3.3: Physical Properties Of Stars Flashcards
What’s the difference between optical double stars and binary stars
Optical double stars merely appear to be closely-aligned(one star may be further away than the other) whereas stars in a binary system are the same distance from us and orbit their common centre of mass
How many times brighter is a star with a magnitude of 5 compared to a star with a magnitude of 1
100 times brighter
How do you work out the brightness ratio
2.5^(the magnitude difference)
What are the 4 thing the apparent magnitude of a star depends on
- total energy radiated by star- depends on stars size and temperature
- distance to star
- amount of interstellar gas
- amount of light absorbed by earth’s us atmosphere
What is the distance modulus formula
M=m+5-(5 log d)
M= absolute magnitude
m=apparent magnitude
d= distance to star in pc
What is the difference between apparent magnitude and absolute magnitude
Apparent magnitude is how bright a star is on a scale of 0-6 from the perspective of earth whereas absolute magnitude is the brightness of a star from a fixed distance of 10pc
What is the inverse square law
1/d^2
Off the distance of a star doubles how much dimmer will it be
4 times dimmer (2^2)
What is 1kpc in pc
1kpc = 1000pc
What is 1 Mpc in pc
1 Mpc = 1,000,000pc
What are the 2 main classes of variable star
Binary stars-two stars orbiting their common centre of mass
Cepheid variables-giant yellow stars that regularly expand and contract in size
What is primary star
The brighter star in a binary system
What is an eclipsing binary
If the stars in orbit on a plane along our line of sight the 2 stars will eclipse one another eg. Algol
In the light curve of aneclipsing binary system showing the primary and secondary dips in intensity
When the secondary star is in front of primary star it blocks much of the light from the brighter star and so a significant dip in intensity
Half a cycle later when primary star in front of secondary star light from secondary star if prevented from reaching us but this not as significant as before because still receiving all the light from brighter star results in smaller dip
What is the time period of binary star
Roughly 14 days
What was the eclipsing binary star Algol associated with
The wrinkling evil eye of Medusa whose slain head was held aloft by the hero Perseus in Greek mythology
How if the light curve for a typical cepheid variable star shown
A sharp rise in intensity followed by a longer decay as the giant yellow star pulsates in size; period is 6.5 days
Why is extremely difficult to determine distances of stars accurately
- stars so far away that time for return signal would be years
- any reflected signal would be so weak it would be undetectable
- stars don’t have hard reflecting surfaces
What is parallax
The apparent motion of near and more distant objects with respect to one another
What is the Heliocentric parallax used for
Uses the apparent shift in position of a ‘nearby’ star due to the Earth’s yearly motion around the sun to determine distances to the closest stars
What is the parallax angle
Half of the angular shift in position
What does 1 acrsec equal
1 arcsec = 1/3600 of a degree
Describe the method of finding out the distance of a star using the heliocentric parallax
D = 1/p
D is distance
1(au) is distance of sun to earth
P is parallax angle
