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Optical and Near Infrared Study of the Open Cluster Czernik 17

Sujatha S., Krishna K. K., Komala S., Babu G. S. D.

Acta Astronomica

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2015

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Vol. 65, No. 3

283--295

EN

In this paper we present the fundamental physical parameters of the poorly studied open cluster Czernik 17. The parameters have been derived from the UBVRI CCD photometric observations obtained with the 2-m Himalayan Chandra Telescope as well as using data taken from the Two-Micron All Sky Survey. This cluster is located in the direction of Camelopardalis constellation with a radial extent of 4' and is estimated to be at a distance of 7 ± 0.5 kpc. The interstellar extinction in the line of sight of the cluster is found to be E(B-V) = 0.72 ± 0.05 mag. Based on the evolutionary stage of the evolved stars the log(age) of the cluster is found to be 8.05 to 8.1 making it a relatively young cluster which can be considered as a spiral arm tracer of the outer arm. We have constructed the luminosity function for the stars within the adopted cluster radius which shows the common trend of the number of stars increasing toward the fainter magnitudes. We also find the presence of Böhm-Vitense gaps in the main-sequence branch of the color-magnitude diagrams of this cluster which may be attributed to surface convection which has the effect of making the stars redder although the luminosity remains unchanged.

2

Statistical Indicators of Astrophysical Parameters

Wąż P., Bielińska-Wąż D., Strobel A., Pleskacz A.

Acta Astronomica

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2010

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Vol. 60, No. 3

283--293

EN

The aim of this paper is to introduce a new tool for a simple identification of spectral types. We use methods of statistical spectroscopy, in particular the method of intensity-distribution moments. The statistical approach revealed a characteristic behavior of moments of the stellar spectra for different spectral types. The transition from one spectral type to another may be expressed as a regular function of appropriate moments of the intensity distribution of the spectra. Moment-based diagrams localize particular spectral types in different areas of the plots. Since the intensity-distribution moments may be easily derived from the observed spectra, the presented method facilitates a simple auxiliary tool for the classification of stars to specific spectral types. It is also helpful in checking the correctness of the existing classifications. The intensity-distribution moments depend on all kinds of stellar characteristics, including the metallicity and the age. Therefore, using an inverse approach, from the knowledge of moments one may predict these properties.

3

Hα Imaging of X-ray Sources in Selected Globular Clusters with the SOAR Telescope

Pietrukowicz P.

Acta Astronomica

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2009

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Vol. 59, No. 3

291--305

EN

We present results of a search for objects with Hα excess, such as cataclysmic variables (CVs) and chromospherically active binaries (ABs), as counterparts to X-ray sources detected with Chandra satellite observatory in six Galactic globular clusters (GCs): M4, M28, M30, M71, M80, NGC 6752. Binary systems play a critical role in the evolution of GCs, serving as an internal energy source countering the tendency of GC cores to collapse. Theoretical studies predict dozens of CVs in the cores of some GCs (eg., 130 for M28, 40 for M30). A number of such binaries is also expected outside the core radius. However, few CVs are known so far in GCs. Using subtraction technique applied to images taken with the 4.1-m SOAR telescope we have found 27 objects with Hα excess in the field of the observed clusters, of which nine are likely associated with the clusters. Four are candidate CVs, four are candidate ABs, one could be either a CV or an AB. One Hα object seems to be a background galaxy, while other 17 detected objects are probably foreground or background stars.

4

Planets in Stellar Clusters Extensive Search. V. Search for Planets and Identification of 18 new Variable Stars in the Old Open Cluster NGC 188

Mochejska B. J., Stanek K. Z., Sasselov D. D., Szentgyorgyi A. H., Cooper R. L., Hickox R. C., Hradecky V., Marrone D., P., Winn J. N., Schwarzenberg-Czerny A.

Acta Astronomica

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2008

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Vol. 58, No. 3

263--278

EN

We have undertaken a long-term project, Planets in Stellar Clusters Extensive Search (PISCES), to search for transiting planets in open clusters. In this paper we present the results for NGC 188, an old, rather populous cluster. We have monitored the cluster for more than 87 hours, spread over 45 nights. We have not detected any good transiting planet candidates. We have discovered 18 new variable stars in the cluster, bringing the total number of identified variables to 28, and present for them high precision light curves, spanning 15 months.

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CURiuos Variables Experiment (CURVE): Variable Stars in the Metal-Poor Globular Cluster M56

Pietrukowicz P., Olech A., Kędzierski P., Złoczewski K., Wiśniewski M., Mularczyk K.

Acta Astronomica

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2008

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Vol. 58, No. 2

121--130

EN

We surveyed a 6.5'×6.5' field centered on the globular cluster M56 (NGC 6779) in a search for variable stars detecting seven variables, among which two objects are new identifications. One of the new variables is an RRLyrae star, the third star of that type in M56. Comparison of the new observations and old photometric data for an RV Tauri variable V6 indicates a likely period change in the star. Its slow and negative rate of -0.005±0.003 d/yr would disagree with post-AGB evolution, however this could be a result of blue-loop evolution and/or random fluctuations of the period.

6

CURious Variables Experiment (CURVE). CCD Photometry and Variable Stars in the Field of Open Cluster NGC 637

Pietrukowicz P., Olech A., Wiśniewski M., Kędzierski P., Mularczyk K., Złoczewski K., Starczewski S., Szaruga K.

Acta Astronomica

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2006

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Vol. 56, No. 3

267--275

EN

We present VI photometry for the open cluster NGC 637 which is located in the Cassiopeia region. Morphology of cluster color-magnitude diagram indicates that it is a young object with age of a few million years. The apparent distance modulus of the cluster is 13.9<(m-M)V<14.3 mag, while reddening is 0.69

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

Kaluzny J.

Acta Astronomica

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2003

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Vol. 53, No. 1

51--62

EN

Two sets of archive time series observations of an old open cluster NGC 6791 were reanalyzed using an image subtraction technique. We report identification of four new variable stars. 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 analyzed 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.

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Empirical Luminosities and Radii of Early-Type Stars after Hipparcos

Jerzykiewicz M., Molenda-Żakowicz J.

Acta Astronomica

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2000

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Vol. 50, No. 3

369--380

EN

Using Hipparcos parallaxes we derive empirical luminosities and radii of the early-type stars for which the effective temperatures are known from directly measured angular diameters and total absolute fluxes. The empirical luminosities allow a direct comparison of the position of these stars in the fundamental HR diagram with evolutionary tracks. The comparison shows an overall agreement with the Y=0.30 and Z=0.02 tracks computed with OPAL opacities and moderate amount of overshooting from the convective core. In addition, we present evidence that systematic errors of the masses read off the evolutionary tracks are below 10%. Consequently, the surface gravities obtained from these "evolutionary" masses and the empirical radii are very nearly model-independent. Spectrographic and photometric observations of these stars can therefore be used for verifying model atmospheres and calibrating photometric log g indices.