Classification of Stars

Question 1

What is apparent magnitude?

Answer 1

The relative brightness of a star when it is viewed on earth

Question 2

What is Absolute magnitude

Answer 2

The relative brightness of a star, if it were placed at a distance of 10 parsecs from the observer

Question 3

What equation Links Apparent (m) and Absolute (M) magnitude?

Answer 3

m-M = 5log(d/10). where d is measured in parsecs from earth

Question 4

What is the hipparcos scale

Answer 4

Early index for classifying the apparent magnitude of stars

Brightness stars at magnitude 1

Faintest stars at magnitude 6

Each increase in magnitude is a 2x increase in brightness

Question 5

Define Parsec

Answer 5

The distance to an object that subtends a parallax angle of one arc second, to the line that runs from the centre of the earth to the centre of the sun

Question 6

Define Light Year (ly)

Answer 6

Distance that light travels in a vacuum in 1 year

Question 7

State Stefans law

Answer 7

The power output of a star is directly proportional to its surface area and to the absolute temperature to the power of 4

P= (stefans constant)(Surface area (m^2))(temperature)^4

Question 8

What are the units to Stefan’s Constant

Answer 8

W m^-2 K^-4

Question 9

State Wein’s Displacement Law

Answer 9

The wavelength of a stars emission at peak intensity is inversely proportional to its absolute temperature

(Landa Max)*T = 2.898 x 10^-3 meters kelvin

Question 10

What is a Black Body?

Answer 10

A Black body absorbs em radiation of all wavelengths and can emit em radiation of all wavelengths

Doesn’t reflect any incident radiation, solely absorbs it

Question 11

Draw 3 black body radiation curves for 3 stars of decreasing absolute temperature

Answer 11

use of weins law —> Use wavelength when intensity is maximum

Question 12

For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines

O

Answer 12

Blue

25000-50000 kelvin

He+, He, H

Question 13

For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines

B

Answer 13

Blue

11000-25000 kelvin

He, H

Question 14

For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines

A

Answer 14

Blue-White

7500-11000 Kelvin

Strongest H , Ionised metals

Question 15

For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines

F

Answer 15

White

6000-7500

Ionised Metals

Question 16

For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines

G

Answer 16

Yellow-White

5000-6000

Ionised and neutral metals

Question 17

For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines

K

Answer 17

Orange

3500-5000

Neutral metals

Question 18

For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines

M

Answer 18

Red

Less then 3500

Neutral atoms , TiO

Question 19

State and Explain how are Stellar Spectral classes O&B relate to Balmer Lines

Answer 19

O- Weak prominence of balmer lines
B- Slightly Stronger prominence of balmer lines

Stars atmosphere is too hot, hydrogen is likely to be ionised

Question 20

State and Explain how are Stellar Spectral class A relates to Balmer Lines

Answer 20

Strongest prominence of balmer lines

High abundance of hydrogen with its electrons in the n=2 state

Question 21

State and Explain how are Stellar Spectral class F relates to Balmer Lines

Answer 21

Weak Prominence of balmer lines

Too Cool ,electrons within hydrogen are unlikely to be excited to the n = 2 state

Question 22

State and Explain how are Stellar Spectral classes G,K & M relate to Balmer Lines

Answer 22

Very weak to nonexistent prominence of balmer lines

Too little atomic hydrogen, far too cool for its electrons to be edited in the n=2 state

Question 23

Describe how a type 1a supernovae forms & explain one of its uses

Answer 23

White dwarf core, accumulates too much matter from a nearby star and explodes above a critical mass

All explosions have the same peak value of absolute magnitude (-19.3)

Can be used as standard candles, to measure distances to nearby galaxies

Question 24

Describe how a Type II Supernovae forms

Answer 24

A Single star, collapses rapidly under its own gravity. Causing outer layers of matter to be ejected.

Question 25

Draw the light curve for a typical 1A supernovae

Answer 25

Question 26

What is a black hole?

Answer 26

A Collapsed star core originally greater then 3 solar masses, that has an escape velocity greater then the speed of light.

Question 27

What is an event Horizon

Answer 27

A spherical surface surrounding a black hole for which any point on that surface has an escape velocity greater then the speed of light

Question 28

How do you calculate the distance the event horizon lies from a black holes centre

Answer 28

Schwartzchild Radius
r= 2GM/C^2

(equating kinetic energy to change in m* gravitational potential)

Question 29

What are all of the limits for each entities in the HertzSprung Russell Diagram

Answer 29

Entity (Spectral Class Range, Absolute magnitude)

Giants (A—>M, -5—>-10)

Dwarfs (O—>A, 15—> 10)

Sun (G, 4.6)

Main sequence = (O——-> , 15—> -10)

Question 30

Draw a Hertzprung Russell Diagram

Answer 30

Question 31

What is the Balmer Series

Answer 31

Dark Lines that correspond to the absorption of photons by an electron within the n=2 state of hydrogen atoms

Stars with temp below 7500k don’t produce any balmer series lines , no electrons in n=2 state

above 11000k , hydrogen atoms start to become ionised and number within n=2 state decrease

Question 32

In Pogsons Contribution to the Hipparchus Scale, 1 order of apparent magnitude contributes to what increases intensity

Answer 32

(100)^1/5

Question 33

Describe the differences between the black body for a hot and cold star

Answer 33

p = (Steffans Constant) * Surface Area * Temperature ^4

Hot stars radiate more power, hence a higher peak luminosity

Emmits more radiation at lower wavelengths, as photons have more energy

Question 34

Explain the concept of Dark Energy

Answer 34