ASTR 1200 Announcements Exam #1 in class, next Tuesday, October 7 Have posted review sheet and sample exam Help room: Mondays 3-5,Duane G2B90 Review Lecture on Thursday Josh review/help session time? Solutions to Problem Sets posted tomorrow Website http://casa.colorado.edu/~wcash/APS1200/APS1200.html

Planetarium We met at the planetarium and spent half the time with a show. In particular, we “flew” from Earth to Prox Cen and back, watching the parallax of the nearby stars. We also “flew” to Orion’s Sword and visited a star-forming region.

Electromagnetic Spectrum Wavelength increases to the right Frequency and energy increase to the left

Stars Come in Different Colors

Stellar Temperature Stars come in different sizes and temperatures. Can the two be linked?

Stellar Classification Full range of surface temperatures from 2000 to 40,000K Spectral Classification is Based on Surface Temperature Hottest O B A F G K M Coolest { Girl } Oh Be A Fine Kiss Me Guy Each Letter has ten subdivisions from 0 to 9 0 is hottest, 9 is coolest

The Spectral Types O Stars of Orion's Belt >30,000 K Lines of ionized helium, weak hydrogen lines <97 nm (ultraviolet)* B Rigel 30,000 K-10,000 K Lines of neutral helium, moderate hydrogen lines 97-290 nm (ultraviolet)* A Sirius 10,000 K-7,500 K Very strong hydrogen lines 290-390 nm (violet)* F Polaris 7,500 K-6,000 K Moderate hydrogen lines, moderate lines of ionized calcium 390-480 nm (blue)* G Sun, Alpha Centauri A 6,000 K-5,000 K Weak hydrogen lines, strong lines of ionized calcium 480-580 nm (yellow) K Arcturus 5,000 K-3,500 K Lines of neutral and singly ionized metals, some molecules 580-830 nm (red) M Betelgeuse, Proxima Centauri <3,500 K Molecular lines strong >830 nm (infrared) *All stars above 6,000 K look more or less white to the human eye because they emit plenty of radiation at all visible wavelengths.

Stellar Classification (2) Sun G2 a Cen G2 + K5 Sirius A1 Antares M1 Rigel B8 O5 40,000K B5 15,500 A5 8500 F5 6580 G5 5520 K5 4130 M5 2800 Letters are odd due to confusion in sorting out temperature scale between 1900 and 1920

Stellar Classification Full range of surface temperatures from 2000 to 40,000K Spectral Classification is Based on Surface Temperature Hottest O B A F G K M Coolest { Girl } Oh Be A Fine Kiss Me Guy Each Letter has ten subdivisions from 0 to 9 0 is hottest, 9 is coolest

The Spectral Types Table 15.1 The Spectral Sequence O Stars of Orion's Belt >30,000 K Lines of ionized helium, weak hydrogen lines <97 nm (ultraviolet)* B Rigel 30,000 K-10,000 K Lines of neutral helium, moderate hydrogen lines 97-290 nm (ultraviolet)* A Sirius 10,000 K-7,500 K Very strong hydrogen lines 290-390 nm (violet)* F Polaris 7,500 K-6,000 K Moderate hydrogen lines, moderate lines of ionized calcium 390-480 nm (blue)* G Sun, Alpha Centauri A 6,000 K-5,000 K Weak hydrogen lines, strong lines of ionized calcium 480-580 nm (yellow) K Arcturus 5,000 K-3,500 K Lines of neutral and singly ionized metals, some molecules 580-830 nm (red) M Betelgeuse, Proxima Centauri <3,500 K Molecular lines strong >830 nm (infrared) *All stars above 6,000 K look more or less white to the human eye because they emit plenty of radiation at all visible wavelengths.

Stellar Luminosity The H-R Diagram By 1915 had lots of spectra and classifications Had a few distances from parallax Once distance was available, luminosity and Absolute Magnitude could be calculated. Herzsprung and Russel, working independently both plotted absolute magnitude (luminosity) vs classification (temperature) The H-R Diagram

The H-R Diagram Plot of Brightness vs Temperature -5 Rigel Giants Capella Sirius Brightness Procyon Sun Main Sequence +5 a Cen B White Dwarfs +10 Sirius B Prox Cen +15 O B A F G K M Spectral Type