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R. A. Benjamin (U. of Wisconsin-Madison), P.R. McCullough (U. of Illinois), G.J. Madsen (U. of Wisconsin-Madison)
We present new spectroscopic observations of an unusual linear ionized filament reported earlier by McCullough and Benjamin (2001, AJ, Vol. 122, p. 1500). This extremely narrow, extremely linear, ionized filament has previously been detected in two independent H-alpha images, and is 2.5 degrees long and has an H\alpha surface brightness of 0.5 rayleighs, and is located at (l,b)=(139,38). The filament is approximately ``Y'' shaped. The widest separation of the two diagonal segments is 5 arcminutes. The two most likely hypotheses for this structure are that it is an unusually linear filamentation associated with a nearby large-angle nebula or a "Fossil Stromgren Trail" left by a low luminosity ionizing source. We discuss the search for an associated ionizing source, resulting in one inconclusive candidate: RSXJ094247.2+700238. Here, we present the first spectra of this filament using WHAM (Wisconsin H-alpha Mapper). These spectra yield the velocity of the filament, confirming that it is indeed Galactic and local. Comparison of emisison lines from [S II], [N II], and H-alpha will also be used to constrain the ionization structure of the filament and its origin. We also discuss how this structure might be useful to constrain the thermal and velocity structure of the nearby interstellar medium.
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