Exoplanet Search Techniques:
Overview
PHY 688, Lecture 28
April 3, 2009
Outline
• Course administration
– final presentations
• see me for paper recommendations 2–3 weeks before talk
• see me with draft of presentation 1 week before talk
– midterm exam discussion
• Review of previous lecture
– exoplanet search techniques: direct imaging
• Exoplanet search techniques (continued)
– comparison of sensitivities
April 3, 2009
PHY 688, Lecture 28
2
Hydrogen Phase Diagram
Hydrogen phase diagram
(From Lecture 14)
7
0.6
ρ
∝
T
T
0
ρ
T∝
.4
7
0 .6
ρ
∝
T
Midterm
April 3, 2009 Problem 1
PHY 688, Lecture 28
(Burrows & Liebert 1993)
3
Lecture 25: Radii of
Very Hot Jupiters
• some large radii cannot be
explained by coreless planet
models with high-altitude
stratospheres:
– extra internal power source?
• stratospheric heat trap
• tidal heating
• damping or orbital eccentricity
and apparent resetting of
planet age?
– host stars are giga-years old
Midterm Problem 2:
Transit
Radius Effect
April 3, 2009
PHY 688, Lecture 28
(Fortney et al. 2007)
4
From Star
To Observer
From Lecture 22:
Exoplanet Transit Spectroscopy
Planet
X
A ray may be wholly, partly, or negligibly absorbed, depending
upon its impact parameter and its wavelength.
Thus, the planet appears larger when observed at wavelengths
that are strongly absorbed.
Midterm
April 3, 2009 Problem 2: Transit Radius
PHY 688,Effect
Lecture 28
5
From Lecture 11: Luminosity
(i.e., Surface Gravity) Effects at A0
Midterm
Old
April 3, 2009 Problem 3: Young and
PHY
688,Brown
Lecture 28 Dwarfs
(figure: D. Gray)
6
From Lecture 11: Gravity-Sensitive
Features in UCDs
Midterm Problem 3:
April 3, 2009
Young and Old Brown Dwarfs
PHY 688, Lecture 28
(McGovern et al. 2004)
7
From Lecture 11:
Gravity in UCDs
Key species:
•
neutral alkali elements
(Na, K)
– weaker at low g
•
hydrides
– CaH weaker at low g
– FeH unchanged
•
oxides
– VO, CO, TiO stronger
at low g
– H2O ~ unchanged
Midterm Problem 3:
Young
and Old
Brownet Dwarfs
(Kirkpatrick
al. 2006)
April 3, 2009
Wavelength (µm)
PHY 688, Lecture 28
8
Outline
• Course administration
– final presentations
• see me for paper recommendations 2–3 weeks before talk
• see me with draft of presentation 1 week before talk
– midterm exam discussion
• Review of previous lecture
– exoplanet search techniques: direct imaging
• Exoplanet search techniques (continued)
– comparison of sensitivities
April 3, 2009
PHY 688, Lecture 28
9
Previously in PHY 688…
April 3, 2009
PHY 688, Lecture 28
10
From Lecture 2: Detection
Techniques for Substellar Objects
brown dwarfs
•
exoplanets
precision radial velocity monitoring
– periodic Doppler shift of host star
spectrum due to planet’s
gravitational pull
•
resolved imaging of binary systems
– seeing-limited, speckle
interferometry, adaptive optics
•
unresolved photometry of hot stars
– e.g., cool infrared excess in an
otherwise much hotter white dwarf
•
large-area sky surveys
– extremely red objects
April 3, 2009
•
•
precision radial velocity monitoring
pulsar timing
– apparent periodicity in pulsar
rotation period due to planet’s
gravitational pull
•
transit photometry
– ~1% dimming of star due to planet
passing in front
•
microlensing
– gravitational lensing of light from
background stars
•
resolved imaging!
– extremely high-contrast adaptive
optics
PHY 688, Lecture 28
11
Planet
Detection
Methods
(statistics as of Oct 2007)
April 3, 2009
PHY 688, Lecture 28
(Perryman 2000)
12
Planet Detection History
318 radial velocity
58 transits
8 microlensing
7 pulsar timing
4 (11) imaging
April 3, 2009
PHY 688, Lecture 28
13
Planet Detection:
Direct Imaging
• 2MASS 1207–3932 B
~ 5 MJup
• primary is a young
(~10 Myr) brown
dwarf
• discovered with
adaptive optics (AO)
on the 8 m Very Large
Telescope (VLT)
April 3, 2009
PHY 688, Lecture 28
(Chauvin et al. 2004)
14
Challenge of Direct Imaging:
Star-Planet Contrast
• In the visible–near-IR
– FSun / FEarth ~ 109
– FSun / FJup ~ 108
– challenging wavefront
control
– small PSF
– can observe from the
ground
• In mid-IR
–
–
–
–
–
FSun / FEarth ~ 106
FSun / FJup ~ 104
easier wavefront control
>10 × larger PSF
need to observe from
space
April 3, 2009
PHY 688, Lecture 28
15
Challenge of Direct Imaging:
Star-Planet Contrast
Keck AO speckles at 2.2 µm
2M 1207 B (~5 MJup)
r = 1″
•
•
•
high angular resolution,
high-contrast imaging
suffers from wavefront
aberrations or order ~ λ
aberrations manifested as
“speckles” of size ~ λ/D
speckles pose as
“fake”planets
April 3, 2009
d
HR 8799 b,c,d (~10–15 MJup)
c
b
exoplanets
PHY 688, Lecture 28
(Kalas 2005)
16
Planet Detection: Imaging
•
•
•
state of the art: contrast of 9 mag at 0.5", 11 mag at 1" in the near-IR
benefits: can perform atmospheric spectroscopy
limitations:
– hot (young), well-separated (>0.5") planets
– no mass, radius information
•
false positives: telescope speckles, distant background stars
April 3, 2009
PHY 688, Lecture 28
17
Outline
• Course administration
– final presentations
• see me for paper recommendations at least 2 weeks before talk
• see me with draft of presentation 1 week before talk
– midterm exam discussion
• Review of previous lecture
– exoplanet search techniques: direct imaging
• Exoplanet search techniques (continued)
– comparison of sensitivities
April 3, 2009
PHY 688, Lecture 28
18
Planet Detection: Precision Radial
Velocity (Doppler Spectroscopy)
April 3, 2009
PHY 688, Lecture 28
(Johnson et al. 2006)
19
Planet Detection: Precision Radial
Velocity (Doppler Spectroscopy)
April 3, 2009
PHY 688, Lecture 28
(Johnson et al. 2006)
20
Planet Detection: Precision Radial
Velocity (Doppler Spectroscopy)
stellar spectrum
April 3, 2009
PHY 688, Lecture 28
21
Planet Detection: Precision Radial
Velocity (Doppler Spectroscopy)
stellar spectrum with I2 lines superposed:
I2 allows precise wavelength calibration
April 3, 2009
PHY 688, Lecture 28
22
Planet Detection: Precision Radial
Velocity (Doppler Spectroscopy)
• state of the art: 0.1–0.5 m/s precision
– HF or iodine cell
– dual optical fiber (one looking at target star, one at ThAr calibration source)
• benefits: orbital solution modulo sin i
• limitations:
– sin i ambiguity;
– radius, atmospheric composition unknown
• false positives: star spots, pulsations
April 3, 2009
PHY 688, Lecture 28
23
Planet
Detection:
Astrometry
1
0
∆y (mas)
–1
–2
–3
–4
–2
April 3, 2009
–1
0
∆x (mas)
1
2
PHY 688, Lecture 28
(Benedict et al. 2006)
24
Planet Detection: Astrometry
• state of the art: ~0.05 mas precision
• benefits: exact orbital solution, dynamical mass
• limitations:
– gets harder with heliocentric distance (>20 pc)
– planet radius, atmospheric composition unknown
• false positives: star spots
April 3, 2009
PHY 688, Lecture 28
25
Planet Detection: Transits
•
HD 209458b was a known extrasolar planet in a = 0.047 AU semi-major axis
April 3, 2009
PHY 688, Lecture 28
(Charbonneau et al. 2000)
26
Planet Detection: Transits
April 3, 2009
PHY 688, Lecture 28
27
!
Planet Detection: Transits
"Fmax
F
2
$
'
$ RP '
RP RS
*2
# & ) # 10 &&
))
% RS (
% RJup RSun (
2
13
13
$
'
$
'
$
'
$
'
RS
RS
P
RS
P
duration #
# 14 hr &
)&
)&
) # 1.3 hr &
)
2+a P
R
11
yr
R
3
days
(
(
% Sun (%
% Sun (%
$ RS RSun '
$ RS RSun '
probability # 0.1%&
) # 10%&
)
a
5
AU
a
0.05
AU
%
(
%
(
•
•
•
•
state of the art: 0.1% photometry
benefits: full orbital solution, temperature, radius, more!
limitations: close-in planets (hot Jupiters)
false positives: F-M star binaries, grazing eclipses of stars, triple
stars with eclipses
April 3, 2009
PHY 688, Lecture 28
28
Planet Detection:
Pulsar Timing
98.2-day
periodicity
subtracted
66-day
periodicity
subtracted
PSR 1527+12 pulse shape, 430 MHz
rotational period:
0.00621853193177 ±
0.00000000000001 s (10–14 s)
April 3, 2009
both periodicities
subtracted
(Wolszczan & Frail 1992)
PHY 688, Lecture 28
29
The Pulsar Planets
•
only one more
pulsar planet
known: around
PSR B1620–26
•
very different from
the original pulsar
planetary system
– planet orbits a
close neutron
star–white dwarf
binary
– ap = 23 AU
– Mp = 2.5±1 MJup
April 3, 2009
PHY 688, Lecture 28
(Wolszczan 2008)
30
Pulsar Timing:
Non-Keplerian Orbital Motions
residuals of
standard pulsar
timing model; no
planets
residuals
including
Keplerian orbits
for 3 planets
residuals including
non-Keplerian
resonant (3:2)
interactions
between planets B
and C
April 3, 2009
PHY 688, Lecture 28
(Konacki & Wolszczan 2003) 31
Pulsar Timing
• state of the art:
– 10–14 s pulsar timing precision
– 3 × 10–6 s residuals after orbital fits
• benefits:
– very high sensitivity to mass: ~10–2 MEarth ~ MMoon
• most sensitive technique to date!
– full orbital solution
• limitations:
– few pulsars known,
– planet radius, atmospheric composition unknown
• false positives:
– pulsar position needs to be known precisely (<0.1")
– first reported pulsar planets (1991) were retracted
April 3, 2009
PHY 688, Lecture 28
32
Planet Detection:
Gravitational Microlensing
April 3, 2009
PHY 688, Lecture 28
33
Planet Detection:
Gravitational Microlensing
• to be presented in more detail by Dharmesh on May 8!
April 3, 2009
PHY 688, Lecture 28
34
Planet Detection
Techniques: Comparison
direct
imaging
• habitable zone
• ~150 planets detected as of
mid-2004:
–
–
–
–
r.v. (blue)
transits (red)
microlensing (yellow)
pulsar timing (purple)
• sample ~doubled by 2009
– added 5 through direct
imaging (magenta, at >20AU)
April 3, 2009
(LawsonPHY
et al.
2004)
688,
Lecture 28
35
Planet Detection
Techniques: Comparison
•
direct
imaging
Super-Jupiters (>1 MJup)
– r.v., astrometry, transits, pulsar timing,
microlensing, direct imaging
•
Jupiters, Neptunes, Super-Earths (>0.01
MJup ≈ 3 MEarth)
– r.v., astrometry, transits, pulsar timing,
microlensing
– lowest mass r.v. planet: Msini = 4.2 MEarth
– lowest mass microlensing planet:
• M = 3.3 MEarth
• orbits a brown dwarf
•
Earths
– pulsar timing
– to be detected through transits by Kepler
•
Lunar/Mercury-mass (0.02 MEarth) planet
– pulsar timing
April 3, 2009
(LawsonPHY
et al.
2004)
688,
Lecture 28
36