Astro - Star Classification Flashcards
Define apparent magnitude. What is the scale?
A measure of the brightness of the star as measured from Earth. Hipparcos scale, 1-6, brightest to dimmest.
What is the equation for I1 / I2 ?
= 2.51^m1-m2
What is an astronomical unit in words?
The average distance from the Sun to the Earth.
What is a lightyear in words?
The distance travelled by moving at the speed of light for one year.
What is a parsec in words?
The distance at which one AU subtends a parallax angle of one arcsecond.
What is one arcsecond?
1/3600 degrees.
Define absolute magnitude.
The apparent magnitude that an object would have if it were observed from a distance 10 parsecs away.
What is the equation for absolute magnitude?
m - M = 5log(d / 10)
m = apparent magnitude
M = absolute magnitude
d = distance in PARSECS
Between which numbers for magnitude of a star would be visible.
1-6.
On a spectral irradiance over wavelength graph what is the peak value of a curve?
Predominant wavelength, wavelength MAX.
What is Wein’s law?
λMAX T = 2.9x10^-3
What is Stephan’s law?
P = 𝜎AT^4
P = luminosity
What is the intensity law?
I = P / 4πd^2
d = distance from star to observer
What are Balmer absorption lines?
A set of visible lines in the spectrum corresponding from n>3 to n=2.
What are the spectral classes?
O - oh
B - bollocks
A - am
F - fucking
G - gonna
K - kill
M - myself
What are the colours of spectral class in order from O to M?
Blue
Blue
Blue/White
White
Yellow/White
Orange
Red
What are the temperatures of spectral class in order from O to M?
25000 - 30000
11000 - 25000
7500 - 11000
6000 - 7500
5000 - 6000
3500 - 5000
< 3500
What are the absorption lines of spectral class in order from O to M?
He+, He, H
He, H
H
ionised metals
ionised metals, neutral metals
neutral metals
neutral atoms
What are the axis of a H-R diagram? What do you need to remember?
Absolute magnitude over temperature. Temperature goes down from 50000 to 2500. M goes up from +15 to -10.
What are the blobs on a H-R diagram and where are they?
White dwarf - round blob, bottom left
Main sequence - long thin diagonal blob, top of y to right of x
- colour classed from hot to cold (O-M)
Blue super giants - round blob between white dwarfs and red super giants
Red super giants - round blob on top right
What are the 4 steps in star formation?
1) interstellar dust cloud collapses under gravity
2) GPE decreases, KE increases, temperature increases
3) When temperature reaches 10 million K H nuclei fuse into He
4) Radiation and gas pressure outward forces = gravity inwards forces
What will happen in the evolution of a star similar to our Sun?
Main sequence - red giant - white dwarf and planetary nebula
What will happen in the evolution of a massive star?
Main sequence - super red giant - supernova - black hole OR neutron star (dependant on mass)
What are the features of a neutron star?
Very dense, 4x10^17 kg/m^3
Small, around 10 km
What are the features of a black hole?
Extremely dense (like you)
Escape velocity > speed of light
How do you derive the equation for the Schwarzschild radius?
0.5 m ve^2 = G M m / rs
rs = 2 G M m / c^2
What are type 1a supernovae? What can they be used for?
Happens with stars about the same mass and same brightness curve, they can be sued as standard candles to determine the distance of objects.
Where are SUPERMASSIVE BLACK HOLES found?
In the centre of galaxies.
