Probing the Local Bubble with diffuse interstellar bands: I. Project overview and southern hemisphere survey

The Sun traverses a low-density, hot entity called the Local Bubble. Besides that, there is some unknown interstellar substance that causes a host of absorption bands across the optical spectrum, called diffuse interstellar bands (DIBs). We have started a project to chart the Local Bubble in a novel way and learn more about the carriers of the DIBs, by using DIBs as tracers of diffuse gas and environmental conditions. We conducted a high signal-to-noise spectroscopic survey of 670 nearby early-type stars to map DIB absorption in and around the Local Bubble. In this first paper in the series, we introduce the overall project and present the results from the southern hemisphere survey. As for the carriers of the DIBs, our observations confirm the notion that these are large molecules whose differences in behaviour are mainly governed by their differing resilience and/or electrical charge, with more subtle differences possibly related to varying excitation.