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| Paper: |
Imaging Spectroscopy of Betelgeuse in the Ultraviolet |
| Volume: |
154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop |
| Page: |
393 |
| Authors: |
Uitenbroek, H.; Dupree, A. K.; Gilliland, R. L. |
| Abstract: |
The bright supergiant Betelgeuse has been imaged in the ultraviolet continuum and with spectroscopic resolution using the Faint Object Camera (FOC) and the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST). FOC images were obtained on two separate occasions, in March 1995 and October 1996. A single bright unresolved area is found in both sets of observations, although with different position and contrast. Spatially resolved spectroscopy obtained with the GHRS in March 1995 shows the chromospheric emission in the Mg 2 h and k lines reaches a diameter of ~300 mas, about twice the size of the ultraviolet continuum images. The signature of the bright spot observed in the March 1995 FOC images occurs in the spectrum as an asymmetry in the intensity measured across the disk at constant wavelength. On the basis of the small number of such hotspots that are present at any one time, and their signature in the Mg 2 resonance lines, as observed with the GHRS, we argue that these spots are not the consequence of convective flows as hypothesized by \activecite{Schwarzschild1975}. Differences in the spatial distribution of the flux between the h and k lines, rather suggest that we are observing a non-spherically symmetric shock wave that propagates radially outward. Because the spectra were obtained scanning across the stellar image, it is possible to determine the axis of rotation of Betelgeuse and estimate its rotational speed. The bright spot in March 1995 appears congruent with the pole of the star suggesting that its angle of inclination is ~20^\circ to the line of sight. |
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