This report covers the workings of Commission 26 over the triennial period 2012-2015 and is the last report of the Commission. Included are reports from Working Groups and the Commission 26 Circular; all of which will be continuing in Commission G1 (Binary and Multiple Stars). Also included is a report of the Splinter Meeting of Commissions 26, 42 & G1, submitted observatory reports and a history of Commission 26.

Main Publications:

Abt, H. A. 2008, The Difference Between Metal-Poor and Metal-Rich Binaries, AJ, 135, 722

Abt, H. A. 2009, Stellar Rotation versus Duplicity in Open Cluster Early-Type Stars, PASP, 121, 1307

Abt, H. A. 2010, The Origin of the Exoplanets, PASP, 122, 1015

Using Hipparcos and Tycho-2 data, together with the radial velocity information, a statistical analysis is applied to all the orbital solutions of planetary candidates, in order to avoid a bias towards small inclinations. There are hints of additional, longer period companions.

The Hipparcos astrometry is used mainly for the derivation of stellar physical quantities such as luminosity, masses and velocity. However, sample selections on data with observational errors or an intrinsic dispersion may lead to biased estimates, especially when the error distributions are non-Gaussian. We review the classical biases and the ways to avoid them through the use of statistical methods.