Z. Cvetkovic

Astronomical Observatory Belgrade, Beograd, Central Serbia, Serbia

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Publications (96)81.87 Total impact

  • Z. Cvetković, R. Pavlović, S. Ninković
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    ABSTRACT: In this paper, we analyze new orbital elements and the quantities that follow from them for eight binaries: WDS 00101+3825 = HDS 23Da,Db, WDS 00321–1218 = HDS 71, WDS 04287+2613 = HDS 576, WDS 04389–1207 = HDS 599, WDS 16206+4535 = HDS 2309, WDS 17155+1052 = HDS 2440, WDS 22161–0705 = HDS 3158, and WDS 23167+3441 = HDS 3315. For seven of them, the orbital elements are calculated for the first time. Binaries, denoted as HDS, were discovered during the Hipparcos mission, and their first observational epoch is 1991.25, the same as the mean epoch of the Hipparcos catalog. We found all other measurements of these binaries in databases. They were obtained in the last 15 yr using the speckle interferometric technique. All studied pairs are close, and all measured separations are less than 0.''4. The resulting orbital periods fall within 26 and 80 yr. In addition to the orbital elements, we also give (O – C) residuals in θ and ρ, masses, dynamical parallaxes, absolute magnitudes, spectral types, and ephemerides for the next 5 yr.
    The Astronomical Journal 02/2014; 147(3):62. · 4.97 Impact Factor
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    ABSTRACT: We report the results of an extensive photometric follow-up of iPTFebh supernova (ATEL#5580, ATEL#5584) classified as type Ia at z=0.013269, located in NGC 890. The telescopes involved in the follow-up operated in the preparatory mode for the forthcoming Gaia Science Alerts follow-up network.
    01/2014;
  • G. Damljanović, Z. Cvetković
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    ABSTRACT: We present comparison results of our Independent Latitude (IL) catalogue of μδ determinations for 1120 bright stars with the Hipparcos, new Hipparcos and Earth Orientation Catalogue (EOC-2) values. Also, we took into consideration the EOC3 and EOC4 (recent versions of EOC catalogues). Our μδ values are based on zenith telescope observations from seven Independent Latitude (IL) observatories. The IL measures are spanning a time baseline of up to 90 years which is the key advantage to the accurate determination of μδ. The short interval of the Hipparcos satellite observations is a disadvantage for a good accuracy of stellar proper motion, especially in the case of double and multiple stars. For this reason many astrometric catalogues have appeared after the publication of the Hipparcos including our IL catalogue. These catalogues are an appropriate combination of the Hipparcos satellite and ground-based data which yields more accurate stellar coordinates and/or their proper motions. Among various types of ground-based observations the latitude and universal time variations obtained from several million observations of stars reduced to the Hipparcos reference system were used for this purpose. These observations were obtained during almost the entire last century and were originally used to determine the Earth Orientation Parameters. It is also possible to use these data in the inverse task of checking the accuracy of stellar coordinates and/or their proper motions listed in the Hipparcos Catalogue. Such latitude and universal time variations data are the basis of the EOC and IL catalogues. In this paper, we computed the differences in μδ values between pairs of catalogues and analyzed the results to characterize the μδ errors for the four catalogues with a special focus on our IL catalogue. The standard errors of μδ for IL stars observed over more than 20 years are mostly smaller than or equal to the Hipparcos errors, and close to the accuracy level of the EOC-2 (EOC-3, EOC-4) and the new Hipparcos. The resulting investigations of errors of differences of μδ, show that all four catalogues have relatively small random and systematic errors which are close to each other meaning that the corresponding μδ values have a high accuracy. Our sample also contains detected double and multiple stars for which the effects of the orbital and proper motions are difficult to separate. The differences of μδ values for these stars generally exceed those obtained for single stars. Also, these discrepancies could be attributed to effect of possible, still unrecognized, astrometric binaries. These investigations about the proper motions and double stars are in line with the activity of the IAU Working Group on Astrometry by Small Ground-Based Telescopes. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Astronomische Nachrichten 08/2013; 334(7). · 1.12 Impact Factor
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    ABSTRACT: Using the 2 m telescope of the Bulgarian National Astronomical Observatory at Rozhen, observations of 222 double or multiple stars were carried out during three nights in 2011. This is the sixth series of measurements of CCD frames of double and multiple stars obtained at Rozhen. Also in 2011, using the 0.6 m telescope of the Serbian Astronomical Station on the mountain of Vidojevica, observations of 208 double or multiple stars were carried out during six nights. This is the first series of measurements of CCD frames of double and multiple stars obtained at this station. In this paper, we present the results for the position angle and angular separation for 337 pairs and residuals for 72 pairs with published orbital elements or linear solutions. These observations have angular separations in the range from 1.''37 to 172.''81, with a median angular separation of 7.''66. We also present the recalculated linear solutions for four pairs and one linear solution that has been calculated for the first time.
    The Astronomical Journal 07/2013; 146(3):52. · 4.97 Impact Factor
  • Viktor Radovic, R. Pavlovic, Zorica Cvetkovic
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    ABSTRACT: We discuss the software developed for the purpose of determining the relative coordinates (position angle θ and separation ρ) for visual double or multiple stars. It is based on application of Fourier transforms in treating CCD frames of these systems. The objective was to determine the relative coordinates automatically to an extent as large as possible. In this way the time needed for the reduction of many CCD frames becomes shorter. The capabilities and limitations of the software are examined. Besides, the possibility of improving is also considered. The software has been tested and checked on a sample consisting of CCD frames of 165 double or multiple stars obtained with the 2m telescope at NAO Rozhen in Bulgaria in October 2011. The results have been compared with the corresponding results obtained by applying different software and the agreement is found to be very good.
    Serbian Astronomical Journal 06/2013; · 1.10 Impact Factor
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    ABSTRACT: On the basis of the first frames obtained by using CCD cameras SBIG ST-10ME and Apogee Alta U42 attached to the 60 cm telescope at Vidojevica, we report the measurements of double and multiple stars and the parameters of the limiting capabilities of the telescope and weather conditions. We also present the results for the position angle, angular separation and residuals for 10 star pairs with published orbital elements or linear solutions. The first linear fits are presented for 2 star pairs of the multiple system ADS 48.
    Publications de l'Observatoire Astronomique de Beograd. 12/2012;
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    ABSTRACT: In this paper, we analyze seven components of system ADS 48. Its number in the Washington Double Star Catalog is 00057+4549. We use the measuring results from our CCD frames obtained between 1994 and 2011. Our aim is to establish which of these components are gravitationally bound, i.e., have an orbital motion around the mass center, and which of them are mutually very distant in space so that only their projections are close in the field of view. In addition to the measurements, we also apply different criteria based on celestial mechanics. Out of seven considered components, only the closest pair STT 547 AB is in orbital motion around the mass center. The other components, except that with the largest separation, are merely projected stars. The most distant component has common proper motion with pair AB.
    The Astronomical Journal 08/2012; 144(3):80. · 4.97 Impact Factor
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    ABSTRACT: The focal length of a telescope is an important parameter in determining the angular pixel size. This parameter is used for the purpose of determining the relative coordinates (angular separation and positional angle) of double and multiple stars, and the precise coordinates of extragalactic radio sources (ERS) that are visible at optical wavelengths. At the Astronomical Station Vidojevica we have collected observations of these objects using two CCD cameras, Apogee Alta U42 and SBIG ST-10ME, attached to the 60 cm telescope. Its nominal focal length is 600 cm as given by the manufacturer. To determine the telescope focal length more precisely for both attached detectors, we used angular-separation measurements from CCD images taken at Astronomical Station Vidojevica. The obtained focal lengths are: F_{42} = (5989±7) mm using the CCD camera Apogee Alta U42 attached to the telescope, and F_{10} = (5972±4) mm with the CCD camera SBIG ST-10ME attached to the telescope.
    Serbian Astronomical Journal 06/2012; · 1.10 Impact Factor
  • Z. Cvetković, S. Ninković
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    ABSTRACT: We consider a sample of 432 visual binaries having orbital elements and belonging to the Main Sequence. We calculate their total masses using the orbital elements and the new Hipparcos parallaxes by applying Kepler's third law. For the same pairs the total masses are also found by applying the mass-luminosity relation. The source for the apparent magnitudes is the Washington Double Star Catalog. The Keplerian total masses show a large scatter. Nevertheless, in a large number of cases the agreement between total masses obtained in these two different ways is quite satisfactory indicating that i) for many visual binaries, as a rule not too distant and with high-quality orbital elements, the Keplerian total masses can be reliable and ii) a correlation between the relative parallax error and orbit grade exists.
    Astronomical and Astrophysical Transactions 01/2012;
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    ABSTRACT: In this paper we present observations of double and multiple stars by using the 2-m telescope of the Bulgarian National Astronomical Observatory at Rozhen in the period from 2004 to 2011. The results of these measurements, i.e. position angles and angular separations, were used for calculation of the orbital or the linear elements. Two new and three recalculated orbits of binaries were obtained. Also, new linear solutions for three pairs are given.
    Bulgarian Astronomical Journal. 01/2012;
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    ABSTRACT: Using the 2 m telescope of the Bulgarian National Astronomical Observatory at Rozhen, observations of 145 double or multiple stars were carried out during three nights on 2010 September 7-9. This is the fifth series of measurements of CCD frames of double and multiple stars obtained at Rozhen. In this paper, we present the results for the position angle and angular separation for 202 pairs and residuals for 45 pairs with published orbital elements or linear solutions. These observations have angular separations in the range 1150-196372, with a median angular separation of 57906. Three linear solutions are presented for the first time and three orbits are recalculated (one pair has both a linear fit and an orbital solution).
    The Astronomical Journal 08/2011; 142(3):73. · 4.97 Impact Factor
  • Z. Cvetkovic, S. Ninkovic
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    ABSTRACT: In the Sixth Catalog of Orbits of Visual Binary Stars we found those belonging to the Main Sequence to form a sample containing 432 visual binaries. Their total masses were obtained dynamically, i.e. they were calculated using the orbital elements and the new Hipparcos parallaxes. For the same pairs the total mass was also found astrophysically - by applying the mass-luminosity relation. The apparent magnitudes of the components were found in two different ways: by deriving them from total magnitudes and magnitude differences, and by taking their values directly from a catalogue. The results for these two approaches show no essential discrepancy. The values of total masses obtained dynamically have a large dispersion involving even completely unrealistic values. This is a clear indication that the input data are not sufficiently reliable. Nevertheless, in a large number of cases the agreement between total masses obtained by us in two different ways is quite satisfactory indicating that i) for many visual binaries, as a rule not too distant and with high-quality orbital elements, the dynamical total masses can be reliable; ii) the mass-luminosity relation yields quite satisfactory estimates for the component masses when they belong to the Main Sequence and iii) a correlation between the relative parallax error and orbit grade exists. (3 data files).
    VizieR Online Data Catalog. 04/2011;
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    Z. Cvetković
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    ABSTRACT: In this paper, we analyze new orbital elements, and quantities that can be derived from them, for six binaries. For four of them, WDS 00251+4803 = HDS 56, WDS 01071–0036 = HDS 144 AB, WDS 06426+3955 = HDS 930, and WDS 21014+4037 = HDS 2995, the orbital elements are calculated for the first time. For the other two, WDS 04195+3800 = HDS 552 and WDS 23209+1643 = HEI 88, the orbital elements are recalculated. Five binaries, denoted as HDS, were discovered during the Hipparcos mission while the remaining binary was discovered somewhat earlier. HEI 88 was measured for the first time in 1978. All studied pairs are close, with almost all measured separations less than 0.3 arcsec. For these binaries the observations were usually performed using the speckle-interferometric technique with the exception of HEI 88, which was observed visually on eight occasions. The resulting orbital periods fall within 13 and 69 years. In addition to the orbital elements, we also give (O-C) residuals in θ and ρ, masses, dynamical parallaxes, absolute magnitudes, spectral types, and ephemerides for the next five years.
    The Astronomical Journal 02/2011; 141(4):116. · 4.97 Impact Factor
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    Z. Cvetkovic, S. Ninkovic, I. Vince
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    ABSTRACT: The orbit of 15 Mon (close pair CHR 168 Aa-Ab) was recently calculated on the basis of speckle measurements only. Four new measurements, performed after the orbit calculation, satisfy this orbit very well. The orbital elements and the mass values expected for the components, as well as their distance moduli, result in a distance of 15 Mon in a very good agreement with the distance to NGC 2264, but disagrees with the trigonometric distance of the binary. On the basis of the orbital elements and mass ratio the line-of-sight velocity of the binary mass centre is determined. It is found that the value of this velocity is within the limits expected for stars belonging to NGC 2264. Its difference from the expected mean in the field of NGC 2264 agrees well with the value mentioned in the literature.
    Publications de l'Observatoire Astronomique de Beograd. 09/2010;
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    Z. Cvetković, R. Pavlović, and S. Ninković
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    ABSTRACT: In this paper, new orbital elements for visual pair WDS 19531–1436 = CHR 90 of the triple system V505 Sgr obtained from speckle interferometric measurements are reported. The first speckle measurement was in 1985 and 22 more speckle measurements have been made since then. For this binary, orbits were previously determined. Our orbit has a period of 94 years, and it is significantly longer than those previously found. In addition to the orbital elements in this paper, the mass, dynamical parallax, and ephemerides for the next five years are also given.
    The Astronomical Journal 05/2010; 140(1):25. · 4.97 Impact Factor
  • Z. Cvetković, B. Novaković
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    ABSTRACT: In this paper new orbital elements are given for eleven binaries. For eight of them, WDS 00003–4417 = I 1477, WDS 00106–7313 = I 43 AB, WDS 00366+5609 = A 914, WDS 00519–4343 = I 47, WDS 01315+1521 = BU 506, WDS 01577+4434 = A 1526, WDS 08144–4550 = FIN 113 AB and WDS 08291–4756 = FIN 315 Aa-Ab, the orbital elements are calculated for the first time. For three of them, WDS 04422+2257 = MCA 16 Aa-Ab, WDS 08275–5501 = FIN 116 and WDS 14567–6247 = FIN 372, the orbital elements are recalculated. One of the eleven binaries, MCA 16 Aa-Ab, was discovered by McAlister in 1980 by speckle interferometry and four pairs were discovered by Finsen between 1929 and 1960. For these five pairs, all measured separations are less than 0″.4 and most of the observations were done by using the interferometric techniques. The orbital periods calculated here are between 39 and 270 years. The remaining six pairs were discovered between 1878 and 1926 and most of the observations are visual. They have longer orbital periods, between 384 and 1637 years. In addition to the orbital elements the masses, dynamical parallaxes, absolute magnitudes and ephemerides for the next five years are also given in this paper (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Astronomische Nachrichten 03/2010; 331(3):304 - 311. · 1.12 Impact Factor
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    Zorica Cvetkovic, Bojan Novakovic
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    ABSTRACT: In this paper new orbital elements are given for eleven binaries. For eight of them, WDS 00003-4417 = I 1477, WDS 00106-7313 = I 43 AB, WDS 00366+5609 = A 914, WDS 00519-4343 = I 47, WDS 01315+1521 = BU 506, WDS 01577+4434 = A 1526, WDS 08144-4550 = FIN 113 AB and WDS 08291-4756 = FIN 315 Aa-Ab, the orbital elements are calculated for the first time. For three of them, WDS 04422+2257 = MCA 16 Aa-Ab, WDS 08275-5501 = FIN 116 and WDS 14567-6247 = FIN 372, the orbital elements are recalculated. One of the eleven binaries, MCA 16 Aa-Ab, was discovered by McAlister in 1980 by speckle interferometry and four pairs were discovered by Finsen between 1929 and 1960. For these five pairs, all measured separations are less than 0".4 and most of the observations were done by using the interferometric techniques. The orbital periods calculated here are between 39 and 270 years. The remaining six pairs were discovered between 1878 and 1926 and most of the observations are visual. They have longer orbital periods, between 384 and 1637 years. In addition to the orbital elements the masses, dynamical parallaxes, absolute magnitudes and ephemerides for the next five years are also given in this paper.
    Astronomische Nachrichten 03/2010; 331(3):304. · 1.12 Impact Factor
  • Z. Cvetković, I. Vince, S. Ninković
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    ABSTRACT: In the paper new orbital elements for 15 Mon obtained from speckle interferometric measurements only are reported. The first speckle measurement originates from 1988 and up to now seven more speckle measurements have been made. For this binary orbits were determined earlier by combining spectroscopic and speckle measurements and spectroscopic and astrometric measurements. New speckle measurements dating after the periastron passage have a significant discrepancy from the ephemeridal values. Our orbit has a period significantly longer than the earlier ones. In the case of the earlier orbits the period was determined from radial velocity data. The existing data of such kind for this binary are reanalyzed here and combined with our orbital elements. Binary 15 Mon is a member of open cluster NGC 2264. The distance to this cluster has been determined many times and different values have been reported. By analyzing the available data we find that the distance to 15 Mon is most likely about 720 pc. Our new orbital elements combined with this distance yield a total mass of 59.1M⊙. This is in a good agreement with values expected according to the spectral types of the components (primary O7V, secondary O9.5Vn).
    New Astronomy 03/2010; · 1.24 Impact Factor
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    Zorica Cvetkovic, S. Ninkovic
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    ABSTRACT: In the Sixth Catalog of Orbits of Visual Binary Stars we found those belonging to the Main Sequence to form a sample containing 432 visual binaries. Their total masses were obtained dynamically, i.e. they were calculated using the orbital elements and the new Hipparcos parallaxes. For the same pairs the total mass was also found astrophysically - by applying the mass-luminosity relation. The apparent magnitudes of the components were found in two different ways: by deriving them from total magnitudes and magnitude differences, and by taking their values directly from a catalogue. The results for these two approaches show no essential discrepancy. The values of total masses obtained dynamically have a large dispersion involving even completely unrealistic values. This is a clear indication that the input data are not sufficiently reliable. Nevertheless, in a large number of cases the agreement between total masses obtained by usin two different ways is quite satisfactory indicating that i) for many visual binaries, as a rule not too distant and with high-quality orbital elements, the dynamical total masses can be reliable; ii) the mass-luminosity relation yields quite satisfactory estimates for the component masses when they belong to the Main Sequence and iii) a correlation between the relative parallax error and orbit grade exists.
    Serbian Astronomical Journal 01/2010; · 1.10 Impact Factor
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    Z. Cvetkovic, R. Pavlovic, S. Boeva
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    ABSTRACT: Using the 2 m telescope of the Bulgarian National Astronomical Observatory at Rozhen observations of 30 double or multiple stars were carried out during two half nights on July 20and 21, 2009. This is the fourth series of measurements of CCD frames of double and multiple stars obtained at Rozhen. In this paper we present the results for the position angle and separation for 23 double and 5 multiple stars (35 pairs) which could have been measured.
    Serbian Astronomical Journal 01/2010; · 1.10 Impact Factor