New Ultraviolet Extinction Curves for Interstellar Dust in M31
  New low-resolution UV spectra of a sample of reddened OB stars in M31 were
obtained with HST/STIS to study the wavelength dependence of interstellar
extinction and the nature of the underlying dust grain populations. Extinction
curves were constructed for four reddened sightlines in M31 paired with closely
matching stellar atmosphere models. The new curves have a much higher S/N than
previous studies. Direct measurements of N(H I) were made using the Ly$\alpha$
absorption lines enabling gas-to-dust ratios to be calculated. The sightlines
have a range in galactocentric distance of 5 to 14 kpc and represent dust from
regions of different metallicities and gas-to-dust ratios. The metallicities
sampled range from Solar to 1.5 Solar. The measured curves show similarity to
those seen in the Milky Way and the Large Magellanic Cloud. The Maximum Entropy
Method was used to investigate the dust composition and size distribution for
the sightlines observed in this program finding that the extinction curves can
be produced with the available carbon and silicon abundances if the metallicity
is super-Solar.
