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Lecture 22

Astronomy 1021 Lecture Notes - Lecture 22: Orbital Period, Geocentric Model, 2M1207


Department
Astronomy
Course Code
ASTR 1021
Professor
Robert Cockcroft
Lecture
22

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Astronomy December 1, 2016
Revolutions in Astronomy
o 5th century
- Earth is no longer flat
o 16th century
- Geocentrism is no longer true
o Mid 18th century
- Sun is no longer the centre of the Galaxy
o Early 20th century
- Galaxy is no longer the centre of the universe
o Mid-1990s
- Solar System is not the only solar system
Naming Convention
o Planets outside of our Solar System are called
extrasolar planets, or exoplanets
o If a star is aed Alie the the eoplaet is aed Alie 
o For planetary systems with multiple planets, the following planets are
aed i alphaetial order: Alie , Alie d, et.
o Alphabet is in order of discovery and not in order of position
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o Direct imaging = taking a photo
o Relative brightness of star makes
it impossible in most cases to
see dim planet:
- In visible light, stars are
billions of times brighter
than a planet
- Star-planet separation
requires small angular
resolution
The Problem An Analogy
o If observer is close to a car headlight, can see reflected light off nearby
insects and can resolve them
o Far from the car, can only see glare of the headlight
Headlight = Star; Insect = Planet
o In our own Solar System, we are close;
we can see planets
o Other solar systems are too far
Detection Methods
o Many ways to find exoplanets
o Oes for this ourse are the folloig…
1. Direct image
2. Indirect
a) Gravitation tugs
i. Astrometry
ii. Radial Velocity (Main Method #1)
b) Transit photometry (Main Method #2)
Direct Imaging (Difficult)
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Possible Solutions
Direct imaging can work if
o Planet is far away from its parent star
o Star is close to us
o “tarlight a e asked
o Planet is relatively bright compared to its
parent star
- In IR, star is only thousand-million
times brighter
- Young planets are usually hotter, so
brighter in IR
o A combination of the above
First DI? 2M1207 and 2M1207 b
o First directly imaged planet (?)
o Brown dwarf = faint type of star
o Planet is warm (1600 K; gravitational
contraction) so it is bright in IR
o Spectrum of planet indicates presence of
water
o Further from star than Pluto from Sun
o Orbital period = 1700 years
First DI? Beta Pictoris b
o Pic is a young star with debris disk still in
place around it
o Super-Jupiter: 7 MJup
o 9 AU
o Low eccentricity
o 20-year period
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