Ultraviolet Spectroscopy of Circumnuclear Star Clusters in M83
  We analyze archival HST/STIS/FUV-MAMA imaging and spectroscopy of 13 compact
star clusters within the circumnuclear starburst region of M83, the closest
such example. We compare the observed spectra with semi-empirical models, which
are based on an empirical library of Galactic O and B stars observed with IUE,
and with theoretical models, which are based on a new theoretical UV library of
hot massive stars computed with WM-Basic. The models were generated with
Starburst99 for metallicities of Z=0.020 and Z=0.040, and for stellar IMFs with
upper mass limits of 10, 30, 50, and 100 M_sol. We estimate the ages and masses
of the clusters from the best fit model spectra, and find that the ages derived
from the semi-empirical and theoretical models agree within a factor of 1.2 on
average. A comparison of the spectroscopic age estimates with values derived
from HST/WFC3/UVIS multi-band photometry shows a similar level of agreement for
all but one cluster. The clusters have a range of ages from about 3 to 20 Myr,
and do not appear to have an age gradient along M83's starburst. Clusters with
strong P-Cygni profiles have masses of a few times 10^4 M_sol, seem to have
formed stars more massive than 30 M_sol, and are consistent with a Kroupa IMF
from 0.1-100 M_sol. Field regions in the starburst lack P-Cygni profiles and
are dominated by B stars.
