benoît mosser, for the siamois team siamois.obspm.fr
DESCRIPTION
Ground-based Doppler asteroseismology after CoRoT and Kepler. Benoît Mosser, for the SIAMOIS team http://siamois.obspm.fr/. Asteroseismology. What do we need after CoRoT, that Kepler, and hopefully PLATO, will not provide? - PowerPoint PPT PresentationTRANSCRIPT
Catania 09/08 SIAMOIS 1/26
Benoît Mosser, for the SIAMOIS teamhttp://siamois.obspm.fr/
Ground-based Doppler asteroseismology after CoRoT and Kepler
Catania 09/08 SIAMOIS 2/26
Asteroseismology
What do we need after CoRoT, that Kepler, and hopefullyPLATO, will not provide?
Doppler velocity(Space-borne observations are photometric)Provide additional informationMore precise for structure inversionGround-based
High duty cycle, continuous measurements Dome C in Antarctica provide excellent observation conditions
Scientific objectives require the observation of a few bright targetsfor convergence of very precise measurementsobserved with a small collector
Asteroseismic program at Dome Csimple, robust, with an easy setup
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Spectrometry
/ Photometry
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Granulation noise
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HD 49933 CoRoT/HARPS dataM
osser et al 2005
App
ourchaux et al 2008, in
press
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Additional Information
l =3 modes not visible in photometry
Granulation noise at low frequency
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Large and small separations
Small separation
1-3
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Doppler / photometry on the Sun
Inversion 4 times more precise with Doppler data
Low low-frequency noise+
l=3 modes
Cou
rtes
y T
hier
ry A
ppou
rcha
ux
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High duty cycle,
long duration time series
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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 (naked eye, Eric Aristidi, 2006 winter)
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Duty cycle: h_sun = -4°
Bad weatherOperations: telescope derotation…Sky brightness
Resulting duty cycle (bright targets) > 90% during 90 days
Mos
ser
& A
ristid
i 200
7
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Duty cycle: h_sun = -8°
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Duty cycle: h_sun = -13°
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Duty cycle at Dome C
Performance at Dome C compared to a 6-site network as GONG(Mosser & Aristidi 2007, PASP)
[GONG data]
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Scientific
program
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Scientific program
High-precision determination of the interior structure of nearby stars• Age determination ~ a few %• Stellar radii (impact for exoplanet radii) ~ a few %• Composition
Comparative study: photometry / Doppler• Convection, damping, excitation mechanisms• Diagnostic of convective cores; depth of convection and of
second Helium ionization zones
Classical pulsators• Non-linear physics, saturation effects, mode coupling• Stochastically excited modes
Slowly rotating targets • Rotation
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Simulations
F6V star, mV = 4, vsini = 5 km/s, 90-day long runModelling: stochastic excitation + intrinsic damping + SIAMOIS characteristics and performance
l = 2 0 3 1
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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)
l = 2 0 3 1
Longer lifetimes at low frequency clear multiplets
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Targets with a 40-cm telescope
Observable solar-like stars with p-mode
oscillations for a dedicated 40-cm
telescope
• 40-cm telescope:- 7 bright targets, type: F, G, K class: IV & V
- many red giants; Scuti (v sin i < 20 km/s) Enough targets for completing the scientific program in 3 to 6 winterings
[for all selected targetsSNR > 6 in 5 nights]
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Targets with a 40-cm telescope
Long duration observation
dedicated collector
Observable targets (solar-like stars with solar-like
oscillations) with SIAMOIS and a 40-cm telescope dedicated to the project
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With a 2-m telescope
• dimmer solar-like targets (e.g. star with exoplanets; Sylvie Vauclair’s cancelled talk)• ro Ap + any target with• doradus vsini < 20 km/s• scuti mV < 10.5• red giants
Out of the scope of SIAMOIS: white dwarfs and subdwarf B stars (too faint magnitude (1319), with a limited number of too broad spectral lines)Don Kurtz’talk; Gerard Vauclair’s cancelled presentation
For bright targets, dedicated small telescope For dimmer targets, shared larger telescope
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Conclusion
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Space / Ground
space groundObservation photometry spectrometry
Max. degree 2 3Targets magnitude faint brightv sin i < 20 km/sInversion 4 times more precise
Precise Doppler measurements on nearby bright targets
+ convergent measurements (interferometry, high resolution spectrometry…)
Determination of a sample of stellar standards
Insights into the physical laws governing stellar interiors
Photometry on faint targets, without any other precise measurements
Statistical approach
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Comparison
CoRoT Kepler PLATO SONG SIAMOIS2 eyes
diam = 12°10° x 10°
(Cygnus-Lyra)20° x 20° || < 30°
4 sites full sky < 45°
Duty cycle
92% ~ 100% ~ 100% (L2) ~ 85% ~ 90%
5-day perf.
0.6 ppm ~ ppm ~ ppm 2-20 cm/s
Max obs. 5 months < 4 years > 4 years 3 months 3 months
Magnitude
> 6 > 9 < 13 <7 < 7
# targets 28 Up to 40 : 4 yrUp to 160 : 1 yrUp to 1000 : 90
d
100 000 >100 > 30
# solar-like
4 ~ few 100 7
Status In operation Launch = 04/ 2009
Assessment study at ESA
Phase A fundedPrototype >
2011Network >
2014
Phase A is OK2013 at Dome
C
Instrument cost
65 M€ Class M project > 12 M€ (6 tel) 0.86 M€ (1 tel)1.02 M€ (2 tel)
Catania 09/08 SIAMOIS 25/26Granada:16 - 18/04/ 08
Doppler asteroseismology
Space-borne observations = photometric observationsMOST, CoRoT, Kepler, Brite, PLATO…
Ground-based observations = Doppler observations- less noise at low frequency- measurement of modes up to degree l= 3 - observation of bright stars very precise inversion and modelling- looking in great detail into nearby stars- identifying the physical processes
Dome C = unique site for asteroseismology3-month continuous observation with duty cycle ~ 90%
* High performance with a 40-cm collector * Scientific program with 40-cm and 2-m collectors
http://siamois.obspm.fr
Nex
t ta
lk
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Additional material
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Perspectives
Asteroseismology requires uninterrupted long-duration time series!
1 dedicated 40-cm telescope:- first season observation- fiber FOV = 5’’ (>> seeing) stellar magnitude < 5 for solar-like oscillations
< 7 for classical pulsators
2 or 3 dedicated small telescopes- next step simultaneous observations of 2 or 3 stars
2-m class telescope?-stellar magnitude < 8.5 for solar-like oscillations- increase of the number of reachable targets possibility to achieve specific observations in selected targetsHowever, a dedicated telescope would be required
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Fourier transformSeismometry:The Doppler signal is retrieved from the interferogram of the stellar spectrum
Fourier Transform Seismometry
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Photometry / activity
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Bright targets
Solar-like targets with solar-like oscillations [A scaled to (L/M)0.7]
- Scuti - Dor - PMS - Red giants
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An example
HD 203608, F8V, mV = 4.2
Observations with HARPS:
- 5 nights
- duty cycle ~ 40 %
- SNR = 5
Precision of interior structure
parameters improved by a
factor 3 to 10
Mosser
et
al 2
00
8