Classification of Stars Flashcards
What is apparent magnitude?
The relative brightness of a star when it is viewed on earth
What is Absolute magnitude
The relative brightness of a star, if it were placed at a distance of 10 parsecs from the observer
What equation Links Apparent (m) and Absolute (M) magnitude?
m-M = 5log(d/10). where d is measured in parsecs from earth
What is the hipparcos scale
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
Define Parsec
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
Define Light Year (ly)
Distance that light travels in a vacuum in 1 year
State Stefans law
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
What are the units to Stefan’s Constant
W m^-2 K^-4
State Wein’s Displacement Law
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
What is a Black Body?
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
Draw 3 black body radiation curves for 3 stars of decreasing absolute temperature
use of weins law —> Use wavelength when intensity is maximum
For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines
O
Blue
25000-50000 kelvin
He+, He, H
For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines
B
Blue
11000-25000 kelvin
He, H
For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines
A
Blue-White
7500-11000 Kelvin
Strongest H , Ionised metals
For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines
F
White
6000-7500
Ionised Metals
For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines
G
Yellow-White
5000-6000
Ionised and neutral metals
For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines
K
Orange
3500-5000
Neutral metals
For Stellar Spectral class below:
Name It’s intrinsic colour, Temperature Range and Prominent absorption lines
M
Red
Less then 3500
Neutral atoms , TiO
State and Explain how are Stellar Spectral classes O&B relate to Balmer Lines
O- Weak prominence of balmer lines
B- Slightly Stronger prominence of balmer lines
Stars atmosphere is too hot, hydrogen is likely to be ionised
State and Explain how are Stellar Spectral class A relates to Balmer Lines
Strongest prominence of balmer lines
High abundance of hydrogen with its electrons in the n=2 state
State and Explain how are Stellar Spectral class F relates to Balmer Lines
Weak Prominence of balmer lines
Too Cool ,electrons within hydrogen are unlikely to be excited to the n = 2 state
State and Explain how are Stellar Spectral classes G,K & M relate to Balmer Lines
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
Describe how a type 1a supernovae forms & explain one of its uses
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
Describe how a Type II Supernovae forms
A Single star, collapses rapidly under its own gravity. Causing outer layers of matter to be ejected.
Draw the light curve for a typical 1A supernovae
What is a black hole?
A Collapsed star core originally greater then 3 solar masses, that has an escape velocity greater then the speed of light.
What is an event Horizon
A spherical surface surrounding a black hole for which any point on that surface has an escape velocity greater then the speed of light
How do you calculate the distance the event horizon lies from a black holes centre
Schwartzchild Radius
r= 2GM/C^2
(equating kinetic energy to change in m* gravitational potential)
What are all of the limits for each entities in the HertzSprung Russell Diagram
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)
Draw a Hertzprung Russell Diagram
What is the Balmer Series
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
In Pogsons Contribution to the Hipparchus Scale, 1 order of apparent magnitude contributes to what increases intensity
(100)^1/5
Describe the differences between the black body for a hot and cold star
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
Explain the concept of Dark Energy
