HW - Ch 17, 18

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:

Annie Cannon

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

M

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?

a sensitive infra-red telescope

A star moving toward the Sun will show:

a shift in the spectral lines toward the blue end (as compared to the laboratory positions of these lines)

A star that is quite hot and has a very small radius compared to most stars is called

a white dwarf

Which of the following can astronomers Not learn from studying the spectrum of a star?

all of these can be learned from studying the spectrum

One of your good friends who is on a diet asks you to point out the stars with the smallest mass on an H-R diagram that you are studying. Where are you sure to find the stars with the lowest mass on any H-R diagram?

among the stars at the bottom right of the main sequence

Two stars that are physically associated (move together through space) are called

binary stars

Stars that do not have what it takes to succeed as a star (i.e. do not have enough mass to fuse hydrogen into helium at their centers) are called:

brown dwarfs

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

brown dwarfs are much lower in mass than planets like Jupiter

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

have different temperatures

If hydrogen is the most common element in the universe, why do we not see the lines of hydrogen in the spectra of the hottest stars?

in the hottest stars, hydrogen atoms are ionized, and so there are no electrons to produce lines in the spectrum

Which of the following characteristics of a single star (one that moves through space alone) is it difficult to measure directly?

its mass

An exhausted-looking astronomer comes off the mountain where her observatory is located and tells you she has been doing photometry all night. What has she been up to?

measuring the brightness of different stars

Most of the stars we can see with the unaided eye from Earth are

more luminous (intrinsically brighter) than the Sun

Which of the following is a method for measuring the diameter of a star?

more than one of these

A team of astronomers discovers one of the most massive stars ever found. If this star is just settling down in that stage of its life where it will be peacefully converting hydrogen to helium in its core, where will we find it on the H-R diagram?

near the very top of the main sequence, in the upper left

Why can astronomers not measure the diameters of stars directly?

stars are so far away, we cannot resolve (distinguish) their diameters

An H-R Diagram plots the luminosity of stars against their: diameter

surface temperature

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

the difference between how bright a star looks at two different wavelength region