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The early stages of low-mass star-formation are characterised by the embedded phases, in which a protostellar envelope harbors the central star and disk system. This envelope contains most of the mass of the protostar and is the main component in the early evolution of low-mass protostars. Although most research has focussed on the cold outer envelope, little is known about the central regions of the envelope, where disk, envelope and outflow interact on scales of a few hundred to a thousand AU. Envelope models developed in the last decade have interpolated results from the cold outer envelope to obtain the structure of the inner envelope. However, little observational evidence exists that probes these scales.
We present data on a sample of 10 southern sources that analyzes and characterizes these regions using new single-dish sub-mm observations at frequencies of 690 and 810 GHz, obtained with the recently commissioned CHAMP+ instrument on APEX. This data provides an unique insight in the warm gas (60 Kelvin) and directly probes the interaction between (inner) envelope and outflow using the higher excited CO, 13CO and C18O 6--5 and 7--6 lines. This data is supplemented by data obtained with the new HARP-B instrument on the JCMT, aimed at characterizing the dense gas residing in the inner regions of protostellar envelopes. This dense gas has proven to play a pivotal role in identifying embedded sources from edge-on disks and obscured sources, both of which are often erronously identified as embedded using IR photometry. A recent survey of the L1688 region in Ophiuchus that reveals that as much as 50 % of the embedded sources in Ophiuchus are edge-on disks or sources obscured by cloud material, will be presented.
This contribution will present an unique view on the physical structure and the evolution of gas and dust envelopes around low-mass protostars.
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