This article describes the SPEAR team's creation of specially-reduced emission line images from pointed observations of the Vela supernova remnant.
The Vela supernova remnant was observed by FIMS-SPEAR in both pointed and sky survey modes. The pointed observations constituted multiple back-and-forth sweeps of the spectrograph over an approximately 6x6 degree area. The average total exposure time was about a factor of 100 greater than the typical sky-survey pixel.
To obtain the highest resolution images, the Vela data were processed differently than the all-sky survey. Because of the telemetry time-delay issue (see Operations and Attitude Correction), stars appeared multiple times in the images when processed with the standard SPEAR software. So instead, time-varying positional corrections in RA and Dec were applied to each photon. The resulting images are about 2 to 3 times the resolution of the all-sky survey, and the total area occupied by stars is less than all-sky survey data products.
The detailed history of continuum subtraction and star removal procedures applied to these data has been lost. Negative values of count and intensity are artifacts of these procedures, leading to the highest negative values in regions occupied by stars. Due to the uncertain data reduction history of these files, it is recommended that they be used as a guide to the spatial morphologies of the emission lines, but not as a measurement of absolute intensity.
As tabulated in greater detail in File Names and Content, maps of six emission lines were extracted from these Vela SNR data: C IV, Si IV, He II, O VI, O III, and C III.