september 17, 20072nd arena conference postdam1 asteroseismology, from space and from the ground...
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September 17, 2007 2nd ARENA Conference Postdam 1
Asteroseismology, from space
and from the ground
Benoît Mosser Observatoire de Paris/LESIA
September 17, 2007 2nd ARENA Conference Postdam 2
Summary
1. Space-borne asteroseismologyCoRoT results
2. Ground-based observationsCurrent results
3. Future projectsSpace, network, Dome C
4. Comparison / complementarityand unique role of Dome C
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Asteroseismology
• Age determination ~ a few %• Stellar radii (impact for exoplanet radii) ~ a few %• Composition
• Diagnostic of convective cores• Depth of convection and of second Helium ionization zones• Excitation mechanisms (convection)
• Rotation and internal structure
Specification: eigenfrequency precision = 0.2 Hz
continuous observations ( > 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 Hz)
• 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 »
0°
30°
60°
90°
120°
150°
180°
210°
240°
270°
300°
330°
0h2h4h6h8h10h12h14h16h18h20h22h
CoRoT eyes: =0, =6h50 and 18h50
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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
A 6th mag F-type star showing daily variability below the 10-3 level
Typically 10 in 30 s
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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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A 7th magnitude giant F star showing very low dispersion of ~10-4
Quiet target
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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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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 ٧ ~ 20 targets
Mode identification ٧ for ~ 12 targets
2-sites observation ٧ 5 targets
Network observation ٧ 1 target (Procyon)
Stellar structure modelling ٧ ~ 2 targets
Rotation, fine structure… ٧ insufficient
precision
Observations limited to a few days
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Single/multi-sites observation
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Proyon: network observations
• Arentoft et al.; Bedding et al, in preparation• time series ~ 9 days
January 2007:Multi-site campaign -AAT-Okoyama-TLS-OHP-NOT-SARG-ESO-Euler-McDonald-Lick
ProcyonmV = 0.42 Gyr1.5 Msun
2.0 Rsun
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Procyon:network result
• Observation durationT
• Eigenfrequency precision ~ 1 / T0.5
• Modelling precision varies as
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 (6080 cm)
• Echelle spectrometer + iodine cell
• Expected schedule: 1 prototype for 2012
>> 2012
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• 40-cm telescope:- solar-like oscillations in solar-like targets (type: F, G, K; class: IV & V)
- red giants; Scuti; Dor; PMS (with vsin i < 20 km/s)
Scientific program: for more than 6 winters complementary to CoRoT
• 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),
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SIAMOIS
• 40-cm telescope small size, low cost, easy ‘antarctization’, dedicated to the projet
• Interferometer fiber fed Fourier Tachometer, operated at room temperature, monolithic interferometer, photon noise limited performance
• Data automatic pipeline reduction, telemetry: limited flow < 100 kb/day
Phase A completed, April 2007
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Space / Ground
space ground
Observation photometry spectrometry
Max. degree 2 3
Targets magnitude
dim bright
Main differences between space-borne and ground-based observations
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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
Inversion 4 times more precise with Doppler data
low frequency noise+
l=3 modes
Gab
riel
et a
l 199
8
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Complementary observations
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
Complementary ground-based observations are necessary - to measure fundamental parameters- to improve the modelling
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Comparison
CoRoT Kepler SONG SIAMOIS2 eyes
diam = 12°10° x 10°
(Cygnus-Lyra)|| < 30° < 45°
Duty cycle 92 % ~ CoRoT ~ 85 % ~ 90 %
5-day perf. 0.6 ppm > 1.2 ppm 2-20 cm/s
Max obs. 5 months 4 years 3 months 3 months
Magnitude > 6 > 9 < 7
# targets 28 Up to 40 : 4 yrUp to 160 : 1 yrUp to 1000 : 90
d
> 30
# solar-like 4 7
Status In operation Launch = 11/ 2008
Phase 0Prototype >
2012
Phase A is OK2012 at Dome C
Instrument cost
65 M€ > 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 > 90% during 84% of the time Average number of consecutive clear days: 6.8 days
Clear sky fraction measured by Eric Aristidi (2006 winter)
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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 runModelling: 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 runPrecision on the eigenfrequency measurement: 0.10 – 0.25 Hz (Libbrecht 1992)
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Conclusion
Space-borne observations = photometric observationsCoRot unique resultsKepler not primilarly specified for asteroseismology
sensitivity for solar-like oscillations?very dim targets uncertainty on fundamental parameters
Ground-based observations = Doppler observationsmeasurement 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 asteroseismology3-month continuous observation with duty cycle
~ 90%High performance with a 40-cm collectorBetter performance than a 6-site network
http://siamois.obspm.fr
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Everything is OK for SIAMOIS
Risk ٧ - CFHT/FTS; GONG helioseismic network- Scientific program
Cost ٧ - Construction < 1 M€- Running cost << network
Logistics ٧ - Automatic instrument; simple setup- Limited operations; low data flow
- Phase A completed- Scientists, engineers, SC at work! http://siamois.obspm.fr ٧
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Budget
SIAMOIS Network
Site 1 site At least 6 sites for similar performance
Construction 860 ME ~ 6 ME
Running cost for 3 months
~ 750 kE / number of projects
600 kE (according to GONG, WET networks)
Observation 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% ! Scientific specification #1 : duty cycle > 85%
Polar night = 3 months 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
FT: simple installation and setup at Dome C
Echelle spectrometer (as HARPS)
tel
Current telescope at Dome C /Telescope available in the near future for long duration observation= dedicated small telescopes
FT
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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
• 2007thermo-mechanical analysisphase A
• 2008-2010PDRFDR integration
• 2010-2011testssummer campaign: Dome C
• 2012
First winterover at Dome C
Budget ~ 860 k€ << budget for an equivalent 6-site network
LESIA (Obs. Paris), IAS (Orsay), LUAN (Nice),
OMP (Toulouse) + SESO
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Performance
Photon noise limited performance, SIAMOIS at Dome C, 40-cm telescope, 120 hours with 90 % duty cycle, mV = 4 SNR on circumpolar targets
Mo
sse
r e
t al 2
003
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Fourier tachometer
• Another advantage: multiplex advantage simultaneous observations of several targets
First step: small telescope + FTThen: multi-targets observation = small telescopes + 1 FT
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Duty cycle at Dome C
Resulting duty cycle (bright targets) > 90% during 90 days
Polar night = 100 nights
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Asteroseismology after COROT
1 - single-site runs, short runs2 - 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: eigenfrequency precision = 0.2 Hz
continuous observations ( > 80 %) long duration (T > 2.5 months)
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SIAMOIS