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W. Pych

Publications and source records attributed to W. Pych.

53 records · Page 3Linked to original sources
arXiv2007

The Clusters AgeS Experiment (CASE). I. V209 omega Cen - An Eclipsing Post-Common Envelope Binary in the Globular Cluster omega Cen

We use photometric and spectroscopic observations of the detached eclipsing binary V209 omega Cen to derive the masses, radii, and luminosities of the component stars. The system exhibits total eclipses and, based on the measured systemic velocity and the derived distance, is a member of the globular cluster omega Cen. We obtain 0.945 +/- 0.043 Msun, 0.983 +/- 0.015 Rsun and 6.68 +/- 0.88 Lsun for the cooler, but larger and more luminous primary component. The secondary component has 0.144 +/- 0.008 Msun, 0.425 +/- 0.008 Rsun and 2.26 +/- 0.28 Lsun. The effective temperatures are estimated at 9370 K for the primary and at 10866 K for the secondary. On the color-magnitude diagram of the cluster, the primary component occupies a position between the tip of the blue straggler region and the extended horizontal branch while the secondary component is located close to the red border of the area occupied by hot subdwarfs. However, its radius is too large and its effective temperature is too low for it to be an sdB star. We propose a scenario leading to the formation of a system with such unusual properties with the primary component ``re-born'' from a former white dwarf which accreted a new envelope through mass transfer from its companion. The secondary star has lost most of its envelope while starting its ascent onto the sub-giant branch. It failed to ignite helium in its core and is currently powered by a hydrogen burning shell.

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arXiv2007

The Clusters AgeS Experiment (CASE). II. The Eclipsing Blue Straggler OGLEGC-228 in the Globular Cluster 47 Tuc

We use photometric and spectroscopic observations of the eclipsing binary OGLEGC-228 (V228) to derive the masses, radii, and luminosities of the component stars. Based on measured systemic velocity, proper motion and distance, the system is a blue straggler member of the globular cluster 47 Tuc. Our analysis shows that V228 is a semi-detached Algol. We obtain M=1.512 +/- 0.022 Msun, R=1.357 +/- 0.019 Rsun, L=7.02 +/- 0.050 Lsun for the hotter and more luminous primary component and M=0.200 +/- 0.007 Msun, R=1.238 +/- 0.013 Rsun, L=1.57 +/- 0.09 Lsun for the Roche lobe filling secondary.

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arXiv2006

Eclipsing binaries in the open cluster NGC 2243 - II. Absolute properties of NV CMa

We present echelle spectroscopic data for five eclipsing binary stars and two giant stars in the field of the open cluster NGC 2243. The average cluster velocity is determined to be +60.4 +- 0.6 km/s. Four of the eclipsing binaries are very likely members of the cluster based on their observed radial velocities. The absolute parameters of cluster member NV CMa are determined by analysing photometric and radial velocity data. We obtain 1.089+-0.010 Msun and 1.221+-0.031 Rsun for the primary, and 1.069+-0.010 Msun and 178+-0.037 Rsun for the secondary. Both components of the binary are located on the Main Sequence, about 1 mag. below the turn-off point on the cluster color-magnitude diagram. Using model age-luminosity and age-radius relations we obtain 4.35+-0.25 Gyr for the age of NV CMa. The derived age is, however, very sensitive to the adopted metallicity of the cluster. We demonstrate that a meaningful determination of the ages of objects like NV CMa based on evolutionary models is possible only if their metallicity is know with a relative accuracy of a few percent. The distance moduli calculated for the components of NV CMa agree closely with each other, and imply an apparent distance modulus of the cluster of (m-M)_V=13.25+-0.08.

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arXiv2005

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

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 P_sh=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 arcmin from the cluster center was detected. It had an amplitude of Delta_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.

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arXiv2005

Cluster AgeS Experiment (CASE): SX Phe stars from the globular cluster Omega Centauri

We present an analysis and interpretation of oscillation spectra for all 69 SX Phoenicis stars discovered in the field of the cluster. For most of the stars we have reliable absolute magnitudes and colors. Except of one, or perhaps two, objects, the stars are cluster members. Their pulsational behaviour is very diversified. Multiperiodic variability with at least part of the excited modes being nonradial is most common but there are also many cases of high amplitude, presumably radial mode, pulsators. In a number of such cases we have evidence for two radial modes being excited. Parameters of radial mode pulsators are in most cases consistent with standard evolutionary models for stars in the mass range 0.9-1.15 Mo. However, in four cases we have evidence that the masses are significantly lower than expected. Three objects show frequency triplets that may be interpreted in terms of rotational frequency splitting of l=1 modes. Implied equatorial velocities of rotation are from 10 to over 100 km/s. Nearly all measured frequencies fall in the ranges predicted for unstable modes. Two cases of low frequency variability are interpreted as being caused by tidal distortion induced by close companions.

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arXiv2005

Cluster AgeS Experiment (CASE): Detection of a dwarf nova in the globular cluster M55

We report the detection of a dwarf nova (DN) in the core region of the globular cluster M55. Six outbursts were observed during 8 observing seasons spanning the period 1997-2004. The variable has an X-ray counterpart detected on images taken with the ROSAT telescope. Although we cannot offer proof of cluster membership, one can see that both the position on the H-R diagram and the X-ray flux are consistent with a bright DN at the cluster distance. According to our outburst statistics, no more than one similar DN could remain undetected in our field of view, centred at the cluster core.

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arXiv2004

Cluster AgeS Experiment. Catalog of Variable Stars in the Globular Cluster Omega Centauri

We present results of a photometric survey for variable stars in the field of the globular cluster Omega Centauri. The observed region was centered roughly on the cluster core and covered 644 arcmin^2. The cluster was monitored on 59 nights in 1999 and 2000. A total of 117 new variables were identified. Among them there are 16 RR Lyr-type stars, 35 SX Phe variables and 26 eclipsing binaries. A comprehensive catalog including all variable stars so far reported from the cluster field is presented. We list basic photometric properties and provide finding charts for a total of 392 objects. For 313 of them new BV light curves were obtained. The presented sample includes several interesting variables, such as SX Phe stars with extremely short periods of pulsation and several candidates for pulsating K giants. Optical counterparts to 9 X-ray sources detected by XMM and Chandra telescopes were identified: all of them are likely to be foreground variables not related to the cluster.

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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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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

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

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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arXiv1999

A photometric survey for variable stars in the globular cluster M5

We present the results of a photometric survey for variable stars in the nearby globular cluster M5. A 14.8x22.8 arcmin^2 field centered on the cluster was monitored for a total of 37 hours with a CCD camera mounted on the 1.0-m Swope telescope. Five new variables were identified: four blue stragglers which are SX Phe pulsating variables, and an eclipsing binary with an orbital period of 0.466 d. The eclipsing binary lies near the main-sequence turnoff on the cluster color-magnitude diagram. We do not confirm the variability of any of the 10 eclipsing binaries identified in the cluster field by Reid (1996) and Yan & Reid (1996). The dwarf nova M5-V101 exhibited two outbursts with full amplitudes of about 2.7 mag during our observations. A V/B-V color-magnitude diagram of the surveyed field was obtained, and a possible extreme HB star located 2 mag below cutoff of the blue HB was identified.

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arXiv1999

BVRI Observations of the Optical Afterglow of GRB 990510

We present $BVRI$ observations of the optical counterpart to the Gamma-Ray Burst (GRB) 990510 obtained with the Las Campanas 1.0-m telescope between 15 and 48 hours after the burst. The temporal analysis of the data indicates steepening decay, independent of wavelength, approaching asymptotically $t^{-0.76\pm 0.01}$ at early times ($t\ll 1 day)$ and $t^{-2.40\pm 0.02}$ at late times, with the break time at $t_0=1.57\pm 0.03 days$. GRB 990510 is the most rapidly fading of the well-documented GRB afterglows. It is also the first observed example of broad-band break for a GRB optical counterpart. The optical spectral energy distribution, corrected for significant Galactic reddening, is well fitted by a single power-law with $ν^{-0.61\pm 0.12}$. However, when the $B$-band point is dropped from the fit, the power-law becomes $ν^{-0.46\pm 0.08}$, indicating a possible deviation from the power-law in the spectrum, either intrinsic or due to additional extinction near the source or from an intervening galaxy at $z=1.62$. Broad-band break behavior broadly similar to that observed in GRB 990510 has been predicted in some jet models of GRB afterglows, thus supporting the idea that the GRB energy is beamed, at least in some cases.

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arXiv1998

RR Lyrae Variables in the Globular Cluster M55. The First Evidence for Non Radial Pulsations in RR Lyr Stars

We present the results of a photometric study of RR Lyrae variables in the field of the globular cluster M55. We have discovered nine new RR Lyrae stars, increasing the number of known variables in this cluster to 15 objects. Five of the newly discovered variables belong to Bailey type RRc and two to type RRab. Two background RRab stars are probable members of the Sagittarius dwarf galaxy. Fourier decomposition of the light curves was used to derive basic properties of the present sample of RR Lyrae variables. From an analysis of the RRc variables we obtain a mean mass of $M=0.53\pm0.03 M_\odot$, luminosity $\log L=1.75\pm0.01$, effective temperature $T_{eff}=7193\pm27$ K, and helium abundance $Y=0.27\pm0.01$. Based on the $B-V$ colors, periods and metallicities of the RRab stars we estimate the value of the color excess for M55 to be equal to $E(B-V)=0.11\pm0.03$. Using this value we derive the colors of the blue and red edges of the instability strip in M55. The blue edge lies at $(B-V)_0=0.20$ mag and the red edge lies at $(B-V)_0=0.38$ mag. We estimate the values of the visual apparent and dereddened distance moduli to be $13.65\pm0.11$ and $13.31\pm0.11$, respectively. The light curves of three of the RRc variables exhibit changes in amplitude of over 0.1 mag on the time scale of less than a week, rather short for the Blazhko effect, but with no evidence for another radial pulsational frequency. However we do detect other periodicities which are clearly visible in the light curve after removing variations with the first overtone radial frequency. This is strong evidence for the presence of non-radial pulsations, a behavior common for $δ$ Scuti stars but not yet observed among RR Lyr variables.

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arXiv1995

CCD Photometry of Dwarf Nova AL Com in Superoutburst

We report a CCD optical photometry of a dwarf nova AL Com in superoutburst. Before superhumps occurred the light curve was highly variable with dominant periods about 41 minutes and 81.5 minutes for different nights. The period of observed superhumps is 82.5 minutes and seems to be stable. The first harmonic of the basic period is also present. We detected a weak signal corresponding to period 78.1 minutes. One of the periods 78.1 or 81.5 is suspected to be a possible signature of orbital motion in the system.

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