3.3 Physical Poperties Of Stars Flashcards
Explain the difference between Optical Double stars and True Binary Stars.
True Binary stars are linked together Gravitationally and orbit a common centre of mass.
e.g. Castor in Gemini.
e.g. Algol in Perseus.
Optical Double stars merely appear nearby but may be light years apart.
How many times brighter is a star with a magnitude of 5 compared with a star with a magnitude of 1
100 times
Dimmer
To work out brightness ratio do
2.5^(the apparent magnitude)
What is Pogson’s ratio?
difference in magnitudes is the 5th route of 100 which equals 2.51
Give 4 factors that affect the apparent magnitude of a star.
Energy radiated by star
○ Size
○ Temperature
Interstellar gas and dust.
Amount of light absorbed by Earth’s atmosphere.
Distance from Earth
What is the apparent magnitude of the brightest star in the sky?
-1.5 Sirius (α Cma)
What’s absolute magnitude
A measure of Apparent magnitude if observed from a distance of 10pc
Name two types of variable stars
Cepheid Variables
True Binaries
What is a True Binary?
Two Stars orbiting around their common centre of mass.
What’s a cepheid variable
A giant yellow star that regularly expands and contracts in size.
What’s an eclipsing binary
If two binary stars orbit each other in a plane along our line of sight, two stars will eclipse each other.
e.g. Algol (β Per)
What’s the primary star
The brighter one
In what way is the variability of light intensity of Cepheid Variables different to that of eclipsing binaries?
One is due to the star pulsating (Cepheid)
The other is due to stars eclipsing each other (eclipsing binaries)
Draw the light curve of a cepheid variable
It goes up and down like a triangle - check photo of a graph
What’s the equation of absolute magnitude
M = m + 5 - 5 log d
1kpc = 1000pc
1Mpc = 1 000 000pc
Draw a light curve of an eclipsing binary
Big dip when little star in front
Small dip when small star behind big one
Check photo
What is parallax
The apparent motion of near and more distant objects in respect to each other, caused by the motion of an observer.
Describe the method of heliocentric parallax to determine the distance to nearby
We measure the angular shift in position of a star from E1 to E2
Half of the angular shift is called the parallax angle (p)
Then we use the formula d=1/p
Distance (in parsecs) = 1/ Parallax angle
What is a parsec
The distance at which a star would have a parallax angle of one arc-second.
Describe how Cepheid Variables can be used to determine stellar distances.
Using the period – luminosity law we can work out the absolute magnitude of the star
Use the distance modulus formula to calculate distance.
