In Search of an Interface between Warm and Hot Gas within the Local Bubble

Abstract

We have examined UV spectra recorded by the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope for three stars, HD32309, 41 Ari, and $\eta$~Tel, that are located well inside the boundary of the Local Hot Bubble in our search for absorption features of Si IV, C IV, and N V that could reveal the presence of an interface between the local warm ($T\sim 7000$ K) neutral medium and a more distant hot ($T\sim 10^6$ K) interstellar medium. In all cases, we failed to detect such ions. Our most meaningful upper limit is that for log N(C IV)< 11.86 toward HD32309, which is below the expectation for a sight line that penetrates either a conductive/evaporative interface or a turbulent mixing layer. We offer conjectures on the reasons for these negative results in terms of either a suppression of a conductive layer caused by the shielding of the local cloud by other clouds, which may make it more difficult for us to sense discrete absorption features from gases at intermediate temperatures, or by the presence of a tangential magnetic field at most locations on the surface of the local cloud.

14 pages, 1 figure, accepted for publication in the Astrophysical Journal

References in corpus (10)

• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• The Structure of the Local Interstellar Medium V: Electron Densities
• Multiphase Gas and the Fractal Nature of Radiative Turbulent Mixing Layers
• The Far Ultraviolet Spectroscopic Explorer Survey of OVI Absorption in the Disk of the Milky Way
• The origin of the 'local' 1/4 keV X-ray flux in both charge exchange and a hot bubble
• The Structure of the Local Hot Bubble
• Numerical Study of Turbulent Mixing Layers with Non-Equilibrium Ionization Calculations
• The interstellar cloud surrounding the Sun: a new perspective
• Numerical Simulations of Supernova Remnant Evolution in a Cloudy Interstellar Medium
• A High Spectral Resolution Study of the Soft X-ray Background with the X-ray Quantum Calorimeter

Cited by in corpus (1)

• The Origin of the Cluster of Local Interstellar Clouds