Surveying Stars

Home , 83 Ursae Majoris, Regulus, Solar luminosity, Stellar parallax

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

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 b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b

b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b

b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b

These two stars have about the same luminosity – which one appears brighter? A) Alpha Centauri B) The Sun

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 16 / 102 Northeastern Illinois Q: Brightness vs Luminosity University

These two stars have about the same luminosity – which one appears brighter? A) Alpha Centauri B) The Sun Alpha Centauri is a little more luminous that the Sun, but it is much farther away.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 16 / 102 Northeastern Illinois Brightness, Distance and Luminosity University

Y X

L b = 4πr2

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 17 / 102 Northeastern Illinois Apparent Brightness University Apparent Brightness: How bright a distant object appears to an observer on Earth. As light travels away from the source, the power (L) is spread over a sphere with surface area: A =4πr2. Apparent Brightness:

b = L/A

Surface Area of Sphere:

2 L b1 A =4πr r1 Apparent Brightness: r 2 L b = 4πr2 b2

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 18 / 102 Northeastern Illinois Brightness vs. Distance University

6 b = L 50 W 4πr2 5 L = b(4πr2) 4 r = L/4πb 3 200 W p

2 Brightness (b)

0 012345678910 Distance (r)

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 19 / 102 Northeastern Illinois Q: Luminosity and distamce University

If the distance between us and a star is doubled, with everything else remaining the same, its luminosity

A) is decreased by a factor of four, and its apparent brightness is decreased by a factor of four.

B) is decreased by a factor of two, and its apparent brightness is decreased by a factor of two.

C) remains the same, but its apparent brightness is decreased by a factor of two.

D) remains the same, but its apparent brightness is decreased by a factor of four.

E) is decreased by a factor of four, but its apparent brightness remains the same.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 20 / 102 Northeastern Illinois Q: Luminosity and distamce University

If the distance between us and a star is doubled, with everything else remaining the same, its luminosity

A) is decreased by a factor of four, and its apparent brightness is decreased by a factor of four.

B) is decreased by a factor of two, and its apparent brightness is decreased by a factor of two.

C) remains the same, but its apparent brightness is decreased by a factor of two.

D) remains the same, but its apparent brightness is decreased by a factor of four.

E) is decreased by a factor of four, but its apparent brightness remains the same.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 20 / 102 Northeastern Illinois Q: Units for Brightness University

What are the standard units for apparent brightness? A) Watts B) Joules C) Newtons D) Watts per second E) Watts per square meter

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 21 / 102 Northeastern Illinois Q: Units for Brightness University

What are the standard units for apparent brightness? A) Watts B) Joules C) Newtons D) Watts per second E) Watts per square meter

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 21 / 102 Northeastern Illinois The Magnitude System University

Hipparchus (190-120 BCE) divided stars into six magnitude classes

Apparent magnitude (m) • m = 1, 20 brightest stars • m = 2 next brightest stars • ... • m = 6 faintest stars

Raphael’s Hipparchus from “The School of Athens” Modern deﬁnition: Five steps in magnitude as a factor of 100 in brightness. Thus, one step in magnitude represents a factor of:

1001/5 ≈ 2.51

step by 012345 6 7 8 9 10 fainter by 1 2.5 6.3 16 40 100 250 630 1600 4000 10,000 c 2012-2018G. Anderson Universe: Past, Present & Future – slide 22 / 102 Northeastern Illinois Apparent Magnitude University Ratio of apparent brightness b 1 = 100(m2−m1)/5 = 102(m2−m1)/5 = {102/5}(m2−m1) =2.512(m2−m1) b2 Solving for ∆m

5 b1 ∆m = m2 − m1 = log 2 b2 Apparent magnitude is logarithmic ﬂux

m = C − 2.5log b

1 Historic convention from α Lyr: mVega = 0.

C =2.5log bVega

1Modern: Black body radiation curve for an ideal stellar surface at 11,000 K c 2012-2018G. Anderson Universe: Past, Present & Future – slide 23 / 102 Northeastern Illinois Apparent Magnitude (m) University

-30 Sun (-26.7) -25 -20 -15 Full moon (-12.6) -10 -5 Venus, at brightest (-4.4) 0 Sirius (-1.44) +5 Naked eye limit (+6) +10 Binocular limit (+10) +15 Pluto (+15) +20 +25 +30 Best Telescopes (+30)

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 24 / 102 Northeastern Illinois 10 Brightest Stars (Apparent) University

m Designation Name Distance(ly) Class 0 -26.74 - (Sun) 0.000016 G2 V 1 -1.46 α CMa Sirius 8.6 A1 V 2 -0.72 α Car Canopus 310 F0 Ia 3 -0.27 α Cen A Rigil Kentaurus 4.3 G2 V 4 -0.04 α Boo Arcturus 37 K1.5 III 5 0.03 α Lyr Vega 25 A0 V 6 0.08 α Aur Capella 42 G8 III 7 0.12 β Ori Rigel 770 B8 Iab 8 0.34 α CMi Procyon 11 F5 IV-V 9 0.42 α Ori Betelgeuse 640 M2 Iab 10 0.50 α Eri Achernar 140 B3 Vpe

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 25 / 102 Northeastern Illinois Q: Visible limit University

The faintest star visible to the naked eye has an apparent magnitude of about A) 10. B) 6. C) 1. D) 0.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 26 / 102 Northeastern Illinois Q: Visible limit University

The faintest star visible to the naked eye has an apparent magnitude of about A) 10. B) 6. C) 1. D) 0.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 26 / 102 Northeastern Illinois Stars vs. Limiting Magnitude University

m ≤ No. Stars Notes +7 15,544 +6 5,044 Zodiacal light visible +5 1,627 Faint Milky Way +4 519 Suburbs +3 177 Major city +2 49 Center of large cities

Table 1: Data from the HIPPARCOS Main Catalog

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 27 / 102

Northeastern Illinois Absolute Magnitude (M) University Apparent and Absolute: m (apparent magnitude): brightness of a star measured from Earth. m⊙ = −26.74 M (absolute magnitude): brightness of a star if it was placed 10 pc (32.6 ly) from Earth. M⊙ =4.83 Five steps in magnitude represents a factor of 100 in brightness which is a factor of 10 in distance (d ∝ b−1/2): d −1/2 = 100(M−m)/5 = 10(m−M)/5 10pc n o Distance modulus: d m − M = 5log 10pc c 2012-2018G. Anderson Universe: Past, Present & Future – slide 29 / 102 Northeastern Illinois Q: Vega University

The star Vega has an absolute magnitude of about 4 and an apparent magnitude of about 0. Based on the deﬁnitions of absolute and apparent magnitude, we can conclude that: A) Vega is nearer than 10 parsecs from Earth. B) Vega has a parallax angle of 1/10 arcsecond. C) Vega’s luminosity is less than that of our Sun. D) Vega’s surface temperature is cooler than the Sun.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 30 / 102 Northeastern Illinois Q: Vega University

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 30 / 102 Northeastern Illinois University

The Night Sky Luminosity & Brightness Distance & Parallax Parallax Angles Stellar Parallax Parsec Q1: Parallax Q2: Parallax Distance & Parallax Hipparcos Hipparcos Stellar Temperatures

HR Diagrams

Binary Systems

Stellar Masses

Star Clusters

Review

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 31 / 102 Northeastern Illinois Parallax University

The apparent shift in position of nearby objects in comparison to more distant objects resulting from the movement of the observer. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 32 / 102 Northeastern Illinois Parallax University

In a circle S θ 360◦ =2π radians R Conversion 2π 1 1◦ = radians ≈ radians 360 60 Circumference: Angular size (radians)

C =2πR S θ = R Arc length: Angular size (degrees) S = Rθ S 360 θ = × for θ in radians R 2π

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 33 / 102 Northeastern Illinois Stellar Parallax University

b b

b b b b

b b b b Jan sky Jun sky Animation p

d d(parsecs) = 1/p(arcseconds)

1 AU

June January

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 34 / 102 Northeastern Illinois Parsec University Parsec: The distance at which a star has a parallax angle of one arc-second. One parsec (pc) is equal to 3.26 light-years. 1 distance (parsecs) = parallax angle (arc seconds)

Example: If p =0.04′′, 1 1 d = = = 25 pc p 0.04

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 35 / 102 Northeastern Illinois Q1: Parallax University

Sirius, α Canis Majoris, has a parallax angle of 0.38 arcseconds, while Procyon, α Canis Minoris, has a parallax angle of 0.29 arcseconds. Which star is closer to Earth? A) Sirius B) Procyon C) we can’t tell

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 36 / 102 Northeastern Illinois Q1: Parallax University

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 36 / 102 Northeastern Illinois Q2: Parallax University

The parallax angle of a star is 1/20=0.05 arcseconds. What is the distance to the star? A) 0.2 light-year. B) 0.2 parsec. C) 20 light-years. D) 20 parsecs. E) impossible to determine.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 37 / 102 Northeastern Illinois Q2: Parallax University

The parallax angle of a star is 1/20=0.05 arcseconds. What is the distance to the star? A) 0.2 light-year. B) 0.2 parsec. C) 20 light-years. D) 20 parsecs. E) impossible to determine. 1 1 d(pc) = = = 20pc p(arcsec) 0.05

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 37 / 102 Northeastern Illinois Hipparcos Satellite University

Astrometry: The precise measurement of the positions of stars and other celestial bodies. Hipparcos: HIgh Precision PARallax COllecting Satellite, hommage to Hipparchus of Nicaea.

Hipparcos satellite, European Space (ESA) • Operated 1989-1993. • Target precision 0.002 arcseconds • Hipparcos Catalogue: 118,200 stars. • Hipparcos Hyades Movie

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 38 / 102 Northeastern Illinois Hipparcos Satellite University

Astrometry: The precise measurement of the positions of stars and other celestial bodies, and their radial velocity. Gia’s Goal: Create the most precise 3D Galactic catalog ever. Gaia satellite, European Space (ESA) • Operated 2013-current

• Orbit at Earth-Sun L2 Lagrange point. • Target precision: 20µ arcseconds • Gaia catalogue: 1% of Galactic stellar population. (1 billion astronomical objects)

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 39 / 102 Northeastern Illinois University

The Night Sky Luminosity & Brightness Distance & Parallax Stellar Temperatures Stellar Temperatures Measuring Temperature Stellar Temperatures Blackbody Rad. Wein’s Law Spectral Type The Harvard Computers Understanding Stellar Spectra Spectral Type The Solar Spectrum Solar Spectrum Spectrum from Procyon Spectrum from Arcturus B-V Color Index Color Index Q: Spectral Type

HR c Diagrams2012-2018G. Anderson Universe: Past, Present & Future – slide 40 / 102 Northeastern Illinois Stellar Temperatures University Hottest Stars T ≈ 50, 000K Solar Temperature

T⊙ ≈ 5800K Coolest Stars T ≈ 3000K

• Most stars in the Milky Way galaxy are smaller, cooler and dimmer than the Sun. • Most main sequence stars that you can see in the night sky are larger, hotter and brighter than the Sun.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 41 / 102 Northeastern Illinois Measuring Temperature University

• Stefan-Boltzmann Law: L = σ(4πR2)T 4 −3 • Wein’s Law: λmT =2.9 × 10 mK • Spectral Type

• Color Index: mB − mV

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 42 / 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 43 / 102 Northeastern Illinois Wein’s Displacement Law University

Hottest

Hotter

Intensity Hot

wavelength λ

Emission is a maximum at λm (Wilhelm Wien 1893)

−3 λmT = constant = 2.898 × 10 mK

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 44 / 102 Northeastern Illinois Spectral Type University

c NASA/NOAA

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 45 / 102 Northeastern Illinois The Harvard Computers University

Harvard College Observatory Collection of Astronomical Photographs. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 46 / 102 Northeastern Illinois Understanding Stellar Spectra University

Selected Contributions: Williamina Fleming: First “computer” hired by Pickering. Helped develop spectral classification system. Discovered horsehead nebula. Annie Jump Cannon: Created the Harvard Classification Scheme. Henrietta Swan Leavitt: Developed the Cepheid period luminosity relationship. Cecilia Payne: In 1925 showed that the spectral classification of stars was related to their suface temperature. Established that stars are mostly hydrogen.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 47 / 102 Northeastern Illinois Spectral Type University

Harvard spectral classiﬁcation

Type Tsurf (K) Mass Radius(MS) %ofMS

O > 30, 000 ≥ 16M⊙ ≥ 6.6R⊙ .00003%

B 10, 000 − 30, 000 2.1 − 16M⊙ 1.8 − 6.6R⊙ 0.13%

A 7, 500 − 10, 000 1.4 − 2.1M⊙ 1.4 − 1.8R⊙ 0.6%

F 6, 000 − 7, 500 1.04 − 1.4M⊙ 1.15 − 1.4R⊙ 3%

G 5, 200 − 6, 000 0.8 − 1.04M⊙ 0.96 − 1.15R⊙ 7.6%

K 3, 700 − 5, 200 0.45 − 0.8M⊙ 0.7 − 0.96R⊙ 12.1%

M 2, 400 − 3, 700 0.08 − 0.45M⊙ ≤ 0.7R⊙ 76.45% Annie Jump Cannon (1863-1941) et al.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 48 / 102 Northeastern Illinois The Solar Spectrum University

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 49 / 102 Northeastern Illinois Solar Spectrum University

c Nigel Sharp, NOAA c 2012-2018G. Anderson Universe: Past, Present & Future – slide 50 / 102 Northeastern Illinois Spectrum from Procyon University

c NASA/NOAA c 2012-2018G. Anderson Universe: Past, Present & Future – slide 51 / 102 Northeastern Illinois Spectrum from Arcturus University

c NASA/NOAA c 2012-2018G. Anderson Universe: Past, Present & Future – slide 52 / 102 Northeastern Illinois B-V Color Index University

Observe stars through blue (B) and visual (V) ﬁlters. The color index is based on the ratio of brighness in blue light to its brightness in visible light.

B − V color index = mB − mV

A smaller color index corresponds to a hotter object. Examples: Sun B − V =0.66, Rigel B − V = −0.03 Intensity

wavelength λ

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 53 / 102 Northeastern Illinois Color Index University

Class B − VU − B V − R R − I Teﬀ (K) O5V -0.33 -1.19 -0.15 -0.32 42,000 B0V -0.30 -1.08 -0.13 -0.29 30,000 A0V -0.02 -0.02 0.02 -0.02 9,790 F0V 0.30 0.03 0.30 0.17 7,300 G0V 0.58 0.06 0.50 0.31 5,940 K0V 0.81 0.45 0.64 0.42 5,150 M0V 1.40 1.22 1.28 0.91 3,840

Table 2: Sample calibration colors

Zombeck, Martin V. (1990). “Calibration of MK spectral types”. Handbook of Space Astronomy and

Astrophysics (2nd ed.). Cambridge University Press. p. 105. ISBN 0-521-34787-4.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 54 / 102 Northeastern Illinois Q: Spectral Type University

Sirius is a star with spectral type A and Rigel is a star with spectral type B star. What can we conclude? A) Rigel has a higher surface temperature than Sirius. B) Rigel has a higher core temperature than Sirius. C) Sirius has a higher core temperature than Rigel. D) Sirius has a higher surface temperature than Rigel.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 55 / 102 Northeastern Illinois Q: Spectral Type University

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 55 / 102 Northeastern Illinois University

The Night Sky Luminosity & Brightness Distance & Parallax Stellar Temperatures

HR Diagrams HR Diagram HR Diagram HR Diagrams Data Sources HR Diagrams HR Diagrams Yerkes Class Q: HR Diagram

Binary Systems

Stellar Masses

Star Clusters

Review

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 56 / 102 Northeastern Illinois Hertzsprung-Russell (H-R) Diagram University Temperature (K) 40,000 10,000 7,000 6,000 5,000 4,000 3,000 2,500 106 −10 O B A b F G K M b

b b

b b ( Magnitude Absolute b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b 4 b b b b b b b b b b b b b b b ) b b b b b −5 b b b b b b 10 b b b b b b b b b b b b b b b b b b b b b ⊙ b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b 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 bb bb b b bb b b b b b b L/L 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 bb 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 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 2 b b b b b b b b b b b b b b b b b b bb bb b b b b b b b bb b b b b b bb b b b b b b b b bb b b b b b b bb 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 bb 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 bb b b b b b bb b b b b b b b b b b b b b b b bb bb b b b bb b b bb b b b b b b b b b b b b b b b b b bb b b bb b b b b b b b b bb b b b b b b b b b b b bb b b b b b b bb b 0 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 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 10 b b 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 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 bb b b b b b b b b b bb b b b bb b b bb 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 bbb 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 bb 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 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 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 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 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 bb 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 bb 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 bb bb b b b b b b bb 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 bb b b b b b b b b b b b b b b b b bb b b b b b bbb 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 bb bbb 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 bb 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 bb b b bb b b bbbb b b bb 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 bb 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 bbb b b b b b b bb b b b b bb b b b b b b b b b b b b bb b bb b b b b b b bb bbb b b b bbb b bb b bb b b b b b b b b b b b b b b b b b b b b b bb bb b b b b b b b b b b b b b b b b bb bb b bbb b b b b b b b bb b bb bb b b b b b b b b b bb bb b b b b b bb 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 bb b b b b b b b bb b b b b b b b b bb b b b b b b b b bb b b b b b b b b b b b b b bb b b b b b b b b bb b bb b b b b b b b b b bb b b b b b b b b b b b b b b bb 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 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 bbbb 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 bb b b b b b b b b b b b b b b b b b b bb 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 bb 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 bb b b b b b b b b b b b b b b b b b b b b b bbb b b b b b b bb b b bbb 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 bb b b b b b b b b bb b b bbb 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 bb b b b b b b b bb 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 bb b b b b b b bb b b b b b b b b bb b b b b b 0 b b b b b bb b b b b b b b b b b bb b b b b b b b b b b b bb b b b b b b b b b b b bb b b b b b b b b b b 5 b b b b b b b b 10 b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b

b M b b b b b b b b b

Luminosity ( 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 V b b b b − b b b 2 b b b b b b b b b bb b b bb b b b b bb b b b b b b b 10 b b b bb b b b b b b b b ) 10 b b b b b b b b b b b b b b b b b b b b b b 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 bb b b bb b b b b b b b b b bb b b b b bbb bb bb b b b b b b b bb b b b b b b b b bb 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 −4 b b b b b b b 15 10 b b −0.5 0 0.5 1.0 1.5b 2.0 Color Index (B − V )

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 57 / 102 Northeastern Illinois Hertzsprung-Russell (H-R) Diagram University O B A F G K M 106 −10 R Denebb R = 10 b = 1000 R ( Magnitude Absolute ⊙ Rigel R Betelgeuseb ⊙ b b b 4 βCen Canopus Antares −5 ) 10 b Spicab b

⊙ R b = Polaris R b Achernarb R ⊙ Bellatrix = 100 R b ⊙ L/L Regulusb Aldebaron b b 2 b b Arcturus Algol Vegab Capella 0 10 R b = 0 b Pollux . Sirius b Procyon 1R b ⊙ Altair

αCenb A b 0 Sun b 5 10 R = 0 αCen B . 01R ⊙ M Luminosity (

−2 V 10 Lalandeb 21185 10 b ) Sirius B

Procyonb B Barnardsb

−4 10 b 15 40,000 20,000 10,000 7,000 5,000 2,500 b Wolf 359 Temperature (K)

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 58 / 102 Northeastern Illinois Data Sources University

Data sources for the H-R diagrams in these lecture notes include: • HYG Database The Astronomy Nexus • Yale Bright Star Catalog • Hipparcos Catalog • The White Dwarf Catalog (Villanova) • Research Consortium on Nearby Stars (RECONS)

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 59 / 102

Northeastern Illinois HR Diagrams University

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 61 / 102 Northeastern Illinois Stellar Luminosity Classes University

A complete classiﬁcation of a star requires the star’s spectral type: OBAFGKM, and a luminosity class (Yerkes Spectral Classiﬁcation):

I Supergiants II Bright Giants III Giants IV Subgiants V Main-sequence stars VI Subdwarfs VII White dwarfs

Examples: Our Sun is classiﬁed as G2 V, Proxima Centauri is M5 V.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 62 / 102 Northeastern Illinois Q: HR Diagram University

You observe a star and you want to plot it on an H-R diagram. You will need to measure all of the following, except the star’s: A) mass B) distance C) apparent brightness D) spectral type

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 63 / 102 Northeastern Illinois Q: HR Diagram University

You observe a star and you want to plot it on an H-R diagram. You will need to measure all of the following, except the star’s: A) mass B) distance C) apparent brightness D) spectral type

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 63 / 102 Northeastern Illinois University

The Night Sky Luminosity & Brightness Distance & Parallax Stellar Temperatures

HR Diagrams

Binary Systems Binary Stars Binary Systems Classiﬁcation Ursa Major Mizar & Alcor Alcor & Mizar Visual Binaries Albireo Eclipsing Binary Q: Dimming Star Doppler Eﬀect Spectroscopic Measuring Masses Q: Stellar Masses

Stellar Masses

Star Clusters

Review c 2012-2018G. Anderson Universe: Past, Present & Future – slide 64 / 102 Northeastern Illinois Binary Stars University

Double star: Two stars which appear close together in the sky. A binary or optical double star. Binary star: Two stars orbiting their common center of mass. Optical double star: Two stars with no physical connection which appear close together from Earth.

Of the stars nearest to the Sun, about half are known to be in multiple star systems.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 65 / 102 Northeastern Illinois Classiﬁcation University Visual Binary: A pair of stars we can see distinctly. Eclipsing Binary: A pair of stars which orbit in our line of sight. Spectroscopic Binary: A binary pair in which is inferred from periodic doppler shifts in the spectrum Astrometric Binary: Measurable, periodic, deviation in the stars position. These methods of detection are not mutually exclusive.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 66 / 102

Northeastern Illinois Mizar and Alcor (Ursa Major) University

b Mizar-Alcor sextuple system, d = 25pc • Mizar (4 stars)

Alcor b

b • Alcor (2 stars, eclipsing binary)

Mizar

b b

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 68 / 102

Northeastern Illinois Visual Binaries University

Alpha, Beta and Proxima Centauri

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 70 / 102 Visual Binary: Albireo (β Cygni) Northeastern Illinois Eclipsing Binary University brightness

Animations: • European Southern Observatory (ESO) • European Southern Observatory (ESO) • OSU • Addison-Wesley

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 72 / 102 Northeastern Illinois Q: Dimming Star University

Careful measurements reveal that a star maintains a steady apparent brightness at most times, except that at precise intervals of 73 hours the star becomes dimmer for about 2 hours. The most likely explanation is that: A) the star is a member of an eclipsing binary star system B) the star is a Cepheid variable C) the star is periodically ejecting gas into space, every 73 hours D) the star is a white dwarf c 2012-2018G. Anderson Universe: Past, Present & Future – slide 73 / 102 Northeastern Illinois Q: Dimming Star University

∆λ v λ ≈ c

Applet

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 74 / 102 Northeastern Illinois Spectroscopic Binary University

approaching

To Earth −→

receding Animations: • McGraw-Hill • OSU • Addison-Wesley

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 75 / 102 Northeastern Illinois Measuring Masses in Binary Systems University

Direct mass measurements are possible only for stars in binary star systems. Measure mass using gravity & Kepler’s Law:

4π2 p2 = a3 G(M1 + M2) where p = period, a = average separation. Need two out of three observables to measure mass: • Orbital period: p • Orbital separation: a • Orbital velocity v For circular orbits, vp =2πa =2πr

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 76 / 102 Northeastern Illinois Q: Stellar Masses University

From which quantities below can we calculate the masses of stars in a binary system: A) orbital period and average orbital distance B) spectral types and distance from Earth C) absolute magnitudes and luminosities D) luminosities and distance from Earth

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 77 / 102 Northeastern Illinois Q: Stellar Masses University

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 77 / 102 Northeastern Illinois University

The Night Sky Luminosity & Brightness Distance & Parallax Stellar Temperatures

HR Diagrams Binary Systems Stellar Masses Stellar Masses Stellar Masses Q: Mass and Spectral Type Stellar Lifetimes 4 MS Stars Properties Q: Stellar Characteristics Metallicity Stellar Populations

Star Clusters

Review

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 78 / 102 Northeastern Illinois Stellar Masses University

Very massive stars are rare. Upper (Eddington) limit on a stars mass:

M . 150M⊙ Low mass stars are common. Lower limit on a stars mass: M ∼> 0.08M⊙

Objects with M . 0.08M⊙ are brown dwarfs, not enough mass to sustain proton-proton nuclear fusion.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 79 / 102 Northeastern Illinois Q: Mass and Spectral Type University

How did astronomers discover the relationship between spectral type and mass for main sequence stars?

A) By measuring the masses and spectral types of main-sequence stars in binary systems

B) By using computer models of hydrogen fusion and stellar structure

C) By measuring stellar radii with very powerful telescopes

D) By comparing stars with the same spectral type but diﬀerent luminosities

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 80 / 102 Northeastern Illinois Q: Mass and Spectral Type University

How did astronomers discover the relationship between spectral type and mass for main sequence stars?

A) By measuring the masses and spectral types of main-sequence stars in binary systems

B) By using computer models of hydrogen fusion and stellar structure

C) By measuring stellar radii with very powerful telescopes

D) By comparing stars with the same spectral type but diﬀerent luminosities

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 80 / 102 Northeastern Illinois Stellar Lifetimes University

Empirical mass-luminosity relationship:

2.3 M < 0.43M⊙ α  4 0.43M⊙ < M < 2M⊙ L ∝ M , α =   3.5 2M⊙ < M < 20M⊙ 1 M > 20M⊙  Larger stars have more hydrogen fuel, but they use it up much more rapidly: Lifetime on Main Sequence (α = 4):

3 10 M L⊙ 10 M⊙ τMS ≈ 10 years = 10 years M⊙ L M Increasing a stars mass by a factor of two decreases its lifetime by a factor of eight. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 81 / 102 Northeastern Illinois Four main-sequence stars University

Sirius Upsilon Orionis A1 V B0 V M =2M⊙ M = 20M⊙ Lifetime 109 years Lifetime 107 years Sun G2 V Lifetime 1010 years

Proxima Centauri M5.5 V M =0.12M⊙ Lifetime 1012 years

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 82 / 102 Northeastern Illinois Stellar Properties University

Luminosity, from brightness and distance:

−4 6 10 L⊙ . L . 10 L⊙

Temperature, from color and spectral type:

3, 000K . T . 50, 000K

Mass, from binary systems:

0.08M⊙ . M . 150M⊙

Applet

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 83 / 102 Northeastern Illinois Q: Stellar Characteristics University

All stars are born with the same basic composition, yet stars can look quite diﬀerent from one another. Which two factors primarily determine the characteristics of a star? A) Its mass and its stage of life B) Its apparent brightness and its distance C) Its age and its location in the galaxy D) Its mass and its surface temperature E) Its apparent brightness and its luminosity

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 84 / 102 Northeastern Illinois Q: Stellar Characteristics University

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 84 / 102 Northeastern Illinois Metallicity University

Mass Fractions:

mH • X Hydrogen: X = M mHe • Y Helium: Y = M m“metals′′ • Z Metallicity: Z = M =1 − X − Y Sample mass fractions:

X⊙ =0.73, Y⊙ =0.25, Z⊙ =0.02

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 85 / 102 Northeastern Illinois Stellar Populations University

Population I: “Metal-rich.” Approximately circular orbits in the disk component of the galaxy. Have a greater abundance of elements heavier than helium compared to population II stars. Z ∼ 0.02

Population II: “Metal-poor.” Have random orbits in the spheroidal component of our galaxy. Age: 10-13 billion years old. M . 0.8M⊙. Z ∼ 0.0001 Population III: “Metal-free.” Extinct population of very massive stars that formed 106 − 107 years after the Big Bang. Z ∼ 0

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 86 / 102 Northeastern Illinois University

The Night Sky Luminosity & Brightness Distance & Parallax Stellar Temperatures

HR Diagrams Binary Systems Star Clusters Stellar Masses

Star Clusters Stellar Clusters Pleiades NGC 346 Cluster Mosaic M80 M13 HR Diagrams Clusters & HR Diagrams Clusters Clusters & HR Diagrams Star Cluster Evolution Q: Cluster Ages

Review c 2012-2018G. Anderson Universe: Past, Present & Future – slide 87 / 102 Northeastern Illinois Stellar Clusters University

• Open clusters: A group of up to several thousand stars, found in the disks of galaxies containing young stars. • Globular clusters: spherical collection of up to a million stars. Globular clusters are found primarily in galactic halos - they orbit galactic cores as a satellite, and contain very old stars.

b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Halob b b b b Globular Clusters b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Bulge b b disk b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b

b b b b b b b b b b b b b b b

b b

b b b b b b b b b b b b b b b b b c 2012-2018G. Anderson b Universe: Past, Present & Future – slide 88 / 102 b b Northeastern Illinois M45 The Pleiades (Seven Sisters) University

c Craig Lent. 35 min. exposure, Canon 10D, ISO 800, 101mm refractor @f/5.4 c 2012-2018G. Anderson Universe: Past, Present & Future – slide 89 / 102 Open Cluster NGC 346

Northeastern Illinois M80 (NGC 6093) Globular Cluster University

c 2012-2018G. Anderson Great Images in NASAUniverse: Past, Present & Future – slide 92 / 102 Globular Cluster: M13 (NGC 6205) Northeastern Illinois HR Diagrams University

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 94 / 102

Northeastern Illinois Q: Stellar Clusters University

The choices below each describe the appearance of an H-R diagram for a diﬀerent star cluster. Which cluster is most likely to be located in the halo of our galaxy?

A) The diagram shows main-sequence stars of every spectral type except O, along with a few giants and super-giants.

B) The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs.

C) The diagram shows main-sequence stars of all the spectral types except O and B, along with a few giants and super-giants.

D) The diagram shows no main-sequence stars at all, but it has numerous super-giants and white dwarfs.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 96 / 102 Northeastern Illinois Q: Stellar Clusters University

The choices below each describe the appearance of an H-R diagram for a diﬀerent star cluster. Which cluster is most likely to be located in the halo of our galaxy?

A) The diagram shows main-sequence stars of every spectral type except O, along with a few giants and super-giants.

B) The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs.

C) The diagram shows main-sequence stars of all the spectral types except O and B, along with a few giants and super-giants.

D) The diagram shows no main-sequence stars at all, but it has numerous super-giants and white dwarfs.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 96 / 102

Northeastern Illinois Star Cluster Evolution University

Animation: • Addison-Wesley • ESA

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 98 / 102 Northeastern Illinois Q: Cluster Ages University

The choices below each describe the appearance of an H-R diagram for a diﬀerent star cluster. Which cluster is the youngest?

A) The diagram shows main-sequence stars of every spectral type except O, along with a few giants and super-giants.

B) The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs.

C) The diagram shows main-sequence stars of all the spectral types except O and B, along with a few giants and super-giants.

D) The diagram shows no main-sequence stars at all, but it has numerous super-giants and white dwarfs.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 99 / 102 Northeastern Illinois Q: Cluster Ages University

The choices below each describe the appearance of an H-R diagram for a diﬀerent star cluster. Which cluster is the youngest?

A) The diagram shows main-sequence stars of every spectral type except O, along with a few giants and super-giants.

B) The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs.

C) The diagram shows main-sequence stars of all the spectral types except O and B, along with a few giants and super-giants.

D) The diagram shows no main-sequence stars at all, but it has numerous super-giants and white dwarfs.

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 99 / 102 Northeastern Illinois University

The Night Sky Luminosity & Brightness Distance & Parallax Stellar Temperatures

HR Diagrams Binary Systems Review Stellar Masses

Star Clusters

Review Review Review II

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 100 / 102 Northeastern Illinois Review University

• What are the units of luminosity? • What is the relationship between apparent brightness, luminosity and distance? • What is the magnitude of the faintest star visible to the naked eye? • How is a parsec deﬁned? How big is a parsec in light-years? • If you measure a parallax angle of 0.2 arc-seconds, how far away is a star in parsecs?

• Why are there no stars with M < 0.08M⊙?

• Why are there no stars with M ∼> 150M⊙? • What is a double star? a binary star? an optical double? • How common are binary stars?

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 101 / 102 Northeastern Illinois Review II University

• As you move along the main sequence from the lower right to the upper left on an HR diagram. How does the mass, surface temperature, luminosity and lifetime of a star change? • How do astronomers determine a star’s mass? • How is a star’s lifetime related to its mass? • Make a quick sketch of a Hertzsprung-Russel diagram. • How do stars on the main sequence obtain energy? • What is a stars spectral type? • Who were Pickering’s computers? • Our Sun is a type G2 V star. What do those letters mean? • How can you determine the age of a cluster from the main sequence turn oﬀ?

c 2012-2018G. Anderson Universe: Past, Present & Future – slide 102 / 102