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ORFEUS II echelle spectra: Absorption by H_2 in the LMC

K. S. de Boer·P. Richter·D. J. Bomans·A. Heithausen·J. Koornneef
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Abstract

We present the first detection of molecular hydrogen (H_2) 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 H_2 for the lowest 5 rotational states in the LMC gas. For these states we find a total column density of N(H_2)=6.6 x 10^18$ 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 H_2 gas in the Milky Way. (Research supported in part by the DARA)

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K. S. de Boer, P. Richter, D. J. Bomans, A. Heithausen, J. Koornneef. 1998-08-24. ORFEUS II echelle spectra: Absorption by H_2 in the LMC. https://arxiv.org/abs/astro-ph/9808256

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