Compact infrared sources : NGC 7538 and the galactic center

• Main Author: Willner, Steven Paul
• Format: Others
• Published: 1976
• Online Access: https://thesis.library.caltech.edu/3225/1/Willner_sp_1976.pdf; Willner, Steven Paul (1976) Compact infrared sources : NGC 7538 and the galactic center. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/YGRP-NJ17. https://resolver.caltech.edu/CaltechETD:etd-08252008-153611 <https://resolver.caltech.edu/CaltechETD:etd-08252008-153611>

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Three infrared and radio sources in NGC 7538 have been observed from 8 to 13 [...] with 1% spectral and 5" spatial resolution. The very small southern source shows a deep silicate absorption feature at 9.7 [...] while the northern extended source shows little or no silicate absorption, but has a 12.8-[...] emission line from Ne II. The data imply that the compact source has a gas to dust ratio of 75 inside the ionized region. The extended source only 10" away has a gas to dust ratio implied by the 10-[...] data alone of 3 x 10[...], but the true ratio must be much lower to account for published 20-[...] measurements. A revised 10-[...] map of the Galactic center with 2[...]3 resolution, broadband photometry of individual sources from 1.2 to 20 [...], and 8 to 13-[...] photometry of individual sources with 1% spectral resolution have been obtained. The principal conclusions of this study are: (1) The five sources with the bluest energy distributions between 1.6 and 3.5 [...] are stars or star clusters. The brightest has a luminosity of 10[...] L[...] while the other four have luminosities of about 10[...] L[...]. (2) There is extended emission from ionized gas and dust. (3) The density of ionized gas in the discrete 10-[...] sources is no higher than that in the extended source. (4) There is at least one compact source that is not associated with the others and has a different energy distribution. (5) Most of the extinction toward the sources observed is interstellar and is moderately uniform. The visual extinction is about 28 magnitudes, and the 9.7-[...] silicate extinction is about 3.7 magnitudes.