MOLECULAR-HYDROGEN IN THE VICINITY OF NGC-7538 IRS-1 AND IRS-2 - TEMPERATURE AND ORTHO-TO-PARA RATIO

We made near-infrared spectroscopic observations of the active star-forming region near NGC 7538 IRS 1 and IRS 2. The relative intensities of the upsilon = 1 --> 0 Q(1), Q(3), and Q(5) lines of molecular hydrogen are used to calculate a rotational excitation temperature. The I(Q)(3):I(Q)(1) line intensity ratio implies a rotational temperature of approximately 763 +/- 27 K. The I(Q)(5):I(Q)(1) line intensity ratio implies a rotational temperature of approximately 971 +/- 37 K. Comparison of the measured intensity of the Q(2) transition relative to the intensity of Q(1) and Q(3) permitted the retrieval of the ratio of ortho-to-para hydrogen. We find that a ortho-to-para ratio of between 1.6 and 2.35 is needed to explain the Q-branch line intensity ratios, depending on the excitation model used. This range in ortho-to-para ratios implies a range of molecular hydrogen formation temperature of approximately 105 K to 140 K.