ORFEUS II echelle spectra: Absorption by H2 in the LMC
K. S. de Boer, P. Richter, D. J. Bomans, A. Heithausen, J. Koornneef
Abstract
We present the first detection of molecular hydrogen (H2) UV absorption profiles on the line of sight to the LMC. The star LH 10:3120 in the LMC was measured with the ORFEUS telescope and the Tuebingen echelle spectrograph during the space shuttle mission of Nov./Dec. 1996. 16 absorption lines from the Lyman band are used to derive the column densities of H2 for the lowest 5 rotational states in the LMC gas. For these states we find a total column density of N(H2)=6.6 x 1018$ cm-2 on this individual line of sight. We obtain equivalent excitation temperatures of T < 50 K for the rotational ground state and T = 470 K for 0 < J < 6 by fitting the population densities of the rotational states to theoretical Boltzmann distributions. We conclude that UV pumping dominates the population of the higher rotational levels, as known from the H2 gas in the Milky Way. (Research supported in part by the DARA)
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