Chap 21 and 22 Flashcards
Give several reasons the Orion molecular cloud is such a useful “laboratory” for studying the stages of star formation.
Its nearby and fairly bright, it also has lots of stars forming at different stages
Why is star formation more likely to occur in cold molecular clouds than in regions where the temperature of the interstellar medium is several hundred thousand degrees?
Cold molecular clouds have colder environments and lower pressure, this can allow stars to gravitationally collapse more easily.
Why have we learned a lot about star formation since the invention of detectors sensitive to infrared radiation?
Visible light can’t go through the dust cloud particles that covers the star during formation, whereas infrared can.
Describe how the T Tauri star stage in the life of a low-mass star can lead to the formation of a Herbig-Haro (H-H) object.
When particles are ejected they collide with surrounding gases and dust, this excited the material and makes it glow/ heat up.
Two protostars, one 10 times the mass of the Sun and one half the mass of the Sun are born at the same time in a molecular cloud. Which one will be first to reach the main sequence stage, where it is stable and getting energy from fusion?
The larger star, 10 times the mass of the Sun will reach main seq phase faster, as larger protostars have more gravitational forces that causes higher core temperatures.
Which types of planets are most easily detected by Doppler measurements? By transits?
Doppler measurements: Larger planets that are close to the star
Transits: Also larger planets that are close because their eclipses are more grander.
Observations suggest that it takes more than 3 million years for the dust to begin clearing out of the inner regions of the disks surrounding protostars. Suppose this is the minimum time required to form a planet. Would you expect to find a planet around a 10(solar)MSun star?
No, because due to the star’s big size, the star would gravitationally attract more dust and form pretty fast, creating a lower amount of time for a planet to form.
Suppose you wanted to observe a planet around another star with direct imaging. Would you try to observe in visible light or in the infrared? Why? Would the planet be easier to see if it were at 1 AU or 5 AU from its star?
Infrared would be better as a planet is not bright (even less bright then brown dwarf) and 5 AU would be best b/c at 1 AU the star’s brightness is too strong.
An exoplanetary system has two known planets. Planet X orbits in 290 days and Planet Y orbits in 145 days. Which planet is closest to its host star? If the star has the same mass as the Sun, what is the semi-major axis of the orbits for Planets X and Y?
Use Kepler’s law, convert days into years, and compare distances to find the closer one.
a^3=p^2
Calculate the transit depth for an M dwarf star that is 0.3 times the radius of the Sun with a gas giant planet the size of Jupiter.
Divide area of Jupiter by area of dwarf star.
Astronomers find that 90% of the stars observed in the sky are on the main sequence of an H–R diagram; why does this make sense? Why are there far fewer stars in the giant and supergiant region?
Main seq is 90% of stars life vs giant and super giant are 10% of its life.
Describe the evolution of a star with a mass similar to that of the Sun, from just after it first becomes a red giant to the time it exhausts the last type of fuel its core is capable of fusing.
After a star becomes a Red Giant it:
1. Helium flashes begin to fuse helium in the stars core, causing it to shrink some
2. Helium and hydrogen fusion is then done in the shell outside the star’s core, making it a red giant again
Why are star clusters so useful for astronomers who want to study the evolution of stars?
In clusters there are a bunch of stars that formed at the same time and that are close together.
Would the Sun more likely have been a member of a globular cluster or open cluster in the past?
Open cluster
Suppose you were handed two H–R diagrams for two different clusters: diagram A has a majority of its stars plotted on the upper left part of the main sequence with the rest of the stars off the main sequence; and diagram B has a majority of its stars plotted on the lower right part of the main sequence with the rest of the stars off the main sequence. Which diagram would be for the older cluster? Why?
