Eddington

Stellar evolution

Habitable planets

Reliable tested theory Detection of habitableof stellar evolution to be Earth-like planets - theirused in astrophysics frequency and properties

Ages of stars, structure, Other planets propertieschemical evolution and planetary systems

Stellar oscillations Planetary TransitsAsteroseismology

High precision long duration relative photometry

Two Major Science Goals

Asteroseismology

1. Observations Power spectrum of flux gives oscillation

frequencies

2. Theory Calculate oscillation frequencies of stellar model

3. TestingCompare model predictions with observations

4. InversionDetermine model that fits the observed

frequencies- pressure, density, core mass, rotation, age,... Techniques tried and tested on

SoHO

Serious problems in stellar modeling

• Effects of rotation – age determination– chemical evolution of massive stars

• Effects of overshoot from convective cores– late evolution, supernovae explosions– evolution of abundances

• Settling of helium and heavier elements– age determination of low-mass stars

Eddington will make fundamental contributions to solving these problems

Stellar EvolutionCentral to Astronomy

Ages of stars, clusters, origin of elements

Dating galactic structure (discs, bulge, halo)

Chemical evolution of our galaxy and other galaxies

Light element abundances (He, Li) and the early Universe

History and future of the Sun - solar terrestrial relations

Solar frequency spectrum from VIRGO on SoHO

Results from helioseismology

• Inversion for solar sound speed– evidence for mixing– test of equation of state

• Inversion for solar rotation– convection-zone dynamics (not available in

stars)– rotation of the deep interior; stellar

rotational evolution

Relative difference in sound speed between Sun and model

Effect of mixing

Inferred solar internal rotation

Base of convectio

n zone

Near solid-body

rotation of interior

But the Sun is just one simple star

• No convective core• Slow rotation• Relatively unevolved• Comparatively simple material physics

Proper investigations of stellar structure and evolution require study of a broad range of stars

Eddington will provide this

Variety of stellar internal structureRed Giant

1 M•

10 M

•

Convective envelope

Convective core

Eddington’s capabilities for asteroseismology

• Study oscillations corresponding to those of the Sun in stars down to magnitude V = 12

• Very high duty cycle (95 %) leads to simple interpretation of frequency spectrum

• Very extended observations of single field during planet-finding phase will give excellent frequency resolution of slow pulsators

• Open clusters with massive pulsating stars, to study pre-supernova evolution

• Open clusters with solar-like pulsators• Old, metal-poor stars as samples of the early

evolution of the Galaxy

The Praesepe Cluster

Eddington’s

limit

COROT’s

limit

Results of inversion for a 1.45 Msun star

Edge of convectiv

e core

Ages Y Z

Pre-Eddington >20% >10% >10%

With separations 1.3% 0.3% 3%

With frequencies <0.1% <0.1% 0.1%

Uncertainties of key parameters for a cluster with moderate-mass stars

Planet searchDetection of habitable Earth-like planets

0.8 < R/REarth < 2.5, 0oC < T < 100oC

How frequent are they? Masses, radii, orbits

Properties of parent stars

Major step in search for life elsewhere in the Universe

Target selection strategy for Darwin

Properties of other planets and planetary systems

Formation of planetary systems

Detected by transits of planets across stellar disc

The Habitable Zone

From Kastings 1996

Are there other worlds? and how many?

Discovery of habitable planets with sizes and temperatures similar to Earth:

R~ 0.8 - 2.5 REarth T= 0 - 100ºC

-> Estimation of abundance of habitable worlds

A necessary step in the detection of bio-activity

Detection of other Earths

loss of atmosphere,no plate tectonics

Will develop into gas giant

The Formation and Evolution of Planets

Planetary Systems Origin

Discovery of Extrasolar Planets has upset conventional theories on Solar System Origin

Distribution of Solar System planets not compatible with

positions of Hot Giant planets - migration? Eddington survey for low-mass planets will lead to generalisation of planetary system origin theories

"Current Theories about Solar-System Origin are observationally driven by Exoplanets"

Photometry of Jupiter-like transit by HST

HD 209458precision: 6x10-5

Earth like

Data: Charbonneau, Brown, Gilliland, 2000

Results from Transit Observations

• reflected light: non-transiting hot giant planets

• amplitude of transit: size of planet

• time between transits: orbital period, distance, temperature

• duration of transit: orbital inclination

• shape of transit: planetary rings, stellar surface

• variations in arrival times of transits:detection of massive planetary moons

time of transit of our Earth varies by5 mins due to presence of Moon

habitable sites around Gas Giants?

Eddington´s Detection Capabilitiesfor Planets around Solar-type (G2V)

star

50 100 150 200 250 300 350 4000

0.5

1

1.5

2

2.5

3

3.5

Period

R/R

Ear

th

+

V=18

V=16

V=14

V=12

Hab. zone

Complete coverageof habitable zone for G,K,M starsEarth

stellarbrightness

Comparison with other missions

Orbital radius (AU)

Pla

net m

ass

(Ear

ths)

rad vel

COROT

SIM(astrometry)

Eddington

For a solar-type star

Eddington and COROTare for threetransits at V=14

SIM is for a star at 5 pc

Radial velocity is for 1 m/s

Hab. zone

Payload Requirements• High photometric precision:

– 1 ppm for V = 11 in 30 d ( 0.3 Hz). = 2-3 x 10-5 magnitude in 1 h for V = 13.– High precision long duration relative photometry– 1.2m telescope - 3o field of view - tiled CCDs

• Large field of view:– ~50,000 stars for asteroseismology (1ppm V < 12).

2 years (1-2 months per field). Cover H-R diagram (masses, ages, abundances, clusters)

– ~500,000 MS stars for planet search (10 ppm V < 17). 3 years on 1 field (20,000 planets with R<15 Rearth, dozens of Earth-like planets in habitable zone)

• High duty cycle: 95% (L2 orbit)

Payload Design

• Telescope: Collecting area + Field of view.– 3º FOV, planar, unvignetted, and fully corrected.– Symmetric PSF, 1 arcsec anywhere in the FOV.– 1.5 x 106 photo-electrons/s for V = 11 – 1.2 m compact TRT with no refractive component.– Heritage from well-studied design

• EddiCam:– Array of 20 CCDs covering the 3º FOV ( 19 cm).– Full-frame mode for planet search (7.4 sq.deg.)– Frame-store buffer shields on 16 CCDs for astero-

seismology (3.25 sq.deg.).– One camera with sequential priority observing modes.– CCD detectors: 20 x 80 mm in size

• 740 x 2900, 27 (1.5 arcsec), pixels. Full-well capacity: 1.6 x 106 e-/pix. Operation at -90o (passive cooling) in L2 orbit.

riveted Al rings

payload / spacecraft I/F

Telescope’s layout

High-Precision Photometry

• Photon-noise limited differential photometry (other sources of noise kept well < 8 x 10-4 s-1 on relevant time scales):– Satellite jitter (0.1 arcsec 1 )– Thermal stability (0.1 K/hr)– Read-out noise (<20 e- per pixel)– Periodic perturbations (< 8 x 10-7 peak-to-peak)

• Defocusing and dynamical range (precision and range versus source confusion and read-out noise): – Asteroseismology: 12 arcsec (8 pix.), 6 < V < 14. – Planet finding: 9 arcsec (6 pix.), 11 < V < 18.

Focal Plane CCD Array

• Target star plus “trailing” and neighbouring stars.• Background; residual stray and zodiacal light.• Flat field structure, including sub-pixel variations.• Spacecraft pointing jitter.• Telescope’s point spread function.• Variations induced by stellar activity.• Dark current (including “telegraphic” noise).• Radiation-induced traps (CTE degradation).• Hot pixels due to high-energy particles.• Cosmic ray hit events.• Integration and read-out procedures.• Algorithms for on-board data processing.

Noise sources

Performance (asteroseismology))

Performance (planet finding)

1) Soyuz-Fregat launcher baselined, launch from Baikonur.

2) Two approaches studied:

Mars Express-based platform.

European standard platforms (e.g. Prima)

3) Assumed launch date is 2008, with 2 years lifetime for design and 6 years for consumables (XMM approach). Earliest technical feasible launch date is on 2006. 4) ESA responsible for the complete programme, including launch, telescope, spacecraft operations and Science Operation Centre.5) CCD camera and the Science Data Centre(s) PI supplied.

6) Mars Express programmatic approach baselined, with all S/C units & assemblies considered in principle off-the-shelf, with 2003 technology maturity.

7) One 15 m ground station (Kourou). One shift, 5 yr operations.

Baseline assumptions

Deployed Satellite

Satellite exploded view

Operational Mission Lifetime 5 years Solar Aspect Angle 35 ° Spacecraft stabilised 3-axis

Observation Duration 1-2 months per star field 3 years for planet-finding

Lift-off Mass (20% sys. marg.) 940 kg

Power (10% system margin) 520 W, 6 yr end-of-life

Average data rate 64 kbps (science) + 2 for HK

Pointing Accuracy (rms): Absolute ± 3 arcmin Relative ± 0.1 arcsec/15 min

(telescope error signal used for attitude information)

Spacecraft design approach

A.S. Eddington 1882-1944Pioneer in stellar structure, oscillating stars,

relativity, cosmology, outreach

“... it is reasonable to hope that ina not too distant future we shall becompetent to understand so simplea thing as a star.” Internal Constitution of the Stars (1926)

“It would indeed be rash to assume that nowhere else in the Universe has nature repeated the strange experiment which she has performed on the Earth.”Nature of the Physical World (1933)

Eddington ScienceA reliable tested theory of stellar evolution

Asteroseismology - stellar oscillations probe the interior

Test models of stellar structure and evolution

Determine key parameters (eg convective overshoot)

Determine the internal structure (pressure, density, rotation)

Physics of stellar interiors: mixing, diffusion, ...

Chemical evolution of stars

Determine the age of stars and stellar systems

Dating machine for components of galactic structure

Eddington ScienceExtrasolar planets

Detection of » 20,000 planets R < 15 RE

Detection of » 500 in the habitable zone (dozens of Earths)

First reliable statistics on the abundance of planets

Earth-like planets for stars as faint as V » 17

Coverage of habitable zone for G, K, M stars

Detection of massive satellites around planets

Detection of hot giant planets by reflected light

Major step in search for habitats for life

Input to Darwin (target selection strategy and statistics)

Eddington Proposal Timeline

• Oct 99: Call for F mission proposals.• Jan 00: 49 proposals received, 6 selected for

assessment studies.• Jul 00: Assessment studies finished.• Sep 00: Presentations made followed by

selection of 2 F-missions (NGST and SOLO) and a “reserve” F-mission (Eddington). Reserve to be implemented depending on NGST and LISA schedules or provision of further resources.

• Oct 00: Selected mission package approved at SPC for 2007-2013.

ESA Planning• Eddington Science Team established in January 01.• ITT for telescope design to be issued in April.• Issue of a “Letter of Interest” for PI provided payload

camera and data centers.• A study of CCD characterization and evaluation of noise

sources to start in April.• First Eddington Workshop to be held in June in Córdoba

(Spain).• ITT for the spacecraft design to start next year.• Final decision on project implementation by the end of

2002.