Astro A2 - Stars

Question 1

What is apparent magnitude scale

Answer 1

The brightness of a star as seen from earth

Question 2

What is luminosity

Answer 2

Total power radiated by a star

Question 3

What is intensity

Answer 3

Power per unit area at the observerq

Question 4

What is the apparent magnitude value for the faintest stars we can see

Answer 4

6

Question 5

How much brighter is a fourth magnitude star compared to a fifth magnitude star

Answer 5

2.51 times

Question 6

What is our Sun’s apparent magnitude

Answer 6

-26

Question 7

What is the astronomical unit

Answer 7

The mean distance from the Sun to the Earth

Question 8

How to define a parsec

Answer 8

The distance from which 1AU subtends an angle of 1 arc second

Question 9

What is the absolute magnitude

Answer 9

The apparent magnitude a star would have at a distance of 10 pc from an observer

Question 10

What is a black body

Answer 10

A body that absorbs all the em radiation that falls on it

Question 11

What does the graph of light intensity look for 3 stars of different temps

Answer 11

Hotter stars have a peak at a shorter wavelength. Hotter stars have a higher intensity of each wavelength of light than colder stars

Question 12

What is the assumption for the use of the inverse-square law

Answer 12

No light is absorbed or scattered between the source and the observer. Source is treated as a point

Question 13

What are the spectral classes in descending temperature

Answer 13

OBAFGKM

Question 14

Describe an O-class star

Answer 14

Blue, 25000-50000K, absorption at He+, He, H

Question 15

Describe a B-class star

Answer 15

Blue, 11000-25000K, absorption at He, H

Question 16

Describe an A-class star

Answer 16

Blue-white, 7500-11000K, absorption at H, ionised metals

Question 17

Describe an F-class star

Answer 17

White, 6000-7500K, absorption at ionised metals

Question 18

Describe a G-class star

Answer 18

Yellow-white, 5000-6000K, absorption at ionised and neutral metals

Question 19

Describe a K-class star

Answer 19

Orange, 3500-5000K, absorption at neutral metals

Question 20

Describe an M-class star

Answer 20

Red, <3500K, absorption at neutral atoms, TiO

Question 21

What are Balmer lines

Answer 21

Spectrum produced when transitions from the energy level n=2 are made

Question 22

Where are balmer lines strongest

Answer 22

A-class star as there is a high abundance of hydrogen in n=2 state

Question 23

Where are balmer lines weak

Answer 23

O (too hot so hydrogen would be ionised), F,G,K,M (too cool to be excited)

Question 24

What are the axis on the Hertzsprung-Russell diagram

Answer 24

Spectral class on x (or temperature from 2500-50000k) and absolute magnitude on y (-10 to 15)

Question 25

Describe the evolution of the Sun

Answer 25

The Sun is currently a G-class star, a main sequence star. As hydrogen is used up, it will fuse hydrogen in the outer layers and expand, to become a giant. It will collapse, increase temp and will initiate helium fusion. Helium shell fusion will then occur and the Sun will expand again. The outer material will then be pushed away to form a planetary nebula leaving a white dwarf. After fusion is complete, it becomes a black dwarf

Question 26

What are supernovae

Answer 26

Objects which exhibit a rapid and enormous increase in absolute magnitude

Question 27

What are type 1a supernovae

Answer 27

They reach the same peak value of absolute magnitude

Question 28

What are standard candles

Answer 28

Absolute magnitude is known

Question 29

What causes a type 1a supernova

Answer 29

A white dwarf star attracts mass from its binary system and fuses again of carbon. When it reaches a critical mass, the white dwarf star explodes

Question 30

What is a neutron star

Answer 30

A core with a mass twice the mass of the Sun

Question 31

Describe the motion of neutron stars

Answer 31

Due to conservation of angular momentum as | the core collapses, they tend to be spinning very rapidly

Question 32

What are pulsars

Answer 32

Radio sources produced by strong magnetic fields and spinning of a neutron star

Question 33

What are black holes

Answer 33

More massive cores (more than about 3 solar masses) can continue to collapse and form black holes

Question 34

What is a key feature of a black hole

Answer 34

Its escape velocity is greater than the speed of light

Question 35

What is the event horizon

Answer 35

The boundary at which the escape velocity is equal to the speed of light

Question 36

What is the Schwarzschild radius

Answer 36

Radius of the event horizon

Question 37

How is a quasar produced

Answer 37

From supermassive black holes at the centre of young active galaxies

Question 38

How can type 1a supernovae be used to measure distance

Answer 38

Type 1a supernovae has the same peak absolute magnitude (-19.3), so apparent magnitude can be measured

Question 39

What is a significant feature of quasars

Answer 39

Bright radio sources; brightest objects in the universe