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T. B. Ake (JHU/CSC), R. D. Robinson (CUA)
22 Vul (G3 Ib + B9 V; period=249d) has become a pivotal laboratory for studying solar-type supergiants and the \zeta Aur phenomenon in general. During the atmospheric eclipse phase of these systems, the B star can be used to directly probe different layers in the atmosphere of the evolved supergiant primary. For 22 Vul, the primary star lies near the dividing line in the HR diagram that separates stars with hot, solar-like coronae from those with extended atmospheres and cool winds. Its short period provides an opportunity to sample the entire orbit in less than a year, compared to other \zeta Aur systems which typically have periods of several years.
We have obtained FUSE observations of 22 Vul during ingress and egress phases for the May-June 2004 eclipse. We find that strong Fe II absorption lines in the \lambda\lambda1141-1155 region are already evident in the first observation at 2.5 RG*. These rapidly increase in strength until a height of ~1.7 RG*, where they start to saturate. Further increases in opacity at lower heights are compensated by strong resonance scattering, which fills in the absorption lines and eventually leads to emission features at totality. The continuum absorption increases slowly with decreasing height until a height of about 1.4 RG*, where it increases dramatically. This increase is coincident with a factor of >10 increase in the hydrogen column mass, which can be deduced from flux suppression due to the wing of Ly\alpha. In totality, the spectrum is dominated by emission lines, such as Fe II and Fe III, arising from the ground state, caused by resonance scattering of the B star photons in the cool star wind. We discuss current efforts underway to model the complex features of these spectra.
Support for this research was provided by NASA research contract NNG04GL77G.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.