Close Quiz 4? (weeks 11 &12) Flashcards
(26 cards)
How are stars classified?
Classified by their temperatures and luminosities into 7 spectral types O B A F G K M
Describe spectral type O stars.
Are the hottest of the stars
Blue in color
Burn out faster
HOT, HIGH MASS, SHORT LIVES & EXPLODE
Describe spectral type M stars.
Coolest of the stars
Red in color
Doesn’t burn fast
COOL, LOW MASS, LIVE LONG LIVES (600- billion to a trillion
What type of star is the Sun?
G star
Why is it that more massive stars are hotter & live shorter lives, while low mass stars are cooler & have very long lifetimes.
The more massive the star the greater the inward force of gravity (the increases pressure from the stars nuclear reacts by pushing outward]
Nuclear fusión is unbalanced
Too much energy
Which types of stars are most likely to have life around them?
K stars (maybe)
What is a brown dwarf?
“Failed” stars - not massive enough to sustain fusion but too massive to be called a plant (not bound to a star;free floating)
Starts warm but cools over time (as they age they get hard to find)
Size: 13-17 times jupiters mass
How does the position of a habitable zones change with the type of the star?
HZs are far from hot stars (much further out) & closer around cool stars
What are some of the problems for planets orbiting close to M type stars?
- They have tiny HZs
- To orbit M stars, earth like planets would have to be very close to a star to get enough heat
- young M stars have intense solar flares that can strip away planetary atmospheres and bombard surfaces
Not the best place to find planets with life
What spectral type star may be the best suited to have planets with life? Why?
K star (maybe) - more common and longer lived than G but without the flaring of M stars (sweet spot)
What are the two kinds of situations where planetary orbits can be stable in binary star systems? What is a circumbinary planet?
- Stars orbit close together & planet(s) orbit far away (circumbinary planet)
- planet(s) orbit the stars common center of mass
- if planet is too close to the stars it’s orbit unstable and ejects from system
- feels like it’s circling 1 star
- Stars orbit far apart & planet (s)
What are the habitable zones like in the two main types of binary systems where planets can be found?
CLOSE BINARY: HZs position is based on the total energy of both stars
WIDE BINARY: an HZ around each star
Describe the direct photography method for finding exoplanets.
Very difficult: photographing a small faint thing next to one brighter that is far away
ONLY 1% OF EXOPLANETS FOUND THIS WAY
to have great chance of success, astronauts use tool known as CORONAGRAPH
What is a coronagraph?
A disk used to block the light of a star so as to be able to see faint objects nearby
Describe the Doppler (aka radial velocity) method for finding exoplanets.
As a planet & star orbit their baycenter (center of mass between 2 bodies), the star moves alternately towards (blueshift) and away (redshift) from us revolving the planet orbital period
ABOUT 19% EXOPLANETS FOUND THIS WAY
Best suited for finding big planets that are close to their stars
Least likely to discover earth like planets around sunlike stars
What is a barycenter?
Center of mass between the two bodies
Describe the transit method for finding exoplanets.
Too far to see as disks so instead the brightness of a star is measured
Planet passes in front of its start dimming its light (eclipse)
MOST SUCCESSFUL ABOUT 77% OF EXOPLANETS FOUND THIS WAY
What are the limitations for this method?
If the orbit is tipped no ras it can be seen
Face on (angle from above): no planet orbit
What is actually “seen” during a planetary transit?
What properties of a planet can be measured from a transit?
A planet passes in front of its star dimming (eclipse)
Transit can tell us the orbitals period, orbital distance, and size of exoplanet
In some cases mass —> mass+size=density
How can a transit be used to investigate a planetary atmosphere?
A transiting exoplanet with an atmosphere will show something similar as it filters the light of its star
CHECK EXOPLANET ATMOSPHERE NOTES
What is microlensing? How can a planet be found through microlensing?
Takes advantage of general relativity (massive objects bending) to magnify images of distant stars
ABOUT 2.5% OF EXOPLANETS FOUND THIS WAY
-detect planets of great distances
-best suited 4 planets that are moderately far from their star
-best way of finding rouges free floating planets
What method for finding exoplanets is best suited for finding Earth-like planets?
Transit method
What is the most common type of planet that has been found?
Bigger than earth but smaller than Neptune
About 5% not found in our solar system
What is a hot Jupiter?
Hot Jupiters are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods. The close proximity to their stars and high surface-atmosphere temperatures resulted in their informal name “hot Jupiters
