Transformation Methods for Trigonometric Parallaxes
H. Smith
University of Florida,
USA
The idea of transforming a measured trigonometric parallax to
some auxiliary variable for the purposes of estimating distances and
absolute magnitudes was suggested by Smith and Eichhorn in 1996. This
approach was proposed as an essentially assumption-free alternative
to Bayesian and modelling methods. At the time there were three major
issues left outstanding: (1) improvement of the method for estimating
absolute magnitude; (2) satisfactory treatment of the uncertainty in
the quantities obtained from the transformations, in particular in the
direction of symmetry of the pdf; and (3) extension of the methods
beyond relative error values of 1-2. Subsequently an additional issue
has arisen, namely the effect of the stellar spatial distribution on the
method. The progress made in resolving these issues will be discussed,
and some comments will be made regarding the role of transformation
methods within the larger framework of distance estimation and the
calibration problem.