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Surveying Stars

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Surveying Stars Surveying Stars Orin Harris and Greg Anderson Department of Physics & Astronomy Northeastern Illinois University Spring 2021 c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 1 / 124 Overview The Night Sky Luminosity & Brightness Distance & Parallax Stellar Temperatures HR Diagrams Binary Systems Stellar Masses Star Clusters Review c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 2 / 124 Our Sun is a star. Other stars are similar but can be brighter/dimmer, bluer/redder, and live shorter/longer lives. Sun as seen from earth Sun as seen from Voyager from 43 AU (4 billion miles) Sun The Night Sky Cassiopeia Stars in the Night Sky Night sky star neighborhood 25 brightest (apparent) stars Resolving Star trails The Night Sky Star Movement Orion with distance Star Movement Luminosity & Brightness Distance & Parallax Stellar Temperatures HR Diagrams Binary Systems Stellar Masses Star Clusters Review c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 4 / 124 Stars in the Night Sky • Outside of the city, on very clear nights you can see thousands of stars. • Under the best conditions the furthest star we can see with the naked eye is a few thousand light years away. • Of the 25 brightest stars, the closest is α Cen. (4 ly), the furthest is Deneb (2600 ly). • Astronomers have catalogued the position/velocity/brightness of over 1 billion stars in our galaxy. Only a handful can be resolved as more than a point of light. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 6 / 124 Stars are mostly seen as points of light Exceptions: just a few of the largest/nearest stars. E.g. π1 Gruis, Antares, and Betelgeuse, each roughly ∼500 ly away and ∼500 R⊙ c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 9 / 124 Star Trails (Atacama Desert, Chile, by ESO) Star Movement c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 11 / 124 Star Movement from GAIA over 105 years Star Movement from GAIA over 105 years Star Movement from GAIA over 105 years Star Movement from GAIA over 105 years Star Movement from GAIA over 105 years Star Movement from GAIA over 105 years Star Movement from GAIA over 105 years Sun The Night Sky Luminosity & Brightness Luminosity Q: L Units Stellar L η Carinae Proxima Luminosity & Centauri Blackbody Rad. Relative L Q: Star L Brightness Motorcycle Q: b vs L App Brightness Bulbs Q: L vs r Q: Units for b Magnitude Sys m chart Bright Stars Q: Visible limit Stars vs. Limiting Magnitude Dark Sky Dark Sky Abs c 2012-2021G.Anderson.,O.Harris Mag (M) Universe:Past,Present&Future – slide 14 / 124 Q: Vega Luminosity 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 15 / 124 Q: Luminosity Units What are the standard units for luminosity? A) Watts B) Joules C) Newtons D) kilograms E) Watts per second c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 16 / 124 Q: Luminosity Units What are the standard units for luminosity? A) Watts B) Joules C) Newtons D) kilograms E) Watts per second c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 16 / 124 Stellar Luminosities 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 17 / 124 η Carinae Eta Carinae (η Car): Located in the Homunculus Nebula in Ca- rina 7500 ly away. Less than 3 million years old, but will go su- pernova soon. One of the most massive stars studied in great detail. Briefly became the 2nd brightest star in the sky in 1843, now faded. M = 150M⊙ −→ 120M⊙ 6 L ≈ 10 L⊙ R ≈ 24R⊙ c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 18 / 124 Proxima Centauri, part of the α-Cen. triple-star system, 0.002L⊙ Blackbody Radiation 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 20 / 124 Relative Luminosity Relative luminosity for stars with radius R and temperature T 4 Lstar σAstarTstar = 4 Lsun σAsunTsun 2 4 σ 4πRstar Tstar = 2 4 σ(4πRsun)Tsun R 2 T 4 = star star Rsun Tsun c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 21 / 124 Q: Star Luminosity 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 22 / 124 b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b 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 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 b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b
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