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Benoît Mosser, for the SIAMOIS teamhttp://siamois.obspm.fr/

Ground-based Doppler asteroseismology after CoRoT and Kepler

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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)

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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