Journal of The Korean Astronomical Society (천문학회지)

The Korean Astronomical Society (한국천문학회)
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ORFEUS OBSERVATIONS OF ULTRAVIOLET EXCITED HIGH-J MOLECULAR HYDROGEN

  • Lee, Dae-Hee (Korea Astronomy and Space Science Institute) ;
  • Dixon, W. Van Dyke (Department of Physics and Astronomy, The Johns Hopkins University) ;
  • Min, Kyoung-Wook (Korea Advanced Institute of Science and Technology) ;
  • Pak, Soo-Jong (Department of Astronomy and Space Science, Kyung Hee University)
  • Published : 2009.12.31
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Abstract

We present measurements of diffuse interstellar $H_2$ absorption lines in the continuum spectra of 10 early-type stars. The data were observed with the Berkeley Extreme and Far-Ultraviolet Spectrometer (BEFS) of the ORFEUS telescope on board the ORFEUS-SPAS I and II space-shuttle missions in 1993 and 1996, respectively. The spectra extend from the interstellar cutoff at 912 $\AA$ to about 1200 $\AA$ with a resolution of ~ 3000 and statistical signal-to-noise ratios between 10 and 65. Adopting Doppler broadening velocities from high-resolution optical observations, we obtain the $H_2$ column densities of rotational levels J" = 0 through 5 for each line of sight. The kinetic temperatures derived from J" = 0 and 1 states show a small variation around the mean value of 80 K, except for the component toward HD 219188, which has a temperature of 211 K. Based on a synthetic interstellar cloud model described in our previous work, we derive the incident UV intensity IUV and the hydrogen density $n_H$ of the observed components to be -0.4 $\leq$ log $I_{UV}\leq2.2$ and $6.3{\leq}n_H2500cm^{-3}$, respectively.

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