Open star clusters in the Milky Way - Comparison of photometric and
  trigonometric distance scales based on Gaia TGAS data
  The global survey of star clusters in the Milky Way (MWSC) is a comprehensive
list of 3061 objects that provides, among other parameters, distances to
clusters based on isochrone fitting. The Tycho-Gaia Astrometric Solution (TGAS)
catalogue, which is a part of Gaia data release 1 (Gaia DR1), delivers accurate
trigonometric parallax measurements for more than 2 million stars, including
those in star clusters. We compare the open cluster photometric distance scale
with the measurements given by the trigonometric parallaxes from TGAS to
evaluate the consistency between these values. The average parallaxes of
probable cluster members available in TGAS provide the trigonometric distance
scale of open clusters, while the photometric scale is given by the distances
published in the MWSC. Sixty-four clusters are suited for comparison as they
have more than 16 probable members with parallax measurements in TGAS. We
computed the average parallaxes of the probable members and compared these to
the photometric parallaxes derived within the MWSC. We find a good agreement
between the trigonometric TGAS-based and the photometric MWSC-based distance
scales of open clusters, which for distances less than 2.3 kpc coincide at a
level of about 0.1 mas with no dependence on the distance. If at all, there is
a slight systematic offset along the Galactic equator between $30^\circ$ and
$160^\circ$ galactic longitude.
