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The past several decades have seen accelerating progress in improving binary stars fundamental parameters determinations, as new observational techniques have produced visual orbits of many spectroscopic binaries with a milli arcsecond precision. Modern astrometry is rapidly approaching the goal of sub-milli arcsecond precision, and although presently this precision has been achieved only for a limited number of binary stars, in the near future this will become a standard for very large number of objects. In this paper we review the representative results of techniques which have already allowed the sub-milli arcsecond precision like the optical long baseline interferometry, as well as the precursor techniques such as speckle interferometry, adaptive optics and aperture masking. These techniques provide a step forward from milli to sub-milli arcsecond precision, allowing even short period binaries to be resolved, and often resulting in orbits allowing precisions in stellar dynamical masses better than 1%. We point out that such unprecedented precisions should allow for a significant improvement of our comprehension of stellar physics and other related astrophysical topics. [ABSTRACT FROM AUTHOR]

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) [ABSTRACT FROM AUTHOR]

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: F42 = (5989 ± 7) mm using the CCD camera Apogee Alta U42 attached to the telescope, and F10 = (5972 ± 4) mm with the CCD camera SBIG ST-10ME attached to the telescope. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The total masses of binaries are calculated on the basis of their orbital elements from the Sixth Catalog of Orbits of Visual Binary Stars. They are then compared with the values resulted from the mass-luminosity relation for the Main Sequence where as the input data are used: trigonometric parallax, total apparent magnitude of the pair (source Hipparcos Catalogue) and magnitude difference (source Hipparcos Catalogue and Photometric Magnitude Difference Catalog). It seems that for the pairs indicated as having qualitative orbital elements the agreement between the total-mass values obtained in these two ways is satisfactory. [ABSTRACT FROM PUBLISHER]