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.