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 59.1 Mȯ. This is in a good agreement with values expected according to the spectral types of the components (primary O7V, secondary O9.5Vn). © 2009 Elsevier B.V. All rights reserved.
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