1ASTR 1040 ASTR 1040 AccelAccelAstroAstro::Stars & GalaxiesStars & GalaxiesProf. Prof. JuriJuriToomreToomreTA: Nicholas NelsonTA: Nicholas NelsonLecture 11 Tues 15 Feb 2011 Lecture 11 Tues 15 Feb 2011 zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomrePleiades Pleiades Star ClusterStar ClusterTodayToday••Why Why temperature and spectral linestemperature and spectral linesare are closely closely linkedlinkedin classifying stars in classifying stars O B AO B A……MM••Proceed to lay the stars out on theProceed to lay the stars out on the““HertzsprungHertzsprung––RussellRussell””(or H(or H--R) diagramR) diagram••Binary stars: measure Binary stars: measure stellar massesstellar masses••ReRe--readreadChap 15, Chap 15, `Surveying the Stars`Surveying the Stars’’, , overview overview readreadChap 17Chap 17, , ‘‘Star StuffStar Stuff’’----complex chapters complex chapters requiring careful attentionrequiring careful attention••New Homework # 5.5 out today, HW # 5 dueNew Homework # 5.5 out today, HW # 5 due••New Discussion Q: Cities of Stars (due next Tues)New Discussion Q: Cities of Stars (due next Tues)Devising the strange temperature codeDevising the strange temperature code••Original classificationOriginal classificationof spectraof spectra(1890) was:(1890) was:AA= strongest hydrogen = strongest hydrogen featurefeatureBB= less strong = less strong hydrogen hydrogen ……CC, , DD, etc., etc.••Annie Jump CannonAnnie Jump Cannonrealized that a realized that a different different sequencesequencemade more made more sense (~1910)sense (~1910)O B A F G K M !!O B A F G K M !!REMINDERREMINDERWhich absorption (dark) lines are strongest?Which absorption (dark) lines are strongest?Spectral Classification: Spectral Classification: O B A F G K MO B A F G K MHottest starsHottest stars::O BO Bionized helium onlyionized helium onlyHot starsHot stars::A FA Fhelium, helium, hydrogenhydrogenCooler starsCooler stars::GGhydrogen, heavier hydrogen, heavier atomsatomsCoolest starsCoolest stars: : MMmolecules, (complex molecules, (complex absorption bands)absorption bands)Which ABSORPTIONWhich ABSORPTIONlines are strongest lines are strongest Cecelia figured out Cecelia figured out WHYWHYstellar spectra stellar spectra are so different: are so different: TEMPERATURETEMPERATURE••She showed that She showed that SURFACE SURFACE TEMPERATURETEMPERATUREis the big is the big factor (not composition)factor (not composition)••She used the newlyShe used the newly--devised devised SAHA EQUATION, SAHA EQUATION, estimating estimating how many how many electronselectronsremain attached remain attached to atoms as temperature is to atoms as temperature is changed changed (or the level of (or the level of ionization)ionization)Cecelia PayneCecelia Payne--GaposchkinGaposchkin((Harvard PhD thesis 1925)Harvard PhD thesis 1925)O B A F G K MO B A F G K Mdecreasing temperaturedecreasing temperature2Why temperatureWhy temperatureand spectral linesand spectral linesare linked?are linked?SAHA givesSAHA givesthe answer:the answer:can estimatecan estimate““population ofpopulation ofdifferent energydifferent energylevelslevels””in in H, He H, He ……and and ionizationionizationSAHA predictsSAHA predictsspectral linespectral linestrengthsstrengthswith temperaturewith temperature••The biggest groundThe biggest ground--based telescopes with based telescopes with adaptive optics can measure a starsadaptive optics can measure a stars’’position to position to accuracies of about accuracies of about 0.05 0.05 arcsecarcsec. How far away . How far away could they map the positions of stars via could they map the positions of stars via parallax?parallax?••A.A.2 pc = 6.5 light years2 pc = 6.5 light years••B.B.20 pc = 65 light years20 pc = 65 light years••C.C.200 pc = 650 light years200 pc = 650 light yearsPuzzle Clicker: Stellar ParallaxPuzzle Clicker: Stellar ParallaxB.B.••B.B.maximum distancemaximum distanceis set by the is set by the accuracyaccuracywith which you can with which you can measure positions in the measure positions in the sky (space does better sky (space does better than ground)than ground)Distance (pc) = Distance (pc) = 1 / 0.05 1 / 0.05 arcsecarcsec= 20 pc = 65 = 20 pc = 65 lylyParallaxParallaxd (in parsecs) =d (in parsecs) =1 / p (in 1 / p (in arcsecarcsec))H H --R NamesakesR NamesakesEjnarEjnarHertzsprungHertzsprungHenry Norris Henry Norris RussellRussellHertzsprungHertzsprung--Russell (HRussell (H--R) R) DiagramDiagramLuminosityLuminosity(magnitude)(magnitude)vsvsSpectral classSpectral class(temperature)(temperature)3LuminosityLuminosity(solar units)(solar units)TemperatureTemperature1010661010--4440,00040,0003,0003,000Sun is:Sun is:G2 VG2 VCOLOR CLASSCOLOR CLASSDECIMAL DECIMAL SUBDIVISIONSUBDIVISIONLUMINOSITYLUMINOSITYCLASSESCLASSESFurtherFurtherrefinements:refinements:MagnitudesMagnitudes: : Apparent Apparent vsvsAbsoluteAbsolute••Giving measures Giving measures to to stellar stellar luminositiesluminosities••Built on choices Built on choices made by Greeks!made by Greeks!StellarStellarMAGNITUDESMAGNITUDESWeird system:Weird system:brighter is smallerbrighter is smallermagnitudemagnitude,,evenevennegative!negative!Of Of cultural cultural importanceimportance, , even if a biteven if a bitconfusingconfusing(secret society!)(secret society!)MeasuringMeasuringBRIGHTNESSBRIGHTNESSmagnitudesmagnitudesmmMMapparent apparent magmag::what looks like in skywhat looks like in skyabsolute absolute magmag::what would look likewhat would look likeif at if at 10pc distance10pc distance( LUMINOSITY )( LUMINOSITY )(Slightly) screwy(Slightly) screwyworld ofworld ofMAGNITUDESMAGNITUDESM = m if atM = m if atdistance 10pcdistance 10pcIF can estimateIF can estimatedistancedistance, then, thencan determine Mcan determine Mgiven m given m4Clicker: Stellar puzzle Clicker: Stellar puzzle ••Two stars, Two stars, Antony Antony andandCleopatraCleopatra, are both , are both of of spectral class M3spectral class M3, and of the , and of the samesameapparent brightness (magnitude)apparent brightness (magnitude)in the in the sky. Cleopatra shows sky. Cleopatra shows narrow absorption narrow absorption lineslinesin her spectrum, Anthony in her spectrum, Anthony broadbroadones. Which star must be far more ones. Which star must be far more distant? distant?