A&A Supplement series, Vol. 123, May II 1997, 31-41
Received May 28; accepted September 6, 1996
E.M. Reynoso
- G.M. Dubner
Send offprint request: E.M. Reynoso
Instituto de Astronomía y Física del Espacio,
C.C.67, Suc. 28, 1428 Buenos Aires, Argentina.
Based on HI maps covering the 3 600 square degrees area delimited by
, we
investigated the neutral hydrogen distribution in the
Gum nebula and its environments. The main result is the appearence of a huge
disk of neutral gas at a kinematical distance compatible with that of the
nebula, and whose angular dimensions coincide with the optical image of
the Gum nebula. The disk, roughly centered at 
, is located at 
and has a radius of 
. We propose that this HI disk is the neutral gas component of the
optical nebula, hence becoming the first time in which a structure with
the dimensions of the optical nebula is detected in other wavelengths. We
analyze the fitting of observations with different theoretical models and
conclude that the most plausible interpretation is that the Gum nebula is a
supershell produced by the action of repeated SN explosions, where the
explosions may have originated in the aged association Vela OB2. In this
context, the thick HI shell shown by Dubner et al. (1992) near
and the Vela SNR are the debris of two of the
several outbursts which started in the region about 
years ago.
The southern boundary is distorted due to the presence of a
radius shell, which appears to be an interstellar bubble driven by the
stellar winds of the O-type star HD 49798.
keywords: ISM: supernova remnants -- ISM: individual objects: Gum nebula -- ISM: bubbles -- radio lines: ISM