We present an analysis of interstellar H2 toward HD 37903, which is a hot, B
1.5 V star located in the NGC 2023 reflection nebula. Meyer et al. (2001) have
used a rich spectrum of vibrationally excited H2 observed by the HST to
calculate a model of the interstellar cloud toward HD 37903. We extend Mayer's
analysis by including the v"=0 vibrational level observed by the FUSE
satellite.
The T01 temperature should not be interpreted as a rotational temperature,
but rather as a temperature of thermal equilibrium between the ortho and para
H2. The ortho to para H2 ratio is lower for collisionally populated levels than
for the levels populated by fluorescence.
The PDR model of the cloud located in front of HD 37903 points to a gas
temperature Tkin=110-377 K, hydrogen density nH=1874-544 cm^-3 and the
star-cloud distance of 0.45 pc
