Astonomy 62 Lecture #10. Last Time. Applications of Stefan-Boltzmann Law Color Magnitudes Color Index

Transcription

1 Last Time Applications of Stefan-Boltzmann Law Color Magnitudes Color Index

2 Standard Visual Band Filters U B V R I

3 Flux through filter X: F x = 0 F S x d F x F x W x Apparent Color Magnitude: m x,1 m x,2 =2.5log F x,2 F x,1 m x,1 m x,2 2.5 log F, 2 x F,1 x x U B V R I (A) W x (A) Å=0.1nm=10 10 m

4 Color Index: B V=2.5 log[ F V F B ] C B V

5 Color Color Diagram for Normal Stars From C&O (Fig. 3.10) T

6 Topics for Today Spectral Types of Stars Kirchhoff's Laws Bohr Atomic Model Reading for today: Reading for next lecture: 8.1

7 Spectral Types of Stars T Credit & Copyright: KPNO 0.9m Telescope, AURA, NOAO, NSF APOD

8 Solar spectrum Spectrum of Planetary Nebula NGC7662

9 Spectroscopy Timeline 1802 Wollaston discovers dark absorption lines in the solar spectrum... gaps separating the colors of the Sun... William Wollaston ( )

10 Spectroscopy Timeline 1802 Wollaston discovers dark absorption lines in the solar spectrum 1814 Fraunhofer catalogs 475 lines and identifies the Na line at ~590 nm. Joseph Fraunhofer ( )

11 Spectroscopy Timeline 1802 Wollaston discovers dark absorption lines in the solar spectrum 1814 Fraunhofer catalogs 475 lines and identifies the Na line at ~590 nm.

12 Spectroscopy Timeline 1802 Wollaston discovers dark absorption lines in the solar spectrum 1814 Fraunhofer catalogs 475 lines and identifies the Na line at ~5900A Fraunhofer observes that spectra of other stars are different from that of the Sun, indicating that the lines cannot have terrestrial origin. 1850's Kirchhoff and Bunsen design a spectrograph. Kirchhoff identifies 70 lines of Fe in the solar spectrum Kirchhoff and Bunsen publish "Chemical Analysis by Spectral Observations". Elements have unique spectral "fingerprint". Absorption and emission lines have the same λ Joseph Lockyer discovered He in the Sun

13 Solar Spectrum λ Element K 3934 A Ca II H 3968 A Ca II G 4340 A H I (H ) F 4861 A H I (H ) b 5184, 5173 A Mg I E 5270 A Fe I D 5896, 5890 A Na I C 6563 A H I (H )

14 Kirchhoff's Laws A hot, dense gas or solid object produces a continuous spectrum with no dark spectral lines. A hot, diffuse gas produces bright spectral lines (emission lines). A cool, diffuse gas in front of a source of continuous spectrum produces dark spectral lines (absorption lines) in the continuous spectrum.

15 Spectroscopy Timeline 1890's Pickering and his assistants cataloged thousands of stellar spectra, labeling them according to strength of hydrogen lines: A, B,... Annie Jump Cannon ( )

16 Spectral Types of Stars T Credit & Copyright: KPNO 0.9m Telescope, AURA, NOAO, NSF APOD

17 Spectroscopy Timeline 1890's Pickering and his assistants cataloged thousands of stellar spectra, labeling them according to strength of hydrogen lines: A, B, Annie Jump Cannon placed the spectra in a temperature sequence: Oh Be A Fine Girl/uy Kiss Me Now

18 Understanding Stellar Spectra 1. Why do atoms emit discreet spectral lines? 2. Do differences between spectral types reflect differences in stellar chemical composition? 3. What role does temperature play in spectral line formation?

19 Spectroscopy Timeline 1885 Johann Balmer found the Balmer formula for H lines 1 =R H n 2 R H = m 1 Rydberg constant 1890's Pickering and his assistants cataloged thousands of stellar spectra, labeling them according to strength of hydrogen lines: A, B, Thomson discovered an electron 1901 Annie Jump Cannon placed the spectra in a temperature sequence 1911 Rutherford discovered an atomic nucleus

20 Spectroscopy Timeline 1913 Bohr develops his atomic model A physicist is just an atom's way of looking at itself. Niels Bohr

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22 H line wavelengths according to Bohr Atomic Model 1 =R H 1 m 2 1 n 2 m=1, 2, 3,... n= m 1, m 2,... R H = e ħ 3 c = m 1 = m e m p m e m p reduced mass

23 Kirchhoff's Laws A hot, dense gas or solid object produces a continuous spectrum with no dark spectral lines. A hot, diffuse gas produces bright spectral lines (emission lines). A cool, diffuse gas in front of a source of continuous spectrum produces dark spectral lines (absorption lines) in the continuous spectrum.

24 The dependence of spectral line strength on temperature Credit & Copyright: C&O, figure 8.11