March 21, 2006 SONG workshop 1/27

SIAMOIS Sismomètre Interferentiel A Mesurer les Oscillations des Intérieurs Stellaires

An asteroseismic network with 1 site... in Antarctica

Benoît Mosser, Tristan Buey, Claude Catala Michel Auvergne, Thierry Appourchaux, Annie Baglin, Caroline Barban, François Bouchy,

Stéphane Charpinet, Marc-Antoine Dupret, Marie-Jo Goupil, Jean-Pierre Maillard, Eric Michel, Reza Samadi, François-Xavier Schmider, Frédéric Thévenin, Gérard Vauclair et al.

 Observatoire de Paris/LESIA, IAP, IAS, UNSA/LUAN, OMP/LATT, OCA

March 21, 2006 SONG workshop 2/27

SUMMARY

• Which program in asterosismology after COROT ?

• Dome C in Antarctica

• SIAMOIS: principle

• SIAMOIS: performances (/ SONG)

• Project: organisation, science

March 21, 2006 SONG workshop 3/27

Ground-based observations, 2006

Ground-based asteroseismic observations remain limited by the window effect

March 21, 2006 SONG workshop 4/27

Ground-based observations, 2006

Even with bi-sites observations

Continuous observations are required for precise structure modelling

Kjeldsen et al 2005

March 21, 2006 SONG workshop 5/27

In 2009, end of COROT

will have done a considerable work !

And after that ???

March 21, 2006 SONG workshop 6/27

Photometry / spectrometry

• Spectrometry less sensitive to granulation than photometry

• Visibility of l = 3 modes enhanced about ~ 3 times in spectometry

Small separation between modes with degrees 1 et 3

Ground-based measurements = spectrometric observationsNecessarily: continuity, long duration network or Antarctica

March 21, 2006 SONG workshop 7/27

Dome C

• Concordia station, Italy + France

75°06’ south, 123°21’ east

• Average temperatures

40°C in summer

60°C in winter• Slow wind• Rare precipitations:

2 to 10 cm snow/year

Polar night: 3 months

March 21, 2006 SONG workshop 8/27

Duty cycle > 90 %during 3 months in winter (K. Agabi)

March 21, 2006 SONG workshop 9/27

(First) observations at Dome C

Specifications for observations at Dome C

• integrated project- has to be fully tested before installation in Antarctica- with limited setup

• small size telescope- pioneering project

• project has to be fully automatic, ~ spatial condition- human intervention limited to routine, or survival - mass, power, telemetry: limited values

• scientific programme has to be- ambitious- unfeasible elsewhere- to make sense after COROT

March 21, 2006 SONG workshop 10/27

Observations at Dome C

-1- dedicated asteroseismometerwith a small size telescopefirst wintering in 2010

-2- 2-m class telescope + spectropolarimeter

• IPEV (Institut Paul-Emile Victor)- in charge of the Concordia base; wintering since 2005- supervises scientific projects

• INSU (National Institute for Astronomy)/ Antarctic group- promotes observations at Dome C- has to identify pioneering projects in astronomy

• PNPS (National programme for stellar physics)- promotes the rapid development of an asteroseismometer at Dome C

March 21, 2006 SONG workshop 11/27

• Principle (Bouchy et al. 2001): photon noise limited performances

• An asteroseismometer has to be extremely stable and efficient

- quality factor Q - number of photoelectrons Ne

• Q depends on:- the spectral type and rotation of the star- the instrument

GS: grating spectrometerFS: Fourier Transform spectrometer

Doppler asteroseismometry

March 21, 2006 SONG workshop 12/27

The quality factor gives a measure of the:- number- depth- widthof the stellar lines

Q # dln A /dln

Stellar quality factor

Cool stars are favoredBetter performances in the blue part of the visible spectrum

March 21, 2006 SONG workshop 13/27

The real quality factor depends on the resolution R of the spectrometer

A high resolution requires a narrow entrance slit as well as a large spectrometer

R # f / d

Seismology with a GS

Grating spectrometer: necessarily a large instrument

March 21, 2006 SONG workshop 14/27

Fourier transformSeismometryThe Doppler signal is searched in the interferogram of part of the stellar spectrum

FS: seismometry by TF

March 21, 2006 SONG workshop 15/27

FT seismometry successfully tested with the FTS at CFHT

Procyon Mosser et al. 1998, A&A 340, 457

JupiterMosser et al. 2000, Icarus 144, 104

Sismometry by TF

• FTS at CFHT: scan of one fringe• Dedicated instrument: simultaneous scan of the fringe signal

March 21, 2006 SONG workshop 16/27

(Mosser et al. 2003, PASP 115, 990)

•Q increases with

- wavenumber

- working path difference opt

- fringe contrast C• A high fringe contrast C requires a narrow bandwidth

… in contradiction with the specification on Ne

FS: quality factor

It is necessary to observe with a post-dispersive device

avec

March 21, 2006 SONG workshop 17/27

Fourier transform seismometry with post-dispersion

The Doppler signal is searched in the interferogram of each spectral element defined by the post-dispersion

FS: post - dispersion

March 21, 2006 SONG workshop 18/27

FS / GS

GS FSFiber double scrambler ( /400)

1"~ 6 m/s

simple scrambler ( /100)

1" ~ 1 cm/s

Quality factorQGS = Q(Q* , R) QFS = Q(Q* , Rpd)

Resolution Dispersion R ~ 105 -----

Post-dispersion Post-dispersion Rpd ~1000

Interference Grating ~ 10 x 40 cm Path difference 1 cm

CCD 4k x 2k 1k x 256

GS: smaller and simpler instrument,monolithic interferometer, no moving parts

possible installation and setup in Antarctica

March 21, 2006 SONG workshop 19/27

Antarctic / network

Projects SONG SIAMOIS

Equatorial network Concordia, Dome C

# sites for

duty cycle > 90%

At least 6 1

Technology; redundancy

?

Site: duty cycle, altitude

Site

Budget N1 k€ by site; N2 sites

N1 x N2 k€

850 k€

On-site maintenance N2 sites ~ space project

Complementary projects

March 21, 2006 SONG workshop 20/27

Performances: GS / FS

GS: HARPS (ref = ThAr lamp) R ~ 90000

FS: SIAMOIS; post-dispersion providing a

spectral resolution R~ 1000.

GS > FS if reference = ThAr lamp (Mosser et al. 2003)GS ~ FS if reference = iodine cell

March 21, 2006 SONG workshop 21/27

GS: performances at Dome C

Photon noise limited performancesSIAMOIS, at Dome C, 40-cm telescope, 120 hours with 95% duty cycle, mV = 4 ‘‘SNR’’ on circumpolar targets

March 21, 2006 SONG workshop 22/27

Targets

Observable targets with SIAMOIS and a

40-cm telescope dedicated to the

project

• 40-cm telescope:- 7 targets, type: F, G, K class: IV & V

- many red giants; Scuti (v sin i < 20 km/s)

Scientific programme for more than 6 winterings

COROT

March 21, 2006 SONG workshop 23/27

Targets

1) K, G, F, class IV & V targets

March 21, 2006 SONG workshop 24/27

Targets

1) K, G, F, class IV & V targets2) red giants3) delta-Scuti

March 21, 2006 SONG workshop 25/27

Instrument

• 40-cm telescope low cost, easy ‘antartization’, dedicated to the project • Interferometer monolithic instrument

no moving parts, reduced sizefiber fed

• Post-dispersion efficiency, photon noise limited performances

March 21, 2006 SONG workshop 26/27

Planning

• 2004- design

• 2006- thermo-mechanical analysis

• 2007- PDR- FDR

• 2008- integration

• 2009- tests- summer campaign: Dome C

• 2010

- first winterover at Dome C

Laboratories: LESIA (Obs. Paris), IAS (Orsay), LUAN (Nice), LATT (Toulouse)

SIAMOIS InterferometerJP Amans, GEPI, Obs Paris

March 21, 2006 SONG workshop 27/27

• Dome C: a unique site for asterosismology3-month continuous observation with duty cycle ~ 90%

• A specific scientific program after• High performances with a 40-cm collector

– Pioneering project at Dome C– FT seismometry: suitable concept for installation and setup at Dome C– Multiplex advantage of FT spectrometry

Conclusion

‘‘Big science’’  at Dome C with a budget < 1 ME