ch 21
An astronomy class is so excited by the discovery of planets around other stars that they decide to do a library exhibit on the subject so that everyone in the school can learn about it. In this exhibit they want to pay tribute to both the astronomers of today who have done the work AND some of the scientists of the past whose work was essential to making the discoveries possible (and directly related to the techniques involved). Which of the following scientists of the past should definitely be included in the exhibit?
Christian Doppler
The Orion Nebula is
a large cloud of gas and dust illuminated by the light of newly formed stars within it
A graduate student is given the assignment to find stars with dusty disks around them. What kind of telescope would it be best for her to use for this purpose?
a large telescope that detects infrared radiation
If an astronomer wants to find and identify as many stars as possible in a star cluster that has recently formed near the surface of a giant molecular cloud (such as the Trapezium cluster in the Orion Nebula), what instrument would be best for her to use?
an infra-red telescope (and camera)
A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?
to the left
The first ordinary star (other than our own Sun) around which planets were definitely discovered was:
51 Pegasi
When astronomers carefully examine the planets found by Kepler and draw conclusions from the Kepler sample, what do they conclude about planets the size of Earth?
Earth-sized planets are common, but so are planets somewhat bigger than Earth
Our solar system has 8 planets orbiting the Sun. Based on the discoveries of exoplanets so far, what can we say about a star with 8 planets?
Even though planets were only discovered starting in 1995, so we can't yet find planets that take centuries to go around their star, we already know other stars with 8 planets and we are likely to find more
The star now called Kepler-444 is 11 billion years old (much older than the Sun) and has five planets orbiting close to it. What has this system taught astronomers about the history of star formation?
If such an old star has planets close to it, where it's really warm, those planets must be made of heavier elements. So heavier elements must have formed before the time this star formed
Which of the following is a reason that astronomers have not found giant planets with the orbit of Neptune around other stars?
Neptune takes 165 years to go around the Sun; getting information about just one cycle of such a planet's orbit around another star would take astronomers 165 years
Why was the Kepler mission not able to find planets smaller than Mars, even though it was in space (and had no Earth atmosphere to deal with)?
Such planets make dips in the light of the star that are too small for Kepler to detect
The first (living) star other than our own Sun found to have more than one planet orbiting it is called
Upsilon Andromedae
8. Astronomers call a ball of matter that is contracting to become a star
a protostar
Which of these stars will take the SHORTEST time to go from the earliest protostar stage to the main sequence?
a star ten times the mass of our Sun
7. Why is it so difficult for astronomers to see new stars in the process of birth?
all of the above
Planets in the habitable zone of their stars:
are at a temperature where water can exist as a liquid
The telescope that allowed astronomers to discover most of the planets found with the transit method was called
b. the Kepler mission
1. If you want to find stars that are just being born, where are the best places to search?
in giant molecular clouds
How did astronomers determine that the planet orbiting the star HD 209458 is a gas giant like Jupiter and not made mostly of rocks or metals?
it took more than one of the above measurements to figure out this problem
The closest star to the Sun, Proxima Centauri, was recently found to have a planet in its habitable zone. Proxima Centauri is a main sequence star with spectral type M. How would its habitable zone differ from the habitable zone of our Sun?
it would be significantly closer to Proxima Centauri than ours is to the Sun
When a star settles down to a stable existence as a main-sequence star, what characteristics determines where on the main sequence in an H-R diagram the star will fall?
its mass
Astronomers believe that disks of material will form around protostars that are spinning. Which of the following observed phenomena is a good indication of the presence of a disk around a protostar?
jets and Herbig-Haro objects
In figuring out the evolutionary tracks on the H-R diagram, astronomers
make model stars on a computer and then follow how their characteristics will change with time
What technique did astronomers use to make the first confirmed discovery of a planet around another star like the Sun?
measure the Doppler shift of the lines in the star's spectrum and look for periodic changes in this shift due to the pull of the planet as it orbits the star
Astronomers were surprised to find so many Jupiter-mass planets so close to their stars. According to their best theories and models, such "hot Jupiters"
must have formed further out from the star and must have "migrated inward" early on
The big surprise about the first planet discovered around another regular star was that it
orbited so close to its star it took only 4 days to go around
Which of the following is NOT one of the reasons planets around other stars are so difficult to detect?
planets only form very late in the life of a star, just when it is ready to die, and thus last only a very short fraction of the star's life
With our current techniques, astronomers can typically only measure the minimum mass of a planet orbiting another star. To know the precise mass of the planet, they must also be able to determine
the angle at which the planet's orbit is tilted relative to us
You are an astronomy graduate student and you are observing the big Orion Nebula from an airplane that has a good-sized infrared telescope built into it (there really is such a plane.) On an infrared image of the Nebula, what would particularly stand out?
the clouds of the nebula that have a lot of dust in them
2. Which of the following are the small regions that are the embryos of stars (where individual stars are most likely to be born)?
the cores within the clumps of molecular clouds
What observations about disks of dusty material around young stars suggest that planets may be forming in such disks?
the disks show lanes that are empty of dust within them
To measure how dense a planet is (to know whether it is made of rock or gas and liquid) they must be able to measure the planet's mass from the Doppler shift and
the planet's radius using the transit method
Astronomers studying regions like the Orion Giant Molecular Cloud have observed that a wave of star formation can move through them over many millions of years. What sustains such a wave of star formation in a giant molecular cloud?
when massive stars form, their ultraviolet radiation and later their final explosions compress the gas in the cloud and cause a new group of stars to form
Astronomers identify the "birth" of a real star (as opposed to the activities of a protostar) with what activity in the star?
when nuclear fusion reactions begin inside its core
9. A Herbig-Haro (HH) object is
where a jet from a star in the process of being born collides with (and lights up) a nearby cloud of interstellar matter
