Testing the chemical tagging technique with open clusters

Abstract

Context. Stars are born together from giant molecular clouds and, if we assume that the priors were chemically homogeneous and well-mixed, we expect them to share the same chemical composition. Most of the stellar aggregates are disrupted while orbiting the Galaxy and most of the dynamic information is lost, thus the only possibility of reconstructing the stellar formation history is to analyze the chemical abundances that we observe today. Aims. The chemical tagging technique aims to recover disrupted stellar clusters based merely on their chemical composition. We evaluate the viability of this technique to recover co-natal stars that are no longer gravitationally bound. Methods. Open clusters are co-natal aggregates that have managed to survive together. We compiled stellar spectra from 31 old and intermediate-age open clusters, homogeneously derived atmospheric parameters, and 17 abundance species, and applied machine learning algorithms to group the stars based on their chemical composition. This approach allows us to evaluate the viability and efficiency of the chemical tagging technique. Results. We found that stars at different evolutionary stages have distinct chemical patterns that may be due to NLTE effects, atomic diffusion, mixing, and biases. When separating stars into dwarfs and giants, we observed that a few open clusters show distinct chemical signatures while the majority show a high degree of overlap. This limits the recovery of co-natal aggregates by applying the chemical tagging technique. Nevertheless, there is room for improvement if more elements are included and models are improved.

Chemical tagging of FGK stars: Testing the Membership of Young Stellar Kinematics Groups

“…See also promising approaches (Mitschang et al 2013) and limitations (Blanco-Cuaresma et al 2015) of the method.…”

Climbing the cosmic ladder with stellar twins

“…Finally, we collected spectra from stars belonging to 11 open clusters analysed by Blanco-Cuaresma et al (2015). The selection criteria for cluster stars was different than for the field stars, in the sense that no colour cut or another selection on the atmospheric parameters was done.…”

“…The reason is that many of the spectra in the clusters had significantly lower SNR (SNR ∼ 15) than the Hipparcos stars, so the measurement of EWs was more uncertain, which produced a larger scatter in fitting the line to the differences in EWs as a function of E.P. We visually inspected the spectra of each of the twin candidates found using the other three criteria listed in 3. cluster stars initially selected from Blanco-Cuaresma et al (2015) had photometry in the four bands required for our present study, in which we need to compare several photometric bands in the same way as the Hipparcos sample. This requirement is especially important in clusters, where extinction and binary fraction can become significantly larger than in the field.…”

Chemical Tagging Can Work: Identification of Stellar Phase-Space Structures Purely by Chemical-Abundance Similarity

“…The first is that the physical assumptions behind the idea may require refinement:-there may be chemical-abundance overlaps among open clusters (Blanco-Cuaresma et al 2015), coeval groups of stars may have similar tags but different birth places (Mitschang et al 2014), and the chemical-abundance space might be low in dimensionality. On the other hand, precise studies of stellar twins (Meléndez et al 2014;Jofré et al 2015) indicate that pairs of stars can be found with unusually similar abundances, open clusters show remarkably uniform chemical abundances (Bovy 2015), and peculiar abundance ratios have been successfully used to identify disrupted cluster members (for example, Majewski et al 2012).…”