An optical--near-IR study of a triplet of super star clusters in the
  starburst core of M82
  We present HST/STIS optical and Gemini/NIFS near-IR IFU spectroscopy, and
archival HST imaging of the triplet of super star clusters (A1, A2 and A3) in
the core of the M82 starburst. Using model fits to the STIS spectra, and the
weakness of red supergiant CO absorption features (appearing at ~6 Myr) in the
NIFS H-band spectra, the ages of A2 and A3 are $4.5\pm1.0$~Myr. A1 has strong
CO bands, consistent with our previously determined age of $6.4\pm0.5$~Myr. The
photometric masses of the three clusters are 4--$7\times10^5$~\Msol, and their
sizes are $R_{\rm eff}=159$, 104, 59~mas ($\sim$2.8, 1.8, 1.0~pc) for A1,2 and
3. The STIS spectra yielded radial velocities of $320\pm2$, $330\pm6$, and
$336\pm5$~\kms\ for A1,2, and 3, placing them at the eastern end of the $x_2$
orbits of M82's bar. Clusters A2 and A3 are in high density (800--1000~\cmt)
environments, and like A1, are surrounded by compact H\two\ regions. We suggest
the winds from A2 and A3 have stalled, as in A1, due to the high ISM ambient
pressure. We propose that the 3 clusters were formed \textit{in-situ} on the
outer $x_2$ orbits in regions of dense molecular gas subsequently ionized by
the rapidly evolving starburst. The similar radial velocities of the 3 clusters
and their small projected separation of $\sim 25$~pc suggest that they may
merge in the near future unless this is prevented by velocity shearing.
