On the Weakness of C I and O I Resonance Line Emission from the Chromosphere of $\alpha$~Ori.

Previous abstract Next abstract

Session 15 -- Flare and Active Stars
Display presentation, Wednesday, January 12, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[15.04] On the Weakness of C I and O I Resonance Line Emission from the Chromosphere of $\alpha$~Ori.

K. Carpenter (LASP-NASA/GSFC), R. Robinson (CSC), P. Judge (HAO/NCAR), D. Ebbets (BASG), J. Brandt (UCO)

The resonance lines from multiplets UV 2 of both O~I and C~I are typically quite strong in emission in the far-UV spectrum of cool stars. However, in the prototypical M-supergiant $\alpha$~Ori, these lines are remarkably weak, although other transitions from the same upper energy levels, O~I (UV~146) and C~I (UV~32), are observed in strong emission despite their much weaker intrinsic strengths. Due to the presence of many lines from other species in the regions around the UV~2 multiplets of O~I and C~I near 1302~\AA\ and 1655~\AA, the lines of interest suffer severe blending and progress in understanding this flux deficiency is difficult based on low resolution IUE and GHRS data. We have therefore obtained medium resolution (R=10,000) GHRS spectra of $\alpha$~Ori of these complex spectral regions, as well as the regions around the O~I (UV~146) and C~I (UV~32) lines near 1640~\AA\ and 1993~\AA, respectively, to resolve the various contributors and allow detailed study of this phenomenon. In this paper, we present the spectra and discuss the formation of the O~I, C~I, Fe~II, and S~I lines which they clearly resolve. Semi-empirical modeling of the outer atmosphere of $\alpha$~Ori and detailed radiative transfer calculations are used to study the creation and destruction of O~I and C~I photons.

Wednesday program listing