Triggered massive-star formation on the borders of Galactic H II regions. III. Star formation at the periphery of Sh2-219
Context: .Massive-star formation triggered by the expansion of H ii regions.
Aims: .To understand if sequential star formation is taking place at the periphery of the H ii region Sh2-219.
Methods: .We present 12CO J=2→ 1 line observations of this region, obtained at the IRAM 30-m telescope (Pico Veleta, Spain).
Results: .In the optical, Sh2-219 is spherically symmetric around its exciting star; furthermore it is surrounded along three quarters of its periphery by a ring of atomic hydrogen. This spherical symmetry breaks down at infrared and millimetre wavelengths. A molecular cloud of about 2000 M_⊙ lies at the southwestern border of Sh2-219, in the H i gap. Two molecular condensations, elongated along the ionization front, probably result from the interaction between the expanding H ii region and the molecular cloud. In this region of interaction there lies a cluster containing many highly reddened stars, as well as a massive star exciting an ultracompact H ii region. More surprisingly, the brightest parts of the molecular cloud form a "chimney", perpendicular to the ionization front. This chimney is closed at its south-west extremity by Hα walls, thus forming a cavity. The whole structure is 7.5 pc long. A luminous Hα emission-line star, lying at one end of the chimney near the ionization front, may be responsible for this structure. Confrontation of the observations with models of H ii region evolution shows that Sh2-219 is probably 105 yr old. The age and origin of the near-IR cluster observed on the border of Sh2-219 remain unknown.
Astronomy and Astrophysics
- Pub Date:
- October 2006
- stars: formation;
- stars: early-type;
- ISM: H ii regions;
- ISM: individual objects: Sh2-219;
- 11 pages, 10 figures. To be published in A&