Transcript ٧ - siamois - Observatoire de Paris

Asteroseismology,
from space
and from the ground
Benoît Mosser
September 17, 2007
Observatoire de Paris/LESIA
2nd ARENA Conference Postdam
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Summary
1. Space-borne asteroseismology
CoRoT results
2. Ground-based observations
Current results
3. Future projects
Space, network, Dome C
4. Comparison / complementarity
and unique role of Dome C
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Asteroseismology
• Age determination
• Stellar radii (impact for exoplanet radii)
• Composition
~ a few %
~ a few %
• Diagnostic of convective cores
• Depth of convection and of second Helium ionization zones
• Excitation mechanisms (convection)
• Rotation and internal structure
Specification:


September 17, 2007
eigenfrequency precision = 0.2 mHz
continuous observations
(h > 80 %)
long duration
(T > 2.5 months)
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CoRoT
• launched on December 27th , 2006
• by Soyuz 2, from Baikonour, Kazakhstan
• low Earth polar orbit, 896 km altitude
• orbital period 6184 s (~1h43mn, 162 mHz)
• high precision photometry
The CoRoT space mission has been
developped and is operated by CNES, with
the contribution of Austria, Belgium, Brazil,
ESA, Germany and Spain
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CoRoT « Eyes »
CoRoT eyes: d=0, a=6h50 and 18h50
12 0°
15 0°
90 °
18 0°
60 °
21 0°
22 h
20 h
18 h
16 h
14 h
12 h
10 h
8h
6h
4h
2h
0h
30 °
24 0°
0°
27 0°
33 0°
30 0°
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CoRoT asteroseismology targets
7 B stars,including 1 known Beta
Ceph,3 Be, 1 ecl. bin.
4 giants (G,F)
12 A stars including 4 known
pulsators, 2 Am, 2 Ap, 2 eclips. Bin.
3 (early) F stars
4 solar-like puls. cand.
5-month long run on each target
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CoRoT first observations
February, March
initial run, 60 days
April
1st short run
May, 11  Oct. 15
1st long run
not yet completed
Raw data
N0
OK
1st corrections
N1
OK
Scientific data
N2
not yet distributed
Sensitivety
0.6 ppm in 5 days, for mV=5.4
as expected
Duty cycle
92% (6% lost in SAA)
better than expected
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Example of light curves
Typically 10-4 in 30 s
A 6th mag F-type star showing daily variability below the 10-3 level
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Light curve
An 9th magnitude suspected delta Scuti showing beat phenomena at a few 10-3
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Light curve
An 8th magnitude B star in an eclipsing binary
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Quiet target
A 7th magnitude giant F star showing very low dispersion of ~10-4
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HD 49933
1st solar-like target, initial run, 60 days
Simulations: Baudin et al. 06
Photon noise
Granulation
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HD 49933, observed
Mosser et al. 2005, 10 days with HARPS, duty cycle ~ 23%
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d Scuti
Example of an 8th magnitude delta Scuti observed with CoRoT.
The red line illustrates common lowest detection limit from the ground.
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Ground-based observations
• solar-like oscillations in solar-like stars
- HARPS @ ESO 3.6-m
- UCLES @ AAT
- CORALIE @ Euler telescope
- SOPHIE @ OHP
+ instruments @ SARG, McD, Okoyama, Lick
Oscillation detection
Mode identification
2-sites observation
Network observation
Stellar structure
modelling
Rotation, fine
structure…
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~ 20 targets
for ~ 12 targets
5 targets
1 target (Procyon)
~ 2 targets
Observations limited
to a few days
insufficient
precision
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Single/multi-sites observation
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Proyon: network observations
January 2007:
Multi-site campaign
-AAT
-Okoyama
-TLS
-OHP
-NOT
-SARG
-ESO
-Euler
-McDonald
-Lick
• Arentoft et al.; Bedding et al, in preparation
• time series ~ 9 days
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Procyon
mV = 0.4
2 Gyr
1.5 Msun
2.0 Rsun
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Procyon:network result
• Observation duration
T
• Eigenfrequency precision
dn ~ 1 / T0.5
• Modelling precision
varies as dn
Despite network observations, the
expected gain for interior structure
modelling is limited, due to a too
limited observation duration
From Matthews et al 2004.
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KEPLER
• NASA; launch = nov 2008
• High precision photometry
• a few fields reserved
for asteroseismology
CoRoT  Kepler :
tel.
27 cm
 95 cm
orbit
polar
 L2
+
duty cycle in L2
-
sensitivety (mV > 9), radiations in L2
?
exact scientific case for asteroseismology?
29-31 October 2007: First KASC workshop, Paris. The Kepler Asteroseismic
Science Consortium (KASC) is an international consortium of researchers
dedicated to the asteroseismic analysis of Kepler data.
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MOST
• Microsatellite for asteroseismology
• Operated by the Canadian Space Agency
since 2004
• High precision photometry
• Best performance ~ 20 ppm
 Many results on pulsators with large amplitudes
 Not sensitive enough for asteroseismology of solar-like stars with
solar-like oscillations (Procyon’s oscillations not detected)
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SONG
• Project currently in phase 0
• Danish asteroseismology centre, Aarhus University
• Network of 6 to 8 small telescopes (6080 cm)
• Echelle spectrometer + iodine cell
• Expected schedule: 1 prototype for 2012
>> 2012
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• Fourier Tachometer
• to be installed at Dome C
• Phase A completed
• Scientific Committee
Th Appourchaux (France, pdt), C Catala
(inst. scientist), S Charpinet (France), D
Kurz (UK), Ph Mathias (France), A Noels
(Belgium), E Poretti (Italy),
• 40-cm telescope:
- solar-like oscillations in solar-like targets (type: F, G, K; class: IV & V)
- red giants; d Scuti; g Dor; PMS (with vsin i < 20 km/s)
 Scientific program:
September 17, 2007
for more than 6 winters
complementary to CoRoT
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SIAMOIS
• 40-cm telescope
• Interferometer
• Data
small size, low cost, easy ‘antarctization’, dedicated to the projet
fiber fed Fourier Tachometer, operated at room temperature,
monolithic interferometer, photon noise limited performance
automatic pipeline reduction, telemetry: limited flow < 100 kb/day
Phase A completed, April 2007
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Space / Ground
Main differences between space-borne and ground-based observations
space
ground
Observation
photometry
spectrometry
Max. degree
2
3
Targets
magnitude
dim
bright
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Doppler / photometry
Solar granulation noise
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Granulation noise
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l=3 modes
l=3 modes
visible in
spectroscopy
Small
separation
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Doppler / photometry
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Gabriel et al 1998
low frequency noise
+
l=3 modes
Inversion 4
times more
precise with
Doppler data
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Complementary observations
Complementary ground-based observations are necessary
- to measure fundamental parameters
- to improve the modelling
Strömgren photometry
Teff , log g, metallicity
High resolution spectrometry
Teff , log g, abundances
Interferometry
angular diameter
Astrometry
distance
Stellar radius determined with enough
precision only for bright stars
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Comparison
CoRoT
Kepler
SONG
SIAMOIS
2 eyes
diam = 12°
10° x 10°
(Cygnus-Lyra)
|d| < 30°
d < - 45°
Duty cycle
92 %
~ CoRoT
~ 85 %
~ 90 %
5-day perf.
0.6 ppm
> 1.2 ppm
Max obs.
5 months
 4 years
Magnitude
>6
>9
<7
# targets
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Up to 40 : 4 yr
Up to 160 : 1 yr
Up to 1000 : 90 d
> 30
# solar-like
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Status
Instrument
cost
September 17, 2007
In operation
65 M€
2-20 cm/s
3 months
3 months
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Launch
= 11/ 2008
Phase 0
Prototype > 2012
Phase A is OK
2012 at Dome C
> 6 M€ (6 tel)
0.86 M€ (1 tel)
1.02 M€ (2 tel)
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Clear sky fraction at Dome C
Clear sky fraction measured by Eric Aristidi (2006 winter)
Clear sky fraction > 90% during 84% of the time
Average number of consecutive clear days: 6.8 days
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Duty cycle
Better performance at Dome C compared to a 6-site network
(Mosser & Aristidi 2007, PASP)
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Simulations
F6V star, mV = 4.5, vsini = 5 km/s, 90-day long run
Modelling: stochastic excitation + intrinsic damping
(Anderson et al 1990)
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Simulations
F6V star, mV = 4.5, vsini = 5 km/s, 90-day long run
Precision on the eigenfrequency measurement: 0.10 –
0.25 mHz (Libbrecht 1992)
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Conclusion
Space-borne observations = photometric observations
CoRot unique results
Kepler
not primilarly specified for asteroseismology
sensitivity for solar-like oscillations?
very dim targets  uncertainty on fundamental parameters
Ground-based observations = Doppler observations
measurement of modes with degree l = 3
much less low frequency noise
 much better inversion and modelling
& observation of low mass stars
Network very late schedule, complex organization
Dome C = unique site for asteroseismology
3-month continuous observation with duty cycle ~ 90%
High performance with a 40-cm collector
Better performance than a 6-site network
http://siamois.obspm.fr
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Everything is OK for SIAMOIS
Risk
Cost
Logistics
٧
- CFHT/FTS; GONG helioseismic network
- Scientific program
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- Construction < 1 M€
- Running cost << network
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- Automatic instrument; simple setup
- Limited operations; low data flow
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September 17, 2007
- Phase A completed
- Scientists, engineers, SC at work!
http://siamois.obspm.fr
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Budget
Site
SIAMOIS
Network
1 site
At least 6 sites for similar
performance
~ 6 ME
Construction 860 ME
Running
cost for 3
months
Observation
September 17, 2007
~ 750 kE /
600 kE (according to
number of
GONG, WET networks)
projects
5 months / year 12 months / year
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SIAMOIS at Dome C
Demanding site ?
Project ~ spatial-like organization (but with human presence)
Quasi automatic, simple setup
Reduced mass, low power, very low telemetry
Seeing ?
Fibre = 5" on the sky
No big telescope at Dome C ? Key science with a 40-cm telescope (or 2 telescopes)
Only circumpolar targets ?
Scientific program for more than 6 winterings
Fourier tachometer ?
As the helioseismic network GONG, as onboard SoHO and
SDO
Duty cycle ~ 90% !
Polar night = 3 months
September 17, 2007
Scientific specification #1 : duty cycle > 85%
Scientific specification #2 : 100-day long runs
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Fourier tachometer
• Why a FT instead of an échelle spectrometer?
• Fourier Tachometer = best solution for
- GONG
(network helioseismology)
- MDI
(helioseismology onboard SoHO)
- Velocity and Magnetic Imager, SDO
Current telescope
at Dome C /
Telescope available
in the near future
for long duration
observation
= dedicated small
telescopes
tel
Echelle spectrometer
(as HARPS)
FT
FT: simple installation and setup at Dome C
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Possible targets
Observable targets
(solar-like stars with
solar-like oscillations)
with SIAMOIS and a
40-cm telescope
dedicated to the project
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Planning & budget
< 2006
principle: monolithic Fourier
Tachometer
• 2007
thermo-mechanical analysis
phase A
• 2008-2010
PDR
FDR
integration
• 2010-2011
tests
summer campaign: Dome C
• 2012
First winterover at Dome C
LESIA (Obs. Paris),
IAS (Orsay), LUAN (Nice),
OMP (Toulouse) + SESO
Budget ~ 860 k€ << budget for an equivalent 6-site network
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Mosser et al 2003
Performance
Photon noise limited performance, SIAMOIS at Dome C, 40-cm telescope,
120 hours with 90 % duty cycle, mV = 4
SNR on circumpolar targets
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Fourier tachometer
• Another advantage:
multiplex advantage
 simultaneous observations of several targets
First step: small telescope + FT
Then: multi-targets observation = small telescopes + 1 FT
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Duty cycle at Dome C
Polar night
=
100 nights
Resulting duty cycle (bright targets) > 90% during 90 days
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Asteroseismology after COROT
1 - single-site runs, short runs
2 - photometry, space-borne observations, MOST,
3 - spectrometry, ground-based observations
Ground-based observations
• Bright stars
• Low mass stars
• Doppler signal
 reduced granulation noise
 modes l=3 for small separation
Specification:


September 17, 2007
eigenfrequency precision = 0.2 mHz
continuous observations
(h > 80 %)
long duration
(T > 2.5 months)
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SIAMOIS
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