Extra-Solar Planets: Detection Schemes
Using Optical and Radio Techniques
R.L. Mutel
University of Iowa
Overview Map of ESP Detection Schemes
First Extra-solar Planet Detection
3 (or 4) planets surrounding pulsar PSR1257+12
(Wolszczan, A. & Frail, D., 1992, Nature )
Pulsar 1257+12
Period 6.2 msec
Mass 0.29 Msun
Distance 800 pc.
Name
M/MEarth) P(days) A(AU)
A
0.015
25.3
0.19
B
3.4
66.5
0.36
C
2.9
98.2
0.47
D
95Mjup
170yr
35
N.B. Planets probably could not have
survived SN explosion, were likely formed
from SN debris!
Second Planet Detection: 51 Peg
(M.Mayor & D.Queloz, 1995, Nature)
Planet Characteristics
P
(days)
ecc
Vel K
(m/s)
Msini
(Mjup)
a
(AU)
4.231
0.01
55.45
0.46
0.05
Stellar Characteristics
Sp. Type
G5V
Mass
(Msun)
1.06
Vel K
(km/s)
54.5
D
(pc)
P
(day)
[Fe/H
]
15.36
28.00
0.20
N.B. Tsurface ~ 1000K for this planet!
• As of mid-2002, there
were over 100 extrasolar planets detected,
most by spectroscopic
technique.
Except for PSR1257, all
are massive planets
(0.2Mjup < 10 Mjup)
Most are much closer
than expected to parent
star and/or more
massive
N.B. Terrestrial
planets would be
found here
Detection of Extra-Solar Planets: Doppler Effect
HD89744 (F7V)
P 256 days
Mass 7MJ
Spectroscopic Technique
Star-planet system moves mutually around common barycenter, so solving 2body problem we have:
1/ 3
 2 G 
V (t )  
2 
PM
s 

 2 t

 2 t

 M p sin i  sin 
    K sin 
 
 P

 P

Solving for the planet mass:
Mp 
1/ 3
K  PM s 


sin i  2 G 
2
Note: Derived mass is
always less than true
mass [by 1/sin(i)]
2K
Most ESP’s detected with spectroscopy have large masses
and small semi-major axes: Why?
Mostly a
selection effect?
Current spectroscopy
detection schemes have
limiting velocity resolution
(σ ~ 10 m/s)
Future space missions
(Kepler, FAME, SIM) will
probe much larger areas
of M-a diagram
Current limit
(σ 1 0 ms/)
Detection of Extra-Solar Planets: Occultations
Detection of ExtraSolar Planets by
Occultation:
HD 209458 (V = 7.6)
First detection by Henry et al. 2001
(0.8 m, Fairborn Observatory,
Tennessee State Univ.)
V = 0.017 (1. 58%)
Transit observed 26-27 July 2000 by Deeg and
Garrido at the 0.9m Sierra Nevada Telescope
STARE Light Curve
Detection of Extra-Solar Planets: STARE Telescope
(currently in Canary Islands)
The current STARE telescope, as of
July, 1999, is a field-flattened Schmidt
working aperture of 4 in, (f/2.9). The
telescope is coupled to a Pixelvision
2K x 2K CCD (Charge-Coupled
Device) camera to obtain images with
a scale of 10.8 arcseconds per pixel
over a field of view 6.1 degrees square.
Broad-band color filters (B, V, and R)
that approximate the Johnson bands
are slid between the telescope and
camera. By taking exposures with
different colored filters, the colors of
stars in the field can be determined.
This is necessary for accurate
photometry.
Transit Photometry Technique parameters
(assumes Rs >> Rp)
• Transit duration
2 Rs

 13h  a AU
GM s
• Transit depth
 Rp 
 Rp 
    0.01  


I
 Rs 
 RJup 
I
2
2
• Probability of occultation
2
2
 Rs 
5
p(a )     2  10  a AU 
 a 
Object
(hr)
(I/I)
P (%)
Mercury
7.1
10-5
10-4
Earth
13
10-4
2·10-5
Jupiter
30
0.01
10-6
HD209458
(a=0.045)
2.8
0.015
0.01
Detection of ESP companion to White Dwarfs
Using Occultations
(Mike Wilson M.S. 2003)
• Planets around white dwarfs have much higher
probability of occultation (2% at 50 RJ)
•
Eclipse is total, not photometrically difficult (< 1%)
• Eclipse duration much shorter (8 min at 25 RJ = 4 Rroche)
Jovian
Planet
White Dwarf
But can planets survive red giant phase?
Interaction with RG envelope
•
When planet is inside RG, drag
force is:
Fd  r    Rp 2   r  v 2  r 
• Drag force acts to reduce V,
hence planet spirals inward. Use
RG models to estimate ρ(r),
integrate equation of motion
Use RG models to estimate
ρ(r) and solve equation of
motion numerically
Fd  r    Rp 2   r  v 2  r 
Sample Calculations (Earth, 1.1 Solar Mass RG)
Mass intercepted
(kg/sec)
vs.vs
normalized
Normalized
radius
time (yrs) radius
Detection by Direct Imaging
Imaging of Gliese 229 with Companion Brown dwarf
No planets so far, but
HST has imaged a
brown dwarf:
M = 6 - 20 RJup
R ~ 1 RJup
a = 44 AU
SIM (Space Interferometry Mission: Space-based
Interferometer with 1 μas Precision (launch 2009)
SIM Instrument and
Mission Parameters
Baseline
10 m
Wavelength range
0.4 - 0.9µm;
Telescope Aperture
0.3 m diameter
Astrometric Field of
Regard
15° diameter
Astrometric Narrow Angle
Field of View
1° diameter
Detector
Si CCD
Orbit
Earth-trailing solar orbit
Science Mission Duration
5 years (launch in 2009)
Wide Angle Astrometry
4 µas mission accuracy
Narrow Angle Astrometry
1 µas single
measurement accuracy
20 mag
Limiting Magnitude
SIM
Discovery
Space
Detection by Low-frequency Radio Emission
•
•
All Solar-system planets with significant magnetospheres emit nonthermal ‘auroral’ radio emission (probably via electron-cyclotron
maser mechanism)
Radio luminosity scales with solar wind flow pressure or energy flux
on the magnetosphere cross-section (Zarka et al. 2001)
Radio emission from
Planets is strongest at
low frequencies
(f <100 MHz)
Very few large
radiotelescopes operate
at low frequencies
Future arrays includes
LOFAR and SKA
Sample dynamic spectra from
Earth and Jupiter
Estimating Radio Power for ESP’s
• Power dissipated in the interaction of a magnetized flow
with an conducting planet with radius Rp and speed V:
Pdiss
•
 B2 
2

V


R

p
2



Radio power emitted (scaling by solar system objects) is:
Pr   Pdiss , 
10
3
• Scaling of magnetic flux with stellar distance (at close distances, radial
component dominates):
Brad  r   r 2
• Hence, radio power scales as:
Pr  r   r
4
LOFAR: Low Frequency Array
Projected Timeline:
Preliminary Design Review ~ end 2002
Site selection ~ end 2002
Critical Design Review ~ early 2004
Initial operations - 2006
Full operations - 2008
The image above is an artist’s conception of
one LOFAR station, made up of more than
100 dual-polarization antenna systems.
LOFAR will consist of ~100 such stations
covering an area ~400 km in diameter at a
site yet to be chosen
Can ESP’s be detected with LOFAR?
• LOFAR sensitivity (5σ) below 100 MHz ~ 1 mJy (5 MHz, 1 hr)
• Jupiter as Pr ~ 106 W at 20 MHz, scales to 0.4 mJy at 1 pc., 4 μJy at
10 pc. but burst timescale is seconds. Hence, too faint.
• But, if scaling with stellar wind power is correct, Jupiter at 0.1pc
would be 625x stronger (250 mJy). This would be an easy detection
with LOFAR.
• But, preliminary VLA searches at 74 MHz (Bastian, et al. 2000,
2002) on several stars (47 UMa, d = 14 pc, 2 Jovians at 2,3 AU; 70
Vir, d = 18 pc, one Jovian 0.5 AU) found no detections (typical limit
40 mJy).