Last Time Applications of Stefan-Boltzmann Law Color Magnitudes Color Index
Standard Visual Band Filters U B V R I
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) 3650 4400 5500 7000 9000 W x (A) 680 980 890 2200 2400 1 Å=0.1nm=10 10 m
Color Index: B V=2.5 log[ F V F B ] C B V
Color Color Diagram for Normal Stars From C&O (Fig. 3.10) T
Topics for Today Spectral Types of Stars Kirchhoff's Laws Bohr Atomic Model Reading for today: 5.1-5.4 Reading for next lecture: 8.1
Spectral Types of Stars T Credit & Copyright: KPNO 0.9m Telescope, AURA, NOAO, NSF APOD
Solar spectrum Spectrum of Planetary Nebula NGC7662
Spectroscopy Timeline 1802 Wollaston discovers dark absorption lines in the solar spectrum... gaps separating the colors of the Sun... William Wollaston (1766-1828)
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 (1787-1826)
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.
Spectroscopy Timeline 1802 Wollaston discovers dark absorption lines in the solar spectrum 1814 Fraunhofer catalogs 475 lines and identifies the Na line at ~5900A. 1817 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. 1860 Kirchhoff and Bunsen publish "Chemical Analysis by Spectral Observations". Elements have unique spectral "fingerprint". Absorption and emission lines have the same λ. 1868 Joseph Lockyer discovered He in the Sun
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 )
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.
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 (1863 1941)
Spectral Types of Stars T Credit & Copyright: KPNO 0.9m Telescope, AURA, NOAO, NSF APOD
Spectroscopy Timeline 1890's Pickering and his assistants cataloged thousands of stellar spectra, labeling them according to strength of hydrogen lines: A, B,... 1901 Annie Jump Cannon placed the spectra in a temperature sequence: Oh Be A Fine Girl/uy Kiss Me Now
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?
Spectroscopy Timeline 1885 Johann Balmer found the Balmer formula for H lines 1 =R H 1 4 1 n 2 R H =1.1 10 7 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,... 1898 Thomson discovered an electron 1901 Annie Jump Cannon placed the spectra in a temperature sequence 1911 Rutherford discovered an atomic nucleus
Spectroscopy Timeline 1913 Bohr develops his atomic model A physicist is just an atom's way of looking at itself. Niels Bohr
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 4 64 3 0 2 ħ 3 c =1.1 107 m 1 = m e m p m e m p reduced mass
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.
The dependence of spectral line strength on temperature Credit & Copyright: C&O, figure 8.11