H2 excitation structure on the sightlines to δ scorpii and ζ ophiuci: First results from the sub-orbital local interstellar cloud experiment

Abstract

We present the first science results from the Sub-orbital Local Interstellar Cloud Experiment (SLICE): moderate resolution 1020-1070 Å spectroscopy of four sightlines through the local interstellar medium. High signal-to-noise (S/N) spectra of η Uma, α Vir, δ Sco, and ζ Oph were obtained during a 2013 April 21 rocket flight. The SLICE observations constrain the density, molecular photoexcitation rates, and physical conditions present in the interstellar material toward δ Sco and ζ Oph. Our spectra indicate a factor of two lower total N(H2) than previously reported for δ Sco, which we attribute to higher S/N and better scattered light control in the new SLICE observations. We find N(H2) = 1.5 × 1019 cm-2 on the δ Sco sightline, with kinetic and excitation temperatures of 67 and 529 K, respectively, and a cloud density of n H = 56 cm-3. Our observations of the bulk of the molecular sightline toward ζ Oph are consistent with previous measurements (N(H2) ≈ 3 × 1020 cm-2 at T 01(H2) = 66 K and T exc = 350 K). However, we detect significantly more rotationally excited H2 toward ζ Oph than previously observed. We infer a cloud density in the rotationally excited component of n H ≈ 7600 cm-3 and suggest that the increased column densities of excited H2 are a result of the ongoing interaction between ζ Oph and its environment; also manifest as the prominent mid-IR bowshock observed by WISE and the presence of vibrationally excited H 2 molecules observed by the Hubble Space Telescope. © 2013. The American Astronomical Society. All rights reserved.