J/ApJ/765/126ivo://CDS.VizieR/J/ApJ/765/126doi:10.26093/cds/vizier.17650126CDSMacDonald J.Mullan D.J.2014-12-14T15:09:49Z2014-12-01T09:42:36ZCDS support team

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

cds-question@unistra.frastronomical-modelsmagnetic-fieldsm-starsopen-star-clustersstellar-radiistellar-massesBy combining rotation periods with spectroscopic determinations of projected rotation velocity, Jackson et al. (2009MNRAS.399L..89J) have found that the mean radii for low-mass M-dwarfs in the young, open cluster NGC 2516 are larger than model predictions at a given absolute I magnitude or I-K color and also larger than measured radii of magnetically inactive M-dwarfs. The relative radius difference is correlated with magnitude, increasing from a few percent at M_I_=7 to greater than 50% for the lowest luminosity stars in their sample at M_I_~9.5. Jackson et al. have suggested that a two-temperature star spot model is capable of explaining the observations, but their model requires spot coverage fractions of at least 50% in rapidly rotating M-dwarfs. Here we examine these results in terms of stellar models that include the inhibiting effects of magnetic fields on convective energy transport, with and without the effects of star spots. We find that a pure spot model is inconsistent with the color-magnitude diagram. The observations of radii versus color and radii versus absolute magnitude in NGC 2516 are consistent with models which include only magnetic inhibition or a combination of magnetic inhibition and spots. At a given mass we find a large dispersion in the strength of the vertical component of the magnetic field in the stellar photosphere but the general trend is that the vertical field increases with decreasing mass from a few hundred Gauss at 0.65M_{sun}_ to 600-900G, depending on spot coverage, in the lowest mass stars in the sample at 0.25M_{sun}_.2013ApJ...765..126Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/765/126CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/MNRAS/423/2966 : Low-mass stars spectroscopy in NGC 2516 (Jackson+, 2012)J/other/A+ARV/18.67 : Accurate masses and radii of normal stars (Torres+, 2010)J/MNRAS/407/2269 : Polarisation of a sample of late M dwarfs (Morin+, 2010)J/MNRAS/407/465 : Fast-rotating M dwarfs in NGC2516 (Jackson+, 2010)J/MNRAS/394/1338 : Stellar effective magnetic fields. II. (Bychkov+, 2009)J/A+A/468/151 : Nearby open clusters radii and masses (Piskunov+, 2007)J/MNRAS/377/741 : VIc photometry of NGC 2516 (Irwin+, 2007)J/A+A/456/977 : XMM observations of NGC 2516 stars (Marino+, 2006)J/A+A/453/101 : UBV(RI)c photometry of 4 open clusters (Lyra+, 2006)J/ApJ/588/1009 : Chandra X-ray observations of NGC 2516 (Damiani+, 2003)J/AJ/123/290 : UBVI CCD photometry of NGC 2516 (Sung+, 2002)J/A+A/375/863 : Photometry in NGC 2516 (Jeffries+, 2001)J/A+A/337/403 : Low-mass stars evolutionary models (Baraffe+ 1998)J/A+A/333/231 : O-M stars model atmospheres (Bessell+ 1998)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/765/126https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/765/126http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/765/126https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/765/126https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/765/126http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/765/126GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tap2.367228618189496e-19 2.6706780932288093e-19defaultJ/ApJ/765/126/table2Different 160Myr isochrone model resultsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTypeModel type (G1)meta.id;stat.fitchardelta[0/0.09] Magnetic inhibition parameter (G2)stat.paramfloatfs[0/1] Equivalent surface fraction covered by dark spots f_s_ (G2)stat.paramfloatMass[0.1/0.7] Stellar masssolMassphys.massfloatlogL[-2.8/-0.7] Log stellar luminositylog(solLum)phys.luminositydoublelogR[-0.8/0.07] Log stellar radiuslog(solRad)phys.size.radiusdoubleTeff[1981/4327] Effective temperatureKphys.temperature.effectivefloatALi[-8.4/2.8] Lithium abundance parameter, as 12+log(N(Li)/N(H))phys.abunddoubleIMag1[6/12.8] BCP Absolute Cousins I magnitude (G3)magphys.magAbsdouble(I-K)1BCP (I-K) color index (G3)magphot.color;em.opt.I;em.IR.KdoubleIMag2NextGen Absolute Cousins I magnitude (G3)magphys.magAbsdouble(I-K)2NextGen (I-K) color index (G3)magphot.color;em.opt.I;em.IR.KdoubleJ/ApJ/765/126/table3Details of the stellar parameters determined from the different model 160Myr isochronesTypeModel type (G1)meta.id;stat.fitcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBCBolometric correction used (BCP or NG) (G3)meta.ref;pos.framechar(I-K)[1.7/3] The (I-K) color index (1)magphot.color;em.opt.I;em.IR.KfloatImag[14.5/18.1] Apparent Cousins I band magnitudemagphot.mag;em.opt.Ifloat(I-K)0Dereddenned (I-K) color indexmagphot.color;em.opt.I;em.IR.KfloatIMag[6.3/10] Absolute Cousins I band magnitudemagphys.magAbs;em.opt.IfloatMass[0.1/0.7] Stellar masssolMassphys.massfloatdelta[0/0.09] Magnetic inhibition parameter (G2)stat.paramfloatfs[0/1] Equivalent surface fraction covered by dark spots f_s_ (G2)stat.paramfloatRad[0.2/0.9] Stellar radiussolRadphys.size.radiusfloatLum[0.005/0.2] Stellar luminositysolLumphys.luminositydoubleTeff[2401/4213] Effective temperatureKphys.temperature.effectivefloat