LAB 09Astronomy 105 Laboratory

LAB QUIZ 09

Last week we used the “Main-sequence Fitting” technique to find the 1. distance to the Pleiades star

cluster.2. size of the Pleiades star

cluster.3. mass of the Pleiades star

cluster.4. age of the Pleiades stars

cluster.

All the stars within a given cluster are assumed to have the same ______.1. spectral class2. distance3. color4. luminosity class

If you were to leave the Earth and travel 4 AUs from the Sun, how would the sun’s brightness change? 1. 1/2 as bright2. 1/4 as bright3. 1/8 as bright4. 1/16 as bright5. 1/32 as bright

What two stellar properties are plotted on a color-magnitude diagram?1. absolute magnitude and spectral

class2. absolute magnitude and color3. apparent magnitude and color4. apparent magnitude and

distance

Color is a measure of a star’s _____.1. temperature2. size3. brightness4. luminosity

The “turn-off point” on the color-magnitude diagram of a star cluster can be used to find the cluster’s1. temperature2. distance3. age4. apparent magnitude

AGES AND DISTANCES TO CLUSTERS

Lab 09

Stellar Main-sequence Lifetime

Stellar Birth Massive stars form quickly Low mass stars form slowly

Main-sequence Stars Fuse hydrogen in their cores High mass stars

consume hydrogen at a furious rate

high luminosities short lifetimes

Low mass stars consume hydrogen at a low rate low luminosities long lifetimes

Giant Stars Core hydrogen exhausted

Main-Sequence Lifetimes

Stars in a Cluster Stars in a Cluster

Common Properties Distance Age Chemical composition

Different Properties Spectral Types (temperature) Luminosity Class (size)

Massive blue stars die first, followed by white, yellow, orange, and red stars

Star clusters help us test models of stellar evolution because they contain stars of same age but at different life stages

Pleiades - Open Cluster

Distance - 380 ly Age - 100 million years

age of cluster = lifetime of stars at main-sequence turnoff point

B6 stars -- 100 million yrs. MS lifetime

M3 - Globular Cluster

distance - 32,000 ly age - 10 billion years old

G stars -- 10 billion yrs. MS lifetime

standard main-sequence

age of cluster = lifetime of stars at main-sequence turnoff point

Interstellar Dust Reddens Light (makes stars appear

cooler) Dims Light (makes stars appear further

away)

Important: Do not write or mark on the

Cluster Handout

M45

D.M. = 5.7

M45 5.7

M45 5.7 130

D.M. = 5.7

Distance = 130 pc

Color Excess = + 0.05

M45 5.7 130 0.05 0.15 5.55 120 391

Color of Turn-off Point = - 0.01

M45 5.7 130 0.05 0.15 5.55 120 391 -0.01

M45 5.7 130 0.05 0.15 5.55 129 420 -0.01 1x108

Color of Turn-off Point = - 0.01

Age = 1 X 108 years

M45 5.7 130 0.05 0.15 5.55 120 391 -0.01 1x108

THE END