The rich ultraviolet spectrum of vibrationally excited interstellar H2 toward HD 37903

Based on recent high-resolution Hubble Space Telescope Space Telescope Imaging Spectrograph observations over the 1160-1360 Angstrom wavelength region, we have discovered that HD 37903 (the illuminating star of the bright reflection nebula NGC 2023 in Orion) exhibits a rich spectrum of vibrationally excited interstellar H(2) absorption. We have identified a total of over 500 H(2) lines arising from various rotational levels (as high as J = 13) in all 14 excited vibrational states of the ground electronic state. Prior to this study, the only published UV absorption measurements of vibrationally excited interstellar H(2) consisted of two weak lines toward the star zeta Ophiuchi. In terms of abundance, the v = 3 J = 1 H(2) column density toward HD 37903 is over 200 times greater than that toward zeta Oph. Overall, the populations of the excited H(2) rovibrational states toward HD 37903 exhibit a nonthermal distribution that is consistent with the UV fluorescent excitation of dense (n(H) approximate to 10(4) cm(-3)) molecular gas located about 0.5 pc from the B1.5 V star. We contrast these results with those provided by near-IR H(2) emission-line studies of NGC 2023 and discuss opportunities for future UV observations of vibrationally excited H(2) toward HD 37903 and other sight lines.