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The G160M grating of the Goddard High Resolution Spectrograph on board the Hubble Space Telescope Spectra has been used to record spectra between 1150 and 1600 Angstroms with an instrumental resolution near 16 km/s. The gaseous interstellar abundances of five heavy elements along the light paths to 23 Ori, 15 Mon, 1 Sco, Pi Sco, and Pi Aqr were determined from the observations. The 1400.450 Angstrom line of Sn II was detected and identified toward three stars; at atomic number Z = 50, tin is the first element from the fifth row of the periodic table to be identified in the interstellar medium. One spectral line of each of Cu II (Z = 29) and Ga II (Z = 31), three lines of Ge II (Z = 32), and two lines of Kr I (Z = 36) were also detected toward some or all of the five stars. The depletions of these five heavy elements generally decrease monotonically with increasing atomic number toward each of the five stars, and tin is generally undepleted within the observational errors. The depletions of 26 elements from the interstellar gas in a typical dense interstellar cloud appear to correlate more closely with the elemental nebular condensation temperatures than with the first ionization potentials. Support for this work was provided by NASA through grant number GO-2251.01-87A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
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