Extra-Solar Planets: Detection Schemes Extra-Solar Planets: Detection Schemes Using Optical and Radio TechniquesUsing Optical and Radio Techniques

R.L. MutelUniversity 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)

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 Mass(Msun)

Vel K(km/s)

D(pc)

P(day)

[Fe/H]

G5V 1.06 54.5 15.36 28.00 0.20

Planet Characteristics

N.B. Tsurface ~ 1000K for this planet!

• As of mid-2002, there were over 100 extra-solar 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

HD89744 (F7V)

P 256 days

Mass 7MJ

Spectroscopic Technique

1/ 32

sin 2s

p

K PMM

i G

1/ 3

2

2 2 2( ) sin sin sinp

s

G t tV t M i K

PM P P

Star-planet system moves mutually around common barycenter, so solving 2-body problem we have:

Solving for the planet mass:

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 Extra-Solar 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%)

STARE Light Curve

Transit observed 26-27 July 2000 by Deeg and

Garrido at the 0.9m Sierra Nevada Telescope

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

• Transit depth

• Probability of occultation

213hs

AU

s

Ra

GM

22

0.01p p

s Jup

R RI

I R R

2

25( ) 2 10sAU

Rp a a

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)

White DwarfJovian Planet

• Eclipse is total, not photometrically difficult (< 1%)

• Eclipse duration much shorter (8 min at 25 RJ = 4 Rroche)

But can planets survive red giant phase?

• Drag force acts to reduce V, hence planet spirals inward. Use RG models to estimate ρ(r), integrate equation of motion

Interaction with RG envelope

• When planet is inside RG, drag force is:

2 2d pF r R r v r

2 2d pF r R r v r

Use RG models to estimate ρ(r) and solve equation of motion numerically

Sample Calculations (Earth, 1.1 Solar Mass RG)

Mass intercepted (kg/sec) vs. normalized radiusNormalized radius vs time (yrs)

Detection by Direct ImagingImaging 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 Astrometry1 µas single measurement accuracy

Limiting Magnitude20 mag

SIM Discovery

Space

Detection by Low-frequency Radio Emission • All Solar-system planets with significant magnetospheres emit non-

thermal ‘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:

22

2 pdiss

BP V R

• Radio power emitted (scaling by solar system objects) is:

3, 10r dissP P • Scaling of magnetic flux with stellar distance (at close distances, radial component dominates):

2radB r r

• Hence, radio power scales as:

4rP r r

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).