Volume 440, Number 1, September II 2005
|Page(s)||163 - 169|
|Section||Interstellar and circumstellar matter|
|Published online||19 August 2005|
Is G84.0+0.8 a high mass star formation site near the edge of the Pelican nebula?
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany e-mail: email@example.com
2 Institute of Astronomy, ETH Hoenggerberg, 8093 Zurich, Switzerland e-mail: firstname.lastname@example.org
3 Departament d'Astronomia i Meteorologia, Universitat de Barcelona, 08028 Barcelona, Spain e-mail: email@example.com
Accepted: 4 May 2005
We present visible and near-infrared observations of the G84.0+0.8 HII region, a bright compact knot projected within the boundaries of the W80 complex dominated by the North America and Pelican nebulae. The spectrum of the nebula indicates a temperature of the ionizing stellar spectrum K (corresponding to a O7–O5 star) and a density of the HII region cm-3, with a foreground extinction of mag. A comparison of narrow-band near-infrared images through the Brγ and the H2 filters shows that G84.0+0.8 consists of a fan-shaped cavity in a molecular cloud at least partly bounded by a photodissociation region, filled with Brγ-emitting ionized gas, and with a compact cluster at the tip of the fan. The brightest star at the position of the cluster is found to be a late G-type interloper. While membership of G84.0+0.8 in the local arm is well established from existing radial velocity measurements of the ionized gas, we find that the ionizing flux estimated from the size and density of the nebula on the one hand, and the radio continuum properties of the nebula on the other hand, are well below the expected ionizing flux of a mid, or even late, O-type star. We consider the possibility that G84.0+0.8 might be externally ionized by a nearby mid-O star. Currently available observations do not definitely confirm or reject the membership of G84.0+0.8 in the W80 complex, although a larger distance seems favored by the available data. Nevertheless, we can firmly rule out the possibility that it represents a massive star forming site in that complex, as its appearance as a compact HII region containing an embedded cluster may lead one to think.
Key words: HII regions / ISM: individual objects: G84.0+0.8 / ISM: individual objects: W80
© ESO, 2005
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