Chemical tagging can work: Identification of stellar phase-space
  structures purely by chemical-abundance similarity
  Chemical tagging promises to use detailed abundance measurements to identify
spatially separated stars that were in fact born together (in the same
molecular cloud), long ago. This idea has not yielded much practical success,
presumably because of the noise and incompleteness in chemical-abundance
measurements. We have succeeded in substantially improving spectroscopic
measurements with The Cannon, which has now delivered 15 individual abundances
for ~100,000 stars observed as part of the APOGEE spectroscopic survey, with
precisions around 0.04 dex. We test the chemical-tagging hypothesis by looking
at clusters in abundance space and confirming that they are clustered in phase
space. We identify (by the k-means algorithm) overdensities of stars in the
15-dimensional chemical-abundance space delivered by The Cannon, and plot the
associated stars in phase space. We use only abundance-space information (no
positional information) to identify stellar groups. We find that clusters in
abundance space are indeed clusters in phase space. We recover some known
phase-space clusters and find other interesting structures. This is the
first-ever project to identify phase-space structures at survey-scale by blind
search purely in abundance space; it verifies the precision of the abundance
measurements delivered by The Cannon; the prospects for future data sets appear
very good.
