B. E. Turnrose

The International Ultraviolet Explorer Spectral Image Processing System

The International Ultraviolet Explorer (IUE) is a scientific satellite operated in re Al time to obtain ultraviolet spectra of astronomical objects in the wavelength range 1000 Å ≤ λ ≤ 3200 Å in either of two selectable dispersion modes. IUE spectra are recorded by SEC vidicon cameras and transmitted digitally to a ground station as two-dimensional images. The reduction of these data begins with the International Ultraviolet Explorer Spectral Image Processing System (IUESIPS), an on-line interactive image processing system which has been in operation for one year. The task of IUESIPS is to remove all known instrumental effects from IUE spectral images and to provide, in a timely fashion, IUE Guest Observers with reduced data - in the form of spectral intensity as a function of wavelength - amenable to immediate astronomical analysis. The current status of this image processing system is discussed and the types of reduction operations which are routinely performed are presented along with the known existing limitations of the system.

Ultraviolet (UV) Emission Line Mapping Of Selected Regions In The Orion Nebula

Low dispersion spectra extending over the wavelength range λλ1150-3250Å have been obtained with the International Ultraviolet Explorer (IUE) satellite at 35 neighboring locations defining a mosaic within the central region of the Orion Nebula. These spectra have been processed in a unique way to assemble monochromatic images of the emission in the wavelengths of the most prominent ultraviolet (UV) spectral lines seen in the nebula: CIII] λ1909, CII] λ2326, and [OII] λ2470. The mosaic images, covering approximately a 0.6 arcminute by 2 arcminute region including part of the bright bar, have a spectral resolution of ≈6Å and a spatial resolution of ≈4-5 arcseconds. The image processing techniques used to extract each 2 arcsecond-by-2 arcsecond picture element of the mosaics from the original IUE spectra are discussed. These procedures include calculation of spectrograph orientation and thermal effects, normalization for exposure time, subtraction of background, correction for sensitivity variation within the 10 arcsecond-by 20 arcsecond IUE spectrograph aperture, correction to an absolute flux scale, sample interpolation, and display on graphic devices. The resulting UV emission line intensity maps may be used in conjunction with observations of comparable resolution in other wavelength regions to infer the spatial distribution of ionization and abundance levels of carbon and oxygen in Orion.