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Title: An investigation of candidate protostars
Author: Chandler, C. J.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1990
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This thesis examines several regions of star formation selected because they were believed to be the youngest of their type. The sources studied are examples of low, medium and high-mass star formation, namely B335, NGC2024 and DR21(OH). High-resolution mapping of the thermal dust emission from B335 shows it to contain a dense core elongated in a direction perpendicular to the orientation of the bipolar outflow. The core is sufficiently gravitationally bound to be able to collimate an initially isotropic wind into the observed bipolar structure. The presence of an evolved outflow from a source of such low luminosity and high extinction means that it does not appear to fit the currently popular models for protostellar evolution. CS and C34S J = 7 - 6 molecular line observations show that most of the six dense cores, FIR1-6, in NGC2024 are too warm to be protostellar condensations. Significant CS 7 - 6 emission with excitation temperatures of 20 to 60 K has been found to be associated with all of the cores. Revised mass estimates lie between 2 and 11 M PROB*LEM, and the corresponding luminosities require the presence of embedded heating sources. FIR4 contains a highly reddened 2μm source and a possible reflection nebula, and FIR6 has a very wide CS 7 - 6 line that is probably the result of the interaction between a very young outflow and the surrounding dense core. A chain of dense cores situated in the DR21 cloud has been mapped in 1.3mm thermal dust emission and the 2 - 1 and 1 - 0 transitions of CS and C^34S. The sources detected have sufficiently high luminosities that the cores must contain embedded young stars. To account for the location of the masers near the brightest source it seems likely that there is a single 15 M PROB*LEM star. The CS spectra indicate the presence of infalling gas along the line-of-sight, and all the spectra are relatively wide with high-velocity emission present towards the east. They have been fitted by a two component model, with warm background gas and cooler foreground gas, and the results indicate that the two components are physically associated. The mass of the cloud core is about 2000 M PROB*LEM, obtained from both the dust emission and the CS data, which together with the CS linewidths indicates that the cloud is approximately in virial equilibrium. All three sources are found to be quite young, although it seems likely that they have already begun nuclear burning and so none is a 'true protostar.' Suggestions for future observations of these sources and for the identification of further candidate protostars are also described.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available