Mathematics
Scientific paper
Oct 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt.........2p&link_type=abstract
PhD Thesis, Combined Faculties for the Natural Sciences and for Mathematics of the University of Heidelberg, Germany. II + 90 pp
Mathematics
Star Formation, Massive Stars, H Ii Regions
Scientific paper
Massive star formation takes place under harsh observational conditions; as time passes, the already formed stars produce an ionised region and dissipate the surrounding molecular cloud, becoming accessible in the NIR. For this reason one of the earliest phases to observationally study massive stars is the UCHII-region phase. This thesis investigates the ionising stars and kinematics of UCHII regions at high spatial and spectral resolution. NIR-polarimetric maps of the reflection nebula that are generally found around these objects are used to rule out the presence of deeply embedded companions of a Young Stellar Object (S106) and to identify multiplicity in the main illuminating sources (also candidates to be the ionising sources) inside G77.96-0.01. This last result could also explain the relationship between some UCHII and their detected extended halos. An extensive analysis of a complex UCHII (G61.58+0.09) shows the problem of completeness of the detected stellar content in the NIR, and thanks to a K-band polarimetric map, the internal ionisation model for the smaller component is predicted and the corresponding stellar counterpart is detected at 3.5 μm. The spectral energy distribution and the presence of Brγ-emission in the stellar spectra translates into the possible presence of a supergiant as part of the population inside this UCHII. The confirmation of the existence of evolved stars in these objects is an evidence of longer lifetimes than expected by the simple expansion of the Strömgren sphere. Finally the study of the kinematical structure of G5.89-0.39, the paradigm of shell-type UCHII and most massive outflow of the Galaxy, reveals that the confirmed shocked molecular hydrogen emission is compatible with a north-south orientation of the outflow, whereas the ionised material seems to trace a secondary outflow structure and therefore a possible secondary star inside G5.89-0.39. The short dynamical age derived for this object (<103yr) confirms that the source/sources driving this outflow must also be in an early evolutionary stage.
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