September 17, 20072nd ARENA Conference Postdam1 Asteroseismology, from space and from the ground...

September 17, 2007 2nd ARENA Conference Postdam 1

Asteroseismology, from space

and from the ground

Benoît Mosser Observatoire de Paris/LESIA


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


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)


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


CoRoT « Eyes »

0°

30°

60°

90°

120°

150°

180°

210°

240°

270°

300°

330°

0h2h4h6h8h10h12h14h16h18h20h22h

CoRoT eyes: =0, =6h50 and 18h50


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


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


Example of light curves

A 6th mag F-type star showing daily variability below the 10-3 level

Typically 10 in 30 s


Light curve

An 9th magnitude suspected delta Scuti showing beat phenomena at a few 10-3


Light curve

An 8th magnitude B star in an eclipsing binary


A 7th magnitude giant F star showing very low dispersion of ~10-4

Quiet target


HD 49933

1st solar-like target, initial run, 60 days

Simulations: Baudin et al. 06

Photon noise

Granulation


HD 49933, observed

Mosser et al. 2005, 10 days with HARPS, duty cycle ~ 23%


Scuti

Example of an 8th magnitude delta Scuti observed with CoRoT.

The red line illustrates common lowest detection limit from the ground.


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


Single/multi-sites observation


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


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.


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.


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)


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


• 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),


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


Space / Ground

space ground

Observation photometry spectrometry

Max. degree 2 3

Targets magnitude

dim bright

Main differences between space-borne and ground-based observations


Doppler / photometry

Solar granulation noise


Granulation noise


l=3 modes

l=3 modes visible in spectroscopy

Small separation


Doppler / photometry

Inversion 4 times more precise with Doppler data

low frequency noise+

l=3 modes

Gab

riel

et a

l 199

8


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


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)


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)


Duty cycle

Better performance at Dome C compared to a 6-site network(Mosser & Aristidi 2007, PASP)


Simulations

F6V star, mV = 4.5, vsini = 5 km/s, 90-day long runModelling: stochastic excitation + intrinsic damping (Anderson et al 1990)


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)


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


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


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


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


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


Possible targets

Observable targets (solar-like stars with

solar-like oscillations) with SIAMOIS and a

40-cm telescope dedicated to the project


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


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


Fourier tachometer

• Another advantage: multiplex advantage simultaneous observations of several targets

First step: small telescope + FTThen: multi-targets observation = small telescopes + 1 FT


Duty cycle at Dome C

Resulting duty cycle (bright targets) > 90% during 90 days

Polar night = 100 nights


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)


SIAMOIS

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September 17, 20072nd ARENA Conference Postdam1 Asteroseismology, from space and from the ground...

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