Searcharxiv⌕ Search

arXiv subjects

Janusz Kaluzny

Publications and source records attributed to Janusz Kaluzny.

16 recordsLinked to original sources
arXiv2012

Dusty origin of the Broad Line Region in active galaxies

The most characteristic property of active galaxies, including quasars, are prominent broad emission lines. I will discuss an interesting possibility that dust is responsible for this phenomenon. The dust is known to be present in quasars in the form of a dusty/molecular torus which results in complexity of the appearance of active galaxies. However, this dust is located further from the black hole than the Broad Line Region. We propose that the dust is present also closer in and it is actually responsible for formation of the broad emission lines. The argument is based on determination of the temperature of the disk atmosphere underlying the Broad Line Region: it is close to 1000 K, independently from the black hole mass and accretion rate of the object. The mechanism is simple and universal but leads to a considerable complexity of the active nucleus surrounding. The understanding the formation of BLR opens a way to use it reliably - in combination with reverberation measurement of its size - as standard candles in cosmology.

astro-ph.CO↗
arXiv2009

Variable Stars in the Globular Cluster NGC 6752

We report time-series photometry for 16 variable stars located in the central part of the globular cluster NGC 6752. The sample includes 13 newly identified objects. The precision of our differential photometry ranges from 1 mmag at V=14.0 to 10 mmag at V=18.0. We detected 4 low amplitude variables located on the extended horizontal branch (EHB) of the cluster. They are candidate binary stars harboring sdB subdwarfs. A candidate degenerate binary was detected about 2 mag below the faint end of the EHB. The star is blue and its light curve is modulated with a period of 0.47 d. We argue that some of the identified variable red/blue stragglers are ellipsoidal binaries harboring degenerate stars. They have low amplitude sine-like light curves and periods from a few hours to a few days. Spectroscopic observations of such objects may lead to the detection of detached inactive binaries harboring stellar mass black holes or neutron stars. No binaries of this kind are known so far in globular clusters although their existence is expected based on the common occurrence of accreting LMXBs and millisecond pulsars. An eclipsing SB1 type binary was identified on the upper main sequence of the cluster. We detected variability of optical counterparts to two X-ray sources located in the core region of NGC 6752. The already known cataclysmic variable B1=CX4 experienced a dwarf nova type outburst. The light curve of an optical counterpart to the X-ray source CX19 exhibited modulation with a period 0.113 d. The same periodicy was detected in the HST-ACS data. The variable is located on the upper main sequence of the cluster. It is an excellent candidate for a close degenerate binary observed in quiescence.

astro-ph.SR↗
arXiv2009

Globular Cluster Ages from Main Sequence Fitting and Detached, Eclipsing Binaries: The Case of 47 Tuc

Age constraints are most often placed on globular clusters by comparing their CMDs with theoretical isochrones. The recent discoveries of detached, eclipsing binaries in such systems by the Cluster AgeS Experiment (CASE) provide new insights into their ages and, at the same time, much needed tests of stellar evolution models. We describe efforts to model the properties of the detached, eclipsing binary V69 in 47 Tuc and compare age constraints derived from stellar evolution models of V69A and B with ages obtained from fitting isochrones to the cluster CMD. We determine, under reasonable assumptions of distance, reddening, and metallicity, the extent to which it is possible to simultaneously constrain the age and He content of 47 Tuc.

astro-ph.SR↗
arXiv2005

Variable Stars in the Large Magellanic Cloud: Discovery of Extragalactic W UMa Binaries

We observed a field in the disk of the LMC on two consecutive nights in search of rapid variable stars. We have found two pulsating stars of type RRab and delta Sct, and four binary stars, among the latter one sdB or CV below the LMC blue Main Sequence and three very close binary systems on the MS. At least one of the MS binaries, and possibly all three, are the first solar-type (W UMa-type) contact binaries to be detected in any extragalactic system and observed to obey the same Mv = Mv(log P, B-V) calibration as the Galactic systems. Given the selection effects due to small amplitudes at faint magnitudes, the frequency of such binaries in the disk of the LMC with its large spread in population ages is not inconsistent with that in the disk of our Galaxy, and contrasts with the lack of binaries found in earlier observations of the much younger LMC cluster LW55.

astro-ph↗
arXiv2004

Variable Stars in the Archival HST Data of Globular Clusters M13, M30 and NGC 6712

We have analyzed archival HST/WFPC2 time-series data of the central parts of globular clusters M13, M30 and NGC 6712 in search of variable objects. Among a total of 21 identified variables there are 15 new discoveries. The sample includes nine RR Lyr stars, two SX Phe stars and seven W UMa-type contact binaries. One object is preliminarily classified as a detached eclipsing binary and another as an ellipsoidal variable.

astro-ph↗
arXiv2004

Searching for Variable Stars in the Central Part of the Globular Cluster M22

Time-series data taken with the Hubble Space Telescope of three fields covering the central part of the globular cluster M22 have been analyzed in search of variable objects. We report identification of 11 periodic variables of which 8 are new discoveries. The sample includes 5 certain contact binaries as well as 1 SX Phe star. Two objects with periods longer than 1 day are preliminarily classified as either spotted variables of BY Dra type or ellipsoidal variables. The most unusual of the identified variables, M22_V11, has I_C=19.9 and is located far to the red of the main sequence in the cluster color-magnitude diagram. It shows variability with a period as short as P=0.066 days or alternatively with P=0.132 days. We propose that it may be an ellipsoidal variable harboring a degenerate component.

astro-ph↗
arXiv2003

Variable Yellow and Red Stragglers in the Old Open Cluster NGC 6791

Two sets of archive time series observations of an old open cluster NGC 6791 were re-analysed using an image subtraction technique. We report identification of four new variables. Proper motion data are available for three of them and indicate that they are likely cluster members. Photometry of these stars is discussed along with the data for two earlier identified variables. The sample analysed includes one yellow and three red stragglers. An eclipsing red straggler V9 is of particular interest. Cluster membership of this RS Cvn type binary would imply that its cooler component is in a stage of thermal inequilibrium. One of variables is a K type red giant showing low-amplitude variability with a period of about 0.33 d.

astro-ph↗
arXiv2002

Time Series Photometry of Variable Stars in the Globular Cluster NGC 6397

Time series BVI photometry is presented for 16 short-period variables located in the central region of the globular cluster NGC 6397. The sample includes 9 newly detected variables. The light curve of cataclysmic variable CV6 shows variability with a period of 0.2356 days. We confirm an earlier reported period of 0.472 days for cataclysmic variable CV1. Phased light curves of both CVs exhibit sine-like light curves, with two minima occurring during each orbital cycle. The secondary component of CV1 has a low average density of 0.83 g/cm^{3} indicating that it cannot be a normal main sequence star. Variables among the cluster blue stragglers include a likely detached eclipsing binary with orbital period of 0.787 days, three new SX Phe stars (one of which has the extremely short period of 0.0215 days), and three low amplitude variables which are possible gamma Doradus variables.

astro-ph↗
arXiv2001

Cluster AgeS Experiment. CCD photometry of SX Phoenicis variables in the globular cluster M 55

We present CCD photometry of SX Phe variables in the field of the globular cluster M 55. We have discovered 27 variables, three of which are probable members of the Sagittarius dwarf galaxy. All of the SX Phe stars in M 55 lie in the blue straggler region of the cluster color-magnitude diagram. Using period ratio information we have identified the radial pulsation modes for one of the observed variables. Inspection of the period-luminosity distribution permits the probable identifications of the pulsation modes for most of the rest of the stars in the sample. We have determined the slope of the period-luminosity relation for SX Phe stars in M 55 pulsating in the fundamental mode. Using this relation and the HIPPARCOS data for SX Phe itself, we have estimated the apparent distance modulus to M 55 to be (m-M)_V=13.86 +- 0.25 mag.

astro-ph↗
arXiv1999

Warsaw Variability Surveys

Four large/medium size photometric surveys are being conducted by Warsaw astronomers: Warsaw-LCO survey of globular clusters, OGLE, DIRECT and ASAS. In this contribution we provide short description of these projects and discuses briefly some results obtained for pulsating variables.

astro-ph↗
arXiv1999

CCD Photometry of Faint Variable Stars in the Globular Cluster NGC 6752

We present the results of a photometric survey for variable stars in the field of the nearby globular cluster NGC 6752. The cluster was monitored in 1996 and 1997 for a total of 54 hours with 3 different CCD cameras mounted on the 1.0-m Swope telescope. Eleven new variables were identified: 3 SX Phe stars, 7 contact binaries and 1 candidate detached eclipsing binary. All 3 SX Phe variables are likely members of the cluster while only 1 out of the 7 contact binaries is a potential cluster member. As a by-product of our survey we obtained UBV photometry for a large sample of stars in the cluster field. Two stars with U-B \approx -1.0 and V=19.3 and V=20.6 were identified. They lie along the extended horizontal branch of the cluster, and are likely to be faint sdB stars from NGC 6752.

astro-ph↗
arXiv1995

Variable stars in the field of the old open cluster NGC 2243

We report results of photometric monitoring of the NGC 2243 field in V and $I$ filters. Two W~UMa-type systems and three detached eclipsing binaries were discovered. Both contact systems are likely members of the cluster. One of detached binaries - variable V1 - has a period P=1.188 day. This variable is located at the cluster's turnoff in the color-magnitude diagram. Determination of parameters for components of V1 can provide direct information about properties of turnoff stars in NGC 2243 as well as to allow direct determination of cluster's distance. A background RR Lyr variable was found in the monitored field. The reddening of NGC 2243 is estimated at E(V-I)=0.10\pm 0.04 based on the V-I color exhibited by this star at minimum light. The observed distribution of colors for the background halo stars shows a cutoff at (V-I)\approx 0.60 what implies $E(V-I)\leq 0.12$ for the cluster.

astro-ph↗
arXiv1995

CCD PHOTOMETRY OF VARIABLE STARS IN THE GLOBULAR CLUSTER RU 106

BV photometry is presented for 12 RR Lyr variables discovered in the presumably young galactic globular cluster Ruprecht 106. All variables are type RRab, and their periods span a narrow range from 0.574 to 0.652 day. We report also on the discovery of 3 SX Phe variables among the cluster blue stragglers. A likely background RR Lyr variable and two foreground contact binaries were also found in the cluster field. The reddening of Ruprecht 106 is estimated at E(B-V)=0.20 based on the (B-V) colors exhibited by the cluster RR Lyr variables at minimum light. Analysis of the "period" versus "amplitude" and "period" versus "rise-time" diagrams suggests similar metallicities of Ruprecht 106 and M3. A peak (or bump) is present in the luminosity function of the red giant branch of Ruprecht 106. Its position relative to the horizontal branch is consistent with a cluster metallicity of [Fe/H]>= -1.6.

astro-ph↗
arXiv1995

CCD Photometry of Distant Open Clusters. II -- NGC 6791

Three new photometric CCD-based datasets are presented for NGC~6791. They consist of deep UBV photometry (to $V_{lim} =24$, $B_{lim}=24$, $U_{lim} = 23$) of the central parts of the cluster and of selected fields around it, and of relatively shallower UBVI photometry for the whole cluster ($23' \times 23'$). The data have been used to discuss the reddening, metallicity and age ofNGC~6791, a cluster which is particularly important because of (1)~its most-advanced age among open clusters, (2)~metallicity higher than solar and (3)~particularly large number of member stars. We discovered two new very blue stars increasing the total of sdB objects in the cluster to ten. They are located in a very narrow range magnitudes $V=17.7 \pm 0.5$; their blue colors strongly constrain our determination of the reddening of the cluster to $E(B-V)=0.17 \pm 0.01$. We detected no other blue stars except a population of faint objects with $V \approx 22$ in the center of the cluster. We have used the new theoretical isochrones in a differential determination of metallicity and age of NGC~6791 using M67 and NGC~188 as two clusters with well-known abundaces and age. We find $[Fe/H] \simeq +0.5$ and age by 1~Gyr older than that of NGC~188. The luminosity function of the cluster is surpisingly flat while the ``secondary'' main-sequence of equal-mass binaries is weaker than in less-populous old open clusters. We explain both features by the large total mass of the cluster which has lead to weak evaporation of low-mass and single stars from the cluster.

astro-ph↗
arXiv1994

Open clusters as tracers of the evolution of the Galaxy

Deep color-magnitude diagrams are presented for poorly known open clusters Cr 261, Be 18, Be 54, Tr 5 and BH176. All clusters are old objects with age\geq 4 Gyr. BH176 is either old open cluster or young globular cluster. Extremely red giants with V-I>3 were identified in the central parts of Cr 261, Be 54 and BH176. These three objects are candidates for very metal-rich clusters.

astro-ph↗