Dr Martin Hendry, Dept of Physics and Astronomy University of Glasgow, UK
The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of...
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Transcript of The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of...
![Page 1: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/1.jpg)
The Search The Search for Extra-for Extra-Solar PlanetsSolar Planets
P1Y*Frontiers of PhysicsFeb 2007
http://www.astro.gla.ac.uk/users/martin/teaching/
Dr Martin HendryDept of Physics and Astronomy
![Page 2: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/2.jpg)
Extra-Solar Planets
One of the most active and exciting areas of astrophysics
Well over 200 exoplanets discovered since 1995
![Page 3: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/3.jpg)
Extra-Solar Planets
One of the most active and exciting areas of astrophysics
Well over 200 exoplanets discovered since 1995
Some important questionso How common are planets?How common are planets?
o How did planets form?How did planets form?
o Can we find Earth-like planets?Can we find Earth-like planets?
o Do they harbour life?Do they harbour life?
![Page 4: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/4.jpg)
Extra-Solar Planets
One of the most active and exciting areas of astrophysics
Well over 200 exoplanets discovered since 1995
What we are going to cover
How can we detect extra-solar planets?
What can we learn about them?
![Page 5: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/5.jpg)
1. How can we detect extra-solar planets?
Planets don’t shine by themselves; they just reflect light from their parent star
Exoplanets are very faint
![Page 6: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/6.jpg)
1. How can we detect extra-solar planets?
Planets don’t shine by themselves; they just reflect light from their parent star
Exoplanets are very faint
We measure the intrinsic brightness of a planet or star by its luminosity
Luminosity, L (watts)
![Page 7: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/7.jpg)
Luminosity varies with wavelength (see later)
e.g. consider Rigel and Betelgeuse in Orion
Rigel
Betelgeuse
![Page 8: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/8.jpg)
Luminosity varies with wavelength (see later)
e.g. consider Rigel and Betelgeuse in Orion
Adding up (integrating) L at all wavelengths
Rigel
Betelgeuse
Bolometric luminosity
W104 26bol L
e.g. for the Sun
![Page 9: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/9.jpg)
Stars radiate isotropically (equally in all directions) at distance r, luminosity spread
over surface area
24 r
(this gives rise to the Inverse-Square Law )
![Page 10: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/10.jpg)
Planet, of radius R, at distance r from star
Intercepts a fraction of
2
2
2
24
r
R
r
Rf
SL
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Planet, of radius R, at distance r from star
Intercepts a fraction of
Assume planet reflects all of this light
2
2
2
24
r
R
r
Rf
SL
2
S
P
2
r
R
L
L
![Page 12: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/12.jpg)
Examples
Sun – Earth:
m104.6 6R
m105.1 11r 10
S
P 106.4 L
L
![Page 13: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/13.jpg)
Examples
Sun – Earth:
Sun – Jupiter:
m104.6 6R
m105.1 11r 10
S
P 106.4 L
L
m102.7 7R
m108.7 11r 9
S
P 101.2 L
L
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2nd problem:
Angular separation of star and exoplanet is tiny
Distance units
Astronomical Unit = mean Earth-Sun distance
m101.496A.U.1 11
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2nd problem:
Angular separation of star and exoplanet is tiny
Distance units
Astronomical Unit = mean Earth-Sun distance
For interstellar distances: Light year
m101.496A.U.1 11
m10461.9yearlight 1 15
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Star Planet
Earth
e.g. ‘Jupiter’ at 30 l.y. r
d
m108.2l.y.30 17d
m105.7A.U.5 11r
d
rtan
radians107.2 6
deg105.1 4
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e.g. ‘Jupiter’ at 30 l.y.
m108.2l.y.30 17d
m105.7A.U.5 11r
d
rtan
radians107.2 6
deg105.1 4
![Page 18: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/18.jpg)
Exoplanets are ‘drowned out’ by their parent star. Impossible to image directly with current telescopes (~10m mirrors)
Keck telescopeson Mauna Kea,Hawaii
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Exoplanets are ‘drowned out’ by their parent star. Impossible to image directly with current telescopes (~10m mirrors)
Need OWL telescope:
100m mirror,planned for nextdecade?
‘Jupiter’ at 30 l.y.
100m
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1. How can we detect extra-solar planets?
They cause their parent star to ‘wobble’, as they orbit their common centre of gravity
![Page 21: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/21.jpg)
1. How can we detect extra-solar planets?
They cause their parent star to ‘wobble’, as they orbit their common centre of gravity
Johannes Kepler Isaac Newton
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Kepler’s Laws of Planetary MotionKepler’s Laws of Planetary Motion
1) Planets orbit the Sun in an ellipse with the Sun at one focus
![Page 23: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/23.jpg)
Kepler’s Laws of Planetary MotionKepler’s Laws of Planetary Motion
1) Planets orbit the Sun in an ellipse with the Sun at one focus
2) During a planet’s orbit around the Sun, equal areas are swept out in equal times
![Page 24: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/24.jpg)
Kepler’s Laws of Planetary MotionKepler’s Laws of Planetary Motion
1) Planets orbit the Sun in an ellipse with the Sun at one focus
2) During a planet’s orbit around the Sun, equal areas are swept out in equal times
![Page 25: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/25.jpg)
Kepler’s Laws of Planetary MotionKepler’s Laws of Planetary Motion
Kepler’s Laws, published 1609, 1619
1) Planets orbit the Sun in an ellipse with the Sun at one focus
2) During a planet’s orbit around the Sun, equal areas are swept out in equal times
3) The square of a planet’s orbital period is proportional to the cube of its mean distance from the Sun
![Page 26: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/26.jpg)
Newton’s law of Universal Gravitation,Published in the Principia: 1684 - 1686
Newton’s gravitational force provided a physical explanation for Kepler’s laws
221
G r
mmGF
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Star + planet in circular orbit about centre of mass, to line of sight
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Star + planet in circular orbit about centre of mass, to line of sight
![Page 29: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/29.jpg)
Star + planet in circular orbit about centre of mass, to line of sight
Can see star ‘wobble’, even when planet is unseen.
But how large is the wobble?…
![Page 30: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/30.jpg)
Star + planet in circular orbit about centre of mass, to line of sight
Can see star ‘wobble’, even when planet is unseen.
But how large is the wobble?…
Centre of mass condition
2211 rmrm
P
SSPS m
mrrrr 1
![Page 31: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/31.jpg)
Star + planet in circular orbit about centre of mass, to line of sight
Can see star ‘wobble’, even when planet is unseen.
But how large is the wobble?…
Centre of mass condition
2211 rmrm
P
SSPS m
mrrrr 1
e.g. ‘Jupiter’ at 30 l.y.
radiansd
rSS
kg109.1
kg100.227
30
P
S
m
m
deg105.1 7
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The Sun’s “wobble”, mainly due to Jupiter, seen from 30 light years away = width of a 5p piece in Baghdad!
Detectable routinely with SIM Planet Quest
(launch date 2010?) but not currently
See www.planetquest.jpl.nasa.gov/SIM/
![Page 33: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/33.jpg)
Suppose line of sight is in orbital plane
Direction to Earth
![Page 34: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/34.jpg)
Direction to Earth
Suppose line of sight is in orbital plane
Star has a periodic motion towards and away from Earth – radial velocity varies sinusoidally
![Page 35: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/35.jpg)
Suppose line of sight is in orbital plane
Star has a periodic motion towards and away from Earth – radial velocity varies sinusoidally
Detectable via the Doppler Effect
Can detect motion from shifts in spectral lines
![Page 36: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/36.jpg)
Spectral lines arise when electrons change energy level inside atoms.
This occurs when atoms absorb or emit light energy.
Since electron energies are quantised , spectral lines occur at precisely defined wavelengths
hc
hE Planck’s constant
![Page 37: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/37.jpg)
Absorption
e -
e -
Electron absorbs photon of the precise energy required to jump to higher level.
Light of this energy (wavelength) is missing from the continuous spectrum from a cool gas
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Emission
e - e -
Electron jumps down to lower energy level, and emits photon of energy equal to the difference between the energy levels.
Light of this energy (wavelength) appears in the spectrum from a hot gas
![Page 39: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/39.jpg)
Hydrogen Spectral Line Series
n = 1
n = 2
n = 4
(ground state)
n = 3
Lyman
Balmer
Paschen
Brackett
Ene
rgy
diff
eren
ce (
eV)
5
10
15
m = 2,3,4,… n = 1
n = 2m = 3,4,5,…
m = 4,5,6,… n = 3
m = 5,6,7,… n = 4Ionised above 13.6 eV
Shown here are downward transitions, from higher to lower energy levels, which produce emission lines. The corresponding upward transition of the same difference in energy would produce an absorption line with the same wavelength.
![Page 40: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/40.jpg)
Star
Laboratory
![Page 41: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/41.jpg)
How large is the Doppler motion? Equating gravitational and circular accleration
For the planet:-
For the star:-
22
r
mmGrmF SP
PPC
22
r
mmGrmF SP
SSC
T
2
Angular velocity
Period of ‘wobble’
![Page 42: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/42.jpg)
How large is the Doppler motion? Equating gravitational and circular accleration
For the planet:-
For the star:-
22
r
mmGrmF SP
PPC
22
r
mmGrmF SP
SSC
T
2
Angular velocity
Period of ‘wobble’
![Page 43: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/43.jpg)
How large is the Doppler motion? Equating gravitational and circular accleration
For the planet:-
For the star:-
Adding:-
22
r
mmGrmF SP
PPC
2
2
r
mmGrr PS
SP
22
r
mmGrmF SP
SSC
T
2
Angular velocity
Period of ‘wobble’
![Page 44: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/44.jpg)
SPS GmmmGT
rr
2
3232 4
![Page 45: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/45.jpg)
SPS GmmmGT
rr
2
3232 4
Kepler’sThird Law
The square of a planet’s orbital period is proportionalto the cube of its mean distance from the Sun
![Page 46: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/46.jpg)
SPS GmmmGT
rr
2
3232 4
Kepler’sThird Law
The square of a planet’s orbital period is proportionalto the cube of its mean distance from the Sun
e.g. Earth:
Jupiter:
A.U.1r year1T
A.U.2.5r 2
3
2
3
J
J
E
E
T
r
T
r years86.112.5 3 JT
![Page 47: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/47.jpg)
Amplitude of star’s radial velocity:-
SS rvP
SPS
m
rmmr
)( From centre of
mass condition
![Page 48: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/48.jpg)
Amplitude of star’s radial velocity:-
SS rvP
SPS
m
rmmr
)( From centre of
mass condition
3
332 )(
P
SPSPS
m
rmmmmG
![Page 49: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/49.jpg)
Amplitude of star’s radial velocity:-
SS rvP
SPS
m
rmmr
)( From centre of
mass condition
3
332 )(
P
SPSPS
m
rmmmmG
2
v
2
v)( 32323 TmTmm
mG SSSPSP
![Page 50: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/50.jpg)
Amplitude of star’s radial velocity:-
SS rvP
SPS
m
rmmr
)( From centre of
mass condition
3
332 )(
P
SPSPS
m
rmmmmG
2
v
2
v)( 32323 TmTmm
mG SSSPSP
PSS mmT
G 3/23/1
2v
![Page 51: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/51.jpg)
PSS mmT
G 3/23/1
2v
Examples
Jupiter:
-2-1311 skgm10673.6 G
kg100.2 30Sun m
kg109.1 27Jup m years86.11T
-1ms4.12v S
![Page 52: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/52.jpg)
PSS mmT
G 3/23/1
2v
Examples
Jupiter:
Earth:
-2-1311 skgm10673.6 G
kg100.2 30Sun m
kg109.1 27Jup m years86.11T
-1ms4.12v S
kg100.6 24Earth m year1T
-1ms09.0v S
Are these Doppler shifts measurable?…
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Stellar spectra are observed using prisms or diffraction gratings, which disperse starlight into its constituent colours
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c
v
0
Stellar spectra are observed using prisms or diffraction gratings, which disperse starlight into its constituent colours
Doppler formula
Wavelength of light as measured in the laboratory
Change in wavelength
Radial velocity
Speed of light
![Page 55: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/55.jpg)
Limits of current technology:
-1sm1v
c
v
0
Stellar spectra are observed using prisms or diffraction gratings, which disperse starlight into its constituent colours
Doppler formula
Wavelength of light as measured in the laboratory
Change in wavelength
Radial velocity
Speed of light
millionth3000
![Page 56: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/56.jpg)
The Search The Search for Extra-for Extra-Solar PlanetsSolar Planets
P1Y*Frontiers of PhysicsFeb 2007
http://www.astro.gla.ac.uk/users/martin/teaching/
Dr Martin HendryDept of Physics and Astronomy
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51 Peg – the first new planetDiscovered in 1995
Doppler amplitude
-1sm55v
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51 Peg – the first new planetDiscovered in 1995
Doppler amplitude
How do we deduce planet’s data from this curve?
-1sm55v
PSS mmT
G 3/23/1
2v
We can observethese directly
We can infer this from spectrum
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Stars of different colours have different surface temperatures
We can determine a star’s temperature from
its spectrum
Stars are good approximations to black
body radiatorsWien’s Law
The hotter the temperature, the shorter the wavelength at which the black body curve peaks
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25000 10000 8000 6000 5000 4000 3000
Surface temperature (K)
O5 B0 A0 F0 G0 K0 M0 M8
Lum
inos
ity
(Sun
=1)
Spectral Type
1
102
104
106
10-2
10-4
-10
-5
0
+5
+10
+15
Abs
olut
e M
agni
tude
0.001 RS
0.01 RS
0.1 RS
1 RS
10 RS
Main Sequence
White dwarfs
Supergiants
1000 RS
100 RS
Giants
When we plot the temperature and luminosity of stars on a diagram most are found on theMain Sequence
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25000 10000 8000 6000 5000 4000 3000
Surface temperature (K)
O5 B0 A0 F0 G0 K0 M0 M8
Lum
inos
ity
(Sun
=1)
Spectral Type
1
102
104
106
10-2
10-4
-10
-5
0
+5
+10
+15
Abs
olut
e M
agni
tude
. . . . .
. . . .
..
...
. ....
.... .. .. .
.....
..............
.........
... ....... ....
........
. .. .
...........
.. ..
..
............ .
..
....Regulus
Vega
Sirius A
Altair Sun
Sirius B
Procyon B
Barnard’sStar
Procyon A
..
.. ... Aldebaran
Mira
Pollux
Arcturus
RigelDeneb
Antares
Betelgeuse
Stars on theMain Sequence turn hydrogen into helium.
Stars like the Sun can do this for about ten billion years
When we plot the temperature and luminosity of stars on a diagram most are found on theMain Sequence
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Main sequence stars obey an approximate mass– luminosity relation
We can, in turn, estimate the mass of a star from our estimate of its luminosity
Llo
gL
Sun
10
0 0.5 1.0-1
0
1
2
3
4
5
mlog mSun
10
L ~ m3.5
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Summary: Doppler ‘Wobble’ method
Stellar spectru
m
Velocity of stellar
‘wobble’
Stellartemperature
Luminosity
Orbital period+
Orbital radius
Planet mass
From Kepler’s Third Law
Stellar mass +
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Complications
Elliptical orbits
Complicates maths a bit, butotherwise straightforward
radius semi-major axis
Orbital plane inclined to line of sight
We measure only
If is unknown, then we obtain a lower limit to
( as )
Multiple planet systems
Again, complicated, but exciting opportunity (e.g. Upsilon Andromedae)
Stellar pulsations
Can confuse signal from planetary ‘wobble’
obssinv iS
i
obssinvv iSS Pm
1sin i
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Transit of Mercury: May 7th 2003
In recent years a growing number of exoplanets have been detected via transits = temporary drop in brightness of parent star as the planet crosses the star’s disk along our line of sight.
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Change in brightness from a planetary transit
Brightness
Time
Star
Planet
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Ignoring light from planet, and assuming star is uniformly bright:
Total brightness during transit
e.g. Sun:
Jupiter:
Earth:
Total brightness outside transit
2
2**
22** 1
S
PP
R
R
RB
RRB
m102.7 7Jup R
m100.7 8Sun R
Brightness change of ~1%
m104.6 6Earth R Brightness change of ~0.008%
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Ignoring light from planet, and assuming star is uniformly bright:
Total brightness during transit
e.g. Sun:
Jupiter:
Earth:
Total brightness outside transit
2
2**
22** 1
S
PP
R
R
RB
RRB
m102.7 7Jup R
m100.7 8Sun R
Brightness change of ~1%
m104.6 6Earth R Brightness change of ~0.008%
If we know the period of the planet’s orbit, we can use the width of brightness dip to relate , via Kepler’s laws, to the mass of the star.
So, if we observe both a transit and a Doppler wobble for the same planet, we can constrain the mass and radius of both the planet and its parent star.
PR
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Another method for finding planets is gravitational lensing
The physics behind this method is based on Einstein’s General Theory of Relativity, which predicts that gravity bends light, because gravity causes spacetime to be curved.
This was one of the first experiments to test GR: Arthur Eddington’s 1919 observations of a total solar eclipse.
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Another method for finding planets is gravitational lensing
The physics behind this method is based on Einstein’s General Theory of Relativity, which predicts that gravity bends light, because gravity causes spacetime to be curved.
This was one of the first experiments to test GR: Arthur Eddington’s 1919 observations of a total solar eclipse.
“He was one of the finest people I have ever known…but he didn’t really understand physics because, during the eclipse of 1919 he stayed up all night to see if it would confirm the bending of light by the gravitational field. If he had really understood general relativity he would have gone to bed the way I did”
Einstein, on Max Planck
GR passed GR passed the test!the test!
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Another method for finding planets is gravitational lensing
If some massive object passes between us and a background light source,
it can bend and focus the light from the source, producing multiple,
distorted images.
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Another method for finding planets is gravitational lensing
If some massive object passes between us and a background light source,
it can bend and focus the light from the source, producing multiple,
distorted images.
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Another method for finding planets is gravitational lensing
If some massive object passes between us and a background light source,
it can bend and focus the light from the source, producing multiple,
distorted images.
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Another method for finding planets is gravitational lensing
If some massive object passes between us and a background light source,
it can bend and focus the light from the source, producing multiple,
distorted images.
Multiple images of the same background quasar, lensed by a foreground spiral galaxy
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Even if the multiple images are too close together to be resolved
separately, they will still make the background source appear (temporarily)
brighter.
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Background stars
Gravitational lens
Lens’ gravity focuses the light of the background star on the Earth
So the background star briefly appears brighter
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Even if the multiple images are too close together to be resolved
separately, they will still make the background source appear (temporarily)
brighter.
We call this case gravitational microlensing. We can plot a light curve
showing how the brightness of the background source changes with time.
Time
The shape of the curve tells about the mass and position of the object which does the lensing
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Even if the multiple images are too close together to be resolved
separately, they will still make the background source appear (temporarily)
brighter.
We call this case gravitational microlensing. We can plot a light curve
showing how the brightness of the background source changes with time.
If the lensing star
has a planet which also
passes exactly between
us and the background
source, then the light
curve will show a second
peak.
Even low mass planets can
produce a high peak (but for
a short time, and we only
observe it once…)
Could in principle detect Earth mass planets!
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What have we learned about exoplanets?Highly active, and rapidly changing, field
Aug 2000: 29 exoplanets
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What have we learned about exoplanets?Highly active, and rapidly changing, field
Aug 2000: 29 exoplanets
Sep 2005: 156 exoplanets
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What have we learned about exoplanets?Highly active, and rapidly changing, field
Aug 2000: 29 exoplanets
Sep 2005: 156 exoplanets
Up-to-date summary at
http://www.exoplanets.org
Now finding planets at larger orbital semimajor axis
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What have we learned about exoplanets?Why larger semi-major axes now?
Kepler’s third law implies longer period, so requires monitoring for many years to determine ‘wobble’ precisely
PSS mmT
G 3/23/1
2v
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What have we learned about exoplanets?Why larger semi-major axes now?
Kepler’s third law implies longer period, so requires monitoring for many years to determine ‘wobble’ precisely
Amplitude of wobble smaller (at fixed ); benefit of improved spectroscopic precision
PSS mmT
G 3/23/1
2v
Pm
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What have we learned about exoplanets?Why larger semi-major axes now?
Kepler’s third law implies longer period, so requires monitoring for many years to determine ‘wobble’ precisely
Amplitude of wobble smaller (at fixed ); benefit of improved spectroscopic precision
PSS mmT
G 3/23/1
2v
Pm
Improving precision also now finding lower mass planets (and getting quite close to Earth mass planets)
i
mmP sin
9.5 EarthFor example:Third planet of GJ876 system
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What have we learned about exoplanets?Discovery of many ‘Hot Jupiters’:
Massive planets with orbits closer to their star than Mercury is to the Sun
Very likely to be gas giants, but with surface temperatures of several thousand degrees.
Mercury
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What have we learned about exoplanets?Discovery of many ‘Hot Jupiters’:
Massive planets with orbits closer to their star than Mercury is to the Sun
Very likely to be gas giants, but with surface temperatures of several thousand degrees.
Mercury
Artist’s impression of ‘Hot Jupiter’ orbiting
HD195019
‘Hot Jupiters’ produce Doppler wobbles of very large amplitude
e.g. Tau Boo:
-1ms474sinv iS
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Existence of Hot Jupiters is a challenge for theories of star and planet formation:-
Star forms from gravitational collapse of gas cloud. Angular momentum conservation proto-planetary disk
Orion Nebula
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Existence of Hot Jupiters is a challenge for theories of star and planet formation:-
Star forms from gravitational collapse of gas cloud. Angular momentum conservation proto-planetary disk
Orion Nebula
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Existence of Hot Jupiters is a challenge for theories of star and planet formation:-
Star forms from gravitational collapse of gas cloud. Angular momentum conservation proto-planetary disk
Orion Nebula
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The nebula spins more rapidly as it collapses
Forming stars Forming stars and planets….and planets….
versusversus
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Forming stars Forming stars and planets….and planets…. versusversus
As the nebula collapses a disk forms
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Forming stars Forming stars and planets….and planets…. versusversus
Lumps in the disk form planets
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Computer modelling indicates that a Hot Jupiter could not form so close to its star and maintain a stable orbit
Current theory is that Hot Jupiters formed further out in the protoplanetary disk, and ‘migrated’ inwards due to tidal interactions with the disk material during its early evolution.
What have we learned about exoplanets?
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Computer modelling indicates that a Hot Jupiter could not form so close to its star and maintain a stable orbit
Current theory is that Hot Jupiters formed further out in the protoplanetary disk, and ‘migrated’ inwards due to tidal interactions with the disk material during its early evolution.
How common are ‘Hot Jupiters’?
We need to observe more planetary systems before we can answer this. Their common initial detection was partly because they give such a large Doppler wobble.
As sensitivity increases, and lower mass planets are found, the statistics on planetary systems will improve.
What have we learned about exoplanets?
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1. The Doppler wobble technique will not be sensitive enough to
detect Earth-type planets (i.e. Earth mass at 1 A.U.), but will
continue to detect more massive planets
Looking to the Future
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1. The Doppler wobble technique will not be sensitive enough to
detect Earth-type planets (i.e. Earth mass at 1 A.U.), but will continue to detect more massive planets
2. The ‘position wobble’ (astrometry) technique will detect Earth-type planets – Space Interferometry Mission after
2010
(done with HST in Dec 2002 for a 2 x Jupiter-mass planet)
Looking to the Future
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1. The Doppler wobble technique will not be sensitive enough to
detect Earth-type planets (i.e. Earth mass at 1 A.U.), but will continue to detect more massive planets
2. The ‘position wobble’ (astrometry) technique will detect Earth-type planets – Space Interferometry Mission after
2010
(done with HST in Dec 2002 for a 2 x Jupiter-mass planet)
3. The Kepler mission (launch 2008?) will detect transits
of Earth-type planets, by observing the brightness dip of stars
Looking to the Future
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1. The Doppler wobble technique will not be sensitive enough to
detect Earth-type planets (i.e. Earth mass at 1 A.U.), but will continue to detect more massive planets
2. The ‘position wobble’ (astrometry) technique will detect Earth-type planets – Space Interferometry Mission after
2010
(done with HST in Dec 2002 for a 2 x Jupiter-mass planet)
3. The Kepler mission (launch 2008?) will detect transits
of Earth-type planets, by observing the brightness dip of stars
(already done in 2000 with Keck, and now becoming routine for Jupiter mass planets, e.g. from OGLE and SuperWASP)
Looking to the Future
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Transit Detection by OGLE III program in 2003
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www.superwasp.org
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Transit detections by SuperWASP from 2006
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Transit detections by SuperWASP from 2006
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1. The Doppler wobble technique will not be sensitive enough to
detect Earth-type planets (i.e. Earth mass at 1 A.U.), but will
continue to detect more massive planets
2. The ‘position wobble’ (astrometry) technique will detect Earth-type planets – Space Interferometry Mission after
2010
(done with HST in Dec 2002 for a 2 x Jupiter-mass planet)
3. The Kepler mission (launch 2008?) will detect transits
of Earth-type planets, by observing the brightness dip of stars
(already done in 2000 with Keck, and now becoming routine for Jupiter mass planets, e.g. from OGLE and SuperWASP)
Looking to the Future
Note that (2) and (3) permit measurement of the orbital inclination Can
determine and not just
PmimP sin
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Saturn mass planet in transit across HD149026
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From Sato et al 2006
From Doppler wobble method From transit method
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4. Gravitational microlensing satellite? Launch date ????
Could detect mars-mass planets
Looking to the Future
Jan 2006: ground-based detection of a 5 Earth-mass planet via microlensing
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5. NASA: Terrestrial Planet Finder ESA: Darwin
Looking to the Future
}~ 2015 launch???
These missions plan to use nulling interferometry to ‘blot out’ the light of the parent star, revealing Earth-mass planets
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5. NASA: Terrestrial Planet Finder ESA: Darwin
Looking to the Future
}~ 2015 launch???
These missions plan to use nulling interferometry to ‘blot out’ the light of the parent star, revealing Earth-mass planets
Follow-up spectroscopy would search for signatures of life:-Spectral lines of oxygen, watercarbon dioxide in atmosphere
Simulated ‘Earth’ from 30 light years
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The Search for Extra-Solar Planets
o The field is still in its infancy, but there are exciting times ahead
o In about 10 years more than 200 planets already discovered
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The Search for Extra-Solar Planets
o The field is still in its infancy, but there are exciting times ahead
o In about 10 years more than 200 planets already discovered
o The Doppler method ultimately will not discover Earth-like planets, but other techniques planned for the next 15 years will
o Search methods are solidly based on well-understood fundamental physics:-
Newton’s laws of motion and gravity Atomic spectroscopy Black body radiation
![Page 118: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/118.jpg)
The Search for Extra-Solar Planets
o The field is still in its infancy, but there are exciting times ahead
o In about 10 years more than 200 planets already discovered
o The Doppler method ultimately will not discover Earth-like planets, but other techniques planned for the next 15 years will
o Search methods are solidly based on well-understood fundamental physics:-
o By ~2020, there is a real prospect of finding not only Earth-like planets, but detecting signs of life on them.
Newton’s laws of motion and gravity Atomic spectroscopy Black body radiation
![Page 119: The Search for Extra-Solar Planets P1Y* Frontiers of Physics Feb 2007 Dr Martin Hendry Dept of Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062404/5515c9a455034693758b4a4b/html5/thumbnails/119.jpg)
The Search for Extra-Solar Planets
o The field is still in its infancy, but there are exciting times ahead
o In about 10 years more than 200 planets already discovered
o The Doppler method ultimately will not discover Earth-like planets, but other techniques planned for the next 15 years will
o Search methods are solidly based on well-understood fundamental physics:-
o By ~2020, there is a real prospect of finding not only Earth-like planets, but detecting signs of life on them.
What (or who) will we find?…
Newton’s laws of motion and gravity Atomic spectroscopy Black body radiation