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S. Redfield (JILA, University of Colorado), J. L. Linsky (JILA, University of Colorado, and NIST), B. E. Wood (JILA, University of Colorado)
We present an analysis of the Local Interstellar Medium (LISM) towards the Hyades star cluster. High resolution (E230H), HST/STIS spectra taken from the HST Data Archive were used. The Mg~II h and k lines of 18 targets were used to calculate relevant ISM parameters (velocity, Doppler parameter, and column density). Three velocity components are observed. Absorption due to the Local Interstellar Cloud (LIC) is seen in all targets. A second cloud, the Hyades Cloud, is observed in ten of the 18 targets. A third component is seen in one object. Deviations from the LIC velocity vector (Lallement et al. 1995) are observed and may have implications for the three-dimensional structure and evolution of the LIC. We discuss the characteristics of all clouds, and make comparisons with previously observed, nearby targets.
Due to the close proximity of the lines of sight, we use this sample to investigate the microstructure of the LISM and LIC. Changes in column density do not exceed a factor of two at angular distances of less than 10\circ. We discuss the implications of the homogeneity or inhomogeneity of the LISM.
This research is funded by NASA grant NGT5-50242.
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