Deep Hα imagery of the Eridanus shells

A deep Hα image of interlocking filamentary arcs of nebulosity has been obtained with a wide-field (≈30° diameter) narrow-band filter camera combined with a charge-coupled device as a detector. The resultant mosaic of images, extending to a galactic latitude of −65°, has been corrected for field distortions and had galactic coordinates superimposed on it to permit accurate correlations with the most recent H i (21 cm), X-ray (0.75 keV) and FIR (IRAS 100 μm) maps. Furthermore, an upper limit of 0.13 arcsec yr−1 to the expansion proper motion of the primary 25° long nebulous arc has been obtained by comparing a recent Hα image obtained with the San Pedro Martir telescope of its filamentary edge with that on a Palomar Observatory Sky Survey E plate obtained in 1951. It is concluded that these filamentary arcs are the superimposed images of separate shells (driven by supernova explosions and/or stellar winds) rather than the edges of a single ‘superbubble’ stretching from Barnard's Arc (and the Orion Nebula) to these high galactic latitudes. The proper motion measurement argues against the primary Hα-emitting arc being associated with the giant radio loop (Loop 2) except in extraordinary circumstances.

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