A Unified tool to estimate Distances, Ages and Masses (UniDAM) from
  spectrophotometric data
  Galactic archaeology - the study of the formation and evolution of the Milky
Way by reconstructing its past from its current constituents - requires precise
and accurate knowledge of stellar parameters for as many stars as possible. To
achieve this a number of large spectroscopic surveys have been undertaken and
are still ongoing. So far consortia carrying out the different spectroscopic
surveys have used different tools to determine stellar parameters of stars from
their derived effective temperatures (Teff), surface gravities (log g) and
metallicities ([Fe/H]) possibly combined with photometric, astrometric,
interferometric or asteroseismic information. Here we aim to homogenise the
stellar characterisation by applying a unified tool to a large set of publicly
available spectrophotometric data. We use spectroscopic data from a variety of
large surveys combined with infra-red photometry from 2MASS and AllWISE and
compare these in a Bayesian manner with PARSEC isochrones to derive probability
density functions (PDFs) for stellar masses, ages and distances. We treat PDFs
of pre-helium-core burning, helium-core burning and post helium-core burning
solutions as well as different peaks in multi-modal PDFs (i.e. each unimodal
sub-PDF) of the different evolutionary phases separately. For over 2.5 million
stars we report mass, age and distance estimate for each evolutionary phase and
unimodal sub-PDF. We report Gaussian, skewed Gaussian, truncated Gaussian,
modified truncated exponential distribution or truncated Student's
t-distribution functions to represent each sub-PDF, allowing to reconstruct
detailed PDFs. Comparisons with stellar parameter estimates from the literature
show good agreement within uncertainties. We present UniDAM - the unified tool
applicable to spectrophotometric data of different surveys to obtain a
homogenised set of stellar parameters.
