6 Conclusions

We have presented and analysed the results of our spectroscopic observations of the $\delta$ Sco binary system during the 2000 periastron passage. The RVcurve derived from our H$\alpha$ line data was used to refine the orbital solution previously derived from published speckle interferometric data. In particular, we determined new values of the periastron epoch and longitude as well as of the orbital inclination angle. The eccentricity value turned out to be close to that in the solution of Hartkopf et al. (1996). The new orbital solution indicates that the binary is detached, and no direct mass transfer takes place. A hypothesis that the primary's nonradial pulsations are amplified at periastron and are responsible for the mass loss is suggested.

Our data, supplemented by the results of visual photometry, suggest a scenario which explains most of the phenomena observed during the 2000/1 $\delta$ Sco observing campaign. For example, the photometric dip centered at periastron and certain changes of the line profiles are attributed to an attenuation of the primary by its disk as well as to variations of the disk's optical depth, density, and size.

We plan to continue studying this remarkable system. This will include follow up spectroscopic, photometric, and polarimetric observations as well as efforts to model the observed phenomena in more detail.

Acknowledgements

We thank W. J. Fischer and I. Mihailov for their help in obtaining spectra at Ritter. A. M. and K. S. B. acknowledge support from NASA grant NAG5-8054. K. S. B. is a Cottrell Scholar of the Research Corporation, and gratefully acknowledges their support. Support for observational research at Ritter Observatory has been provided by The University of Toledo, by NSF grant AST-9024802 to B. W. Bopp, by an AAS small grant (NASA funding), and by a grant from the Fund for Astrophysical Research. Technical support is provided by R. J. Burmeister. P. R. acknowledges partial support from the European Union Training and Mobility of Researchers Network Grant ERBFMRX/CT98/0195. The G. D. Cassini telescope is operated at the Loiano Observatory by the Osservatorio Astronomico di Bologna. The SAAO spectrum was obtained as part of a different project, which results have not been published yet. I. N. would like to thank D. A. H. Buckley for his help with the observations at SAAO and J. J. Rodes for pre-processing of the data. This research has made use of the SIMBAD database operated at CDS, Strasbourg, France.