Peculiarities in the Spectrum of the Early-type System MY Ser

MY Ser is an eclipsing early-type contact system. Both components are of spectral type O6 III. Using ESO archive spectra, we show that the radial velocity of the third body, which contributes about half of the total luminosity, changed from 2006 to 2009. The line profiles of the eclipsing system have peculiar shapes and strengths; namely around conjunctions, they are affected by circumbinary matter.