Stellar Spectra ASTR 2110 Sarazin. Solar Spectrum

Stellar Spectra ASTR 2110 Sarazin Solar Spectrum

Test #1 Monday, October 9, 11-11:50 am Ruffner G006 (classroom) You may not consult the text, your notes, or any other materials or any person Bring pencils, paper, calculator ~2/3 Quantitative Problems (like homework problems) ~1/3 Qualitative Questions Multiple Choice, Short Answer, Fill In the Blank questions No essay questions

Test #1 (Cont.) Equation/Formula Card: You may bring one 3x5 inch index card with equations and formulae written on both sides. DO NOT LIST pc, AU, M, L, R DO NOT INCLUDE ANY QUALITATIVE MATERIAL (text, etc.)

Material: Test #1 (Cont.) Chapters: Preface, 1-3, 5-7, 13, 19.3 Introduction, Coordinates & Time, Motions of Planets, Early Astronomy (Greeks Renaissance), Kepler s Laws, Newton s Laws, Gravity, Light, Telescopes, Doppler Effect, Basic Stellar Properties, Binary Stars, the Sun, Atomic Physics (Qualitative Only) Homeworks 1-5 Know pc, AU, M, L, R

Test #1 (Cont.) No problem set week of October 2 9 to allow study for test Review Session: Discussion session Friday, October 6, 3-4 pm

Stellar Spectra ASTR 2110 Sarazin Solar Spectrum

Theory of Stellar Atmospheres Divide stars into Atmosphere Narrow outer layer, 1 mean free path, τ 1 Makes light we see Interior Not directly observable

Stellar Spectra and Stellar Atmospheres Determined by (in decreasing order of importance) 1. T eff 2. g * 3. Composition

Stellar Spectra hotter cooler

Stellar Spectra ions hotter molecules cooler

Stellar Spectra ions molecules hotter 50000 25000 10000 8000 6000 5000 4000 3000 Temperature cooler

Spectral Classification ~1900, done by Annie Jump Cannon, assistant to Prof. E. C. Pickering at Harvard

Annie Jump Cannon

Spectral Classification ~1900, before atomic theory, spectral lines hard to understand Use Balmer lines of hydrogen

Stellar Spectra Hβ hotter Hα cooler

Spectral Classification ~1900, before atomic theory, spectral lines hard to understand Use Balmer lines of hydrogen From excited states Hα Hβ n = 4 n = 3 n = 2 n = 1

Stellar Spectra ions molecules hotter 50000 25000 10000 8000 6000 5000 4000 3000 Temperature cooler

Stellar Spectra Hα strength 3000 4000 5000 6000 8000 10000 25000 50000 Temperature

Stellar Spectra Hα strength 3000 4000 5000 6000 8000 10000 25000 50000 Temperature Excitation to n=2 n 2 /n 1 = exp(- E / kt) Hα Hβ n = 4 n = 3 n = 2 n = 1

Stellar Spectra Hα strength 3000 4000 5000 6000 8000 10000 25000 50000 Temperature Ionization of hydrogen Hα Hβ n = 4 n = 3 n = 2 n = 1

Spectral Classification ~1900, before atomic theory, spectral lines hard to understand Use Balmer lines of hydrogen Alphabetical system (A - P) based mainly on strength of hydrgen Balmer lines A = strongest

Stellar Spectra Hα strength K G F A B C D E M O 3000 4000 5000 6000 8000 10000 25000 50000 Temperature

Stellar Spectral Classes T eff 50,000 K 2,000 K O B A F G K M L T Oh, be a fine { } guy girl kiss me Memorize L, T = brown dwarfs

Stellar Spectra ions molecules hotter cooler

Spectral Types

Stellar Spectra and Stellar Atmospheres Determined by (in decreasing order of importance) 1. T eff 2. g * 3. Composition

Spectral Luminosity Classes g * = G M * / R * 2 R * M * 0.75 for normal (main sequence) stars g * doesn t vary too much Giants, supergiants big R * White dwarfs small R * g * mainly determined by R * Fixed T eff, L = 4π R * 2 σ T eff 4 R * changes L g * gives L or R *

Spectral Luminosity Classes

Stellar Spectra and Stellar Atmospheres Determined by (in decreasing order of importance) 1. T eff 2. g * 3. Composition

Stellar Composition Mainly hydrogen and helium

Solar Composition Element Abundance by mass Hydrogen 73.5% Helium 24.8% Oxygen 0.788% Carbon 0.326% Nitrogen 0.118% Iron 0.162%

Stellar Composition Mainly hydrogen and helium X = mass fraction of hydrogen ~ 0.74 (90% of atoms) Y = mass fraction of helium ~ 0.24 (10% of atoms) Z = mass fraction of heavier elements ~ 0.02 in Sun (0.1 % of atoms) Fraction of heavy elements varies Population I = like Sun, Z ~ 0.01 Population II = low abundances, Z ~ 0.001

The HR Diagram ASTR 2110 Sarazin

HR Diagram Study stars: Individually, in detail? Statistically, in large numbers? Need simple, easily observed properties L, T or color, M, R? M, R mainly from binaries, harder to get large sample L vs. T or color Also called Color-Magnitude diagram

Analogy: The Human Diagram Study people: Individually, in detail? Statistically, in large numbers? Need simple, easily observed properties How about Weight (Wt) vs. Height (Ht)?

Analogy: The Human Diagram Wt Ht

Analogy: The Human Diagram Wt Newborn nursery Basketball team Depends on sample: Ht

Analogy: The Human Diagram Wt Ht Why linear? Aging of individuals: both Wt and Ht increase as we grow Intrinsic differences in people: some people are bigger

Hertzsprung-Russell Diagram Hertzsprung Russell

Hertzsprung-Russell Diagram Luminosity Or Absolute Mag Temperature (or Spectral Type or Color)

Hertzsprung-Russell Diagram Sample? Aging of individual stars = stellar evolution? Intrinsic differences in stars (big and small stars)? Luminosity Or Absolute Mag Temperature (or Spectral Type or Color)

Local H-R Diagram

Local H-R Diagram Points: Most stars on main sequence (luminosity class V) = normal stars Giants and Supergiants White Dwarfs Why? Aging vs. Intrinsic Differences?

H-R Diagram - Radii L=4π R * 2 σ T eff 4 R * = (L/4πσT eff4 ) 1/2

H-R Diagram - Luminosity Classes

Local HR Diagram - Problems Brighter stars favored, can be seen to larger distances Distances uncertain? Hodge-podge: Young stars and old stars Massive stars, low mass stars Differing abundances

Cluster HR Diagrams Stars often found in clusters Distances of all stars are same Cluster stars were formed together from same material All have same age All have same abundances Different clusters have different ages Open (Galactic) clusters = younger Globular clusters = older

Open Star Clusters NGC 265 Pleides

Globular Star Clusters M5 Omega Centauri

Open Cluster HR Diagrams

Globular Cluster HR Diagrams

Cluster HR Diagrams As clusters age Upper main sequence disappears O -> B -> A -> F -> G Giants, supergiants, and white dwarfs appear Conclude that Stars start on main sequence Main sequence = sequence due to intrinsic differences in star Giants, supergiants, white dwarfs are due to aging = stellar evolution

HR Diagram