New clues on outburst mechanisms and improved spectroscopic elements of the black hole binary V4641 Sagittarii

摘要: We present spectroscopic observations of the black hole binary V4641 Sagittarii, obtained between 2004 July 4 and 2005 March 28, which cover minor outburst star in early quiescence variations on 19 nights scattered over six months. During outburst, peaked approximately 3 mag brighter than usual, our spectra were dominated by broad hydrogen, helium iron emission lines. The very first showed P Cygni profiles, disappeared within a few hours, indicating rapid changes matter ejection. Hα line had multiple components, one being blueshifted wing exceeding 5000 km s -1 . simultaneously observed 10-min photometric flare up, equivalent width Ha temporarily decreased, implying that it was continuum. overall spectral appearance similar to 1999 September active phase, suggests mass-ejection processes associated with both eruptions. In quiescence, those early-type secondary showing its orbital motion around primary. By measuring cross-correlation radial velocities, we give an improved set elements. Whereas measure same velocity amplitude (K 2 = 211.3 ± 1.0 ), errors, as Orosz et al., centre-of-mass (y 72.7 3.3 ) differs significantly from previously published value (107.4 2.9 ). However, find evidence difference is caused systematic error data reduction previous study, rather gravitational effects invisible third component.