Star formation: Submillimeter observations and data reduction techniques

Details Star formation: Submillimeter observations and data reduction techniques Star formation: Submillimeter observations and data reduction techniques

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010phdt.......192a&link_type=abstract

ProQuest Dissertations And Theses; Thesis (Ph.D.)--The University of Western Ontario (Canada), 2010.; Publication Number: AAT NR

Astronomy and Astrophysics

Astrophysics

Scientific paper

The process of star formation is key to astrophysics and its understanding remains a fundamental problem. The following chapters describe recent work on this subject with instrumentation at the Caltech Submillimeter Observatory. Chapter 1 provides an introduction to this thesis. Chapter 2 describes a new data reduction technique for dual-array polarimeters. This technique is meant to address a potential problem with these instruments; artificial polarization signals are introduced into the data when misalignments between the subarrays and pointing drifts are present during the data acquisition process. The correction algorithm presented is meant to treat for this problem, and has been tested using simulated and actual data. The results indicate that this approach is effective at removing up to 60% of the artificial polarization. Chapter 3 discusses an analysis of the low-mass star forming region NGC 1333 IRAS 4 involving SHARP 350 mum polarimetry and HCN J=4→3 emission spectra. The polarimetry indicates a uniform magnetic field morphology over a 20" radius from the peak continuum flux of IRAS 4A, in agreement with models of magnetically supported cloud collapse. The magnetic field morphology around IRAS 4B appears to be quite distinct however, with indications of depolarization observed towards the peak flux of this source. Inverse P-Cygni profiles are observed in the HCN J=4→3 line spectra towards IRAS 4A, providing a clear indication of infall gas motions. Taken together, the evidence gathered appears to support the scenario that IRAS 4A is a cloud core in a critical state of support against gravitational collapse. Chapter 4 covers SHARP 450 mum polarimetry obtained over the high-mass star forming region NGC 6334 I(N). The "Method 2" approach described in a recent paper by G. Novak and collaborators is applied here to combine our data with results from the Hertz and SPARO polarimeters. This is done in order to estimate the intrinsic angular dispersion deltathetaint of the magnetic field over a spatial range of eight octaves. We compare our estimate for deltathetaint with numerical simulations to place a constraint on the embedded magnetic field strength. Our findings show that an intermediate to weak field is likely present in this cloud. Keywords: instrumentation, polarimeters, data analysis, image processing, submillimeter, star formation, magnetic fields, dust, NGC 6334 I(N), NGC 1333 IRAS 4A, molecules

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