estimate the density of stars in the star cluster surrounding the black hole. We calculate the probability of lensing by the black hole, the rate of the new events and the influence of lensing on the velocity distribution of proper motions of stars. The relative importance of lensing has its maximum at distances ≈10 mas from the star cluster center. The measurement of the proper motion of stars on the scale of ≈3 mas would be necessary to investigate the orbits of stars at distances ≈103rg from the black hole. In principle the deformation of the projected orbit shape by lensing may serve as a way to estimate the angular momentum of the black hole.

20

Astrometric Shifts in the OGLE-1 Microlensing Events

Goldberg D. M., Woźniak P. R.

Acta Astronomica

|

1998

|

Vol. 48, No. 1

19--34

EN

We measure the astrometric shifts of the light centroids for the microlensing events in the OGLE-1 database. Of the 15 consistently detected events, 7 had significant shifts which we were able to measure with a fair degree of confidence. Those events with large shifts are also expected to be unresolved with a background "blend", and thus, we suggest that we have identified events in the OGLE-1 catalog which are strongly blended. Though we concentrate on the OGLE-1 database, and use the DOPHOT package in order to perform our analysis, we suggest that this shift is a generic effect, and should be observable in any crowded field.