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Scientific paper
Jul 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003ans...324...59l&link_type=abstract
Astronomische Nachrichten, Supplementary Issue 3, Vol. 324, Short Contributions of the Annual Scientific Meeting of the Astronom
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Radio Interferometry, Ysos, High-Mass Star Formation, Individual Objects: G31.41+0.31, Ggd 27 Irs
Scientific paper
The early stages during the formation of massive stars are deeply enshrouded due to the presence of dense and dusty natal material. This prevents observations in the optical and often also in the near-infrared. The emission of the star-forming regions peaks in the far-infrared and sub-mm regime, but at these wavelengths, single-dish observations are restricted in spatial resolution and can give only upper limits on the energetics of the objects of interest. Interferometry at mm wavelengths is one appropriate technique to overcome these limitations. We have started an extensive programme to observe pre-selected massive star-forming regions. Our tool is the VLA and its 7-mm receiver system. The VLA can be operated in several antenna configurations delivering resolutions from 1.5 arcsec down to 0.05 arcsec, which is superior to other current mm-interferometers. Sub-arcsec resolution is strongly needed to disentangle the often crowded regions of high-mass star formation and to clearly separate our objects of interest from the adjacent ultracompact HII regions. At 7 mm we are on the save ground of the Rayleigh-Jeans limit even for emission of cold dust (a fact that is not always true for observations at smaller wavelengths). Almost all circumstellar density configurations are optically thin at 7 mm, thus, the observations will trace the total dust content. However, at 7 mm also the free-free emission from ionised gas (caused by the UV emission of the young massive stars) can contribute to the observed signal. Therefore, we have to identify and remove these "parasitic" constituents by extrapolating interferometric data obtained at cm-wavelengths. The targets are either taken from the list of Molinari (Molinari et al. 2000, A&A, 355, 617) or are well-known massive star-forming complexes, for which we have already acquired additional data at other wavelengths. We have started with observations at lower and medium resolution (1.5 - 0.5 arcsec) to distinguish candidates for follow-up observations with higher resolution. For the majority of our sample targets we have revealed pronounced 7-mm emission. Especially interesting is G31.41+0.31 where we could resolve the 7-mm emission arising from a so-called hot molecular core. For GGD27, we found the 7-mm counterpart of the object that illuminates this region in the near-infrared and that also acts as the driving source of the associated outflow system HH80/81. Consequently, this detection establishes GGD27 as a key candidate regarding the search for an accretion disk around a forming high-mass star. Furthermore, we demonstrate some synergy effects between radio and infrared data concerning the interpretation of the nature of those very young massive stars. H.L. and B.S. are supported by DFG grant Ste 605/17-2. P.H. acknowledges partial support from the Research Corporation grant No CC4996, as well as from NSF grant AST-0098524.
Araya Esteban
Hofner Peter
Linz Hendrik
Stecklum Bringfried
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