J/A+A/611/A97ivo://CDS.VizieR/J/A+A/611/A97doi:10.26093/cds/vizier.36110097CDSPasquet-Itam J.Pasquet J.2019-12-23T08:31:04Z2018-04-10T08:17:56ZCDS support team

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

cds-question@unistra.frquasarsvisible-astronomysloan-photometryWe have applied a convolutional neural network (CNN) to classify and detect quasars in the Sloan Digital Sky Survey Stripe 82 and also to predict the photometric redshifts of quasars. The network takes the variability of objects into account by converting light curves into images. The width of the images, noted w, corresponds to the five magnitudes ugriz and the height of the images, noted h, represents the date of the observation. The CNN provides good results since its precision is 0.988 for a recall of 0.90, compared to a precision of 0.985 for the same recall with a random forest classifier. Moreover 175 new quasar candidates are found with the CNN considering a fixed recall of 0.97. The combination of probabilities given by the CNN and the random forest makes good performance even better with a precision of 0.99 for a recall of 0.90. For the redshift predictions, the CNN presents excellent results which are higher than those obtained with a feature extraction step and different classifiers (a K-nearest-neighbors, a support vector machine, a random forest and a Gaussian process classifier). Indeed, the accuracy of the CNN within |{DELTA}z|<0.1 can reach 78.09%, within |{DELTA}z|<0.2 reaches 86.15%, within |{DELTA}z|<0.3 reaches 91.2% and the value of root mean square (rms) is 0.359. The performance of the KNN decreases for the three |{DELTA}z| regions, since within the accuracy of |{DELTA}z|<0.1, |{DELTA}z|<0.2, and |{DELTA}z|<0.3 is 73.72%, 82.46%, and 90.09% respectively, and the value of rms amounts to 0.395. So the CNN successfully reduces the dispersion and the catastrophic redshifts of quasars. This new method is very promising for the future of big databases such as the Large Synoptic Survey Telescope.2018A&A...611A..97Phttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/611/A97CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/AJ/134/973 : SDSS Stripe 82 star catalogs (Ivezic+, 2007)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/611/A97https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/611/A97http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/611/A97https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/611/A97https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/611/A97http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/611/A97GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/611/A97/qso (Quasar candidates)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/611/A97/qso?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/611/A97/qso?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/611/A97/qso?GETtext/xml+votable180.050000true351.917633891.261301940.0055555555555555565/7514 6/0 12290 17407 17661 17743 17746-17747 17755 17758-17759 17767 17770 17806 17816 17818 17820-17822 17829-17832 17838 18002 18007 18012 18020 18025 18030 18034 18062 18065-18066 18071-18073 18081 18085 18087 18090 18096-18097 18114 18177-18178 18750 18765-18766 18770 18775 18777 18786 18790 18792 18796-18797 18829 18834 18837 18839 18842-18843 18845 18851 18854-18855 18857 18859 18882 19021 19023 19030 19037 19043-19044 19050-19051 19056-19058 19086 19090-19091 19095 19102 19105-19106 19111 19114 19120-19122 19137 19202 19456 19458 23138 23143 23154 23183 23195 23203 23205 23208 23210 23214 23232 30013 30015 30030 30037 30039 30042 30046 30050-30053 30055 30060-30061 30064 30066 30099-30100 30106 30108 30110 30144-30145 49149https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/611/A97?format=asciiOpticaldefaultJ/A+A/611/A97/qsoQuasar candidatesSimbadNameSimbad column added by the CDSmeta.idcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIDStripe 82 identification numbermeta.id;meta.mainintRAJ2000Right ascension (J2000.0)degpos.eq.ra;meta.mainDEJ2000Declination (J2000.0)degpos.eq.dec;meta.mainRF[0/1] label given by the Random Forest (0=quasar, 1=other) (1)meta.codecharrmagSDSS r-median magnitude (2)magphot.mag;em.opt.Rfloatu-gSDSS u-g color index (2)magphot.color;em.opt.U;em.opt.Bfloatg-rSDSS g-r color index (2)magphot.color;em.opt.B;em.opt.Rfloatr-iSDSS r-i color index (2)magphot.color;em.opt.R;em.opt.Ifloati-zSDSS i-z color index (2)magphot.color;em.opt.I;em.opt.IfloatSloanDisplay the online SDSS data for this objectmeta.ref.urlchar