Northeastern Illinois University Surveying Stars Greg Anderson Department of Physics & Astronomy Northeastern Illinois University Fall 2018 c 2012-2018G. Anderson Universe: Past, Present & Future – slide 1 / 102 Northeastern Illinois Overview University The Night Sky Luminosity & Brightness Distance & Parallax Stellar Temperatures HR Diagrams Binary Systems Stellar Masses Star Clusters Review c 2012-2018G. Anderson Universe: Past, Present & Future – slide 2 / 102 Northeastern Illinois University The Night Sky Cassiopeia Stars in the Night Sky Star Trails Lower Canyons Luminosity & Brightness Distance & Parallax Stellar The Night Sky Temperatures HR Diagrams Binary Systems Stellar Masses Star Clusters Review c 2012-2018G. Anderson Universe: Past, Present & Future – slide 3 / 102 c T. Credner & S. Kohle, AlltheSky.com Northeastern Illinois Stars in the Night Sky University • Outside of the city, on very clear nights you can see thousands of stars. • Of the 25 brightest stars, the furthest away is Deneb (≈ 800 pc). • Under the best conditions the furthest star we can see with the naked eye is a few thousand light years away. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 5 / 102 G. Anderson: Star Trails in the Lower Canyons Northeastern Illinois University The Night Sky Luminosity & Brightness Luminosity Q: L Units Stellar L η Carinae Blackbody Rad. Relative L Luminosity & Q: Star L Motorcycle Q: b vs L b vs. d Brightness App Brightness Bulbs Q: L vs r Q: Units for b Magnitude Sys Apparent Magnitude m chart Bright Stars Q: Visible limit Stars vs. Limiting Magnitude Darks Sky Abs Mag (M) Q: c Vega2012-2018G. Anderson Universe: Past, Present & Future – slide 7 / 102 Distance & Northeastern Illinois Luminosity University Luminosity: The total amount of power (energy per unit time) emitted by a star or other object. Units: watts. • A 100-watt light-bulb emits half the power of a 200-watt light-bulb. It is half as bright. • The Sun has a luminosity of 26 L⊙ ≈ 4 × 10 watts 26 L⊙ ≈ 4 × 10 watts Lbulb = 100watts c 2012-2018G. Anderson Universe: Past, Present & Future – slide 8 / 102 Northeastern Illinois Q: Luminosity Units University What are the standard units for luminosity? A) Watts B) Joules C) Newtons D) kilograms E) Watts per second c 2012-2018G. Anderson Universe: Past, Present & Future – slide 9 / 102 Northeastern Illinois Q: Luminosity Units University What are the standard units for luminosity? A) Watts B) Joules C) Newtons D) kilograms E) Watts per second c 2012-2018G. Anderson Universe: Past, Present & Future – slide 9 / 102 Northeastern Illinois Stellar Luminosities University Solar Luminosity: 26 L⊙ ≈ 4 × 10 watts Eddington Limit: Upper limit for stellar luminosity. Above this, radiation pressure exceeds gravity. 6 L . 10 L⊙ Least luminous stars: −4 L ≈ 10 L⊙ Dim stars are much more common than bright stars. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 10 / 102 Northeastern Illinois η Carinae University Eta Carinae (η Car): Binary system less than 3 million years old, located in the Homuncu- lus Nebula in Carinae. One of the most massive stars studied in great detail. M = 150M⊙ −→ 120M⊙ 6 L ≈ 10 L⊙ R ≈ 24R⊙ c 2012-2018G. Anderson Universe: Past, Present & Future – slide 11 / 102 Northeastern Illinois Blackbody Radiation University Blackbody radiation: thermal radiation emitted by opaque bodies. (perfect absorbers) Stefan-Boltzmann law for Luminosity: 4 L = σAT Stefan-Boltzmann constant σ =5.67 × 10−8 W/m2 · K4 T = Temperature A = Area c 2012-2018G. Anderson Universe: Past, Present & Future – slide 12 / 102 Northeastern Illinois Relative Luminosity University Stefan-Boltzmann Law: radiated power L = = σT 4 area A eff Stefan-Boltzmann constant: σ =5.67 × 10−8 W/m2 · K4 Relative luminosity for stars with radius R and temperature T L R 2 T 4 star = star star Lsun Rsun Tsun c 2012-2018G. Anderson Universe: Past, Present & Future – slide 13 / 102 Northeastern Illinois Q: Star Luminosity University The luminosity of a star is the: A) apparent brightness of the star in our sky. B) surface temperature of the star. C) lifetime of the star. D) total amount of energy that the star will radiate over its entire lifetime. E) total amount of energy that the star radiates each second. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 14 / 102 Northeastern Illinois Q: Star Luminosity University The luminosity of a star is the: A) apparent brightness of the star in our sky. B) surface temperature of the star. C) lifetime of the star. D) total amount of energy that the star will radiate over its entire lifetime. E) total amount of energy that the star radiates each second. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 14 / 102 b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b