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1

Fundamental Parameters of the Open Cluster Kronberger

Sujatha S., Krishna Kumar K., Komala S.

Acta Astronomica

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2016

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Vol. 66, No. 3

333--345

EN

In this paper, we present the fundamental physical parameters and the present-day mass function of the open cluster Kronberger 1. The cluster radius is estimated to be 3′ and the interstellar extinction E(B-V) in the line-of-sight of the cluster is found to be 0.45±0.05 mag. This cluster is located in the direction of Auriga constellation at a distance of 2.5±0.2 kpc. From the appropriate theoretical isochrones, the log(age) of the cluster is found to be 7.65. The mass function slope for Kronberger 1 is derived for the first time and it is estimated to be α = 2.72±0.2 which is in agreement with the slope of α = 2.35 given by Salpeter. Similar results are obtained from a near infrared study performed using data from the Two Micron All Sky Survey thus substantiating the results obtained from the optical analysis. These results indicate that Kronberger 1 is a suitable object for mapping the spiral arm structure of our Galaxy and for understanding the behavior of mass function in the Galactic disk.

2

Concerning the Distance to the Center of the Milky Way and Its Structure

Majaess D.

Acta Astronomica

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2010

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Vol. 60, No. 1

55--74

EN

The distance to the Galactic center inferred from OGLE RR Lyr variables observed in the direction of the bulge is R0=8.1±0.6 kpc. An accurate determination of R0 is hindered by countless effects that include an ambiguous extinction law, a bias for smaller values of R0 because of a preferential sampling of variable stars toward the near side of the bulge owing to extinction, and an uncertainty in characterizing how a mean distance to the group of variable stars relates to R0. A VI-based period-reddening relation for RR Lyr variables is derived to map extinction throughout the bulge. The reddening inferred from RR Lyr variables in the Galactic bulge, LMC, SMC, and IC 1613 match that established from OGLE red clump giants and classical Cepheids. RR Lyr variables obey a period-color (VI) relation that is relatively insensitive to metallicity. Edge-on and face-on illustrations of the Milky Way are constructed by mapping the bulge RR Lyr variables in tandem with cataloged red clump giants, globular clusters, planetary nebulae, classical Cepheids, young open clusters, HII regions, and molecular clouds. The sample of RR Lyr variables do not trace a prominent Galactic bar or triaxial bulge oriented at φ≅25°.

3

The Distance to the Magellanic Clouds

Paczyński B.

Acta Astronomica

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2001

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Vol. 51, No. 2

81--89

EN

The distance to the LMC and SMC is a subject of controversy, with the difference between the extreme values in distance moduli exceeding 0.5 mag. While currently the best calibrated method is based on red clump giants, and the near future improvement is most likely to come from detached eclipsing binaries, the ultimate goal is to have a purely geometrical determination. The best prospect will be to use relatively wide binary stars, for which spectroscopic orbits will be obtained with large ground based telescopes, and astrometric orbits will be obtained either with SIM, or with future ground based interferometers. A preliminary list of 25 candidate systems is presented. It is based on OGLE catalogs of BVI photometry.

4

Surface Brightness-Color Relation for Eclipsing Binaries with ubvy Photometry

Semeniuk I.

Acta Astronomica

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2001

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Vol. 51, No. 1

75--80

EN

The relation between visual surface brightness and (b-y)0 color index is constructed for eclipsing binaries with Hipparcos parallaxes and photometry in the Strömgren four-color ubvy system. The relation is consistent with the Popper relation derived for stars with angular diameters obtained mainly from interferometry or from the lunar occultation method. It is shown that the Lutz-Kelker correction to magnitudes is in this case negligible.

5

Eclipsing Binaries and the Lutz-Kelker Bias

Jerzykiewicz M.

Acta Astronomica

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2001

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Vol. 51, No. 2

151--158

EN

Using examples from the literature, we demonstrate that ignoring the Lutz-Kelker bias may degrade agreement between results derived from eclipsing binaries and those based on trigonometric parallaxes. In addition, we show that eclipsing binaries are excellent standard candles.

6

Comparison of Parallaxes from Eclipsing Binaries Method with Hipparcos Parallaxes

Semeniuk I.

Acta Astronomica

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2000

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Vol. 50, No. 3

381--386

EN

The parallaxes determined by Lacy (1979) by means of eclipsing binaries method are compared with the Hipparcos parallaxes for 19 systems. The residual scatter of the distance moduli inferred from eclipsing binaries method - after allowing for known errors as given by Lacy and Hipparcos - is equal to 0.18 mag. It decreases to 0.08 mag when obviously not fitting semi-detached systems and systems with chromospheric activity of components are removed from the sample.

7

Nearby Hipparcos Eclipsing Binaries for Color - Surface Brightness Calibration

Kruszewski A., Semeniuk I.

Acta Astronomica

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1999

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Vol. 49, No. 4

561--575

EN

This paper contains the list of Hipparcos eclipsing binaries that fulfill the following conditions: the star is classified in the Hipparcos Catalogue as EA-type eclipsing binary and its parallax is either larger than 5 mas or it is five times larger than its mean error. An eclipsing binary with known distance and with photometric and double-line spectroscopic orbits determined can be used in the process of calibrating the relation between the stellar surface brightness and the color that is crucial for the method of the distance determination by means of eclipsing binaries. This list is being published in order to draw attention of observers using small telescopes to these bright, potentially useful and in the most cases poorly observed objects. The advantages of the eclipsing binary method of the distance determination are discussed.

8

BVI CCD Photometry of the Globular Cluster 47 Tuc

Kaluzny J., Wysocka A., Stanek K. Z., Krzemiński W.

Acta Astronomica

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1998

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Vol. 48, No. 3

439--453

EN

We present BVI photometry for about 16000 stars from a 220 square arcmin field centered 8 arcmin East of the center of 47 Tuc. We have identified eight likely blue stragglers located in the outer parts of the cluster. Four of these objects are easy targets for spectroscopic studies with ground-based telescopes. Six candidates for blue horizontal branch stars were identified. However, it is possible that all or most of them belong in fact to the SMC halo. One faint blue star being candidate for a cataclysmic variable was found close to the cluster center. The average I-band magnitude for stars forming the red giant branch clump is determined at I0=13.09±0.005 mag. This in turn implies distance modulus of the cluster (m-M)0,47Tuc=13.32±0.03±0.036 mag (statistical plus systematic error), if we adopt MI,m=-0.23±0.03 mag for the average absolute luminosity of Hipparcos-calibrated clump giants, following Paczyński and Stanek and Stanek and Garnavich. This distance modulus of 47 Tuc is lower by 0.2-0.25 mag than its recent estimates based on Hipparcos parallaxes for subdwarfs. We discuss possible reasons for this discrepancy. The photometric data are available through the anonymous ftp service.