Computer Science
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd...4e...3t&link_type=abstract
The Ultraviolet Universe: Stars from Birth to Death, 26th meeting of the IAU, Joint Discussion 4, 16-17 August 2006, Prague, Cze
Computer Science
Scientific paper
The High Temperature Region (HTR) that surrounds the photospheres of Be stars is studied in order to derive observational constraints for modelling Be stars, in particular for the region where superionization takes place. 50 Be stars, representative of a considerable range of temperature, were chosen. From archival, high-dispersion IUE spectra, different lines that originate in the HTR region were considered, namely the resonance lines of Si IV, C IV and Al III, and He II λ 1640. Equivalent widths (corrected for photospheric contribution), optical depths, atom columns and expansion velocities were measured. From this observational data several correlations between different observables were obtained. These correlations permit us to discuss the geometry, density distribution and heat input of the lines formation regions (LFRs). The major results can be summarised as follows: 1) The circumstellar material contributes to the resonance lines of Si IV, C IV, Al III and to the He II λ 1640 at all inclination angles. 2) In Si IV, C IV and Al III the equivalent widths have a tendency to increase in objects with high rotational velocities. 3) Si IV and C IV equivalent widths are also correlated to the kinetic energy of the expansion velocity. This means that dissipation of mechanical energy is one of the heating mechanisms. 4)On the basis of the expansion velocities and the line profiles, we establish a sequence for the LFRs: The LFR of He II is at the base of the wind and the closest to the central star. The LFRs of Si IV and C IV are inmersed in the stellar wind. The LFR of Al III is an interface between the HTR and the cool envelope. The analysis followed in this work is completely model-independent. Consequently, these results could be useful to decide which are the facts that are to be considered when modelling Be stars.
Ringuelet Adela E.
Torres Francis A.
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