Granada:16 - 18/04/ 08 Spectroscopy at Dome C 1
SIAMOIS : asteroseismic observations after CoRoT: the need for spectroscopic measurements
Benoit Mosser - LESIA (presented by Jean-Pierre Maillard, IAP)
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 2
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:16 - 18/04/ 08 Spectroscopy at Dome C 3
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 dν = 0.2 μHz
continuous observations ( > 80 %) long duration (dν = 1/T) (T > 2.5 months)
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 4
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 was developped and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA, Germany and Spain
CoRoT light curves
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 5
Variability below the 10-3 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:16 - 18/04/ 08 Spectroscopy at Dome C 6
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:16 - 18/04/ 08 Spectroscopy at Dome C 7
Photometry (2)
Stellar granulation: important contribution at low frequency limits the spectrum SNR for f < 2 mHz
HD 181420, mV=6.7, F2V, first long run (150 days)
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 8
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
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 9
Spectroscopic result (1)
Procyon, 10-day network observation (11 observatories, Jan. 2007) Identification of mixed modes Definitely a post-MS starMosser et al 2008, A&A 478, 197Bedding 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 10
Spectroscopic result (2)
HD 203608 ; F6V ; mV = 4.8Old star of the thick galactic disk5 days observation with HARPSduty cycle 40%
Stellar modellingbefore with asteroseismic
constraints
L/Lo 1.40 ± 0.13 1.38 ± 0.045M/Mo 0.88 ± 0.07 0.928 ± 0.028R/Ro 1.04 ± 0.12 1.06 ± 0.02T (K) 6070 ±150 6051 ± 45 Fe/H 0.60 ± 0.10 0.55 ± 0.05 Age (Gyr) 10.5 ± 4 7.2 ± 0.3
Precision still hampered by poor frequency resolution and duty cycle
Mosser et al 2008, submitted to A&A
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 11
• 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
Doppler asteroseismometry
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 12
The quality factor Q gives a measure of the:- number- depth- widthof the lines in the stellar spectrum
Q # dln A /dln
Quality factor
Better Q factor for cooler starsBetter 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 13
Photometry
Spectrometry Q = stellar oscillation quality factor
Oscillation amplitudes 1 ppm 10 cm/s
Comparison: Photometry/Spectrometry
Target Quality factor
Photometry
hyp: Ne,p ~ 1012
mV ~ 6
Tachometrywith Ne,v ~ Ne,p / 3
m
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
Photometric observations: dimmer targets, or smaller telescope1 ppm sensitivity require space-borne observations
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 14
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 15
Granulation noise
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 16
l=3 modes
l=3 modes have higher visibility in spectroscopy
Small separation
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 17
Doppler / photometry on the Sun
Inversion 4 times more precise with Doppler data
low frequency noise+
l=3 modes
Gab
riel
et a
l 199
8
Core size determination
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 18
Space / Ground
space groundObservation photometry spectrometry
Max. degree 2 3Targets magnitude
Dim Bright
Spectral type T > Tsun Anyv sin i -- < 15 km/sInversion 1 4 time more
precise
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 19
Fourier transformSeismometry:The Doppler signal is retrieved from the interferogram of the stellar spectrum
Fourier Transform Seismometry
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 20
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
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:16 - 18/04/ 08 Spectroscopy at Dome C 21
(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:16 - 18/04/ 08 Spectroscopy at Dome C 22
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:16 - 18/04/ 08 Spectroscopy at Dome C 23
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 ~ 115000
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 24
GS / FS
GS FSInput Fiber double scrambler ( /400)
1"~ 6 m/s
simple scrambler ( /100)
1" ~ 1 cm/s
Quality factorQGS = Q(Q* , R) QFS = Q(Q* , Rpd)
Resolution R ~ 105 Path difference ~1 cm
Rpd ~1000
Grating ~ 10 x 40 cm Two ~5x5 cm
CCD 4k x 2k 1k 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 25
• 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:16 - 18/04/ 08 Spectroscopy at Dome C 26
SIAMOIS 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
SIAMOIS performances at Dome C
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 27
SIAMOIS with post-disperser R = 1000 at Dome C for 3 solar-like stars
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 28
Targets
1) K, G, F, class IV & V targets2) Red giants3) 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:16 - 18/04/ 08 Spectroscopy at Dome C 29
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:16 - 18/04/ 08 Spectroscopy at Dome C 30
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:16 - 18/04/ 08 Spectroscopy at Dome C 31
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 32
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:16 - 18/04/ 08 Spectroscopy at Dome C 33
Simulations
F6V star, mV = 4.5, vsini = 5 km/s, 90-day long runModelling: stochastic excitation + intrinsic damping Lorentzian profiles (Anderson et al 1990)
l = 2 0 3 1
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 34
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)
l = 2 0 3 1
Longer lifetimes at low frequency clear multiplets
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 35
Fourier tachometer
• Another advantage: multi-object advantage simultaneous observations of several targets
First step: small telescope + FTThen: multi-targets observation = small telescopes + 1 FT
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 36
Planning & budget < 2006
principle: monolithic Fourier Tachometer
• 2007thermo-mechanical analysisphase A
• 2009-2011PDRFDR integration
• 2011-2012testssummer 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:16 - 18/04/ 08 Spectroscopy at Dome C 37
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 targetsHowever, a dedicated telescope would be required
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 38
Other projects: 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.
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 39
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 2012-2013
>> 2012
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 40
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 OK2013 at Dome C
Instrument cost
65 M€ > 6 M€ (6 tel) 0.86 M€ (1 tel)1.02 M€ (2 tel)
Granada:16 - 18/04/ 08 Spectroscopy at Dome C 41
Conclusions
Space-borne observations = photometric observationsCoRot unique resultsKepler not primarily specified for asteroseismology
sensitivity for p-mode oscillations under question very dim targets uncertainty on fundamental parameters
Ground-based observations = Doppler observationsmeasurement 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 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