Far Ultraviolet Spectroscopic Explorer () observations of emitting and absorbing gas in the Local Interstellar Chimney

¹ Experimental Astrophysics Group, Space Sciences Laboratory, UC Berkeley, Berkeley, CA 94720, USA
² Eureka Scientific, 2452 Delmer Street, Oakland, CA 94602-3017, USA
³ Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089, USA
⁴ Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
⁵ Service d'Aéronomie du CNRS, 91371 Verrières-le-Buisson, France

Corresponding author: B. Y. Welsh, bwelsh@ssl.berkeley.edu

Received: 12 March 2002
Accepted: 7 August 2002

Abstract

We present Far Ultraviolet Spectroscopic Explorer () satellite measurements of the absorption and emission characteristics of interstellar gas associated with the Local Interstellar Chimney, which is an extension of the rarefied Local Bubble cavity that extends outward from the galactic disk towards the lower galactic halo. Far ultraviolet (FUV) diffuse background emission has been detected in the high ionization line of O VI (λ1032 Å) for two lines-of-sight (, ) and (, ) at emission levels of  photons cm^-2 s^-1 sr^-1 (LU) and  LU respectively. These levels of O VI emission are very similar to those found for four other lines-of-sight sampled thus far by the satellite, implying a fairly constant level of average O VI surface brightness emission at high galactic latitudes of about 2700 LU with a standard deviation of 450 LU.
These emission-line data are supplemented by FUV interstellar absorption line measurements taken towards the hot DA white dwarf star, REJ 1032+532 (, ), whose distance of 116 pc places it within the Local Bubble region. No high ionization interstellar O VI λ1032 Å absorption has been detected  cm^-2), which is consistent with the non-detections of interstellar C IV and Si IV absorption reported towards this star by Holberg et al. ([CITE]). Taken together, our FUV absorption and emission data may be explained by a scenario in which the O VI emission and absorption lines are formed at the conductive interface of the neutral boundary to the Local Bubble. For the presently sampled sight-lines we have found no correlation between the OVI emission line intensity and the associated 0.25 keV soft X-ray background flux as measured in the R1 and R2 bands by the satellite. The OVI line intensities also show no correlation with the soft X-ray background flux attributable to emission from the million degree K gas of the Local Hot Bubble as modeled by Kuntz & Snowden ([CITE]). Any (new) model of the Local Bubble must now be able to explain (i) the low levels of variability in both the O VI emission-line intensity and the associated soft X-ray background flux for galactic sight-lines > °, (ii) the observed pressure of  cm^-3 K for the local hot interstellar gas, and (iii) the paucity of high ionization absorption lines observed within the local ISM and the sudden increase in their measured column density for distances beyond the Local Bubble neutral boundary.