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ASTR 1040 ASTR 1040 AccelAccel AstroAstro:: Stars & GalaxiesStars & Galaxies

Prof. Prof. JuriJuri ToomreToomre TA: Nick FeatherstoneTA: Nick FeatherstoneLecture 11 Tues 20 Feb 07Lecture 11 Tues 20 Feb 07

zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomre

PlanetaryPlanetaryNebulaNebulaNGC 3132NGC 3132

TodayToday•• Why Why temperature and spectral linestemperature and spectral lines are are closely closely

linkedlinked in 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•• Weird scale forWeird scale for stellar magnitudesstellar magnitudes•• Absolute Absolute vsvs apparent magnitudeapparent magnitude•• Observatory Night # 3Observatory Night # 3 this Thursthis Thurs•• ReRe--readread Chap 15, Chap 15, `Surveying the Stars`Surveying the Stars’’•• Start Start overview readoverview read Chap 17,Chap 17, `Star Stuff`Star Stuff’’•• Will return graded Will return graded Exam 1 Exam 1 on Thurson Thurs•• Homework # 4 turned in today, new HW # 5 Homework # 4 turned in today, new HW # 5

Brightness / Distance Brightness / Distance Clicker Q Clicker Q

•• Leonardo and Guinevere are two stars Leonardo and Guinevere are two stars that have the that have the same apparent brightness.same apparent brightness.Leonardo has a Leonardo has a larger parallax anglelarger parallax anglethan Guinevere. Which star is more than Guinevere. Which star is more luminous?luminous?

•• A.A. LeonardoLeonardo•• B.B. GuinevereGuinevere•• C.C. Cannot determine from data givenCannot determine from data given

B.B.

•• Leonardo has a Leonardo has a larger parallax anglelarger parallax angle ----thus he is closer to usthus he is closer to us

•• They both have the same APPARENT They both have the same APPARENT brightness, but Leo is closerbrightness, but Leo is closer

•• B.B. GuinevereGuinevere must be more luminousmust be more luminous

Brightness / DistanceBrightness / Distance

•• 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 years

Puzzle Clicker: Stellar ParallaxPuzzle Clicker: Stellar Parallax

B.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 lyly

ParallaxParallax

d (in parsecs) =d (in parsecs) =1 / p (in 1 / p (in arcsecarcsec))

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SpectraSpectra help classify starshelp classify stars Devising the strange temperature codeDevising the strange temperature code

•• Original classificationOriginal classificationof spectraof spectra (1890) was:(1890) was:AA = strongest = strongest hydrogenhydrogenfeaturefeatureBB = less strong = less strong hydrogen hydrogen ……CC, , DD, etc., etc.

•• Annie Jump CannonAnnie Jump Cannonrealized that a realized that a different different sequencesequence made more made more sense (~1910)sense (~1910)

O B A F G K M !!O B A F G K M !!

REMINDERREMINDER

Spectral Classification: Spectral Classification: O B A F G K MO B A F G K M

Hottest starsHottest stars:: O BO Bionized helium onlyionized helium only

Hot starsHot stars:: A FA F helium, helium, hydrogenhydrogen

Cooler starsCooler stars:: GGhydrogen, heavier hydrogen, heavier atomsatoms

Coolest starsCoolest stars: : MMmolecules, (complex molecules, (complex absorption bands)absorption bands)

Which ABSORPTIONWhich ABSORPTIONlines are strongest lines are strongest

Cecelia figured out Cecelia figured out WHYWHY stellar spectra stellar spectra are so different: are so different: TEMPERATURETEMPERATURE

•• She showed that She showed that SURFACE SURFACE TEMPERATURETEMPERATURE is 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 electronselectrons remain 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 temperature

Spectral Classification: Spectral Classification: O B A F G K MO B A F G K M

Hottest starsHottest stars: : ionized ionized helium onlyhelium only

Hot starsHot stars: : helium, helium, hydrogenhydrogen

Cooler starsCooler stars: : hydrogen, heavier hydrogen, heavier atomsatoms

Coolest starsCoolest stars: : molecules, (complex molecules, (complex absorption bands)absorption bands)

Why 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 ionizationionization

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SAHA predictsSAHA predictsspectral linespectral linestrengthsstrengthswith temperaturewith temperature

SURFACE TEMPERATURESURFACE TEMPERATURE explains itexplains it

•• Cecelia PCecelia P--G used the G used the new new SAHA EQUATION SAHA EQUATION to estimate to estimate how many how many electronselectrons remain remain attached to atoms as attached to atoms as temperature changes temperature changes ((or level of ionizationor level of ionization))

Cecelia PayneCecelia Payne--GaposchkinGaposchkin

O B A F G K MO B A F G K M decreasing temperaturedecreasing temperature

(Harvard PhD thesis 1925)(Harvard PhD thesis 1925)

REMINDERREMINDER

FurtherFurtherrefinements:refinements:

DECIMAL DECIMAL SUBDIVISIONSUBDIVISION

LUMINOSITYLUMINOSITYCLASSESCLASSES

Sun is:Sun is:G2 VG2 V

COLOR CLASSCOLOR CLASS

HertzsprungHertzsprung--Russell (HRussell (H--R) R) DiagramDiagram

LuminosityLuminosity(magnitude)(magnitude)

vsvsSpectral classSpectral class(temperature)(temperature)

H H -- R NamesakesR Namesakes

EjnarEjnar HertzsprungHertzsprung Henry Norris Henry Norris RussellRussell

LuminosityLuminosity

(solar units)(solar units)

TemperatureTemperature

101066

1010--44

40,00040,000 3,0003,000

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Reading Clicker Q Reading Clicker Q

•• The The luminosityluminosity of a star isof a star is•• A.A. apparent brightness of the star in the skyapparent brightness of the star in the sky

•• B.B. surface temperature of the starsurface temperature of the star

•• C.C. lifetime of the starlifetime of the star

•• D.D. total amount of light that the star will radiate total amount of light that the star will radiate over its entire lifetimeover its entire lifetime

•• E.E. total amount of light that the star radiates total amount of light that the star radiates every secondevery second

E.E. Oh to describe a star !Oh to describe a star !

•• Which is a Which is a red red supergiantsupergiant ??

•• A. Spectral type G2, luminosity class VA. Spectral type G2, luminosity class V•• B. Spectral type M2, luminosity class IB. Spectral type M2, luminosity class I•• C. Spectral type O9, luminosity class IC. Spectral type O9, luminosity class I•• D. Spectral type M1, luminosity class VD. Spectral type M1, luminosity class V

B.B.

MagnitudesMagnitudes: : Apparent Apparent vsvs AbsoluteAbsolute

•• Giving measures Giving measures to to stellar stellar luminositiesluminosities

•• Built on choices Built on choices made by Greeks!made by Greeks!

StellarStellarMAGNITUDESMAGNITUDES

Weird system:Weird system:brighter is smallerbrighter is smallermagnitudemagnitude, even, evennegative!negative!

Of Of cultural cultural importanceimportance, , even if a biteven if a bitconfusingconfusing(secret society!)(secret society!)

(Slightly) screwy(Slightly) screwyworld ofworld of

MAGNITUDESMAGNITUDES

M = m if atM = m if atdistance 10pcdistance 10pc

IF can estimateIF can estimatedistancedistance, then, thencan determine Mcan determine Mgiven m given m

MeasuringMeasuringBRIGHTNESSBRIGHTNESS

magnitudesmagnitudes

mm

MM

apparent apparent magmag::what looks like in skywhat looks like in sky

absolute absolute magmag::what would look likewhat would look likeif at if at 10pc distance10pc distance( LUMINOSITY )( LUMINOSITY )