DETECTION OF HIGHLY IONIZED C iv GAS WITHIN THE LOCAL CAVITY

We present high resolution (R = 114,000) ultraviolet measurements of the interstellar absorption line profiles of the C iv (1550 Å) high ionization doublet recorded toward the nearby B2Ve star HD 158427 (d ∼ 74 pc). These data, which were recorded with the recently re-furbished Space Telescope Imaging Spectrograph instrument on the Hubble Space Telescope, represent the most convincing detection yet of highly ionized C iv absorption that can be associated with interstellar gas located within the boundary of the Local Cavity (LC). Two highly ionized gas clouds at V1 = −24.3 km s−1 and V2 = −41.3 km s−1 are revealed in both C iv absorption lines, with the V1 component almost certainly being due to absorption by the Local Interstellar Cloud (d < 5 pc). Although the observed column densities for both cloud components can be explained by the predictions of current theoretical models of the local interstellar medium, the narrow Doppler width of the V2 line profile (b = 6.8 km s−1) indicates an unusually low gas temperature of ⩽34,000 K for this highly ionized component. It is conjectured that the V2 cloud may be due to an outflow of highly ionized and hot gas from the nearby Loop I superbubble. These new data also indicate that absorption due to highly ionized gas in the LC can be best described as being “patchy” in nature.