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UBC Theses and Dissertations

Line and continuum studies of some star forming regions Sato, Takashi


Two sets of protostellar objects have been studied using the James Clerk Maxwell Tele- scope 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 ob- servational database has been extended to include the (sub)millimetre continuum and J = 3 → 2 and 2 → 1lines of CO,¹³C0 and C¹⁷O, and J = 7 → 6 and 5 → 4 lines of CS andC³⁴S. 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 hydro- gen densities have been derived for most of the sources studied and have been found to cluster around n ~ 10⁵cm⁻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” (ΔV ~ 150 kms⁻¹) wings of CO are seen around NGC 6334 I and the outflow is found to be bipolar. The outfiowing material has been shown using radiative transfer models to contain gas at a density of n ~ 5 x 10³cm⁻³ for a total mass of 2.5Mʘ in the wings. This corresponds to a mass flow rate of 8 x10⁻⁴ Mʘ yr⁻¹ and a mechanical luminosity of 89 Lʘ. 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 x 10⁻⁴ Mʘ yr⁻¹. The CO line wings at peak I(North) are much less prominent, with ΔV ~ 20 kms⁻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 H₂ densities at a large number of beam positions. This yields n ~ 1.3 x l0⁷cm⁻³ for peak I while for I(North) the gas density is only ~ 4.5 x 10⁵cm⁻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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