J/A+A/612/A98ivo://CDS.VizieR/J/A+A/612/A98doi:10.26093/cds/vizier.36120098CDSGarcia-Dias R.Allende Prieto C.Sanchez Almeida J.Ordovas-Pascual I.2018-05-17T11:06:52Z2018-05-04T10:13:00ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frinfrared-astronomyspectroscopymorgan-keenan-classificationThe volume of data generated by astronomical surveys is growing rapidly. Traditional analysis techniques in spectroscopy either demand intensive human interaction or are computationally expensive. In this scenario, machine learning, and unsupervised clustering algorithms in particular, offer interesting alternatives. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) offers a vast data set of near-infrared stellar spectra, which is perfect for testing such alternatives. Our research applies an unsupervised classification scheme based on K-means to the massive APOGEE data set. We explore whether the data are amenable to classification into discrete classes. We apply the K-means algorithm to 153,847 high resolution spectra (R~22,500). We discuss the main virtues and weaknesses of the algorithm, as well as our choice of parameters. We show that a classification based on normalised spectra captures the variations in stellar atmospheric parameters, chemical abundances, and rotational velocity, among other factors. The algorithm is able to separate the bulge and halo populations, and distinguish dwarfs, sub-giants, RC, and RGB stars. However, a discrete classification in flux space does not result in a neat organisation in the parameters' space. Furthermore, the lack of obvious groups in flux space causes the results to be fairly sensitive to the initialisation, and disrupts the efficiency of commonly-used methods to select the optimal number of clusters. Our classification is publicly available, including extensive online material associated with the APOGEE Data Release 12 (DR12). Our description of the APOGEE database can help greatly with the identification of specific types of targets for various applications. We find a lack of obvious groups in flux space, and identify limitations of the K-means algorithm in dealing with this kind of data.2018A&A...612A..98Ghttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/612/A98CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/612/A98https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/612/A98http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/612/A98https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/612/A98https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/612/A98http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/612/A98GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapInfraredOpticaldefaultJ/A+A/612/A98/tableb2Star labelsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAPOGEEStar ID as defined in APOGEE DR12meta.id;meta.maincharClass? K-means classmeta.code.classintnullableJ/A+A/612/A98/tableb34Mean spectra of the 50 classes (table B3) within class standard deviation (table B4)class16Mean normalized flux of class 16phot.flux;arith.ratiodoubleclass28Mean normalized flux of class 28phot.flux;arith.ratiodoublerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintWavelengthWavelength in vacuum0.1nmem.wldoubleMask[0/1] 1 if the pixel is used in k-means, 0 otherwise.meta.codeintclass00Mean normalized flux of class 0phot.flux;arith.ratiodoublee_class00Standard deviation of normalised flux in class 0stat.errordoubleclass01Mean normalized flux of class 1phot.flux;arith.ratiodoublee_class01Standard deviation of normalised flux in class 1stat.errordoubleclass02Mean normalized flux of class 2phot.flux;arith.ratiodoublee_class02Standard deviation of normalised flux in class 2stat.errordoubleclass03Mean normalized flux of class 3phot.flux;arith.ratiodoublee_class03Standard deviation of normalised flux in class 3stat.errordoubleclass04Mean normalized flux of class 4phot.flux;arith.ratiodoublee_class04Standard deviation of normalised flux in class 4stat.errordoubleclass05Mean normalized flux of class 5phot.flux;arith.ratiodoublee_class05Standard deviation of normalised flux in class 5stat.errordoubleclass06Mean normalized flux of class 6phot.flux;arith.ratiodoublee_class06Standard deviation of normalised flux in class 6stat.errordoubleclass07Mean normalized flux of class 7phot.flux;arith.ratiodoublee_class07Standard deviation of normalised flux in class 7stat.errordoubleclass08Mean normalized flux of class 8phot.flux;arith.ratiodoublee_class08Standard deviation of normalised flux in class 8stat.errordoubleclass09Mean normalized flux of class 9phot.flux;arith.ratiodoublee_class09Standard deviation of normalised flux in class 9stat.errordoubleclass10Mean normalized flux of class 10phot.flux;arith.ratiodoublee_class10Stanard deviation of normalised flux in class 10stat.errordoubleclass11Mean normalized flux of class 11phot.flux;arith.ratiodoublee_class11Standard deviation of normalised flux in class 11stat.errordoubleclass12Mean normalized flux of class 12phot.flux;arith.ratiodoublee_class12Standard deviation of normalised flux in class 12stat.errordoubleclass13Mean normalized flux of class 13phot.flux;arith.ratiodoublee_class13Standard deviation of normalised flux in class 13stat.errordoubleclass14Mean normalized flux of class 14phot.flux;arith.ratiodoublee_class14Standard deviation of normalised flux in class 14stat.errordoubleclass15Mean normalized flux of class 15phot.flux;arith.ratiodoublee_class15Standard deviation of normalised flux in class 15stat.errordoublee_class16Standard deviation of normalised flux in class 16stat.errordoubleclass17Mean normalized flux of class 17phot.flux;arith.ratiodoublee_class17Standard deviation of normalised flux in class 17stat.errordoubleclass18Mean normalized flux of class 18phot.flux;arith.ratiodoublee_class18Standard deviation of normalised flux in class 18stat.errordoubleclass19Mean normalized flux of class 19phot.flux;arith.ratiodoublee_class19Standard deviation of normalised flux in class 19stat.errordoubleclass20Mean normalized flux of class 20phot.flux;arith.ratiodoublee_class20Standard deviation of normalised flux in class 20stat.errordoubleclass21Mean normalized flux of class 21phot.flux;arith.ratiodoublee_class21Standard deviation of normalised flux in class 21stat.errordoubleclass22Mean normalized flux of class 22phot.flux;arith.ratiodoublee_class22Standard deviation of normalised flux in class 22stat.errordoubleclass23Mean normalized flux of class 23phot.flux;arith.ratiodoublee_class23Standard deviation of normalised flux in class 23stat.errordoubleclass24Mean normalized flux of class 24phot.flux;arith.ratiodoublee_class24Standard deviation of normalised flux in class 24stat.errordoubleclass25Mean normalized flux of class 25phot.flux;arith.ratiodoublee_class25Standard deviation of normalised flux in class 25stat.errordoubleclass26Mean normalized flux of class 26phot.flux;arith.ratiodoublee_class26Standard deviation of normalised flux in class 26stat.errordoubleclass27Mean normalized flux of class 27phot.flux;arith.ratiodoublee_class27Standard deviation of normalised flux in class 27stat.errordoublee_class28Standard deviation of normalised flux in class 28stat.errordoubleclass29Mean normalized flux of class 29phot.flux;arith.ratiodoublee_class29Standard deviation of normalised flux in class 29stat.errordoubleclass30Mean normalized flux of class 30phot.flux;arith.ratiodoublee_class30Standard deviation of normalised flux in class 30stat.errordoubleclass31Mean normalized flux of class 31phot.flux;arith.ratiodoublee_class31Standard deviation of normalised flux in class 31stat.errordoubleclass32Mean normalized flux of class 32phot.flux;arith.ratiodoublee_class32Standard deviation of normalised flux in class 32stat.errordoubleclass33Mean normalized flux of class 33phot.flux;arith.ratiodoublee_class33Standard deviation of normalised flux in class 33stat.errordoubleclass34Mean normalized flux of class 34phot.flux;arith.ratiodoublee_class34Standard deviation of normalised flux in class 34stat.errordoubleclass35Mean normalized flux of class 35phot.flux;arith.ratiodoublee_class35Standard deviation of normalised flux in class 35stat.errordoubleclass36Mean normalized flux of class 36phot.flux;arith.ratiodoublee_class36Standard deviation of normalised flux in class 36stat.errordoubleclass37Mean normalized flux of class 37phot.flux;arith.ratiodoublee_class37Standard deviation of normalised flux in class 37stat.errordoubleclass38Mean normalized flux of class 38phot.flux;arith.ratiodoublee_class38Standard deviation of normalised flux in class 38stat.errordoubleclass39Mean normalized flux of class 39phot.flux;arith.ratiodoublee_class39Standard deviation of normalised flux in class 39stat.errordoubleclass40Mean normalized flux of class 40phot.flux;arith.ratiodoublee_class40Standard deviation of normalised flux in class 40stat.errordoubleclass41Mean normalized flux of class 41phot.flux;arith.ratiodoublee_class41Standard deviation of normalised flux in class 41stat.errordoubleclass42Mean normalized flux of class 42phot.flux;arith.ratiodoublee_class42Standard deviation of normalised flux in class 42stat.errordoubleclass43Mean normalized flux of class 43phot.flux;arith.ratiodoublee_class43Standard deviation of normalised flux in class 43stat.errordoubleclass44Mean normalized flux of class 44phot.flux;arith.ratiodoublee_class44Standard deviation of normalised flux in class 44stat.errordoubleclass45Mean normalized flux of class 45phot.flux;arith.ratiodoublee_class45Standard deviation of normalised flux in class 45stat.errordoubleclass46Mean normalized flux of class 46phot.flux;arith.ratiodoublee_class46Standard deviation of normalised flux in class 46stat.errordoubleclass47Mean normalized flux of class 47phot.flux;arith.ratiodoublee_class47Standard deviation of normalised flux in class 47stat.errordoubleclass48Mean normalized flux of class 48phot.flux;arith.ratiodoublee_class48Standard deviation of normalised flux in class 48stat.errordoubleclass49Mean normalized flux of class 49phot.flux;arith.ratiodoublee_class49Standard deviation of normalised flux in class 49stat.errordouble