Isochrone fitting in the Gaia era
  Context. Currently galactic exploration is being revolutionized by a flow of
new data: Gaia provides measurements of stellar distances and kinematics;
growing numbers of spectroscopic surveys provide values of stellar atmospheric
parameters and abundances of elements; and Kepler and K2 missions provide
asteroseismic information for an increasing number of stars. Aims. In this work
we aim to determine stellar distances and ages using Gaia and
spectrophotometric data in a consistent way. We estimate precisions of age and
distance determinations with Gaia end-of-mission and TGAS parallax precisions.
Methods. To this end we incorporated parallax and extinction data into the
isochrone fitting method used in the Unified tool to estimate Distances, Ages,
and Masses (UniDAM). We prepared datasets that allowed us to study the
improvement of distance and age estimates with the inclusion of TGAS and Gaia
end-of-mission parallax precisions in isochrone fitting. Results. Using TGAS
parallaxes in isochrone fitting we are able to reduce distance and age estimate
uncertainties for TGAS stars for distances up to 1 kpc by more than one third,
compared to results based only on spectrophotometric data. With Gaia
end-of-mission parallaxes in isochrone fitting we will be able to further
decrease our distance uncertainties by about a factor of 20 and age
uncertainties by a factor of two for stars up to 10 kpc away from the Sun.
Conclusions. We demonstrate that we will be able to improve our distance
estimates for about one third of stars in spectroscopic surveys and to decrease
log(age) uncertainties by about a factor of two for over 80% of stars as
compared to the uncertainties obtained without parallax priors using Gaia
end-of-mission parallaxes consistently with spectrophotometry in isochrone
fitting .
