Transcript 24exoplanets5s

Extra-Solar Planets
Astronomy 311
Professor Lee Carkner
Lecture 24
How is energy transported from the
core of the sun to the Earth?
a)
b)
c)
d)
By radiation
By convection
By convection then radiation
By radiation, then convection, then
radiation again
e) By conduction
What causes the 11 year sunspot
cycle?
a) The 11 year convection cycle
b) The 11 year orbit of Jupiter
c) The 11 year winding of the magnetic
field
d) The 11 year proton-proton cycle
e) The 11 year coronal mass ejection
cycle
End of Semester
Observing project due Friday
Should be neat, legible and organized
Answer questions on a separate sheet of
paper
Final exam Monday, 3 pm
Finding Exoplanets
How do you find a planet around another star?
Planets are much too faint to be seen with a
telescope

As the planet orbits the star, the star also orbits
the planet

The motion of the star is quite small, but can be
detected as a slight shift in the spectral lines of
the star
Finding Exoplanets
The Doppler Effect
When you observe a moving object, the
wavelengths of light you observe change

Moving towards -- wavelength decreases -- blue
shift
Example:
The faster the motion the larger the change
By measuring the shift of lines in a spectrum,
you can determine how fast the object is moving
Doppler Effect
Searching For Exoplanets

Measurements are made over a long period
of time and plotted

As the star moves around in its orbit the velocity
should go from positive to zero to negative and
back to positive again

We find exoplanets by noticing changes in
the spectral lines that indicate a planet
tugging on the star
Inducing Stellar Motion
Vplanet
Center
of Mass
Star
Planet
Vstar
Orbits of a Star+Planet System
Light Curve of 51 Peg
Planetary Properties

Use Kepler’s 3rd Law (P2=a3)

Larger planets produce a larger velocity

Large velocities and short periods are
easier to measure
Star --
What is a Planet?
Mass > 0.08 MSun (84 MJupiter)
Brown Dwarf -Mass > 10 MJupiter
Planet -Mass < 10 MJupiter
Planets and brown dwarfs can be hard
to tell apart
Known Exoplanets
About 250 exoplanets are known

Masses range from
Orbits range from
Searches are biased towards large planets
in tight orbits
Sample
Exoplanets
Data
Exoplanet Orbits

Most systems have only one known planet
but we are starting to find more

Long term observations are needed to see the
longer periods

Are the mostly circular orbits of our solar system
atypical?
Velocity Plots for Upsilon And
System
Orbits in Upsilon And System
A Multiple Exoplanet System
Orbit Evolution
How do you get a large planet in a close
orbit?

Not enough material to form a large core

The magnetic field of the star may produce a
“hole” in the inner disk, stopping the motion
before the planet hits the star
Exoplanets and Habitability
Are any of the new planets habitable?
No,

They are almost all gas giants with no surface
However,

Example: 47 UMa, Rorbit=2.1 AU

The velocities they produce are too small to
measured via Doppler shift
Transits

For orbits seen edge on, the planet passes in
front of the star once per orbit

We can measure and time this slight dimming with
CCD cameras
By measuring the degree and length of the
dimming the size and orbit of the planet can be
found
Transit Light Curve
Space Interferometry
One idea to find low mass planets is with an
interferometer

A two telescope, Space Interferometry
mission (SIM) may be launched in 2015 (?)

Would be able to detect the movement of a
star in the sky as it is being pulled by its
planets (astrometry)

Very large interferometers could take spectra
of planets to look for signs of life
Planetary Spectra
Next Time
Read Chapter 28
Summary
Recently many planets around other stars
have been found
The planets are detected by measuring the
motions they induce in the central star
The period and velocity of the motions
allows the determination of the mass and
orbit of the planet
New missions in the next 20 years will allow
for the detection of many new planets,
including Earth-like, habitable ones
Summary: Exoplanet
Properties
Most known exoplanets are large
(~MJupiter) and in close orbits
They may form further out and then move
in
A few are near the habitable zone
We are starting to find additional
planets in the systems