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   51057
   From recent Timing observation, the CGRO BASTE determined that the 38-s
   X-ray pulsar OAO 1657-415 is an eclipsing binary with an orbital period
   10.4436, and eclipse duration 1.70 d. Hence, this binary pulsar, OAO
   1657-415 is a system very similar with Vela X-1; they are just twin. We
   propose to observe this X-ray pulsar throughout its eclipse transition
   covering the phase of full eclipse, pre-eclipse ingress and post-
   eclipse egress. From the observation we investigate (1) iron emission
   during non-eclipse phase if it is 6.6 keV as was reported, (2)
   recombination emission lines from photo-ionization plasma during
   eclipse, (3) companion star atmosphere from eclipse transion, and (4)
   interstellar dust halo from soft-band image. These results will be
   compared with those of Vela X-1.
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