A 21-cm line study of an expanding HIl region.

Abstract

view Abstract Citations (24) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A 21-cm line study of an expanding HIl region. Wade, Campbell M. Abstract Observations have been made of the 21-cm line of neutral hydrogen in the vicinity of the nearly spherical HIl region surrounding the O8 star X' Orionis. The 6o-foot paraboloidal antenna, with beamwidth 40' between half-power points, at the Agassis Station of the Harvard College Observatory was used. The apparent diameter of the HIl region is about 70 The observations were all made along a strip at galactic latitude - Io?5, which passes through the center of the nebula. The centers were spaced at intervals of 30' in galactic longitude over a span of 150 centered on the HIl region. Analysis of the line profiles has led to the following conclusions: a) The HIl region is surrounded by a thick, relatively dense shell of neutral hydrogen which is expanding at a velocity about 8 km/sec. The shell is very nearly spherical. b) The thickness of the shell is approximately 28 parsecs, or about 50 per cent greater than the radius of the HIl region. c) There is a local excess of hydrogen in the vicinity of the HIl region; the mean density of hydrogen, both ionized and neutral, in the volume enclosed by the outer boundary of the HI shell is greater than that in the surrounding region by about a factor of 4. The total mass of the HI shell is approximately 45,000 solar masses. d) The derived density distribution in the HI shell, as a function of distance from the center of the HIl region, is given in the following table: r (pc) Nxi (atoms cm-3) O~I8* 0* 20 1. 1 22 3.2 24 4.2 26 4.5 28 5.1 30 5.2 32 5.3 34 5.9 36 6.8 38 5.9 40 4.3 42 3.5 44 3.0 46 2.2 48 i.8 50 `.5 * H~I region. Harvard College Observatory, Cambridge, Mass. Publication: The Astronomical Journal Pub Date: July 1957 DOI: 10.1086/107502 Bibcode: 1957AJ.....62..148W full text sources ADS |