Observations of the W43 Star Forming Region and SIS Receivers for the BIMA Array.

Details Observations of the W43 Star Forming Region and SIS Receivers for the BIMA Array. Observations of the W43 Star Forming Region and SIS Receivers for the BIMA Array.

Jan 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........35t&link_type=abstract

Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, BERKELEY, 1993.Source: Dissertation Abstracts International, Volume: 55-07, Section: B

Computer Science

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1

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This thesis is divided into two major sections. Part I describes the heterodyne receiving system of the six element Berkeley Illinois Maryland Association interferometer. The primary receiving elements are Superconductor-Insulator -Superconductor (SIS) junction mixers, operated at 4 K. We have developed a closed-cycle helium refrigerator, based on the Gifford-McMahon cycle, to maintain the SIS mixers at this temperature. The refrigerator uses a rare earth compound, Er_3Ni, for enhanced heat exchange between the inlet and exhaust gas streams. We discuss the design issues, present test results, and analyze the performance of our prototype refrigerators. A detailed description of the mechanical and electrical aspects of the receiving system is also presented in part I. We have implemented a fully automated system designed to optimize the receiver performance at the desired observing frequency. All receivers are tuned simultaneously via commands from a central computer, aided by control and monitoring hardware. We describe the control electronics and software developed for this task. We also discuss the automated generation of lookup tables used by the tuning algorithm. Part II of this work discusses observations of the massive star forming region W43. We present mosaicked interferometric images of the 3 mm continuum emission and the J = 1 to 0 line of HCO ^+. We incorporate data from the NRAO 12 m telescope to produce composite images with no missing flux. The continuum emission is dominated by thermal brehmsstrahlung from ionized gas surrounding a cluster of massive, young stars. The HCO^+ spectra show evidence of strong self absorption, primarily in the southern part of the cloud. The molecular gas distribution and kinematics are consistent with a shell-like geometry. We discuss a sequential star formation scenario in which the infrared source W43 IRS 1 has triggered the formation of a second generation of massive stars.

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