Chapter 15 Flashcards
Planet
Brown Dwarf
Star
Stars, planets, and brown dwarfs are all formed from the basic material (molecular clouds);
Stars: more massive than 0.08M(sun).
Brown Dwarfs: between 0.08M(sun) and 0.013M(sun).
Planets: Less than 0.013M(sun).
Radial Velocity / Doppler Shift Method
An unseen planet can be discovered by indirectly measuring the “wobble” of its host star. This wobble is b/c the planet-star system orbits its common center of mass, which is located somewhere inside the star. The wobble is detected due to the Doppler shift, which causes light from a source moving toward you to become bluer, while light from a source moving away is reddened. The mass of the star can be determined using this.
Transit Method
A planet can be detected by the slight dip in the light of the host star which happens periodically as the planet orbits. When and if the planet passes between the observer and the star, a small chunk of starlight will be blocked out, causing the overall light from the system to be dimmed.
The radius of the planet can be determined using this technique.
Hot Jupiter
Many detected exoplanets are “hot Jupiters” or planets the size of Jupiter which orbit close (within 1 AU) to their host star.
Direct Imaging
A direct way of detecting plants. The star and planet are both imaged, and the light from the star is blocked out using a coronograph. Angular resolution and brightness contrast are two issues with this method.
It is good at detecting large planets far from their host star.
Adaptive Optics
This method involves using deformable mirrors to “undo” the distortion of starlight due to variations in the Earth’s atmosphere. It helps us achieve a better angular resolution.
Gravitational Microlensing
The presence of an unseen planet can be inferred from the signal it causes when it “lenses” (magnifies) the light from a background star.
