Other
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........19s&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF BRITISH COLUMBIA (CANADA), 1995.Source: Dissertation Abstracts International, Volume: 56-08,
Other
1
Protostellar Objects, Ngc 6334
Scientific paper
Two sets of protostellar objects have been studied using the James Clerk Maxwell Telescope as the main observational facility. The first set is a selection of sources from the IRAS Point Source Catalog, originally observed as part of a survey of protostellar candidates. In this present work, the observational database has been extended to include the (sub)millimetre continuum and J = 3 --> 2 and 2 --> 1 lines of CO, 13CO and C 17O, and J = 7 --> 6 and 5 --> 4 lines of CS and C34S. The continuum mapping was able to resolve each source in addition to making flux measurements. The analysis of these flux values using dust emission models is reported in a separate paper. The molecular lines have been analysed using radiative transfer models in the Large Velocity Gradient (LVG) approximation. Molecular hydrogen densities have been derived for most of the sources studied and have been found to cluster around n ~ 10^5rm cm^{-3} . No apparent correlations are seen among the observed and derived parameters. NGC 6334 I and NGC 6334 I(North) comprise the second set of objects and are located at the northern end of the molecular cloud complex NGC 6334. This region has been observed using the same lines, and in particular, mapped in CO (J = 3 --> 2) and CS (J = 7 --> 6). "Extreme High Velocity" (Delta V ~ 150 {km s}^{-1}) wings of CO are seen around NGC 6334 I and the outflow is found to be bipolar. The outflowing material has been shown using radiative transfer models to contain gas at a density of n ~ 5 times 10^3 {cm}^{-3} for a total mass of 2.5Modot in the wings. This corresponds to a mass flow rate of 8 times 10^ {-4}Modotyr ^{-1} and a mechanical luminosity of 89 Lodot . A neutral H I wind ejected at high velocity from the star is inferred to be driving this molecular flow. The implied stellar mass loss rate is 4 times 10^{-4}M_&sun;yr^{-1} . The CO line wings at peak I(North) are much less prominent, with Delta V~ 20 km s^{-1}, although significant wings are present. They are not, however, in the form of bipolar lobes. Another feature, an extension 30 arcseconds to the northwest of I, has been newly identified. LVG model analysis has been used to derive H_2 densities at a large number of beam positions. This yields n ~1.3 times 10^7cm^{ -3} for peak I while for I(North) the gas density is only ~4.5 times 10^5cm^{ -3}. This contrast in gas density, combined with the lack of a luminous thermonuclear source detected around I, supports the suggestion that NGC 6334 is a very young stellar object but that I(North) is an even younger one. A lower limit of ~3000 yr for the age difference between the two systems is inferred from the time scales of the bipolar outflow at NGC 6334 I.
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