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The New Photometric Study of a Possible Three-body System AV CMi



We present new results based on the photometric study of an eclipsing object AV CMi. Liakos and Niarchos (2010) obtained preliminary parameters of the system from photometric measurements and discovered a possible low-mass third body which they placed on an unusual inner orbit around one of the binary components. We confirmed depressions in the light curve and analysed observed changes in the whole light curve. The third body system explanation was tested, but we suggest a new, more realistic, alternative interpretation: a blend of two eclipsing binaries with periods of 2.277751 d and 1.03843 d. Astrometric measurements of the centroid position unfortunately yield no evidence about their angular separation.
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In 1986 Svechnikov M.A. had published the "Catalogue of orbital elements, masses and luminosities" [1] of 246 eclipsing binary systems with known photometric and spectroscopic elements on comparatively early stages of their evolution (on the stage of the main sequence and during or after the "first change of mass") and belonging to DM, SD, DS, KE, KW, DW and AR evolutionary types (see lower) according to Svechnikov's classification [2,3,4]. However the representative eclipsing systems in this catalogue make up only a small share (about 5%) from discovered ones to all eclipsing variable stars of mentioned types (the general catalogue of variable stars [5] (which is called further GCVS IV) contains the information approximately of about 5000 eclipsing binary stars of different types). It is of a great interest for statistic research to give if only the approximate estimations of relative and absolute elements of those systems for which elements of the spectroscopic orbits are unknown and the direct calculation of their absolute characteristics is impossible. For this approximate estimation the statistic relations (mass - luminosity, mass - radius, mass - spectrum etc.) obtained for the components of different type systems [6-9] and a number of other statistic dependences which have been found from study of 246 eclipsing systems mentioned (for example, the dependence of orbital inclination I on the depth of main minimum A1, the dependence of the main component spectral classes for the KE- and KW-systems on the period P etc.) were used. For definition of the approximate elements it was used the information from GCVS IV about the morphological type of systems (EA, EB, EW), its period, the spectral classes of systems, amplitudes A1 and A2 of the main and second minima, duration of eclipse D1 and duration of constant light phase D2 in the main minimum etc., it was made the classification of eclipsing variable stars with the help of a simple test, worked out in [4], and the statistic dependences obtained for the stars of a given type was used later on the question about reliability of approximate relative and absolute elements which have been founded by this way was studied earlier in [8]. The accuracy of these elements is essentially higher for systems with certain spectra of main components (SP1). This fact was taken into account in catalogue by giving the essentially a higher weights to elements of those systems. There are about 1200 systems with the certain meaning SP1 in our catalogue, it is about 1/3 from all eclipsing systems in it. On the whole the elements (with different reability) for about 3800 eclipsing variable stars of DM, SD, DS, KE, KW and DW types are given in catalogue which makes up the overwhelming majority of eclipsing variable stars with the certain period from GCVS IV. Because of the possible mistakes in our classification wrong or incomplete data given in GCVS IV and also because of the fact that used statistic dependences for definition of elements have an approximate character, it should be expect that founded in catalogue the approximate elements for many systems are inaccurate and even wrong. By our estimation, elements will be grossly wrong for about 10-15% of systems given in this catalogue (which principally have a small weights), for about 20- 25% of systems the founded elements will turn out essentially different from veritable, however, we hope that for 60-70% of systems the photometric and absolute elements will turn out quite similar to elements which will be received the more exact methods later on. The elements, given in catalogue, may be used in the different statistic researches and also as an initial approximation for the calculation of photometric and absolute elements of these eclipsing stars with more exact methods. (4 data files).
The tasks of the DAOPHOT program, developed to exploit the capability of photometrically linear image detectors to perform stellar photometry in crowded fields, are discussed. Raw CCD images are prepared prior to analysis, and following the obtaining of an initial star list with the FIND program, synthetic aperture photometry is performed on the detected objects with the PHOT routine. A local sky brightness and a magnitude are computed for each star in each of the specified stellar apertures, and for crowded fields, the empirical point-spread function must then be obtained for each data frame. The GROUP routine divides the star list for a given frame into optimum subgroups, and then the NSTAR routine is used to obtain photometry for all the stars in the frame by means of least- squares profile fits. The process is illustrated with images of stars in a crowded field, and shortcomings and possible improvements of the program are considered.
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