AAS 196th Meeting, June 2000
Session 40. High Resolution Spectroscopy at Visible and Ultraviolet Wavelengths
Topical Contributed Display, Wednesday, June 7, 2000, 10:00am-7:00pm, Empire Hall South

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[40.04] STIS Observations of the Interstellar Medium Toward the Disk Star HD 202347. I. Properties of the +39 km s-1 ~Cloud.

C. M. Oliveira, K. R. Sembach, H. W. Moos (Johns Hopkins University)

We present high resolution Space ~Telescope ~Imaging ~Spectrograph spectra of ultraviolet absorption in an interstellar cloud with vLSR~ \approx +39 km ~s-1 toward HD 202347 (l = 88\circ.22, b = -2\circ.08, d~\approx 900~±~400 pc). The use of the near-UV and far-UV high resolution echelles at a resolving power \lambda / \Delta\lambda=228,000 results in a velocity resolution of 2.6 km ~s-1 and 1.3 km~s-1 (FWHM) respectively, with a S/N ~ 30~-~50. This unique datatset is composed of spectra with a wavelength coverage from 1160~Å~to 2660~Å.

Absorption by this cloud is present in ultraviolet lines of C~I, C~I\star, C~I\star\star, C~II, C~II\star, N~I, O~I, Si~II, S~II and Fe~II. Photoionization equilibrium of CI/CII and SI/SII combined with line width measurements of high resolution optical absorption by Ca II may suggest an electron density as high as ne~~~15~cm-3 and a temperature T~~~13000 K.

The velocity of this cloud is not consistent with models of differential Galactic rotation in this direction, which predict -32~km~s-1~\leq~vLSR~\leq~0~km~s-1 for this line of sight. There is no detectable HI 21 cm emission at this velocity indicating perhaps that most of the hydrogen is ionized or that this is a low column density cloud. In this paper we explore possible ionization conditions within the cloud and its elemental abundances.

Support for this work at JHU is provided by NASA contract NAS5-30403 from the Space Telescope Science Institute.

The author(s) of this abstract have provided an email address for comments about the abstract: oliveira@pha.jhu.edu

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