Mapping the Local Interstellar Medium with High-Resolution UV Absorption Spectroscopy

Observations using the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope have provided high-resolution near ultraviolet (UV) spectra showing MgII, FeII and MnII absorption due to the local interstellar medium (LISM). Spectra were analyzed towards 34 stars within 100 parsecs and across a wide range of spectral types. Observations span the entire sky, probing previously unobserved regions of the LISM. The heavy ions studied in this survey produce narrow absorption features that make possible the identification of multiple interstellar components. Simultaneous fits of the MgII, FeII, and MnII multiplets reveal anywhere from one to six individual absorption components in a particular sight line, where the number of absorbers roughly correlates with the length of the sight line. The simultaneous fitting procedure reduces the systematic errors involved in continuum placement and in determining the number of absorbers. Sight lines show evidence of previously unidentified clouds within the Local Bubble. These measurements will be added to a growing data set of 81 near UV sight lines. The increase in the number of sight lines will test and improve a three-dimensional dynamical model of the local interstellar medium. With an improved understanding of the LISM’s kinematical structure, it will be possible to distinguish blended components within the absorption features of lighter ions. Specifically, the MAST Archive contains far UV observations of interstellar absorption by low mass ions (DI, CII, NI, OI) along the same sight lines. The combination of these data will constrain properties of the LISM such as temperature, turbulence, ionization, abundances and depletions.