Iron II Asymmetries: the Kinematics of the Chromosphere of the Cool Supergiant Alpha Orionis

Details Iron II Asymmetries: the Kinematics of the Chromosphere of the Cool Supergiant Alpha Orionis Iron II Asymmetries: the Kinematics of the Chromosphere of the Cool Supergiant Alpha Orionis

Jan 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........37s&link_type=abstract

Thesis (PH.D.)--UNIVERSITY OF COLORADO AT BOULDER, 1995.Source: Dissertation Abstracts International, Volume: 57-02, Section: B,

Computer Science

1

Radiative Transfer

Scientific paper

Ultraviolet observations of the outer atmosphere of alpha Ori were examined in order to understand the dynamics of the outer atmosphere. High signal-to-noise spectra from the GHRS were examined, as well as IUE data, for clues about its evolution over the past decade. Asymmetries observed in unblended Fe II line profiles in this dataset were found to contradict previous ideas about their formation (e.g. Carpenter (1984)). No systematic relationship between line asymmetry and atomic parameters seemed to exist. However, a wavelength dependent relationship was found and exploited. Radiative transfer calculations were performed on model atmospheres to help understand the problem of line formation, especially Fe II, in this star. A variety of outflow profiles were examined using the MULTI radiative transfer code (Carlsson 1986). None of the one-component models could reproduce the observed asymmetries. Recognizing that the wavelength dependence of the asymmetry corresponded with a large change in the assumed background opacity, a two-component velocity model was constructed. This model combines a ubiquitous outflow deep in the atmosphere which is disrupted as it flows into a more turbulent region. The second component consists of a series of outflowing pockets in the upper chromosphere which penetrate the turbulent region. These pockets cover only a fraction of the stellar surface, roughly 10%. The line cores and inner wings of the Fe II lines are greatly influenced by these pockets. For lines below 2500 A, the entire line profile is formed in the region of these pockets and have asymmetries indicative of outflow. The wings of longer wavelength lines are formed deeper in the atmosphere, in the region of the ubiquitous outflow. This outflow blueshifts the emission profile enough to change the asymmetry of the line.

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