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Title:
First Image of the Surface of a Star with the Hubble Space Telescope
Authors:
Gilliland, Ronald L.; Dupree, A. K.
Publication:
Astrophysical Journal Letters v.463, p.L29 (ApJL Homepage)
Publication Date:
05/1996
Origin:
APJ
Astronomy Keywords:
STARS: INDIVIDUAL CONSTELLATION NAME: ALPHA ORIONIS, STARS: CHROMOSPHERES, STARS: SUPERGIANTS, ULTRAVIOLET: STARS
DOI:
10.1086/310043
Bibliographic Code:
1996ApJ...463L..29G

Abstract

A direct image of the surface of a star, Betelgeuse (= alpha Ori; M2 Iab), has been obtained with the Faint Object Camera on the Hubble Space Telescope. Images in two ~300 A--wide bands centered at 2550 and 2800 A cover ~10 resolution elements on the stellar disk. The ultraviolet diameter of Betelgeuse of 125 +/- 5 mas at 2500 A (corresponding to 108 +/- 4 mas, FWHM) is a factor of 2.2 larger than the optical diameter, thus indicating a substantially extended chromosphere in this supergiant. A single bright, unresolved area is present in the southwest quadrant of the disk (P.A. = 235 deg) in both images, with a peak amplitude of 1.3--1.8 as compared to the surrounding disk and a temperature differential in excess of 200 K. This feature may be the result of magnetic activity, atmospheric convection, or global pulsations and shock structures that heat the chromosphere. Spatially resolved spectroscopy of the Mg II lambda lambda 2795, 2802 doublet with the Goddard High Resolution Spectrograph suggests complicated dynamics, with outflowing material in the chromosphere indicated by the Mg II emission.

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