SIAMOIS : asteroseismic observations after Co. Ro. T: the need for spectroscopic measurements Benoit Mosser - LESIA Granada: 16 - 18/04/ 08 (presented by Jean-Pierre Maillard, IAP) Spectroscopy at Dome C 1
Outline 1. Asteroseismology - Photometric observations with Co. Ro. T - 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: 16 - 18/04/ 08 Spectroscopy at Dome C 2
Asteroseismology purpose • Age determination • Stellar radii (impact for exoplanet radii) • Stellar composition ~ a few % • Diagnostic of convective cores • Depth of convection and of second helium ionization zones • Mode excitation mechanisms (convection) • Rotation and internal structure Specification: Granada: 16 - 18/04/ 08 eigenfrequency resolution continuous observations long duration (dν = 1/T) Spectroscopy at Dome C dν = 0. 2 μHz (h > 80 %) (T > 2. 5 months) 3
Co. Ro. T • launched on December 27 th , 2006 • by Soyuz 2, from Baikonour, Kazakhstan • low Earth polar orbit, 896 km altitude • orbital period 6184 s (~1 h 43 mn, 162 m. Hz) • high precision photometry The Co. Ro. T space mission was developped and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA, Germany and Spain Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 4
Co. Ro. T light curves Typical Co. Ro. T light curve Photon noise limited performance ~ 1 ppm 150 days Duty cycle ~ 92% Typically 10 -4 in 30 s Variability below the 10 -3 level over 20 days of a 6 th magnitude F star Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 5
Photometry (1) HD 49933, m. V=5. 7, F 5 V, 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: 16 - 18/04/ 08 Spectroscopy at Dome C 6
Photometry (2) HD 181420, m. V=6. 7, F 2 V, first long run (150 days) Stellar granulation: important contribution at low frequency limits the spectrum SNR for f < 2 m. Hz Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 7
Ground-based observations • solar-like oscillations in solar-like stars - HARPS @ ESO 3. 6 -m - UCLES @ AAT - CORALIE @ Euler telescope - SOPHIE @ OHP + instruments @ SARG, Mc. D, Okoyama, Lick Oscillation detection Mode identification 2 -sites observation Network observation Stellar structure modelling Rotation, fine structure… Granada: 16 - 18/04/ 08 ٧ ٧ ٧ ~ 20 targets for ~ 12 targets 5 targets 1 target (Procyon) ~ 2 targets Observations limited to a few days insufficient precision Spectroscopy at Dome C 8
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: 16 - 18/04/ 08 Spectroscopy at Dome C 9
Spectroscopic result (2) HD 203608 ; F 6 V ; m. V = 4. 8 Old star of the thick galactic disk 5 days observation with HARPS duty cycle 40% Stellar modelling before L/Lo M/Mo R/Ro T (K) Fe/H Age (Gyr) with asteroseismic constraints 1. 40 ± 0. 13 0. 88 ± 0. 07 1. 04 ± 0. 12 6070 ± 150 -0. 60 ± 0. 10 10. 5 ± 4 1. 38 ± 0. 045 0. 928 ± 0. 028 1. 06 ± 0. 02 6051 ± 45 -0. 55 ± 0. 05 7. 2 ± 0. 3 Mosser et al 2008, submitted to A&A Precision still hampered by poor frequency resolution and duty cycle Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 10
Doppler asteroseismometry • Principle : photon noise limited performances - Q quality factor of the spectrum - Ne 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 Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 11
Quality factor The quality factor Q gives a measure of the: - number - depth - width of the lines in the stellar spectrum Q # dln A /dln l Better Q factor for cooler stars Better performances in the blue part of the visible spectrum Supposes a high resolving power (~ 100 000) of the grating spectrometer Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 12
Comparison: Photometry/Spectrometry Photometry Spectrometry Q = stellar oscillation quality factor Oscillation amplitudes Target 1 ppm 10 cm/s Dm Quality factor Photometry hyp: Ne, p ~ 1012 m. V ~ 6 Tachometry Type K low vsini 1500 1 ppm 0. 36 m/s 3 Type F vsini = 12 km/s 500 1 ppm 1. 1 m/s 5 with Ne, v ~ Ne, p / 3 Photometric observations: dimmer targets, or smaller telescope 1 ppm sensitivity require space-borne observations Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 13
Doppler / photometry on the Sun Solar granulation noise: photometric observations 50 times noisier at low frequency than Doppler measurements Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 14
Granulation noise Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 15
l=3 modes have higher visibility in spectroscopy Small separation Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 16
Doppler / photometry on the Sun Core size determination Granada: 16 - 18/04/ 08 Spectroscopy at Dome C Gabriel et al 1998 low frequency noise + l=3 modes Inversion 4 times more precise with Doppler data 17
Space / Ground space ground Observation photometry spectrometry Max. degree 2 3 Bright Targets magnitude Dim Spectral type T > Tsun v sin i -- Any < 15 km/s Inversion 1 4 time more precise Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 18
Fourier Transform Seismometry Fourier transform Seismometry: The Doppler signal is retrieved from the interferogram of the stellar spectrum Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 19
Fourier Transform Seismometry 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 • FTS at CFHT: repeated scan of one selected fringe of the interferogram • shift of the fringe signal with time Doppler signal Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 20
FS: quality factor with • Q (Mosser, Maillard, Bouchy 2003, PASP 115, 990) increases with - wavenumber s 0 - working path difference dopt - fringe contrast C • 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 Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 21
FS: Q with post-dispersion Fourier transform seismometry with post-dispersion The Doppler signal is searched in the interferogram of each spectral element defined by the postdisperser Q factor as a function of the post-dispersion resolution and the spectral type for 3 vsini Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 22
GS / FS GS: HARPS (ref = Th. Ar lamp) R ~ 115000 FS: post-dispersion resolution R~ 1000 δv(GS) / δv(FS) as a function of v sini and T of the star GS > FS if reference = Th. Ar lamp (Mosser et al. 2003) GS ~ FS if reference = iodine cell Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 23
GS / FS GS Input Fiber Quality factor Resolution FS double scrambler ( /400) 1"~ 6 m/s simple scrambler ( /100) 1" ~ 1 cm/s QGS = Q(Q* , R) QFS = Q(Q* , Rpd) R ~ 105 Path difference ~1 cm Rpd ~1000 Grating CCD ~ 10 x 40 cm Two ~5 x 5 cm 4 k x 2 k 1 k 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: 16 - 18/04/ 08 Spectroscopy at Dome C 24
SIAMOIS = Système Interférentiel A Mesurer les Osc. Illations Stellaires • 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), Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 25
SIAMOIS performances at Dome C Photon noise limited performances SIAMOIS, at Dome C, 40 -cm telescope, 120 hours with 95% duty cycle, m. V = 4 ‘‘SNR’’ on circumpolar targets Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 26
SIAMOIS performances at Dome C SIAMOIS with post-disperser R = 1000 at Dome C for 3 solar-like stars Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 27
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 Co. Ro. T program Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 28
Targets with a 40 -cm telescope COROT 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; d Scuti (v sin i < 20 km/s) ® Scientific program for more than 6 winterings ® Program complementary to Co. Ro. T Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 29
Clear sky fraction at Dome C Clear sky fraction measured by Eric Aristidi (2006 winter) Clear sky fraction > 90% during 84% of the time Average number of consecutive clear days: 6. 8 days Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 30
Duty cycle Better performance at Dome C compared to a 6 -site network (Mosser & Aristidi 2007, PASP) Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 31
SIAMOIS • 40 -cm telescope • Interferometer • Data small size, low cost, easy ‘antarctization’, dedicated to the project fiber fed Mach Zehnder interferometer, operated at room temperature, monolithic no moving parts, photon noise limited performance automatic pipeline reduction, telemetry: limited flow < 100 kb/day Phase A completed, April 2007 Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 32
Simulations l= 2 0 3 1 F 6 V star, m. V = 4. 5, vsini = 5 km/s, 90 -day long run Modelling: stochastic excitation + intrinsic damping Lorentzian profiles (Anderson et al 1990) Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 33
Simulations Longer lifetimes at low frequency clear multiplets l= 2 0 3 1 F 6 V star, m. V = 4. 5, vsini = 5 km/s, 90 -day long run Precision on the eigenfrequency measurement: 0. 10 – 0. 25 m. Hz (Libbrecht 1992) Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 34
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: 16 - 18/04/ 08 Spectroscopy at Dome C 35
Planning & budget < 2006 principle: monolithic Fourier Tachometer • 2007 thermo-mechanical analysis phase A • 2009 -2011 PDR FDR integration • 2011 -2012 tests summer campaign: Dome C • 2013 First winterover at Dome C LESIA (Obs. Paris), IAS (Orsay), LUAN (Nice), OMP (Toulouse) + SESO Budget ~ 860 k€ << budget for an equivalent 6 -site network Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 36
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: 16 - 18/04/ 08 Spectroscopy at Dome C 37
Other projects: KEPLER • NASA; launch = nov 2008 • High precision photometry • a few fields reserved for asteroseismology Co. Ro. T Kepler : tel. 27 cm 95 cm orbit polar L 2 + duty cycle in L 2 - sensitivety (m. V > 9), radiations in L 2 ? 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. Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 38
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 -2013 >> 2012 Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 39
Comparison Co. Ro. T Kepler SONG SIAMOIS 2 eyes diam = 12° 10° x 10° (Cygnus-Lyra) |d| < 30° d < - 45° Duty cycle 92 % ~ Co. Ro. T ~ 85 % ~ 90 % 5 -day perf. 0. 6 ppm > 1. 2 ppm Max obs. 5 months 4 years Magnitude >6 >9 <7 # targets 28 Up to 40 : 4 yr Up to 160 : 1 yr Up to 1000 : 90 d > 30 # solar-like 4 Status Instrument cost Granada: 16 - 18/04/ 08 In operation 2 -20 cm/s 3 months 7 Launch = 11/ 2008 Spectroscopy at Dome C Phase A is OK 2013 at Dome C > 6 M€ (6 tel) 65 M€ Phase 0 Prototype > 2012 0. 86 M€ (1 tel) 1. 02 M€ (2 tel) 40
Conclusions Space-borne observations = photometric observations Co. Rot Kepler unique results 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 Network very 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 http: //siamois. obspm. fr Granada: 16 - 18/04/ 08 Spectroscopy at Dome C 41
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