Exam 17: Analyzing Starlight

Starting in 2009, astronomers have been discovering really cool objects out there (cool here meaning low-temperature, as well as really interesting), which they have called Y dwarfs. What distinguishes these brown dwarfs from others that astronomers have discovered?

Why are astronomers much more interested in the luminosity of a star than its apparent brightness?

A graduate student has done a careful analysis of the spectrum of a star. While she has found lines from many elements, there was not a trace of the element helium in the spectra she has been analyzing. From this she can now conclude:

An astronomer whose secret hobby is riding merry-go-rounds has dedicated his career to finding the stars that rotate the most rapidly. But the stars are all very far away, so none of them can be seen to spin even when he looks through the largest telescopes. How then can he identify the stars that rotate rapidly?

A team of astronomers takes spectra of thousands of different stars in different parts of the sky. The spectra show significant differences. The main reason the spectra of the stars do not all look alike is that the stars

Studies of the spectra of stars have revealed that the element that makes up the majority of the stars (75% by mass) is

In recent decades, astronomers discovered stars even cooler than the traditional spectral type M stars recently. Astronomers gave these cool stars a new spectral type, L. If you wanted to go out and find more such type L stars, what kind of instrument would it be smart to use?

The first astronomer who did photometry in a systematic way (even though he did not have a telescope) was

One similarity in the spectra of T dwarf stars and giant planets in our solar system is that their spectra show:

The astronomer who, at the turn of the century, measured the spectra of hundreds of thousands of stars, leaving a catalog that astronomers used for the rest of the century, was:

Two stars have the exact same luminosity, but star Y is four times dimmer looking that star X. This means that

Astronomers call the motion of a star across the sky (perpendicular to our line of sight) its

When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about:

When an astronomer measures a color index for a star, what is she measuring?

Which of the following looks the brightest in the sky?

One key difference that astronomers use to distinguish between brown dwarfs and high-mass planets is that:

Using a good pair of binoculars, you observe a section of the sky where there are stars of many different apparent brightnesses. You find one star that appears especially dim. This star looks dim because it is:

Imagine that a brilliant but quirky scientist in the biology department manages to put you in a deep freeze and you wake up in a million years. Which of the following statements about the sky you would see in that future time is correct?

After a lot of work, a group of graduate students has finally measured the wavelengths of many dozens of lines in the spectrum of a distant star. If a number of the lines come from molecules such as titanium oxide, the star is likely to be which spectral type:

Which color star is likely to be the hottest?