Unit 3 Physical Properties of Stars Flashcards
What is an optical double star?
Two stars that are totally unrelated to one another yet appear to be closely aligned.
What is a binary star system?
Where two stars are the same distance from us and orbit the same common centre of mass.
True or false, the stars in a cluster are linked gravitationally.
True.
What is magnitude?
Brightness of a star.
What is apparent magnitude?
It is the brightness of the star as it appears to the observer.
What is absolute magnitude?
The brightness of a star when observed from a standard distance of 10 parsecs.
How is magnitude measured?
On a scale where each number corresponds to the magnitude being 2.5 times brighter/dimmer than the last.
What factors do apparent magnitude of stars depend upon?
Total energy radiated (depends upon size and temperature.
Distance of star.
Amount of interstellar gas and dust.
Amount of light absorbed by the Earth’s atmosphere.
What is the distance modulus formula?
It relates apparent and absolute magnitude. M=m + 5 - 5 log d When: M = Absolute Magnitude m = Apparent Magnitude d = Distance in parsecs
What is a variable star?
A star that’s magnitude can vary.
What are the two types of variable star?
Binary star.
Cepheid variables.
How does a binary star vary in magnitude?
As the two stars orbit each other if the stars eclipse each other the light intensity will drop.
How does a Cepheid variable star vary in magnitude?
The star pulsates as it expands and contracts having a dramatic effect on it’s luminosity.
Why can we not use the radar technique to measure distances to stars?
They are so far away it takes to long for the signal to return.
A reflected signal would be so weak we would not be able to distinguish it from the background.
Stars are spheres of gas and do not have hard reflecting surfaces.
What is parallax?
The apparent motion of a star against distant objects.
What is heliocentric parallax?
The technique used to determine distances to stars by measuring the movement (parallax) of a star over 6 months (when the Earth is farthest from where it was 6 months earlier in its orbit).
What is parallax angle?
Half the shift in position over the 6 month measuring period of the position of a star.
What is the formula that relates distance and parallax angle?
d = 1/p
When:
d = distance in parsec
p = seconds of arc (arcsec)
What is an arcsec?
One degree is 60 minutes of an arc and one minute is 60 seconds of an arc, so one arcsec is one three thousand six hundredth of a degree.
What is a parsec?
The distance at which a star would have the parallax angle of one arcsec.
How can period luminosity law be used to calculate distance?
Period luminosity law is the law that links pulsation period to mean absolute magnitude. With this absolute magnitude and an apparent magnitude we can calculate the star’s distance.
