AAT and HST Spectroscopy of Small-Scale Interstellar Structure toward the Binary MU CRU

Details AAT and HST Spectroscopy of Small-Scale Interstellar Structure toward the Binary MU CRU AAT and HST Spectroscopy of Small-Scale Interstellar Structure toward the Binary MU CRU

Dec 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...191.5102l&link_type=abstract

American Astronomical Society, 191st AAS Meeting, #51.02; Bulletin of the American Astronomical Society, Vol. 29, p.1295

Astronomy and Astrophysics

Astronomy

Scientific paper

Observations of interstellar absorption lines toward both members of resolvable binary star systems provide a sensitive probe of small-scale structure in the diffuse ISM. Optical observations of Na 1 and Ca 2 at very high spectral resolution (Delta v=0.3 km s(-1) ) toward both members of the binary mu Cru have revealed line strength variations in at least 4 velocity components, indicative of ISM structure on scales less than the projected binary separation of 6600 AU (Meyer & Blades 1996, ApJL, 464, L179). We present new observations of the \ion{Na{1} D_2} line towards this binary taken with the Ultra-High Resolution Facility (UHRF) on the Anglo-Australian Telescope, as well as HST GHRS echelle observations of multiple lines of C 1, Mg 1, Cr 2, and Zn 2 for both stars. The \ion{Na{1} D_2} measurements show no variations in the line profile in either star between observations taken 21 months apart. This constancy coupled with the cold, quiescent nature of the gas responsible for most of the variation suggests that this material is not circumstellar. Of particular interest is the narrow (b=0.4 km s(-1) ) absorption component observed at v_{helio ~ -8.6 km s(-1) } towards mu (1) Cru, which is not seen in the spectrum of mu (2) Cru. Preliminary profile fits to the GHRS data using the component structure from the higher-resolution Na 1 data yield column density ratios for the neutral species of N(\ion{C{1})/N(Na 1) ~ 10} and N(\ion{Mg{1})/N(Na 1) ~ 6} for this component. These ratios differ from those typically seen in cold interstellar gas, and we explore a number of different models for the structure and physical conditions of the cloud in which this absorption arises.

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