Astrophysics - Stellar Classification Flashcards
(37 cards)
Define apparent magnitude
Perceived brightness of a star seen from Earth
How many times brighter is a magnitude 1 star compared to a magnitude 6 star
100 times brighter
For every star for example between 1 and 2, brightness decreases by 100^1/5
Define luminosity
Luminosity = total power radiated by all wavelengths [W]
Intensity = power per unit area [Wm^-2]
Difference between luminosity and brightness and why they’re useful
Luminosity = total power radiated but brightness is the power as measured on earth
Helpful for measuring how far it is away from Earth
How do you calculate Intensity using area and luminosity
For any given star luminosity is constant
Define AU
Mean distance from centre of earth to the centre of sun
Define light year and how do you calculate it
Distance travelled by light in one year
You can calculate distance by distance = speed x time
Where speed is the speed of light and time is 1 year in seconds
Define parsec and state everything you need to know about it
Define absolute magnitude
Apparent magnitude if it was observed 10 parsecs away from the Earth
For all spectral classes, state temperature range, absorption lines and intrinsic colour
For each spectral class, explain their respective prominence of the balmer lines
Draw the Hertzsprung-russel diagram
Draw and describe evolutionary path of a solar mass star
(from A to B) : protostar to main sequence
(from B to C) : Main sequence to red giant
(From C to D) : red giant to white dwarf
The black body temperature of each star is approximately 9200 K.
Explain why a Hydrogen Balmer line was chosen for the analysis of wavelength variation.
Temperature indicates spectral class is A
Hydrogen Balmer lines are strongest in A class stars and therefore would be more easily measured.
In m-M = 5logd/10 which is the absolute and apparent magnitude
m is apparent
M is absolute magnitude
Which of these three stars appears the brightest
Lowest value of apparent magnitude indicates brightest star
Vega has lowest apparent magnitude so is brightest
Which of these three stars is the largest
Deneb is largest
It has approximately same temperature but has a much greater absolute magnitude and therefore greater power output
P = OAT^4
To have a much greater power output for a similiar temperature, it must have a greater area
Draw a black-body radiation curve
You only need to draw one curve, do not need three temperatures and the colours
Draw hertzsprung Russell diagram but it’s absolutele magnitude against temperature
You must remember that absolute magnitude is 15 to -10 and temperature is 50,000 to 3,500
Matar has an absolute magnitude of -2.1. Sun has an absolute magnitude of 5. They have similiar temperatures, which is the largrer star
Matar since the more negative the absolute magnitude, the brighter the star. As increase in absolute magnitude means larger power output, Matar must be larger
Which of the two starts is closer to earth
B) why does spectrum of Betelgeuse not contain prominent hydrogen balmer lines
B) temperature too low to have hydrogen in n=2 state
A) State which star is likely to appear orange
B) appears brightest from Earth
A) shedir as it is spectral class K which is towards red end
B) shedir as it has smallest apparent magnitude value