H2 Excitation Structure on the Sightlines to delta Scorpius and zeta Ophiucus - 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 1020-1070A spectroscopy of four sightlines through the local interstellar medium. High signal-to-noise (S/N) spectra of eta Uma, alpha Vir, delta Sco, and zeta Oph were obtained during a 21 April 2013 rocket flight. The SLICE observations constrain the density, molecular photoexcitation rates, and physical conditions present in the interstellar material towards delta Sco and zeta Oph. Our spectra indicate a factor of two lower total N(H2) than previously reported for delta Sco, which we attribute to higher S/N and better scattered light control in the new SLICE observations. We find N(H2) = 1.5 x 1019 cm-2 on the delta Sco sightline, with kinetic and excitation temperatures of 67 and 529 K, respectively, and a cloud density of nH = 56 cm-3. Our observations of the bulk of the molecular sightline toward zeta Oph are consistent with previous measurements (N(H2) ~ 3 x 1020 cm-2 at T01 = 66 K and Texc = 350 K). However, we detect significantly more rotationally excited H2 towards zeta Oph than previously observed. We infer a cloud density in the rotationally excited component of nH ~ 7600 cm-3 and suggest that the increased column densities of excited H2 are a result of the ongoing interaction between zeta Oph and its environment; also manifest as the prominent mid-IR bowshock observed by WISE and the presence of vibrationally-excited H2 molecules observed by HST.