Classification of stars Flashcards
What is luminosity?
The total energy emitted as EM radiation per second. Also known as power output.
What is the intensity or brightness of a star?
Power received from a star per unit are on earth. (P/ 4πr^2)
What is apparent magnitude?
A subjective measure of a stars brightness when observed from earth.
What is the difference between levels in the apparent magnitude scale?
approx 2.51 or 10^1/5 as a star five levels below another star is 100x brighter.
What is absolute magnitude?
The apparent magnitude of a star if it were 10 parsecs from earth. SO, it is just dependant on power output/luminosity rather than distance.
Define black body
A body that absorbed all EM radiation of all wavelengths and can emit all wavelengths of EM radiation.
How do black body curves of objects change as they get hotter?
The peak increases in height an moves towards the shorter wavelengths.
What are the differences in radiation emitted by a hot black body and a cold one?
The hot one:
More radiation emitted
Shorter wavelength radiation
Higher power output per surface area
Why may a hotter star appear less bright than a colder one?
Less of the radiation emitted is visible.
How are line absorption spectra of stars produced?
Stars emit a continuous spectrum of EM radiation which can be collected. Absorption lines will occur where elements in the stars atmosphere have absorbed some of this radiation (photoelectric effect).
What are Balmer lines?
In stars of high enough temps, the electrons in hydrogen atoms exist in n=2. The lines on emission spectra that show movement between n=2 and other levels in hydrogen atoms are called Balmer lines.
Why are Balmer lines more prominent in absorption spectra from stars in a certain temp range?
Above a certain temperature the hydrogen will be in a constant state of n=3 or ionised completely, in stars with a lower temp, the h atoms won’t have enough energy to exist in this partially excited state.
What are the spectral classes of stars in order of temp?
O oh
B boy
A a
F fat
G giraffe
K kicked
M me
What are the colours of the spectral classes of stars in order
Blue (big)
Blue (bosses)
Blue (buy)
White (white)
Yellow (yachts)
Orange (on)
Red (rivers)
What temp range is O class?
25 000 -> 50 000 K
What temp range is B class?
11 000 -> 25 000 K
What temp range is A class?
7 500 -> 11 000 K
What temp range is F class?
6 000 -> 7 500 K
What temp range is G class?
5 000 -> 6 000 K
What temp range is K class?
3 500 -> 5 000 K
What temp range is M class?
< 3 500 K
What are the prominent absorption lines of O class stars?
He+, He, H
What are the prominent absorption lines of B class stars?
He, H
What are the prominent absorption lines of A class stars?
H, ionised metals
