The M31 globular cluster system: ugriz and K-band photometry and
  structural parameters
  We present an updated catalogue of M31 globular clusters (GCs) based on
images from the Wide Field CAMera (WFCAM) on the UK Infrared Telescope and from
the Sloan Digital Sky Survey (SDSS). Our catalogue includes new,
self-consistent ugriz and K-band photometry of these clusters. We discuss the
difficulty of obtaining accurate photometry of clusters projected against M31
due to small scale background structure in the galaxy. We consider the effect
of this on the accuracy of our photometry and provide realistic photometric
error estimates. We investigate possible contamination in the current M31 GC
catalogues using the excellent spatial resolution of these WFCAM images
combined with the SDSS multicolour photometry. We identify a large population
of clusters with very blue colours. Most of these have recently been proposed
by other work as young clusters. We distinguish between these, and old
clusters, in the final classifications. Our final catalogue includes 416 old
clusters, 156 young clusters and 373 candidate clusters. We also investigate
the structure of M31's old GCs using previously published King model fits to
these WFCAM images. We demonstrate that the structure and colours of M31's old
GC system are similar to those of the Milky Way. One GC (B383) is found to be
significantly brighter in previous observations than observed here. We
investigate all of the previous photometry of this GC and suggest that this
variability appears to be genuine and short lived. We propose that the large
increase in its luminosity my have been due to a classical nova in the GC at
the time of the previous observations in 1989.
