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Session 19 - Hot Stars.
Display session, Monday, January 15
North Banquet Hall, Convention Center

[19.05] H\alpha Variability in the A0 Ia-Type Supergiant HR 1040

N. D. Morrison, K. D. Gordon (U. Toledo)

HR 1040 (= HD 21389) is a well-known example of a luminous star with mass loss, photometric and radial-velocity variability, and a variable H\alpha profile. Caplinger (1991, M.\ S.\ thesis, U.\ Toledo) found that the H\alpha profile shows, at various times, different morphologies: P Cygni, inverse P Cygni, and Type III P Cygni (emission on both sides of the absorption). This result indicates that this star's wind is not steady and/or not spherically symmetric.

We studied 43 CCD échelle spectra obtained between 1993 Sep.\ and 1994 Dec.\ with the 1-m telescope of Ritter Observatory. The spectral resolution of this material is 0.23 Å\ at \lambda5800, and the continuum SNR is usually comfortably above 100 in an exposure time of 20 min or less. The spectral coverage consists of 9 disjoint 70-Å\ regions in the yellow and red; features of interest in these spectra are H\alpha, He I \lambda5876, and Si II \lambda\lambda6347, 6371.

In addition to confirming the morphological variability found by Caplinger, our data show two episodes of dramatic increases in the width and the equivalent width of the absorption component of H\alpha, with the equivalent width attaining values as large as 2 Åas compared to a baseline value around 0.5 ÅDuring these episodes, the absorption feature often showed two or more sub-components. In addition, the equivalent width of Si II \lambda6347 increased by amounts up to 50%. Presumably, these events can be interpreted as episodes of enhanced mass loss.

Collection and analysis of spectra of this star are continuing at Ritter Observatory. If this star is typical of A-type supergiants in the variability of its H\alpha profile, our results can be used to assess the accuracy of distance estimates to external galaxies based on mass loss as a luminosity indicator in these stars (Kudritzki et al.\ 1992, Aamp;A 257, 655).

Program listing for Monday