A&A 436, 615-632 (2005)
Highly ionized gas in the local ISM: Some like it hot?B. Y. Welsh1 and R. Lallement2
1 Experimental Astrophysics Group, Space Sciences Laboratory, UC Berkeley, Berkeley, CA 94720, USA
2 Service d'Aéronomie du CNRS, 91371 Verrières-le-Buisson, France
(Received 23 December 2004 / Accepted 18 February 2005 )
We present -STIS medium-resolution spectra ( km s-1) of the ultraviolet interstellar absorption lines observed towards 4 early-type stars located within the local interstellar medium (ISM), with sight-line distances <186 pc in the general direction of the Loop I superbubble ( , ). These data have been supplemented with high resolution ( km s-1) visible absorption observations of the NaI D-lines towards these 4 stars. Our main discovery is the detection of highly ionized absorption components of CIV, SiIV and NV towards the two most distant targets, HD 127381 and HD 142256. These lines-of-sight are known to cross both the near and far neutral interface boundaries to the Loop I cavity, in addition to intersecting the fragmented shell of neutral and partially ionized gas that defines the boundary to the Local Bubble. However, the presently measured narrow line profile-widths and their measured absorption intensities are found to be incompatible with theoretical models that predict high ion absorption due to the presence of evaporating cloud conduction interfaces. We conclude that the formation of high ions in the local ISM is highly dependent on the location of the absorbing gas clouds with respect to nearby sources of both hot X-ray emitting gas and/or photo-ionization.
Key words: ISM: bubbles -- ISM: kinematics and dynamics
© ESO 2005