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