DETECTION OF HIGHLY IONIZED C IV GAS WITHIN THE LOCAL CAVITY

Abstract

We present high resolution (R = 114,000) ultraviolet measurements of the interstellar absorption line profiles of the CIV (1550 A) high ionization doublet recorded towards the nearby B2Ve star HD 158427 (d~74pc). These data, which were recorded with the recently re-furbished STIS instrument on the HST, represent the most convincing detection yet of highly ionized CIV absorption that can be associated with interstellar gas located within the boundary of the Local Cavity. Two highly ionized gas clouds at V1 = -24.3 km/s and V2 = -41.3 km/s are revealed in both CIV absorption lines, with the V1 component almost certainly being due to absorption by the Local Interstellar Cloud (d<5pc). 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) indicates an unusually low gas temperature of less than 34,000K 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 Local Cavity can be best described as being 'patchy' in nature.