2000A&A...357..621C -
Astronomy and Astrophysics, volume 357, 621-636 (2000/5-2)
Internal variation of electron density in galactic HII regions.
COPETTI M.V.F., MALLMANN J.A.H., SCHMIDT A.A. and CASTANEDA H.O.
Abstract (from CDS):
A study on the internal variation of the electron density in galactic HII regions has been conducted on a sample of 15 objects of different sizes and evolutionary stages. The [SII] λ6716/λ6731 line ratio was adopted as electron density indicator. Long slit spectrophotometry of high signal-to-noise ratio with spectral dispersion of 0.75Å/pxl and spatial scale of 0.90"/pxl were obtained at different slit positions and orientations. No systematic spatial variation of electron density was detected in nearly half of the objects studied (
S 255,
S 257,
S 271,
S 285,
S 301,
S 305,
NGC 3372 and
IC 1275). They are in general the most diffuse and probably evolved objects with low mean densities in the range N
e≃20-140cm
–3. The remaining objects (
S 288,
S 307,
NGC 2579,
NGC 3503,
Gum 62,
Gum 64a and
M 20) with mean densities N
e≃80-360cm
–3, have shown a statistically significant electron density dependence on position. In most of these cases, the spatial variation of density may be interpreted as a radial gradient with the density decreasing from the centre to the edges.
M 20 shows a systematic non-radial variation of electron density with maximum values occurring at its prominent dark lanes. A mean filling factor of the order of φ=0.1 was found compatible with the data. Based on their density profiles,
NGC 2579,
Gum 62,
Gum 64a and possibly
NGC 3503 were indicated as candidates of showing a `champagne flow'.
Abstract Copyright:
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Journal keyword(s):
ISM: general - ISM: HII regions
Simbad objects:
31
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