Binary Stars Interactive (102.0K)
Why are binary stars – especially eclipsing binary stars – so useful to astronomers? One reason is their light curves are loaded with information about the masses and sizes of the stars. This Interactive lets you custom - build a binary star, and then observe its light curve. What will you see when the stars are similar in mass versus when they are very different in mass? How does the distance between them come into play? How do mass and luminosity correlate? Check it out with the Binary Stars Interactive.

1			Which of these statements about eclipsing binary systems is FALSE? Need a Hint?
			A)	Eclipses are most likely if the orbital inclination is 90 degrees.
			B)	If an eclipse is just partial, the minimum will have a "V" shape, as opposed to a flat bottom.
			C)	The primany eclipse always involves the hotter star passing in front of the cooler one.
			D)	The duration of the eclipses, combined with speed data from doppler shifts, can let us find their diameters.

When a binary star eclipses its companion, this fortunate alignment can yield a lot of information. The sizes, masses, orbital inclinations, speeds, and even shapes of the stars can be learned from the interpretation of the light curve. Let's explore practical uses of this technology.

2			In the interactive, we had several relationships well show by the mass sliders. Which of these was not shown? Need a Hint?
			A)	More massive stars are going to be larger.
			B)	More massive stars are going to be much more luminous.
			C)	More massive stars are more likely to have inclinations that produce eclipses.
			D)	More massive stars will eclipse more often.

This is a good interactive, but it is a little too simple. Notice that as you add mass, the size and luminosity increases are very predictable. What assumption is being made, and why is it not always valid.

3			Why would many pairs of eclipsing binary stars not follow the patterns illustrated in this interactive? Need a Hint?
			A)	It would be almost impossible to find a pair with exactly a 90 degree tilt.
			B)	More massive stars have higher gravity, so are smaller than lower mass stars.
			C)	in reality, mass increase causes the star's size to increase much more than its luminosity.
			D)	Many eclipsing binaries involve giants as well as main sequence stars, since larger giants are more likely to produce eclipses.

Now we are expanding our photometric studies to also include transits of large jovian planets in front of their stars, with again information about the size, density, and mass of the planets to be gained. Let's explore practical uses of this technology

4			For some of the hot jupiters, we have now observed transits where the cold, dark planet dimmed the star's light while it passed in front of the star. How much smaller than a star like the Sun in diameter would its jovian companion be if the loss of light were 1% during this transit? Need a Hint?
			A)	This planet is 1/100 th the Sun's diamter.
			B)	This planet is a tenth the Sun's diameter, comparable to Jupiter.
			C)	This planet is a fifth the Sun's diameter, or twice the size of Jupiter.
			D)	This planet is a third the size of the star.

When a binary star eclipses its companion, this fortunate alignment can yield a lot of information. The sizes, masses, orbital inclinations, speeds, and even shapes of the stars can be learned from the interpretation of the light curve. In the W Virginis eclipsing binaries, the light curve is never flat, but is sinuous and varying constantly.

5			Given that W Ursae majoris stars all have very short periods, why is the light curve so "curvy" instead of the straight intervals depicted in the interactive? Need a Hint?
			A)	They are so close that we are seeing gravitational lensing of the star's light.
			B)	Because the pairs are so close, they are distorted into ellipsoids, not spheres.
			C)	Because they are so close, they must collide.
			D)	Because they are so close, they must share a common envolope of gas.