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Session 45 - Interstellar Medium I.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center

[45.11] The UV Interstellar Extinction in Nearby Galaxies: M31

L. Bianchi (STScI and O.A.TO), G. C. Clayton (CASA), R. Bohlin (STScI), J. B. Hutchings (DAO), P. Massey (KPNO-NOAO)

The wavelength dependence of the extinction gives information on dust in galaxies, which is an important tracer of global heavy element abundances. The steepness of the FUV extinction affects the ionisation and molecular chemistry of a galaxy, and is an important clue to the galaxy's global evolution. Knowledge of the extinction curve also enables us to make accurate corrections of observed stellar fluxes, and ultimately relating dust properties to global galaxy parameters has a broad astrophysical impact, allowing better extinction corrections in distant galaxies and AGN. For these reasons we are pursuing a broad observational program to study extinction properties in different galaxies.

We studied the UV IS extinction in M31 with Hubble Space Telescope (HST)-Faint Object Spectrograph (FOS) spectra of luminous stars in OB associations in M31, having a modest range of reddenings. We determined the UV extinction by: (a) comparing stars with the same spectral type, but different extinction amounts, in M31. This method eliminates both the foreground Galactic extinction and uncertainties in using standard stars from other galaxies, or model atmospheres for stars in other galaxies (with associated metallicity effects); (b) comparing M31 stars with model atmospheres, and with Galactic stars. The resulting average M31 extinction curve has a weak 2175 Åbump and moderatly steep FUV extinction. Unlike previously published curves, the extinction in M31 rises into the far UV like the extinction in the Galaxy.

Program listing for Tuesday