Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.........5j&link_type=abstract
Ph.D. Thesis California Univ., Berkeley.
Astronomy and Astrophysics
Astronomy
Asymptotic Giant Branch Stars, Josephson Junctions, Millimeter Waves, Receivers, Sis (Superconductors), Stellar Envelopes, Heterodyning, Metallicity, Planetary Nebulae, Stellar Winds
Scientific paper
A heterodyne receiver designed for astronomical use between 450 and 520 GHz has been constructed. Very low capacitance (C approximately = 5-10 fF) Superconductor-Insulator-Superconductor (SIS) junctions have been fabricated as the detectors; these junctions lie on the edges of niobium thin films and form Nb-Al-Al2O3-Al-Nb sandwiches. The double sideband (DSB) receiver noise temperature is between 400 K and 800 K throughout the 70 GHz band. In addition, detailed modelling and analysis of astronomical observations of two post-AGB (Asymptotic Giant Branch) stars was performed. The observations were made with an SIS receiver designed for 345 GHz. CO observations and modelling of the young planetary nebula NGC 7027 provided the best determination yet of its AGB mass loss rate, the first direct evidence for bipolarity in its AGB mass loss, evidence for close hydrodynamic coupling between the planetary nebula and the relic AGB wind, and evidence for evolution in the metallicity of the stellar wind. Observations of the proto-planetary nebula CRL 2688 found evidence for spatially extended fast wind emission with a non-bipolar morphology, and evidence for evolution in elemental abundances in the stellar wind.
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