Granada: /04/ 08Spectroscopy at Dome C1 SIAMOIS : asteroseismic observations after CoRoT: the need for spectroscopic measurements Benoit Mosser - LESIA (presented by Jean-Pierre Maillard, IAP)

Granada: /04/ 08Spectroscopy at Dome C2 Outline 1.Asteroseismology -Photometric observations with CoRoT -Spectroscopic results from ground (HARPS, …) 2.Performance comparison -Photometric measurements -Doppler measurements 3.Doppler measurements -Grating spectrometer -Fourier tachometer 4. SIAMOIS -Principle -Scientific program -Schedule

Granada: /04/ 08Spectroscopy at Dome C3 Asteroseismology purpose Age determination~ a few % Stellar radii ( impact for exoplanet radii )~ a few % Stellar composition Diagnostic of convective cores Depth of convection and of second helium ionization zones Mode excitation mechanisms (convection) Rotation and internal structure Specification: eigenfrequency resolution d ν = 0.2 μHz  continuous observations (  > 80 %)  long duration ( d ν = 1/T) (T > 2.5 months)

Granada: /04/ 08Spectroscopy at Dome C4 CoRoT launched on December 27 th, 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 was developped and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA, Germany and Spain

CoRoT light curves Granada: /04/ 08Spectroscopy at Dome C5 Variability below the level over 20 days of a 6th magnitude F star Typically 10  in 30 s Typical CoRoT light curve  Photon noise limited performance ~ 1 ppm  150 days  Duty cycle ~ 92%

Granada: /04/ 08Spectroscopy at Dome C6 Photometry (1) HD 49933, mV=5.7, F5V, observed during the initial run (60 days) Mode amplitudes ~ 1 few ppm  observation of p-mode oscillations in solar-like stars not achievable by photometric ground-based measurements

Granada: /04/ 08Spectroscopy at Dome C7 Photometry (2) Stellar granulation: important contribution at low frequency  limits the spectrum SNR for f < 2 mHz HD , mV=6.7, F2V, first long run (150 days)

Granada: /04/ 08Spectroscopy at Dome C8 Ground-based observations solar-like oscillations in solar-like stars - ESO 3.6-m - AAT - Euler telescope - OHP + 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

Granada: /04/ 08Spectroscopy at Dome C9 Spectroscopic result (1) Procyon, 10-day network observation (11 observatories, Jan. 2007)  Identification of mixed modes  Definitely a post-MS star Mosser et al 2008, A&A 478, 197 Bedding et al 2008, in preparation Day aliases (11.57 Hz) still present; too short duration compared to stellar rotation period

Granada: /04/ 08Spectroscopy at Dome C10 Spectroscopic result (2) HD ; F6V ; mV = 4.8 Old star of the thick galactic disk 5 days observation with HARPS duty cycle 40% Stellar modelling beforewith asteroseismic constraints L/Lo1.40 ± ± M/Mo 0.88 ± ± R/Ro 1.04 ± ± 0.02 T (K)6070 ± ± 45 Fe/H  0.60 ± 0.10  0.55 ± 0.05 Age (Gyr)10.5 ± ± 0.3 Precision still hampered by poor frequency resolution and duty cycle Mosser et al 2008, submitted to A&A

Granada: /04/ 08Spectroscopy at Dome C11 Principle : photon noise limited performances - Q quality factor of the spectrum - N e number of photoelectrons collected Q depends on: - the spectral type and the v.sini (rotation) of the star - the type of instrument GS: grating spectrometer FS: Fourier Transform spectrometer Doppler asteroseismometry

Granada: /04/ 08Spectroscopy at Dome C12 The quality factor Q gives a measure of the: - number - depth - width of the lines in the stellar spectrum Q # dln A /dln Quality factor Better Q factor for cooler stars Better performances in the blue part of the visible spectrum Supposes a high resolving power (~ ) of the grating spectrometer

Granada: /04/ 08Spectroscopy at Dome C13 Photometry Spectrometry Q = stellar oscillation quality factor Oscillation amplitudes 1 ppm  10 cm/s Comparison: Photometry/Spectrometry TargetQuality factor Photometry hyp: N e,p ~ mV ~ 6 Tachometry with N e,v ~ N e,p / 3 mm Type K low vsini ppm0.36 m/s3 Type F vsini = 12 km/s 5001 ppm1.1 m/s5 Photometric observations: dimmer targets, or smaller telescope 1 ppm sensitivity require space-borne observations

Granada: /04/ 08Spectroscopy at Dome C14 Doppler / photometry on the Sun Solar granulation noise: photometric observations 50 times noisier at low frequency than Doppler measurements

Granada: /04/ 08Spectroscopy at Dome C15 Granulation noise

Granada: /04/ 08Spectroscopy at Dome C16 l=3 modes l=3 modes have higher visibility in spectroscop y Small separation

Granada: /04/ 08Spectroscopy at Dome C17 Doppler / photometry on the Sun Inversion 4 times more precise with Doppler data low frequency noise + l=3 modes  Gabriel et al 1998 Core size determination

Granada: /04/ 08Spectroscopy at Dome C18 Space / Ground spaceground Observationphotometryspectrometry Max. degree2 3 Targets magnitudeDim Bright Spectral typeT > T sun Any v sin i-- < 15 km/s Inversion14 time more precise

Granada: /04/ 08Spectroscopy at Dome C19 Fourier transform Seismometry: The Doppler signal is retrieved from the interferogram of the stellar spectrum Fourier Transform Seismometry

Granada: /04/ 08Spectroscopy at Dome C20 FT seismometry successfully tested with the FTS at CFHT Procyon Mosser et al. 1998, A&A 340, 457 Jupiter Mosser et al. 2000, Icarus 144, 104 Fourier Transform Seismometry FTS at CFHT: repeated scan of one selected fringe of the interferogram shift of the fringe signal with time  Doppler signal

Granada: /04/ 08Spectroscopy at Dome C21 ( Mosser, Maillard, Bouchy 2003, PASP 115, 990) Q increases with - wavenumber   - working path difference  opt - fringe contrast C FS: quality factor A high fringe contrast C requires a narrow bandwidth To be compatible with a high Ne factor requires a dispersion of the fringes (post-disperser) = many adjacent narrow bandwiths with

Granada: /04/ 08Spectroscopy at Dome C22 Fourier transform seismometry with post-dispersion The Doppler signal is searched in the interferogram of each spectral element defined by the post- disperser FS: Q with post-dispersion Q factor as a function of the post-dispersion resolution and the spectral type for 3 vsini

Granada: /04/ 08Spectroscopy at Dome C23 GS / FS FS: post-dispersion resolution R~ 1000 GS > FS if reference = ThAr lamp (Mosser et al. 2003) GS ~ FS if reference = iodine cell δv(GS) / δv(FS) as a function of v sini and T of the star GS: HARPS (ref = ThAr lamp) R ~

Granada: /04/ 08Spectroscopy at Dome C24 GS / FS GSFS Input Fiberdouble scrambler ( /400) 1"~ 6 m/s simple scrambler ( /100) 1" ~ 1 cm/s Quality factor Q GS = Q(Q *, R)Q FS = Q(Q *, R pd ) Resolution R ~ 10 5 Path difference ~1 cm R pd ~1000 Grating ~ 10 x 40 cmTwo ~5x5 cm CCD4k x 2k1k x 256 FS: smaller and simpler instrument than a GS monolithic interferometer = no moving parts (SIAMOIS concept)  possible installation and setup at Dome C

Granada: /04/ 08Spectroscopy at Dome C25 A Fourier Spectrometer dedicated to asteroseismology with no moving parts to be installed at Dome C behind a 40-cm telescope phase A completed P.I. B. Mosser 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 = Système Interférentiel A Mesurer les OscIllations Stellaires

Granada: /04/ 08Spectroscopy at Dome C26 SIAMOIS performances at Dome C Photon noise limited performances SIAMOIS, at Dome C, 40-cm telescope, 120 hours with 95% duty cycle, mV = 4 ‘‘SNR’’ on circumpolar targets

SIAMOIS performances at Dome C Granada: /04/ 08Spectroscopy at Dome C27 SIAMOIS with post-disperser R = 1000 at Dome C for 3 solar-like stars

Granada: /04/ 08Spectroscopy at Dome C28 Targets 1)K, G, F, class IV & V targets 2)Red giants 3)Delta-Scuti, gamma Dor, PMS… Since long-duration observations are required, a 40-cm telescope provides already a scientific program on p-mode oscillation in solar-like targets as large as the CoRoT program

Granada: /04/ 08Spectroscopy at Dome C29 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)  Scientific program for more than 6 winterings COROT  Program complementary to CoRoT

Granada: /04/ 08Spectroscopy at Dome C30 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)

Granada: /04/ 08Spectroscopy at Dome C31 Duty cycle Better performance at Dome C compared to a 6-site network (Mosser & Aristidi 2007, PASP)

Granada: /04/ 08Spectroscopy at Dome C32 SIAMOIS 40-cm telescope small size, low cost, easy ‘antarctization’, dedicated to the project Phase A completed, April 2007 Interferometer fiber fed Mach Zehnder interferometer, operated at room temperature, monolithic no moving parts, photon noise limited performance Data automatic pipeline reduction, telemetry: limited flow < 100 kb/day

Granada: /04/ 08Spectroscopy at Dome C33 Simulations F6V star, mV = 4.5, vsini = 5 km/s, 90-day long run Modelling: stochastic excitation + intrinsic damping  Lorentzian profiles (Anderson et al 1990) l =

Granada: /04/ 08Spectroscopy at Dome C34 Simulations F6V star, mV = 4.5, vsini = 5 km/s, 90-day long run Precision on the eigenfrequency measurement: 0.10 – 0.25  Hz (Libbrecht 1992) l = Longer lifetimes at low frequency  clear multiplets

Granada: /04/ 08Spectroscopy at Dome C35 Fourier tachometer Another advantage: multi-object advantage  simultaneous observations of several targets First step: small telescope + FT Then: multi-targets observation = small telescopes + 1 FT

Granada: /04/ 08Spectroscopy at Dome C36 Planning & budget < 2006 principle: monolithic Fourier Tachometer 2007 thermo-mechanical analysis phase A PDR FDR integration tests summer campaign: Dome C 2013 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

Granada: /04/ 08Spectroscopy at Dome C37 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 targets However, a dedicated telescope would be required

Granada: /04/ 08Spectroscopy at Dome C38 Other projects: KEPLER NASA; launch = nov 2008 High precision photometry a few fields reserved for asteroseismology CoRoT  Kepler : tel. 27 cm  95 cm orbitpolar  L2 + duty cycle in L2 - sensitivety (mV > 9), radiations in L2 ?exact scientific case for asteroseismology? 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.

Granada: /04/ 08Spectroscopy at Dome C39 SONG Project currently in phase 0 Danish asteroseismology centre, Aarhus University Network of 6 to 8 small telescopes (60  80 cm) Echelle spectrometer + iodine cell Expected schedule: 1 prototype for >> 2012

Granada: /04/ 08Spectroscopy at Dome C40 Comparison CoRoTKeplerSONGSIAMOIS 2 eyes diam = 12° 10° x 10° (Cygnus-Lyra) |  | < 30°  <  45° Duty cycle 92 %~ CoRoT~ 85 %~ 90 % 5-day perf. 0.6 ppm> 1.2 ppm2-20 cm/s Max obs. 5 months  4 years3 months Magnitude > 6> 9< 7 # targets 28Up to 40 : 4 yr Up to 160 : 1 yr Up to 1000 : 90 d > 30 # solar-like 47 Status In operationLaunch = 11/ 2008 Phase 0 Prototype > 2012 Phase A is OK 2013 at Dome C Instrument cost 65 M€> 6 M€ (6 tel)0.86 M€ (1 tel) 1.02 M€ (2 tel)

Granada: /04/ 08Spectroscopy at Dome C41 Conclusions Space-borne observations = photometric observations CoRot unique results Kepler not primarily specified for asteroseismology sensitivity for p-mode oscillations under question very dim targets  uncertainty on fundamental parameters Ground-based observations = Doppler observations measurement of modes up to degree l = 3 much less low frequency noise  much better inversion and modelling observation of low mass stars Networkvery late schedule, complex organization Dome C= unique site for asteroseismology 3-month continuous observation with duty cycle ~ 90% High performance with a 40-cm collector Better performance than a 6-site network