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
