The present-day mass function of the Quintuplet cluster
  Context: The stellar mass function is a probe for a potential dependence of
star formation on the environment. Only a few young clusters are known to
reside within the Central Molecular Zone and can serve as testbeds for star
formation under the extreme conditions in this region. Aims: We determine the
present-day mass function of the Quintuplet cluster, a young massive cluster in
the vicinity of the Galactic centre. Methods: We use two epochs of high
resolution near infrared imaging data obtained with NAOS/CONICA at the ESO VLT
to measure the individual proper motions of stars in the Quintuplet cluster in
the cluster reference frame. An unbiased sample of cluster members within a
radius of 0.5 pc from the cluster centre was established based on their common
motion with respect to the field and a subsequent colour-cut. Initial stellar
masses were inferred from four isochrones covering ages from 3 to 5 Myr and two
sets of stellar evolution models. For each isochrone the present-day mass
function of stars was determined for the full sample of main sequence cluster
members using an equal number binning scheme. Results: We find the slope of the
present-day mass function in the central part of the Quintuplet cluster to be
alpha = -1.66+-0.14 for an approximate mass range from 5 to 40M_Sun, which is
significantly flatter than the Salpeter slope of alpha = -2.35. The flattening
of the present-day mass function may be caused by rapid dynamical evolution of
the cluster in the strong Galactic centre tidal field. The derived mass
function slope is compared to the values found in other young massive clusters
in the Galaxy.
