High-resolution imaging of ultracompact HII regions^*,**

III. G11.11-0.40 and G341.21-0.21

¹ Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Schillergäßchen 3, 07745 Jena, Germany
² Max-Planck-Institut für Astronomie, Königsstuhl 17, 69117 Heidelberg, Germany
³ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany

Corresponding author: M. Feldt, mfeldt@mpia-hd.mpg.de

Received: 2 October 2000
Accepted: 7 February 2001

Abstract

We present the first near-infrared images of the two massive southern star-forming regions G11.11-0.40 and G341.21-0.21, obtained with adaptive optics at sub-arcsecond resolution. Together with conventional narrow-band near-infrared images and polarization maps, mid-infrared data, millimetre and radio data, we were able to determine the morphological structure and to constrain the stellar content of the regions. In both cases the molecular cloud cores have masses of about 500 and contain clusters of OB stars. This supports the view that massive stars do not form in isolation. In the case of G11.11-0.40 we could identify the central O star responsible for the ionization of the ultracompact Hii region. Our results for G341.21-0.21 indicate that this source is a precursor of an ultracompact Hii region.