Contributed Talk

Using Diffuse Interstellar Bands to Probe the Local Bubble

¹Mandy Bailey, ¹Jacco van Loon, ²Keith Smith, ²Peter Sarre (¹Keele University, ²University of Nottingham)

The Local Bubble (LB) is a region which extends for ~100 pc in the plane of the Galaxy and hundreds of parsecs vertically. The presence of the LB was inferred by observations of diffuse soft-X-ray background emissions, which indicated that the Sun is surrounded a region of low density, highly ionized (million K) gas. However, there are observational inconsistencies including the failure by the NASA CHIPS satellite to detect the EUV line-emission, which should be emitted by such a volume of hot gas. In order to understand the nature of gas in high temperature environments such as the Local Bubble we are using absorption in the Diffuse Interstellar Bands (DIBs). The carriers of DIBs are thought to be large molecules such as polycyclic aromatic hydrocarbons (PAHs) and such molecules are resistant to UV radiation. Observations of DIBs have shown that they are sensitive to their environment with some known to exist in hot, UV-irradiated environments. The ratio of l5780/ l5797 equivalent widths is indicative of the transition between diffuse atomic and diffuse molecular gas, with a high l5780/ l5797 ratio indicating the existence of interfaces between cool/warm-hot gas. Here I present results from our survey of DIB absorption in the spectra of nearby stars being conducted with the New Technology Telescope (NTT) at La Silla. These results map the distribution of the DIB carriers in and around the LB and give an insight into how the conditions change within the LB as traced by the relative strengths of various families of DIBs and atomic absorption (Na I D). I will discuss the possibility of neutral structures located within the bubble itself, the kinematics of the ISM and how our survey provides a first point of reference for an ongoing systematic investigation of time-varying interstellar absorption which will ultimately probe the tiny-scale structure of the local ISM. Results from a similar experiment, with the Anglo-Australian Telescope (AAT), targeting early-type stars in the Magellanic Clouds are also presented; here contributions from the ISM within the Magellanic Clouds can be separated from those originating in the Galactic Halo and Disc.

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