Chemical Tagging can Work: Identificaton of Stellar Phase-Space Structures Purely by Chemical-Abudance Similarity

Hogg, David W. and Casey, Andrew R. and Ness, Melissa and Rix, Hans-Walter and Foreman-Mackey, Daniel and Mészáros, Szabolcs (2016) Chemical Tagging can Work: Identificaton of Stellar Phase-Space Structures Purely by Chemical-Abudance Similarity. ASTROPHYSICAL JOURNAL, 833 (2). ISSN 1538-4357

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Abstract

Chemical tagging promises to use detailed abundance measurements to iden- tify 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 abun- dances for ∼ 105 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 in- formation (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 abun- dance measurements delivered by The Cannon; the prospects for future data sets appear very good.

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