54,018 research outputs found
UPMASK: unsupervised photometric membership assignment in stellar clusters
We develop a method for membership assignment in stellar clusters using only
photometry and positions. The method, UPMASK, is aimed to be unsupervised, data
driven, model free, and to rely on as few assumptions as possible. It is based
on an iterative process, principal component analysis, clustering algorithm,
and kernel density estimations. Moreover, it is able to take into account
arbitrary error models. An implementation in R was tested on simulated clusters
that covered a broad range of ages, masses, distances, reddenings, and also on
real data of cluster fields. Running UPMASK on simulations showed that it
effectively separates cluster and field populations. The overall spatial
structure and distribution of cluster member stars in the colour-magnitude
diagram were recovered under a broad variety of conditions. For a set of 360
simulations, the resulting true positive rates (a measurement of purity) and
member recovery rates (a measurement of completeness) at the 90% membership
probability level reached high values for a range of open cluster ages
( yr), initial masses (M_{\sun}) and
heliocentric distances ( kpc). UPMASK was also tested on real data
from the fields of the open cluster Haffner~16 and of the closely projected
clusters Haffner~10 and Czernik~29. These tests showed that even for moderate
variable extinction and cluster superposition, the method yielded useful
cluster membership probabilities and provided some insight into their stellar
contents. The UPMASK implementation will be available at the CRAN archive.Comment: 12 pages, 13 figures, accepted for publication in Astronomy and
Astrophysic
Evaluating the role of quantitative modeling in language evolution
Models are a flourishing and indispensable area of research in language evolution. Here we highlight critical issues in using and interpreting models, and suggest viable approaches. First, contrasting models can explain the same data and similar modelling techniques can lead to diverging conclusions. This should act as a reminder to use the extreme malleability of modelling parsimoniously when interpreting results. Second, quantitative techniques similar to those used in modelling language evolution have proven themselves inadequate in other disciplines. Cross-disciplinary fertilization is crucial to avoid mistakes which have previously occurred in other areas. Finally, experimental validation is necessary both to sharpen models' hypotheses, and to support their conclusions. Our belief is that models should be interpreted as quantitative demonstrations of logical possibilities, rather than as direct sources of evidence. Only an integration of theoretical principles, quantitative proofs and empirical validation can allow research in the evolution of language to progress
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