Candidates of Halpha emitting regions in Magellanic Stream IV cloud
  From H\alpha narrow band observations, we identified three H\alpha emitting
regions in the direction of Magellanic Stream IV (MS IV). They consist of three
parallel filaments with 2 arcmin width and 6 -- 30 arcmin length at 12 arcmin
intervals. The mean surface brightness of them is $\sim 2 \times 10^{-18}$ erg
s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. Because of their low surface brightness, the
regions were not detected in previous H\alpha surveys. In HI map, the position
of the filaments overlap MS, suggesting that they are parts of MS, but there
also exists a local HI structure. If the filaments associate with MS, the sizes
are 30 pc $\times$ 100 -- 500 pc. The filaments lie at the leading edge of a
downstream cloud, which supports a shock heating and its propagation (shock
cascade) model for the ionizing source. If they are local objects, on the other
hand, Fossil Str\"omgren Trails of more than two stars is a possible
interpretation, and the sizes would be 0.1 pc $\times$ 0.3 -- 1.5 pc at 180 pc
distance. The positional information of the H\alpha filaments presented in this
letter enables us future spectroscopic observations to clarify their nature.
