Gas and star content and spatial distribution in the giant extragalactic H II region TOL 89

Details Gas and star content and spatial distribution in the giant extragalactic H II region TOL 89 Gas and star content and spatial distribution in the giant extragalactic H II region TOL 89

Feb 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985a%26a...143..347d&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 143, no. 2, Feb. 1985, p. 347-354.

Astronomy and Astrophysics

Astrophysics

21

H Ii Regions, Interstellar Gas, Ionized Gases, Star Distribution, Ultraviolet Spectra, Wolf-Rayet Stars, Abundance, Hot Stars, Photoionization, Spectrophotometry, Spiral Galaxies, Stellar Evolution, Stellar Winds

Scientific paper

Tol 89 is a giant H II region 2.5 kpc in diameter, located in one of the arms of the spiral galaxy NGC 5398. We have observed this object in the Uv with the International Ultraviolet Explorer, and at optical wavelengths with long slit spectrophotometric equipment. The UV spectrum of Tol 89 reveals P Cygni profiles, characteristic of stars with strong stellar winds, including WoIf-Rayet (WR) stars. The optical spectrum is typically that of an H II region, with a very blue continuum and strong emission lines, among which is a broad emission band at λ 4650 confirming the presence of WR stars. The spatial distribution of the stars and the gas is strongiy peaked at the centre (C) of Tol 89, however the fraction of hotter ionizing stars is maximum off centre. The heavy elements are found to be underabundant by a factor of about 6 compared with solar values. Star formation in Tol 89 has occurred in bursts as suggested by the UV and optical energy distribution and the large WR to O star ratio, roughly equal to 0.35. The recent burst of star formation is a few 106 yr old as derived from the average type of WR stars present, young and fairly massive WN 7-8 stars, and the dereddened continuum spectrum. Only high dispersion long slit spectroscopy observations will allow to find out whether or not this giant H II region is selfgravitating. The total mass of stars created during the last burst is far too small to bind this stellar cluster.

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