Determination of Stellar AgesPHY 521Stanimir MetchevDec 1, 2011 PHY 521, Lecture 25 2Outline• Ages of stellar populations– isochronal ages– main-sequence turn-off– age-metallicity relation• Ages of individual stars– isochronal ages– Li depletion– rotation-activity relation– surface gravity as a proxy for age– kinematic ages: young stellar moving groups• Identifying Young StarsDec 1, 2011 PHY 521, Lecture 25 3IsochronalAges ofStellarPopulationsPalla & Stahler (2000, ApJ, 540, 255)• isochrones: 1,3, 10, 30 Myr• evolutionarytracks: 0.1, 0.2,0.4, 0.6, 0.8,1.0, 1.2, 1.5,2.0, 2.5, 3.0,3.5 MDec 1, 2011 PHY 521, Lecture 25 4IsochronalAges ofStellarPopulations• isochrones: 1,3, 10, 30 Myr• evolutionarytracks: 0.1, 0.2,0.4, 0.6, 0.8,1.0, 1.2, 1.5,2.0, 2.5, 3.0,3.5 MPalla & Stahler (2000, ApJ, 540, 255)Dec 1, 2011 PHY 521, Lecture 25 5Ages Spreads in Young Stellar Associations?• Upper Scorpius ages spread < +/-3 Myr• But variability binaries cannot explain age spread in sigma Ori and Cep OB3(Burningham et al. 2005)Slesnick et al. (2008, ApJ, 688, 377)Dec 1, 2011 PHY 521, Lecture 25 6Comparison of Evolutionary TracksMathieu et al. (2007)Dec 1, 2011 PHY 521, Lecture 25 7Comparison of Evolutionary TracksMathieu et al. (2007)G2 star K6 starDec 1, 2011 PHY 521, Lecture 25 8EvolutionaryTracks vs.DynamicalMasses• solid lines: mainsequence stars• dotted lines: pre-main sequencestars• modeluncertaintiesdominated by Teffand L*Hillenbrand & White. (2008)Dec 1, 2011 PHY 521, Lecture 25 9Main Sequence Turn-Off Ages4 Gyr6 GyrDec 1, 2011 PHY 521, Lecture 25 10Age-MetallicityRelationMilvang-Jensen (1997)Dec 1, 2011 PHY 521, Lecture 25 11Age-Metallicity RelationIbukiyama & Arimoto (2002)Dec 1, 2011 PHY 521, Lecture 25 12Outline• Ages of stellar populations– isochronal ages– main-sequence turn-off– age-metallicity relation• Ages of individual stars– isochronal ages– Li depletion– rotation-activity relation– surface gravity as a proxy for age– kinematic ages: young stellar moving groups• Identifying Young StarsDec 1, 2011 PHY 521, Lecture 25 13Isochronal Stellar Age• The age of the starGQ Lupi– solid symbols:different data sets– open symbols: afterde-reddening due todust– open stars: othermembers of theLupus I star-forming cloudMcElwain et al. (2007)Dec 1, 2011 PHY 521, Lecture 25 14Isochronal Stellar Age• The age ofthequdrauplesystemGG TauMcElwain et al. (2007)White et al. (1999)Dec 1, 2011 PHY 521, Lecture 25 15The GG Tau Quadruple SystemWhite et al. (1999)• A-Baseparation:1400 AU• Aa-Abseparation:35 AUDec 1, 2011 PHY 521, Lecture 25 16Lithium Depletion• EW(Li)dependent on:– temperature– pressure– nuclearburning• Li decreaseswith age• Large scatterDec 1, 2011 PHY 521, Lecture 25 17Rotation-Activity RelationMamajek & Hillenbrand (2008)Dec 1, 2011 PHY 521, Lecture 25 18Surface Gravity as a Proxy of AgeSlesnick et al. (2006)Dec 1, 2011 PHY 521, Lecture 25 19Kinematic Ages:Young Moving GroupsLopez-Santiago (2006)Dec 1, 2011 PHY 521, Lecture 25 20Outline• Ages of stellar populations– isochronal ages– main-sequence turn-off– age-metallicity relation• Ages of individual stars– isochronal ages– Li depletion– rotation-activity relation– surface gravity as a proxy for age– kinematic ages: young stellar moving groups• Identifying Young StarsDec 1, 2011 PHY 521, Lecture 25 21Identifying Young Stars: ClustersSubaru Telescope image ofOrion Nebular Cloud (0-3 Myr)Young clusters in the L1641 molecularcloud from Strom et al. (1993)Dec 1, 2011 PHY 521, Lecture 25 22>10 Myr Stars Difficult to Find• Dispersequickly• Fieldcontaminationis