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Fig. 1

image

Schematic view explaining the origin of absorption lines towards the GC. Part of the absorption is taking place in the Earth’s atmosphere (left). This is usually calibrated using reference stars. However, residuals may still be present or genuine astrophysical absorption lines may be difficult to access if they fall onto an atmospheric line. Part of the absorption may take place in the cold, dense, and diffuse ISM in the LOS towards the GC (middle, Whittet et al. 1997). Most of this absorption probably takes place within the final few hundred parsecs. Goto et al. (2014) point out that the absorptions cover a wide range of velocities and LOS locations within the central molecular zone close to the central stellar cluster. Within the central 10 pc there are a few molecular cloud complexes that come quite close to the LOS (right). Following Lee et al. (2008) some of them are indicated here. The 50 km s−1 cloud has been indicated in light blue. See comments on the 50 km s−1 extension inthe caption of Fig. 6. Finally, individual absorptions in the local environment of the central cluster maytake place (right inset). This may happen against the minispiral or against the bowshocks, shells, and circumstellar envelopes of some or the MIR excess sources in the central cluster. Some representative structures have been indicated in the inset.

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