Variations in the light curve of V 505 Sagittarii and their interpretation

Details Variations in the light curve of V 505 Sagittarii and their interpretation Variations in the light curve of V 505 Sagittarii and their interpretation

Sep 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26a...101..369w&link_type=abstract

Astronomy and Astrophysics, vol. 101, no. 3, Sept. 1981, p. 369-376.

Astronomy and Astrophysics

Astrophysics

14

Eclipsing Binary Stars, Light Curve, Periodic Variations, Variable Stars, Annual Variations, Brightness Distribution, Electrophotometry, Sagittarius Constellation, Ubv Spectra

Scientific paper

UBV observations of V 505 Sgr, obtained between 1972 and 1979 at La Silla and published in a separate paper (Paper I), are discussed. For the epoch 1976-78 conspicuous deformations, especially in the second half of the light curves, and an increase of the orbital period were found. It seems probable that also the increased brightness of the system which was observed in B and U in 1978 (in 1977 no observations were made) was connected with the active phase of increased mass transfer.
For the first quarter of the light curve outside primary eclipse (section a) and for observations during the secondary eclipse the deviations of the single observations from the mean light curves showed clear variations with a period of somewhat more than 300d. Because of the change of period after 1976 for the mean light curves of the primary eclipse only the observations from 1972-76 were used. The deviations of the single observations at primary eclipses from the mean values were found to be surprisingly large for the "normal" years 1972-75. Since the depth of the primary and the secondary minima showed an opposite long period variation, it seemed most efficient to test the differences of the depths of both minima in dependence on time. These differences were found to vary by about 0m.05 with the long period. A similar variation of these differences could be derived from the photoelectric observations of V 505 Sgr which were obtained in 1949-53 by Magalashvili and Razmadze (1953). The most probable value of the long period seems to be 310d.
This period is interpreted to be the precessional period of the rotational axis of the primary component, which is somewhat inclined against the orbital plane. In a first rough outline it could be made probable that this hypothesis is suited for a model by which the observed phenomena could be explained. The results show the importance to observe Algol systems over long intervals. In particular, systems with partial eclipses give here chances to study unequal distributions of brightness on the disks of the primary components, which are connected with the changing position of the axes.

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