Anomalous O`Connell effect in early-type contact binaries
Authors:
Pribulla, T., Vanko, M., Chochol, D., Hambalek, L., Parimucha, S.
Image & caption:
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Image caption::
The O’Connell effect for all contact binaries identified in the Hipparcos catalogue. Contact binaries in multiple systems with third light L3/(L1 + L2) > 0.03 are plotted with open symbols. It is clear that W-type systems show a small amplitude of the O’Connell effect, with randomly distributed sign, while several early-type systems show the first quadrature being systematically the brighter of the two.
Description:
New photoelectric observations of the eclipsing binary systems DU Boo and AG Vir show that the systems are similar – both are A-type contact binaries with the maximum following the primary minimum being the brighter one. This light curve asymmetry is extremely temporally stable. The phase dependence of the colour indices is unexpectedly small for the observed amplitude of the O’Connell effect, amounting to about 0.1 mag in the optical wavelength range which indicates a very large heated area with a temperature contrast of 1000–1500 K. The broadening functions (BFs) of the systems do not show any dark solar-type photospheric spots. On the other hand, there are significant differences of BFs between the quadratures (surprisingly similar in both systems) indicative of stream of matter or bright region causing additional emission seen between the components around the phase 0.25. Absolute parameters of the components slightly depend on the adopted model. Long orbital period of both contact binaries combined with late spectral type indicate that the primary components of either of the systems (but particularly in case of DU Boo) already evolved off the main sequence.
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