arXiv subjects

J. Kaluzny

Publications and source records attributed to J. Kaluzny.

At least 73 records · Page 4Linked to original sources

arXiv2003

Cluster AgeS Experiment (CASE): RR Lyrae stars from the globular cluster Omega Centauri as standard candles

New photometry of RRab and RRc stars in Omega Cen is used to calibrate their absolute magnitudes M_V as a function of: a) metallicity; and b) the Fourier parameters of light curves in the V band. The zero point of both calibrations relies on the distance modulus to the cluster derived earlier by the CASE project based on observations of the detached eclipsing binary OGLE GC17. For RRab variables we obtained a relation of M_V=(0.26\pm 0.08)[Fe/H]+(0.91\pm 0.13). A dereddened distance modulus to the LMC based on that formula is $μ_{0}=18.56\pm 0.14$ mag. The second calibration of M_V, which is based on Fourier coefficients of decomposed light curves, results in the LMC distance of $μ_{0}=18.51\pm 0.07$ mag.

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arXiv2003

DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. IX. Variables in the Field M31Y Discovered with Image Subtraction

The DIRECT Project aims to obtain direct distances to two Local Group galaxies, M31 and M33, which occupy a crucial position near the bottom of the cosmological distance ladder. The first step is to search for detached eclipsing binaries (DEBs) and Cepheids using 1 m class telescopes to select good candidates, which will be followed up spectroscopically on 6.5-10 m class telescopes. In this ninth paper we present a catalog of variable stars discovered with image subtraction in field M31Y [RA=10.97 deg, Dec=41.69 deg, J2000.0]. The data were obtained with the FLWO 1.2 m telescope on 25 nights, over a period of 6 months. In our search covering 22x22 arcmin we discovered 41 eclipsing binaries, 126 Cepheids, and 97 other periodic or nonperiodic variables, including a LBV candidate, a nova and a galactic CV. The catalog of variables, as well as their photometry and finding charts, is available electronically via anonymous ftp and the World Wide Web. The complete set of the CCD frames is available upon request.

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arXiv2003

Long-term variability survey of the old open cluster NGC 6791

We present the results of a long-term variability survey of the old open cluster NGC 6791. The BVI observations, collected over a time span of 6 years, were analyzed using the ISIS image subtraction package. The main target of our observations were two cataclysmic variables B7 and B8. We have identified possible cycle lenghts of about 25 and 18 days for B7 and B8, respectively. We tentatively classify B7 as a VY Scl type nova-like variable or a Z Cam type dwarf nova. B8 is most likely an SS Cygni type dwarf nova. We have also extracted the light curves of 42 other previously reported variable stars and discovered seven new ones. The new variables show long-period or non-periodic variability. The long baseline of our observations has also allowed us to derive more precise periods for the variables, especially for the short period eclipsing binaries.

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arXiv2002

Photometry and Spectroscopy of the Optical Companion to the Pulsar PSR J1740-5340 in the Globular Cluster NGC 6397

We present photometric and spectroscopic observations of the optical companion to the millisecond radio pulsar PSR J1740-5340 in the globular cluster NGC 6397. An analysis of the photometric variability in the B, V, and I-bands indicates an inclination of the system of 43.9+-2.1 degrees if the optical companion fills its Roche lobe (a semi-detached configuration). The spectroscopic data show a radial velocity variation with a semi-amplitude of K=137.2 +- 2.4 km/sec, and a system velocity gamma=17.6 +- 1.5 km/sec, consistent with cluster membership. We use these results to derive a mass of the optical companion of M1=0.296 +- 0.034 Msol and M2=1.53 +- 0.19 Msol for the pulsar. There is evidence for secular change of the amplitude of the optical light curve of the variable measured over seven years. The change does not have interpretation and its presence complicates reliable determination of the absolute parameters of the binary.

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arXiv2002

The Strongly Polarized Afterglow of GRB 020405

We report polarization measurements and photometry for the optical afterglow of the gamma-ray burst GRB 020405. We measured a highly significant 9.9% polarization (in V band) 1.3 days after the burst and argue that it is intrinsic to the GRB. The light curve decay is well fitted by a $t^{-1.72}$ power-law; we do not see any evidence for a break between 1.24 and 4.3 days after the burst. We discuss these measurements in the light of several models of GRB afterglows.

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arXiv2002

Clusters AgeS Experiment. Hot subdwarfs and luminous white dwarf candidates in the field of the globular cluster M4

We present UBV color magnitude diagrams (CMDs) for the globular cluster M4. The CMDs show a sequence of four luminous blue stars (V<20, U-V<-0.6) which appear to be cluster hot subdwarfs. We present spectra for the three brightest ones. We also note the presence of a population of faint blue objects, likely to be hot, young white dwarfs (WDs) belonging to the cluster. We have selected five objects above V=22 mag, bright enough for follow-up ground-based spectroscopy and present their coordinates and finding charts. We show a spectrum for variable V46 (Kaluzny et al. 1997) which suggests that it is a hot subdwarf, along with a new light curve obtained with the ISIS image subtraction package (Alard 2000). The light curve is unstable, but only one period of variability is apparent. Two new variables have been discovered, both located on the cluster red giant branch (RGB). We also present a differential E(B-V) reddening map and a fiducial sequence for the main sequence, subgiant branch and red giant branch on the V/B-V CMD for a selected region with uniform reddening. Based on a comparison with the M5 fiducial sequence we obtain a reddening estimate of E(B-V)=0.41 mag towards M4, consistent with previous determinations.

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arXiv2001

Photometry and Spectroscopy of Eclipsing Binaries in omega Centauri

Detached eclipsing double line spectroscopic binaries are accurate distance indicators. They can be used for the direct determination of distances to globular clusters in which such systems can be identified. The results of major photometric surveys aimed at identification of variable stars in omega Cen are summarized. Over 43 eclipsing binaries have been identified so far in the cluster field of which only 8 objects are true detached systems. Distance and age determinations are presented for the system OGLEGC-17. The apparent distance modulus is (m-M)_{V}=14.09\pm 0.04 and the age of this binary is tau=11.8\pm 0.6 Gyr.

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arXiv2001

DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. VIII. Additional Variables in the Field M33B Discovered with Image Subtraction

DIRECT is a project to obtain directly the distances to two Local Group galaxies, M31 and M33, which occupy a crucial position near the bottom of the cosmological distance ladder. As the first step of the DIRECT project we have searched for detached eclipsing binaries (DEBs) and new Cepheids in the M31 and M33 galaxies with 1m-class telescopes. In this eighth paper we present a catalog of variable stars discovered in the data from the followup observations of DEB system D33J013337.0+303032.8 in field M33B [(RA,Dec)= (23.48, 30.57), J2000.0], collected with the Kitt Peak National Observatory 2.1m telescope. In our search covering an area of 108 sq. arcmin. we have found 895 variable stars: 96 eclipsing binaries, 349 Cepheids, and 450 other periodic, possible long period or non-periodic variables. Of these variables 612 are newly discovered. Their light curves were extracted using the ISIS image subtraction package. For 77% of the variables we present light curves in standard V and B magnitudes, with the remaining 23% expressed in units of differential flux. We have discovered a population of first overtone Cepheid candidates and for six of them we present strong arguments in favor of this interpretation. The catalog of variables, as well as their photometry (about 9.2*10^4 BV measurements) and finding charts, is available electronically via anonymous ftp and the World Wide Web. The complete set of the CCD frames is available upon request.

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arXiv2001

The DIRECT project: Catalogs of stellar objects in nearby galaxies. II. Eastern arm and NGC 206 in M31

DIRECT is a project to directly obtain the distances to two important galaxies in the cosmological distance ladder, M31 and M33, using detached eclipsing binaries and Cepheids. As part of our search for these variables, we have obtained photometry and positions for thousands of stellar objects within the monitored fields, covering an area of 557.8 arcmin^2. In this research note we present the equatorial coordinates and BVI photometry for 26712 stars in the M31 galaxy, along the eastern arm and in the vicinity of the star forming region NGC206.

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arXiv2001

DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. VII. Additional Variables in the Field M33A Discovered with Image Subtraction

DIRECT is a project to obtain directly the distances to two Local Group galaxies, M31 and M33, which occupy a crucial position near the bottom of the cosmological distance ladder. As the first step of the DIRECT project we have searched for detached eclipsing binaries (DEBs) and new Cepheids in the M31 and M33 galaxies with 1m-class telescopes. In this seventh paper we present a catalog of variable stars discovered in the data from the followup observations of DEB system D33J013346.2+304439.9 in field M33A [(RA,Dec)= (23.55, 30.72), J2000.0], collected with the Kitt Peak National Observatory 2.1m telescope. In our search covering an area of 108 sq. arcmin. we have found 434 variable stars: 63 eclipsing binaries, 305 Cepheids, and 66 other periodic, possible long period or non-periodic variables. Of these variables 280 are newly discovered, mainly short-period and/or faint Cepheids. Their light curves were extracted using the ISIS image subtraction package. For 85% of the variables we present light curves in standard V and B magnitudes, with the remaining 15% expressed in units of differential flux. We have discovered a population of first overtone Cepheid candidates and for eight of them we present strong arguments in favor of this interpretation. We also report on the detection of a non-linearity in the KPNO T2KA and T1KA cameras. The catalog of variables, as well as their photometry (about 7.8*10^4 BV measurements) and finding charts, is available electronically via anonymous ftp and the World Wide Web. The complete set of the CCD frames is available upon request.

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arXiv2001

The DIRECT Project: Catalogs of Stellar Objects in Nearby Galaxies. I. The Central Part of M33

The DIRECT project aims to determine direct distances to two important galaxies in the cosmological distance ladder -- M31 and M33 -- using detached eclipsing binaries (DEBs) and Cepheids. The search for these variables requires time-series photometry of large areas of the target galaxies and yields magnitudes and positions for tens of thousands of stellar objects, which may be of use to the astronomical community at large. During the first phase of the project, between September 1996 and October 1997, we were awarded 95 nights on the F. L. Whipple Observatory 1.2 m telescope and 36 nights on the Michigan-Dartmouth-MIT 1.3 m telescope to search for DEBs and Cepheids in the M31 and M33 galaxies. This paper, the first in our series of stellar catalogs, lists the positions, three-color photometry, and variability indices of 57,581 stars with 14.4 < V < 23.6 in the central part of M33. The catalog is available from our FTP site at ftp://cfa-ftp.harvard.edu/pub/kstanek/DIRECT/star_catalog/M33ABC/

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arXiv2001

DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. VI. Variables in the Central Part of M33

The DIRECT project aims to determine direct distances to two important galaxies in the cosmological distance ladder - M31 and M33 - using detached eclipsing binaries (DEBs) and Cepheids. We present the results of the first large-scale CCD-based search for variables in M33. We have observed two fields located in the central region of M33 for a total of 95 nights on the F. L. Whipple Observatory 1.2-m telescope and 36 nights on the Michigan-Dartmouth-MIT 1.3-m telescope. We have found a total of 544 variables, including 251 Cepheids and 47 eclipsing binaries. The catalog of variables is available online, along with finding charts and BVI light curve data (consisting of 8.2x10^4 individual measurements). The complete set of CCD frames is available upon request.

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arXiv2000

Cluster AgeS Experiment: The Age and Distance of the Globular Cluster omega Centauri Determined from Observations of the Eclipsing Binary OGLEGC17

We use masses, radii, and luminosities of the detached eclipsing binary OGLEGC17 derived from photometric and spectroscopic observations to calculate the age and distance of the globular cluster omega Cen. Age versus turnoff mass and age versus luminosity relations from Girardi et al. (2000) yield two independent estimates of the age, 9.1<t<16.7 Gyr and 12.9<t<18.5 Gyr. The distance and distance modulus derived by use of the infrared versus surface brightness relation are d =5385+-300 pc and (m-M)_V=14.06+-0.11. Distances derived from our infrared surface brightness versus color relation and the Teff versus B-V color relation of Sekiguchi & Fukugita (2000) disagree by about 10 per cent. Major improvements in the accuracy in estimated age and distance can be made with better measurements of the masses of the components of OGLEGC17.

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arXiv2000

Image-Subtraction Photometry of Variable Stars in the Field of the Globular Cluster NGC 6934

(Abridged) We present CCD BVI photometry of 85 variable stars from the field of the globular cluster NGC 6934. The photometry was obtained with the image subtraction package ISIS. 35 variables are new identifications: 24 RRab stars, 5 RRc stars, 2 eclipsing binaries of W UMa-type, one SX Phe star, and 3 variables of other types. Both detected contact binaries are foreground stars. The SX Phe variable belongs most likely to the group of cluster blue stragglers. Large number of newly found RR Lyr variables in this cluster, as well as in other clusters recently observed by us, indicates that total RR Lyr population identified up to date in nearby galactic globular clusters is significantly (>30%) incomplete. Fourier decomposition of the light curves of RRc variables was used to estimate the basic properties of these stars: M=0.63 M_odot, log(L/L_odot)=1.72, T_eff=7300 and Y=0.27. Using RRab variables we obtain: M_V=0.81, [Fe/H]=-1.53 and T_eff=6450. From the B-V color at minimum light of the RRab variables we obtained E(B-V)=0.09+-0.01. Different calibrations of absolute magnitudes of RRab and RRc available in literature were used to estimate apparent distance modulus of the cluster: (m-M)_V= 16.09+-0.06. We note a likely error in the zero point of the HST-based V-band photometry of NGC 6934 recently presented by Piotto et al. Among analyzed sample of RR Lyr stars we have detected a short period and low amplitude variable which possibly belongs to the group of second overtone pulsators (RRe subtype variables). The BVI photometry of all variables is available electronically via anonymous ftp. The complete set of the CCD frames is available upon request.

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arXiv2000

UBVI Color-Magnitude Diagrams in Baade's Window: Metallicity Range, Implications for the Red Clump Method, Color ``Anomaly'' and the Distances to the Galactic Center and the Large Magellanic Cloud

(Abridged) We analyze the UBVI color-magnitude diagrams towards the Galactic bulge in a relatively low-reddening region of Baade's Window. The dereddened red giant branch is very wide [~1.0 mag in (U-B)_0 and ~0.4 mag in (B-V)_0 and (V-I)_0], indicating a significant dispersion of stellar metallicities, which by comparison with the theoretical isochrones and data for Galactic clusters we estimate to lie between approximately -0.7< [Fe/H] < +0.3. We also discuss the metallicity dependence of the red clump I-band brightness and we show that it is between 0.1-0.2 mag dex^{-1}. This agrees well with the previous empirical determinations and the models of stellar evolution. The de-reddened (V-I)_0 color of the red clump in the observed bulge field is <(V-I)_0> = 1.066, sigma_{(V-I)_0} = 0.14, i.e. 0.056 mag redder than the local stars with good parallaxes measured by Hipparcos. When we use our data to re-derive the red clump distance to the Galactic center, we obtain the Galactocentric distance modulus μ_{0,GC}=14.69 +- 0.1 mag (R_0=8.67 +- 0.4 kpc), with error dominated by the systematics of photometric calibration. We then discuss the systematics of the red clump method and how they affect the red clump distance to the Large Magellanic Cloud. We argue that the value of distance modulus μ_{0,LMC}=18.24 +- 0.08 (44.5 +- 1.7 kpc), recently refined by Udalski, is currently the most secure and robust of all LMC distance estimates. This has the effect of increasing any LMC-tied Hubble constant by about 12%, including the recent determinations by the HST Key Project and Sandage et al. The UBVI photometry is available through the anonymous ftp service.

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arXiv2000

Clusters AgeS Experiment. RR Lyr Variables in the Globular Cluster NGC 6362

We present V and B-band CCD photometry of 35 RR Lyr stars in the southern hemisphere globular cluster NGC 6362. Fourier decomposition of the light curves was used to estimate the basic properties of these variables. From the analysis of the RRc stars we obtain a mean mass of M=0.531+/-0.014 $M_\odot$, luminosity log L=1.656+/-0.006, effective temperature Teff=7429+/-20, and helium abundance Y=0.292+/-0.002. The mean values of the absolute magnitude, metallicity (on Jurcsik's scale) and effective temperature for 14 RRab stars with "regular" light curves are: M_V=0.86+/-0.01, [Fe/H]=-0.93+/-0.04 and Teff=6555+/-25, respectively. From the B-V colors, periods and metallicities of the RRab stars we estimate the color excess for NGC 6362 to be equal to E(B-V)=0.08+/-0.01. Using this value we derive the colors of the blue and red edges of the instability strip in NGC 6362 to be $(B-V)^{BE}_0=0.17$ and $(B-V)^{RE}_0=0.43$. From the relations between the Fourier coefficients of RRab and RRc stars and their absolute magnitudes we estimate the apparent distance modulus to NGC 6362 to be (m-M)_V=14.46+/-0.10. From the mean value of log L of the RRc stars we obtain 14.59+/-0.03. The V-band light curves of three of the RRc stars exhibit changes in amplitude of over 0.1 mag on the time scale of around one week. Near the radial 1st overtone frequency we find one or two peaks, which strongly suggests that these variables belong to the newly identified group of non-radial pulsating RR Lyr stars.

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arXiv2000

Variable stars in the field of the globular cluster E3

We present the results of a search for variable stars in the faint sparse globular cluster E3. We have found two variable stars: an SX Phe variable (V1) and a W UMa eclipsing binary (V2). We have applied period-luminosity and period-color-luminosity relations to the variables to obtain their distance moduli. V1 seems to be a blue straggler belonging to E3, based on its distance modulus and location on the CMD. V2 is probably located behind the cluster, in the Milky Way halo. We also present V/B-V and V/V-I color magnitude diagrams of E3.

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arXiv2000

RR Lyrae Variables in the Globular Cluster M5

We present V-band CCD photometry of 65 RR Lyr variables from the globular cluster M5. We have estimated the basic physical parameters for 16 RRc stars and 26 RRab stars using a Fourier decomposition of the light curves of the variables. The mean values of mass, luminosity, effective temperature and relative helium abundance for the RRc stars are measured to be ${\cal M}=0.54{\cal M}_\odot$, log L = 1.69 T_{eff}=7353 K and Y=0.28, respectively. For the RRab variables the derived mean values of absolute magnitude, metallicity and effective temperature are: M_V=0.81, [Fe/H]=-1.23 and T_{eff}=6465 K. We find that the V amplitude of an RRab star for a given period is a function of metal abundance rather than Oosterhoff type. We find significant problems with the calibration of both the zero point and the scale of the luminosities measured with the Fourier technique. The apparent distance modulus derived from RRc stars is equal to $14.47\pm0.11$ and it is in good agreement with recent determinations. On the other hand distance modulus obtained from the sample of RRab stars (calibrated by the Baade-Wesselink observations of field RR Lyr variables) is significantly smaller and equal to $14.27\pm0.04$

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