Wyniki wyszukiwania - BazTech

1

Over 38 000 RR Lyrae Stars in the OGLE Galactic Bulge Fields

Soszyński I., Udalski A., Szymański M. K., Pietrukowicz P., Mróz P., Skowron J., Kozłowski S., Poleski R., Skowron D., Pietrzyński G., Wyrzykowski L., Ulaczyk K., Kubiak M.

Acta Astronomica

|

2014

|

Vol. 64, No. 3

177--196

EN

We present the most comprehensive picture ever obtained of the central parts of the Milky Way probed with RR Lyr variable stars. This is a collection of 38 257 RR Lyr stars detected over 182 square degrees monitored photometrically by the Optical Gravitational Lensing Experiment (OGLE) in the most central regions of the Galactic bulge. The sample consists of 16 804 variables found and published by the OGLE collaboration in 2011 and 21 453 RR Lyr stars newly detected in the photometric databases of the fourth phase of the OGLE survey (OGLE-IV). 93% of the OGLE-IV variables were previously unknown. The total sample consists of 27 258 RRab, 10 825 RRc, and 174 RRd stars. We provide OGLE-IV I- and V-band light curves of the variables along with their basic parameters. About 300 RR Lyr stars in our collection are plausible members of 15 globular clusters. Among others, we found the first pulsating variables that may belong to the globular cluster Terzan 1 and the first RRd star in the globular cluster M54. Our survey also covers the center and outskirts of the Sagittarius Dwarf Spheroidal Galaxy enabling studies of the spatial distribution of the old stellar population from this galaxy. A group of double-mode RR Lyr stars with period ratios around 0.740 forms a stream in the sky that may be a relic of a cluster or a dwarf galaxy tidally disrupted by the Milky Way. Three of our RR Lyr stars experienced a pulsation mode switching from double-mode to single fundamental mode or vice versa. We also present the first known RRd stars with large-amplitude Blazhko effect.

2

OGLE-BLG-RRLYR-12245: An RR Lyrae Star that Switched from a Double- to Single-Mode Pulsation

Soszyński I., Dziembowski W. A., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K., Poleski R., Kozłowski S., Pietrukowicz P., Skowron J., Mróz P.

Acta Astronomica

|

2014

|

Vol. 64, No. 1

1--9

EN

We report the discovery of an RR Lyr star that experienced a switching of its pulsation mode. OGLE-BLG-RRLYR-12245 was discovered as a double-mode RRd star based on observations conducted in the years 2001-2006 during the third phase of the Optical Gravitational Lensing Experiment (OGLE-III). The OGLE-IV observations carried out since 2010 reveal that this object is now a fundamental-mode RRab star, with no sign of the first-overtone pulsation. The analysis of the OGLE photometry shows that the final stage of the mode switching occurred on a relatively short timescale of a few months in 2005. We study the behavior of the star during this process, showing changes of the pulsational amplitudes and periods. We also discuss possible reasons for the mode switching in RR Lyr stars.

3

Constraining the Hydrogen Envelope Mass of a Pulsating sdB Star KIC 10670103 Through Asteroseismology

Krzesinski J., Blokesz A., Baran A. S., Bachulski S.

Acta Astronomica

|

2014

|

Vol. 64, No. 2

151--165

EN

In this paper we present our study of KIC 10670103, a pulsating hot subdwarf located in the Kepler field. The study is based on three years of data taken by the Kepler spacecraft during Q5-16. Using Fourier analysis, we investigate periodic signals associated with pulsations. Using asymptotic relationships and rotational multiplets we identify modal degrees. The amplitude spectrum appears to be rich in l=1 and 2 multiplets, allowing derivation of a 90 days rotation period for this star. Comparing the pattern of identified gravity mode period spacings with theoretical models, we show that KIC 10670103 is a thick-envelope sdB star.

4

A New Subdwarf-OB Pulsator J23341+4622

Pakštiene E., Qvam J. K. T., Østensen R. H., Telting J. H.

Acta Astronomica

|

2014

|

Vol. 64, No. 4

349--358

EN

A new sdOB variable star, J23341+4622 (SDSS J233406.10+462249.3), was discovered during photometric observations with the Nordic Optical Telescope (La Palma). We found its main pulsation frequency at 7422(±9) μHz with an amplitude of 4.5(±0.5) mma. The star is possibly a complex pulsator, as we found another significant peak at 7759(±11) μHz with an amplitude of 2.0(±0.3) mma and a possible subharmonic of the main frequency at 3508 μHz with an amplitude of 2.3 mma.

5

A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. IX. NGC 457

Moździerski D., Pigulski A., Kopacki G., Kołaczkowski Z., Stęślicki M.

Acta Astronomica

|

2014

|

Vol. 64, No. 2

89--114

EN

We present results of a BVIC variability survey in the young open cluster NGC 457 based on observations obtained during three separate runs spanning almost 20 years. In total, we found 79 variable stars, of which 66 are new. The BVIC photometry was transformed to the standard system and used to derive cluster parameters by means of isochrone fitting. The cluster is about 20 Myr old, the mean reddening amounts to about 0.48 mag in terms of the color excess E(B-V). Depending on the metallicity, the isochrone fitting yields a distance between 2.3 kpc and 2.9 kpc, which locates the cluster in the Perseus arm of the Galaxy. Using the complementary Hα photometry carried out in two seasons separated by over 10 years, we find that the cluster is very rich in Be stars. In total, 15 stars in the observed field of which 14 are cluster members showed Hα in emission either during our observations or in the past. Most of the Be stars vary in brightness on different time scales including short-period variability related most likely to g-mode pulsations. A single-epoch spectrum of NGC 457-6 shows that this Be star is presently in the shell phase. The inventory of variable stars in the observed field consists of a single β Cep-type star, NGC 457-8, 13 Be stars, 21 slowly pulsating B stars, seven δ Sct stars, one γ Dor star, 16 unclassified periodic stars, 8 eclipsing systems and a dozen of stars with irregular variability, of which six are also B-type stars. As many as 45 variable stars are of spectral type B which is the largest number in all open clusters presented in this series of papers. The most interesting is the discovery of a large group of slowly pulsating B stars which occupy the cluster main sequence in the range between V=11 mag and 14.5 mag, corresponding to spectral types B3 to B8. They all have very low amplitudes and about half show pulsations with frequencies higher than 3 d-1. We argue that these are most likely fast-rotating slowly pulsating B stars, observed also in other open clusters.

6

Variability Survey in the Open Cluster Stock 14 and the Surrounding Fields

Drobek D., Pigulski A., Shobbrook R. R., Narwid A.

Acta Astronomica

|

2013

|

Vol. 63, No. 3

339--368

EN

We present the results of a photometric variability survey in the young open cluster Stock 14 and the surrounding fields. In total, we detected 103 variable stars of which 88 are new discoveries. We confirm short-period, low-amplitude light variations in two eclipsing members of the cluster, HD 101838 and HD 101794. In addition, we find two new β Cep stars of which one, HD 101993, is also a member. The sample of pulsating cluster members is supplemented by one multimode slowly pulsating B-type star and several single-mode candidates of this type. The other pulsating stars in our sample are mostly field stars. In particular, we found fourteen δ Sct stars including one γ Dor/δ Sct hybrid pulsator. From our UBV photometry we derived new parameters of Stock 14: the mean reddening E(B-V)=0.21±0.02 mag, the true distance modulus, 11.90±0.05 mag, and the age, 20±10 Myr. Finally, we use the new photometry to analyze changes of the 6.322-d orbital period of the bright eclipsing binary and the member of the cluster, V346 Cen. In addition to the known apsidal motion, we find that another effect, possibly light-time effect in a hierarchical system of a very long orbital period, affects these changes. The updated value of the period of apsidal motion for this system amounts to 306±4 yr. The open cluster Stock 14 was found to be a fairly good candidate for successful ensemble asteroseismology.

7

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. Type II Cepheids in the Galactic Bulge - Supplement

Soszyński I., Udalski A., Pietrukowicz P., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K., Poleski R., Kozłowski S.

Acta Astronomica

|

2013

|

Vol. 63, No. 1

37--40

EN

We report the discovery of additional 22 RV Tau stars located in the OGLE-II and OGLE-III fields toward the Galactic bulge, increasing to 357 objects the OGLE-III catalog of type II Cepheids in the Galactic center. Four of the newly detected RV Tau stars belong to the RVb class, i.e., they show large-amplitude, long-period modulation of the mean luminosity. In the updated catalog, the relative number of RV Tau stars in the whole sample of the Galactic bulge type II Cepheids is similar to the Magellanic Cloud samples.

8

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. XV. Long-Period Variables in the Galactic Bulge

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

Acta Astronomica

|

2013

|

Vol. 63, No. 1

21--36

EN

The fifteenth part of the OGLE-III Catalog of Variable Stars (OIII-CVS) contains 232406 long-period variables (LPVs) detected in the OGLE-II and OGLE-III fields toward the Galactic bulge. The sample consists of 6528 Mira stars, 33235 semiregular variables and 192643 OGLE small amplitude red giants. The catalog data and data resources that are being published include observational parameters of stars, finding charts, and time-series I- and V-band photometry obtained between 1997 and 2009. We discuss statistical features of the sample and compare it with collections of LPVs in the Magellanic Clouds. The vast majority of red giant stars in the Galactic bulge have an oxygen-rich chemistry. Mira variables form a separate group in the period-amplitude diagram, which was not noticed for oxygen-rich Miras in the Magellanic Clouds. We find a clear deficit of long-secondary period stars toward the Galactic center compared to the sample of Magellanic Clouds' LPVs.

9

Mt. Suhora Survey - Searching for Pulsating M Dwarfs. III

Baran A. S., Winiarski M., Siwak M., Fox-Machado L., Kozieł-Wierzbowska D., Krzesinski J., Dróżdz M., Winans A.

Acta Astronomica

|

2013

|

Vol. 63, No. 1

41--52

EN

We present our final report on the search for pulsating M dwarfs. We used moderate (<1 m) ground-based telescopes. Our detection was limited to 1 ppt, which is roughly 0.1% of flux variation. We employed both the Fourier technique and Phase Dispersion Minimization (PDM) method. Our data analyses revealed no detection of pulsations in M dwarfs down to the above amplitude level. The results of our survey cannot reject or confirm the theoretical calculations suggesting the M dwarfs can pulsate, however, if the pulsations exist in these stars their amplitudes must be lower than 1 ppt. As a by-product of our search we found several new variable stars, including pulsating stars, binary systems and flare stars.

10

Detection of Multiplets of Degree ℓ=3 and ℓ=4 in the Subdwarf-B Pulsator KIC 10139564

Baran A. S., Østensen R. H.

Acta Astronomica

|

2013

|

Vol. 63, No. 1

79--90

EN

We present up-to-date results on the short-period sdB pulsator in the Kepler field, KIC 10139564, including 27 months of near continuous photometric data. With this extended dataset we significantly lower the detection threshold, which allows us to detect multiplet components that were missing in our previous analysis based on 15 months of data. We conclude that two regions in the amplitude spectrum of KIC 10139564 contain modes of degree ℓ=3 and ℓ=4, respectively. We also identify many combination frequencies, in both the sub- and super-Nyquist regions, as well as several pulsation modes which show strong frequency or amplitude variability.

11

The Optical Gravitational Lensing Experiment. Gaia South Ecliptic Pole Field as Seen by OGLE-IV

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

Acta Astronomica

|

2012

|

Vol. 62, No. 3

219--245

EN

We present a comprehensive analysis of the Gaia South Ecliptic Pole (GSEP) field, 5.3 square degrees area around the South Ecliptic Pole on the outskirts of the LMC, based on the data collected during the fourth phase of the Optical Gravitational Lensing Experiment, OGLE-IV. The GSEP field will be observed during the commissioning phase of the ESA Gaia space mission for testing and calibrating the Gaia instruments. We provide the photometric maps of the GSEP region containing the mean VI photometry of all detected stellar objects and their equatorial coordinates. We show the quality and completeness of the OGLE-IV photometry and color-magnitude diagrams of this region. We conducted an extensive search for variable stars in the GSEP field leading to the discovery of 6789 variable stars. In this sample we found 132 classical Cepheids, 686 RR Lyr type stars, 2819 long-period, and 1377 eclipsing variables. Several objects deserving special attention were also selected, including a new classical Cepheid in a binary eclipsing system. To provide empirical data for the Gaia Science Alert system we also conducted a search for optical transients. We discovered two firm type Ia supernovae and nine additional supernova candidates. To facilitate future Gaia supernovae detections we prepared a list of more than 1900 galaxies to redshift about 0.1 located in the GSEP field. Finally, we present the results of astrometric study of the GSEP field. With the 26 months time base of the presented here OGLE-IV data, proper motions of stars could be detected with the accuracy reaching 2 mas/yr. Astrometry allowed to distinguish galactic foreground variable stars detected in the GSEP field from LMC objects and to discover about 50 high proper motion stars (proper motion ≥ 100 mas/yr). Among them three new nearby white dwarfs were found. All data presented in this paper are available to the astronomical community from the OGLE Internet archive.

12

Puzzling Frequencies in First Overtone Cepheids

Dziembowski W. A.

Acta Astronomica

|

2012

|

Vol. 62, No. 4

323--341

EN

The OGLE project led to the discovery of earlier unknown forms of multiperiodic pulsation in Cepheids. Often, the observed periods may be explained in terms of simultaneous excitation of two or rarely three radial modes. However, a secondary variability at about 0.6 of the dominant period, detected in a number of the first overtone (1O) pulsators inhabiting the Magellanic Clouds, seems to require a different explanation. After reviewing a possibility of explaining this signal in terms of radial and nonradial modes, I find that only unstable modes that may reproduce the observed period ratio are f-modes of high angular degrees (ℓ=42-50). I discuss in detail the driving effect behind the instability and show that it is not the familiar opacity mechanism. Finally, I emphasize the main difficulty of this explanation, which requires high intrinsic amplitudes implying large broadening of spectral line.

13

Mode Identification of Three Pulsating Subdwarf B Stars via Multiplets and Period Spacing

Baran A. S., Winans A.

Acta Astronomica

|

2012

|

Vol. 62, No. 4

343--355

EN

We present an analysis of three pulsating subdwarf B stars residing in short period binaries discovered by the Kepler spacecraft. We followed the analysis presented in Baran. Most of the peaks we detected were assigned to mode degrees and, in the case of the multiplet components, the azimuthal numbers. We confirmed the spin rates for all three stars to be tens of days rather than hours as the binary frequencies may suggest. Using the average period spacings of each object we produced an échelle diagram which shows a common feature at a period of nearly 5000 s. The period spacing between consecutive overtones is quite regular, which confirms that the mode trapping is not significant as previously predicted by the models.

14

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. XIV. Classical and Type II Cepheids in the Galactic Bulge

Soszyński I., Udalski A., Pietrukowicz P., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K., Poleski R., Kozłowski S.

Acta Astronomica

|

2011

|

Vol. 61, No. 4

285--301

EN

The fourteenth part of the OGLE-III Catalog of Variable Stars (OIII-CVS) contains Cepheid variables detected in the OGLE-II and OGLE-III fields toward the Galactic bulge. The catalog is divided into two main categories: 32 classical Cepheids (21 single-mode fundamental-mode F, four first-overtone 1O, two double-mode F/1O, three double-mode 1O/2O and two triple-mode 1O/2O/3O pulsators) and 335 type II Cepheids (156 BL Her, 128 W Vir and 51 RV Tau stars). Six of the type II Cepheids likely belong to the Sagittarius Dwarf Spheroidal Galaxy. The catalog data include the time-series photometry collected in the course of the OGLE survey, observational parameters of the stars, finding charts, and cross-identifications with the General Catalogue of Variable Stars. We discuss some statistical properties of the sample and compare it with the OGLE catalogs of Cepheids in the Large and Small Magellanic Clouds. Multi-mode classical Cepheids in the Galactic bulge show systematically smaller period ratios than their counterparts in the Magellanic Clouds. BL Her in the Galactic bulge stars seem to be brighter than the linear extension of the period-luminosity relations defined by the longer-period type II Cepheids. We also show individual stars of particular interest, like two BL Her stars with period doubling.

15

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

Soszyński I., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K., Poleski R., Kozłowski S., Pietrukowicz P.

Acta Astronomica

|

2011

|

Vol. 61, No. 3

217--230

EN

The thirteenth part of the OGLE-III Catalog of Variable Stars (OIII-CVS) contains 19 384 long-period variables (LPVs) detected in the Small Magellanic Cloud. The sample is composed of 352 Mira stars, 2222 semiregular variables (SRVs) and 16 810 OGLE Small Amplitude Red Giants (OSARGs). Sources are divided into oxygen-rich and carbon-rich stars. The catalog includes time-series VI photometry obtained between 1997 and 2009. Methods used to select and classify variable stars are described. We show some statistical properties of the sample, and compare it with LPVs in the Large Magellanic Cloud. Additionally, we present objects of particular interest, e.g., a SRV with outbursts, and a Mira star with the longest known pulsation period P=1860 days.

16

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. XI. RR Lyrae Stars in the Galactic Bulge

Soszyński I., Dziembowski W. A., Udalski A., Poleski R., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K., Kozłowski S., Pietrukowicz P.

Acta Astronomica

|

2011

|

Vol. 61, No. 1

1--23

EN

The eleventh part of the OGLE-III Catalog of Variable Stars (OIII-CVS) contains 16 836 RR Lyr stars detected in the OGLE fields toward the Galactic bulge. The total sample is composed of 11 756 RR Lyr stars pulsating in the fundamental mode (RRab), 4989 overtone pulsators (RRc), and 91 double-mode (RRd) stars. About 400 RR Lyr stars are members of the Sagittarius Dwarf Spheroidal Galaxy. The catalog includes the time-series photometry collected in the course of the OGLE survey, basic parameters of the stars, finding charts, and cross-identifications with other catalogs of RR Lyr stars toward the Milky Way center. We notice that some RRd stars in the Galactic bulge show unusually short periods and small ratio of periods, down to PF≈0.35 days and P1O/PF≈0.726. In the Petersen diagram double-mode RRLyr stars form a parabola-like structure, which connects shorter- and longer-period RRd stars. We show that the unique properties of the bulge RRd stars may be explained by allowing for the wide range of the metal abundance extending up to [Fe/H]≈-0.36. We report the discovery of an RR Lyr star with additional eclipsing variability with the orbital period of 15.2447 days. Some statistical features of the RRLyr sample are presented. We discuss potential applications of our catalog in studying the structure and history of the central region of the Galaxy, mapping the interstellar extinction toward the bulge, studying globular clusters and the Sagittarius Dwarf Galaxy.

17

Mt. Suhora Survey - Searching for Pulsating M Dwarfs in Kepler Public Dataset

Baran A. S., Fox-Machado L., Lykke J., Nielsen M., Telting J. H.

Acta Astronomica

|

2011

|

Vol. 61, No. 4

325--343

EN

We present our analysis of Kepler short cadence public data to search for stellar pulsations in M dwarfs. Theoretical calculations predict that these stars may suffer from a fundamental radial mode driven by the nuclear ε mechanism. First results published thus far show no significant signal around the expected frequency of 36 c/d down to 1 ppt (parts per thousand). In this paper we include new results obtained from a sample of 86 stars, although a real number of M dwarfs after spectral classification turned out to be small. Unluckily, we have not detected any significant signal typically down to 1-10 ppm (parts per million) in M dwarfs and since the sample of these stars consists of 6 objects only, we cannot make any strong conclusion if the ε mechanism drives perturbation in radius to propagate to a detectable amplitude at the surface. As a by-product of our work we provide a spectral classification of 86 Kepler objects, along with their variability and thus far unknown artifacts residing in Kepler photometry.

18

Mt. Suhora Survey - Searching for Pulsating M Dwarfs. I

Baran A. S., Winiarski M., Krzesiński J., Fox-Machado L., Kawaler S. D., Dróżdż M., Faltenbacher A., Thompson M. A., Reed M. D.

Acta Astronomica

|

2011

|

Vol. 61, No. 1

37--58

EN

We present the first results of our M dwarf survey in search for stellar pulsation in low mass main sequence stars. Theoretical calculations predict that ε mechanism might drive a fundamental radial mode in these stars and therefore pulsations could be observed photometrically. Although M dwarfs are known for their flare and spot activity they have not yet been the subject of dedicated time-series surveys for pulsation. In this work we include the light curves and amplitude spectra of 46 M dwarfs, which have been observed during the first two years of our survey. We did not detect any pulsations yet. As a by-product of our search, we describe the light curves of some flare M dwarfs. The survey will last for two more years and during that period more than a hundred of M0-M4 type main sequence stars will be observed.

19

Dwarf Nova V1040 Centauri and Variable Stars in its Vicinity

Rutkowski A., Pietrukowicz P., Olech A., Ak T., Złoczewski K., Poleski R., Tappert C., Eker Z.

Acta Astronomica

|

2011

|

Vol. 61, No. 4

345--357

EN

We present the results of a photometric campaign of the dwarf nova V1040 Cen. The light curve shows two normal outbursts with recurrence time ≈40 days and amplitude ≈2.5 mag. Quiescence data show oscillations with periods in the range ≈0.1 days (2.4 h) to ≈0.5 days (12 h) of unknown origin. We measured the orbital period of V1040 Cen to be Porb=0.060458(80) days (1.451±0.002 h). Based on the MV-Porb relation we found the distance of V1040 Cen to be 137±31 pc. In this paper we also report the detection of eleven new variable stars in the field of the monitored dwarf nova.