3.3: Physical Properties Of Stars

Question 1

What’s the difference between optical double stars and binary stars

Answer 1

Optical double stars merely appear to be closely-aligned(one star may be further away than the other) whereas stars in a binary system are the same distance from us and orbit their common centre of mass

Question 2

How many times brighter is a star with a magnitude of 5 compared to a star with a magnitude of 1

Answer 2

100 times brighter

Question 3

How do you work out the brightness ratio

Answer 3

2.5^(the magnitude difference)

Question 4

What are the 4 thing the apparent magnitude of a star depends on

Answer 4

• total energy radiated by star- depends on stars size and temperature
• distance to star
• amount of interstellar gas
• amount of light absorbed by earth’s us atmosphere

Question 5

What is the distance modulus formula

Answer 5

M=m+5-(5 log d)

M= absolute magnitude
m=apparent magnitude
d= distance to star in pc

Question 6

What is the difference between apparent magnitude and absolute magnitude

Answer 6

Apparent magnitude is how bright a star is on a scale of 0-6 from the perspective of earth whereas absolute magnitude is the brightness of a star from a fixed distance of 10pc

Question 7

What is the inverse square law

Answer 7

1/d^2

Question 8

Off the distance of a star doubles how much dimmer will it be

Answer 8

4 times dimmer (2^2)

Question 9

What is 1kpc in pc

Answer 9

1kpc = 1000pc

Question 10

What is 1 Mpc in pc

Answer 10

1 Mpc = 1,000,000pc

Question 11

What are the 2 main classes of variable star

Answer 11

Binary stars-two stars orbiting their common centre of mass

Cepheid variables-giant yellow stars that regularly expand and contract in size

Question 12

What is primary star

Answer 12

The brighter star in a binary system

Question 13

What is an eclipsing binary

Answer 13

If the stars in orbit on a plane along our line of sight the 2 stars will eclipse one another eg. Algol

Question 14

In the light curve of aneclipsing binary system showing the primary and secondary dips in intensity

Answer 14

When the secondary star is in front of primary star it blocks much of the light from the brighter star and so a significant dip in intensity

Half a cycle later when primary star in front of secondary star light from secondary star if prevented from reaching us but this not as significant as before because still receiving all the light from brighter star results in smaller dip

Question 15

What is the time period of binary star

Answer 15

Roughly 14 days

Question 16

What was the eclipsing binary star Algol associated with

Answer 16

The wrinkling evil eye of Medusa whose slain head was held aloft by the hero Perseus in Greek mythology

Question 17

How if the light curve for a typical cepheid variable star shown

Answer 17

A sharp rise in intensity followed by a longer decay as the giant yellow star pulsates in size; period is 6.5 days

Question 18

Why is extremely difficult to determine distances of stars accurately

Answer 18

• stars so far away that time for return signal would be years
• any reflected signal would be so weak it would be undetectable
• stars don’t have hard reflecting surfaces

Question 19

What is parallax

Answer 19

The apparent motion of near and more distant objects with respect to one another

Question 20

What is the Heliocentric parallax used for

Answer 20

Uses the apparent shift in position of a ‘nearby’ star due to the Earth’s yearly motion around the sun to determine distances to the closest stars

Question 21

What is the parallax angle

Answer 21

Half of the angular shift in position

Question 22

What does 1 acrsec equal

Answer 22

1 arcsec = 1/3600 of a degree

Question 23

Describe the method of finding out the distance of a star using the heliocentric parallax

Answer 23

D = 1/p

D is distance
1(au) is distance of sun to earth
P is parallax angle