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.
