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 V 1 = −24.3 km s −1 and V 2 = −41.3 km s −1 are revealed in both C iv absorption lines, with the V 1 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 V 2 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 V 2 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.