J/A+A/499/129ivo://CDS.VizieR/J/A+A/499/129doi:10.26093/cds/vizier.34990129CDSLopez-Santiago J.Micela G.Montes D.2017-11-28T13:21:20Z2009-07-14T17:57:51ZCDS support team

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

cds-question@unistra.frdwarf-starsx-ray-sourcesinfrared-photometryThe associations and moving groups of young stars are excellent laboratories to investigate the stellar formation in the solar neighborhood. Past results confirmed that a non-negligible fraction of old main-sequence stars is present in the lists of members of the young stellar kinematic groups. A detailed study on the properties of these samples is needed to separate the young stars from old main-sequence stars with similar space motion, in order to identify the origin of these structures. Our intention is to characterize the sample of stars members of the young moving groups and determine their age distribution to quantify the contamination by old main-sequence stars, in particular, in the Local Association. For our study, we used the sample of stars possible members of the young (~10-650Myr) moving groups from the literature. In order to determine the age of the stars, we used several age indicators well suited for young main sequence stars: X-ray fluxes from the Rosat All-sky Survey database, photometric data from the Tycho-2, Hipparcos, and 2MASS database. We also used spectroscopic data, in particular the equivalent width of the lithium line LiI lambda6707.8{AA} and Halpha, to constrain the range of ages of the stars in the sample. The combination of photometric and spectroscopic data permitted to separate the young stars (10-650Myr) from the old (>1Gyr) field ones. In particular, the member list of the Local Association results contaminated by ~30% of old field stars. This value must be considered as the contamination of our particular sample, not to the entire Local Association. In other young moving groups it is more difficult to estimate the fraction of old stars in the samples of possible members. However, the X-ray emission level can help to separate, at least, two age populations: stars with 200Myr and stars older than this. The samples of candidates of the classical moving groups contain a non-negligible amount of old field stars that should be considered in studies on the stellar birthrate in the solar neighborhood. Our results agree with the scenario of the moving groups being composed by groups of young stars formed in a recent star formation episode and old field stars with similar space motion. Only combining both X-ray and optical spectroscopic data it is possible to distinguish between the two age populations.2009A&A...499..129Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/499/129CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)IX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/499/129https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/499/129http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/499/129https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/499/129https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/499/129http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/499/129GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/499/129/catalog (Data of the cross-correlation with the RASS and the 2MASS of the stars in the sample)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/499/129/catalog?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/499/129/catalog?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/499/129/catalog?GETtext/xml+votable180.050000true0.58958311.0062220.0055555555555555566/60 217 247 309 336 340 377 411 428 548 674 712 725 770 811 814-815 819 890 892 940 1098 1260 1408 1505 1603 1762 1873 1875 1907 2317 2323 2366 2391 2520 2574 2737 3020 3031 3063 3291 3383 3509 3591 3715 3786 3932 3986 4079 4289 4297 4344 4366 4444 4468 4528 4566 4591 4603 4642 4695 4734 4805 4920 5000 5009 5095 5108 5154 5309 5322 5413 5434 5522 5590 5677 5718 5853 5872 5948 5970 6073 6217 6384-6385 6410 6418 6420 6529 6672 7285 7314 7471 7582 7611 7665 7757 7763 7810 7854 7866 7874 8009 8041 8133 8224 8342 8357 8424 8440 8496 8617 8689 8699-8700 8717 8790 8843 8910 8985 8996 9074 9093 9281 9668 9772 10004 10023 10089 10149 10203 10238 10303 10420 10464 10543 10548 10741 10826 10914 10954 11075 11103 11126 11128 11142 11145 11165 11177 11197 11204 11225 11408 11500 11510 11671 11856 11878 12092 12146 12204 12388 12400 12454 12567 12592 12616 12644 12770 12865 12983 13036 13065 13122 13203 13243 13414 13427 13451 13487 13512 13693 13743 13778 13802 14005 14208 14252 14426 14437 14456 14549 14902 14917 15014 15052 15091 15177 15227 15311 15373 15409 15432 15686 15806 16059 16061 16134 16201 16220 16268 16342 16379 16689 16758 16834 16986 17017 17124 17199 17219 17391 17486 17541 17605 17740 17752 17768 17907 18034 18425 18496 18506 18623 18666 18693 18802 18821 18921 19027 19108 19133 19237 19555 19649 19777 19867 19905 20023 20127 20129 20145 20327-20328 20332 20357 20460 20572 20676 20691 20701 20747 20776 21060 21118 21594 21647 21703 21726 21838 21953 21956 22010 22036 22146 22148 22219 22252 22254 22277 22289 22325 22645 22764 22878 22904 22964 22981 23137 23140 23201 23213 23230 23342 23363 23369 23525 23529 23546 23564 23661 23678 23731 23774 23895 23932 23997 24117 24160 24239 24790 24842 24944 25015 25182 25192 25309 25477 25512 25593 25793 25814 25939 25998 26133 26216 26221 26313 26555 26614 26651 26716 26764 26772 26779 26924 26972 26997 27014 27201 27260 27335 27385 27392 27419 27459 27462 27574 27581 27725 27791 27829 28011 28018 28062 28072 28101 28122-28123 28245 28258 28268 28283 28341 28343 28432 28456 28496 28696 28955 29458 29513 29519 29665 29721 29734 29753 29756 30345 30638 30771 30859 30883 30965 31191 31287 31358 31425 31692 31751 31998 32058 32063 32099 32147 32500 32520 32633 32930 33116 33211 33340 33691 33717 33965 34074 34217 34345 34520 34825 34829-34830 34856-34857 34896 35497 35690 35802 36069 36248 36261 36288 36379 36483 36526 36577 36664 36713 37327 37333 37419 38322 38355 38461 38558 38765 38897 38932 38936 38977 39257 39284 39562 39638 39789 39994 40195 40264 40408 40426 40430 40442 40563 40581 40703 40717 40784 41055 41290 41565 41612 41763 41798 42290 42463 42555 42700 42760 42876 43012 43187 43296 43639 44316 44652 44730 44792 44833 44921 44936 45382 45419 45430 45538 45544 45551 45613 45811 45874 45879 45927 45944 45962 45970 45976 46249 46640 46925 47101 47133 47205-47206 47211-47212 47287 47385 47598 47689 47706 47758 47910 48105 48163 48188 48223 48263 48274 48596 48749 48807 48871 48923 491138.650015785639275e-20 1.7003137259100215e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/499/129?format=asciiX-rayInfrareddefaultJ/A+A/499/129/catalogData of the cross-correlation with the RASS and the 2MASS of the stars in the samplerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameStar namemeta.id;meta.maincharRAJ2000Right ascension (J2000.0)pos.eq.ra;meta.mainDEJ2000Declination (J2000.0)pos.eq.dec;meta.mainPlxParalaxmaspos.parallaxfloatVmag? V magnitudemagphot.mag;em.opt.VfloatnullableV-Ic? V-Ic colour indexmagphot.color;em.opt.V;em.opt.Ifloatnullable2MASS2MASS Identificationmeta.id.crosscharJmag? 2MASS J magnitudemagphot.mag;em.IR.JfloatnullableHmag? 2MASS H magnitudemagphot.mag;em.IR.HfloatnullableKmag? 2MASS K magnitudemagphot.mag;em.IR.KfloatnullableRASSRASS Identificationmeta.id.crosscharCR? Count-rate in the ROSAT energy bandct/sphot.count;em.X-rayfloatnullableHR1? Hardness-ratio 1 of the RASS cataloguephot.flux;arith.ratiofloatnullableHR2? Hardness-ratio 2 of the RASS cataloguephot.flux;arith.ratiofloatnullablelogLX? Logarithm of the X-ray luminosity in the ROSAT energy bandlog(1e-07W)phys.luminosity;em.X-rayfloatnullableMDisplay the 2MASS and RASS datameta.ref.urlcharSimbadNameSimbad column added by the CDSmeta.idchar