Transcript Extrasolar Planets

Extrasolar Planets
Instructor: Calvin K. Prothro; P.G., CPG
(John Rusho)
Section 003: F343, T Th 11:00 p.m. to 12:15 p.m.
Section 004: F381, T Th 12:30 p.m. to 1:45 p.m
OCC - Onondaga Community College
How Do We Find These Things?
Current Progress
• To date (January 2006)
176 planets in more
than 153 systems have
been discovered using
a variety of methods
• Fun Facts
– Largest semimajor
axis: 5.9 AU
– Lowest mass planet:
0.02 MJ
– Largest Number of
Planets: 4
• At around five
times the mass
of Earth, the
newest planet,
designated
OGLE–2005BLG-390Lb,
is the lowestmass planet
ever detected
outside the
solar system.
•
How Do We Find These Things?
• To date there have been 5 methods
successfully used to detect extrasolar
planets:
• Pulsar Timing
• Transit Photometry
• Gravitational Microlensing
• Direct Detection
• Doppler Spectroscopy
Pulsar timing
• The first method used to discover extra-solar planets.
• This method observes the anomalies in the regularity of
pulses from a pulsar. This led to the 'discovery' of the
first planet with the orbital period of one year.
• It also led to the discovery of the PSR B1620-26c a
planet orbiting a primary (a pulsar) and secondary
(White Dwarf) in a circumbinary orbit . This planet is the
only known planet to orbit two stars.
• The Transmit method
detects a planet's
shadow when it
transits in front of its
host star.
• This method only
works for the small
percentage of planets
whose orbits happen
to be perfectly in line
with the astronomers'
vantage point.
• This method can be
used on very distant
stars.
Transit method
Gravitational Microlensing
• The gravitational microlensing effect occurs when
the gravitational field of a planet and its parent star
act to magnify the light of a distant background star.
• For the effect to work the planet and star must pass
almost directly between the observer and the distant
star.
• Since such events are rare, a very large number of
distant stars must be continuously monitored in order
to detect planets at a reasonable rate.
• This method is most fruitful for planets between
earth and the center of the galaxy, as the galactic
center provides a large number of background stars.
Gravitational Microlensing
This graphic illustrates the principle of gravitational microlensing. The
observatory on Earth sees the source (more distant) star appear to
brighten dramatically when the lens (closer) star passes between them.
The planet orbiting the lens star causes a variation in that brightening.
This is an infrared image of the
star GQ Lupi (A). It is 400
light years from our Solar
System and is approximately
70% of our Sun's mass.
Direct
Detection
It is orbited by a planet (b) at a
distance of approximately 20
times the distance between
Jupiter and our Sun.
It is unclear what the mass of
the planet is, but it is estimated
to be between 1 and 42 times
the mass of Jupiter.
European Southern Observatory
Direct Detection
• The best way to gain information on the
composition of the greatest number of stars is
through direct detection.
• This is made quite difficult because of the 109
and 1010 contrast ratio in the reflected light of
Jupiterlike and Earthlike planets respectively.
• For young extrasolar planets we could look to
the planet’s thermal emission whose contrast
ratio is much more favorable, perhaps by as
many as four orders of magnitude at 5-10
microns.
Direct observation
• In March 2005 it was announced that
scientists using the Spitzer Space Telescope
were able to detect infrared radiation
emitted from two extrasolar planets.
Extra Solar Planet Detection by
the Doppler Detection method
• Dr. Jaquin’s Powerpoint on Extrasolar
Planets is located on his website in Unit 2
Supplemental Material # 6.
• GOOD LUCK!
Doppler
Wobble
• As the star moves toward the Earth, the light waves coming from it
are compressed and shifted toward the blue (shorter-wavelength)
end of the spectrum.
• As the star moves away from us, the light waves are stretched out
toward the red (longer-wavelength) end of the spectrum.
Summary of Steps in the Doppler
Detection method
1.
2.
3.
4.
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Many separate measurements of a star’s velocity are made over a
long period of time.
If the star “wobbles” then it has an unseen companion causing the
wobble. It may be a planet or a low-mass star.
The period P of the wobble equals the orbital period of the
unseen companion.
Using Kepler’s 3’rd law the semi-major axis r of the unseen
companion’s orbit can be calculated from the period of its orbit.
Using the equation for the orbital velocity, the unseen
companion’s orbital velocity v PL can be calculated from its
orbital semi-major axis.
Using the conservation of momentum principle, the mass of the
unseen companion MPL can be estimated from the planet’s orbital
velocity, the mass of the star and the star’s observed maximum
velocity, K
The estimated mass is only a lower limit for the mass because the
orbital inclination i is unknown and cannot be determined from
the Earth. The planet’s mass may be larger.
EXAMPLE: 47 Ursae Majoris
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Type of Star: Yellow Dwarf
Spectral Class:
G1V
Distance:
46 Lightyears
Luminosity: 1,82 L
Mass:
1,03 Solar Masses
Surface Temperature:
5800 K
47 Ursae Majoris
NOTE: The planet orbiting 47 Ursae Majoris is close enough to
its sun for liquid water to exist on any of its moons.
51 Pegasi
Jupiter doppler effect intensity
• 55 Cancri is one
of the most
interesting
planetary systems
discovered so far.
It holds the record
for number of
planets, most
distant Jovian
planet and least
massive planet
The Coolest So Far
The End…
or maybe just the beginning ?