Hot stars, halos, and cooling flows: Far-UV spectroscopy with the Hopkins ultraviolet telescope.

摘要

This dissertation presents results based upon observations of a variety of objects and astrophysical phenomena obtained with the Hopkins Ultraviolet Telescope (HUT), an ultraviolet spectrograph that flew as part of the Astro-1 and Astro-2 space shuttle missions in 1990 and 1995.; HUT spectra of three UV-bright stars in globular clusters, UV5 in NGC 1851, vZ 1128 in M3, and BS in 47 Tuc, are fit with model stellar atmospheres to determine the stars' effective temperatures, surface gravities, and luminosities. All three stars lie on the Schonberner post-AGB evolutionary tracks, but their relatively low surface gravities indicate that non-LTE effects may be important in their atmospheres.; The spectrum of the globular cluster M79 is used to constrain the distribution of stars along the cluster's horizontal branch. Fits of model stellar spectra indicate that these stars have surface gravities significantly lower than predicted by canonical HB evolutionary models. This result is consistent with the findings of Moehler et al. (A&A, 294, 65 (1995)) for individual HB stars in M15 but remains to be explained.; The galaxy NGC 1275 is surrounded by a bright emission-line nebula. Its far-UV spectrum shows a faint continuum and emission from redshifted Lyman {dollar}alpha{dollar}, C IV {dollar}lambdalambda{dollar}1548, 1551, and He II {dollar}lambda{dollar}1640. The redshifted C IV line has a broad component due to the galactic nucleus and a narrow component that we associate with the surrounding nebula. Current nebular emission models cannot reproduce both the observed luminosities and line ratios. The continuum spectrum is well fit by a continuous star-formation model, but a recent burst of star formation cannot be excluded.; O VI {dollar}lambdalambda{dollar}1032, 1038 emission from coronal gas in the Galactic halo is present in four spectra obtained during Astro-2. Three of the detections lie near regions of enhanced soft X-ray emission associated with Radio Loop I; the fourth may represent a more typical region of the halo. Our limit to I(O VI)/I(C IV) {dollar}geq{dollar} 3.4 is consistent with the predictions of self-photoionizing galactic fountain models but higher than those of turbulent mixing layer models.