Prsentation PowerPoint

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SIAMOIS asteroseismic observations after CoRoT
the need for spectroscopic measurements
Benoit Mosser - LESIA (presented by
Jean-Pierre Maillard, IAP)
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Outline

• Asteroseismology
• Photometric observations with CoRoT
• Spectroscopic results from ground (HARPS, )
• Performance comparison
• Photometric measurements
• Doppler measurements
• Doppler measurements
• Grating spectrometer
• Fourier tachometer
• 4. SIAMOIS
• Principle
• Scientific program
• Schedule

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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? 0.2 µHz ? continuous observations (h gt
80 ) ? long duration (d? 1/T) (T gt 2.5
months)
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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 mHz)
• 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

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CoRoT light curves

• Typical CoRoT 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 6th magnitude F star
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Photometry (1)
HD 49933, mV5.7, 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
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Photometry (2)
HD 181420, mV6.7, F2V, first long run (150 days)
Stellar granulation important contribution at
low frequency ? limits the spectrum SNR for
f lt 2 mHz
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Ground-based observations

• solar-like oscillations in solar-like stars
• HARPS _at_ ESO 3.6-m
• UCLES _at_ AAT
• CORALIE _at_ Euler telescope
• SOPHIE _at_ OHP
• instruments _at_ SARG, McD, Okoyama, Lick

Observations limited to a few days
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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, AA 478, 197
• Bedding et al 2008, in preparation

Day aliases (11.57 Hz) still present too short
duration compared to stellar rotation period
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Spectroscopic result (2)
HD 203608 F6V mV 4.8 Old star of the thick
galactic disk 5 days observation with HARPS duty
cycle 40
Stellar modelling before with
asteroseismic constraints L/Lo 1.40
0.13 1.38 0.045 M/Mo 0.88 0.07 0.928
0.028 R/Ro 1.04 0.12 1.06 0.02 T (K) 6070
150 6051 45 Fe/H -0.60 0.10 -0.55 0.05
Age (Gyr) 10.5 4 7.2 0.3
Mosser et al 2008, submitted to AA
Precision still hampered by poor frequency
resolution and duty cycle
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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

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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
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Comparison Photometry/Spectrometry
Photometry Spectrometry Q stellar
oscillation quality factor Oscillation
amplitudes 1 ppm ?? 10 cm/s
Photometric observations dimmer targets, or
smaller telescope 1 ppm sensitivity require
space-borne observations
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Doppler / photometry on the Sun
Solar granulation noise photometric observations
50 times noisier at low frequency than Doppler
measurements
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Granulation noise
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l3 modes
l3 modes have higher visibility in spectroscopy
Small separation
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Doppler / photometry on the Sun
Core size determination
low frequency noise l3 modes
?
Inversion 4 times more precise with Doppler data
Gabriel et al 1998
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Space / Ground
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Fourier Transform Seismometry
Fourier transform Seismometry The Doppler signal
is retrieved from the interferogram of the
stellar spectrum
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Fourier Transform Seismometry
FT seismometry successfully tested with the FTS
at CFHT Procyon Mosser et al. 1998, AA 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

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FS quality factor
with

• (Mosser, Maillard, Bouchy 2003, PASP 115, 990)
• Q increases with
• wavenumber s0
• 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

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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 post-disperser
Q factor as a function of the post-dispersion
resolution and the spectral type for 3 vsini
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GS / FS
GS HARPS (ref ThAr lamp) R 115000
FS post-dispersion resolution R 1000
dv(GS) / dv(FS) as a function of v sini and T
of the star
GS gt FS if reference ThAr lamp (Mosser et al.
2003) GS FS if reference iodine cell
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GS / FS
FS smaller and simpler instrument than a GS
monolithic interferometer no moving parts
(SIAMOIS concept) ? possible
installation and setup at Dome C
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SIAMOIS Système Interférentiel A Mesurer les
OscIllations 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),

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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
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SIAMOIS performances at Dome C

SIAMOIS with post-disperser R 1000 at Dome C
for 3 solar-like stars
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Targets

• K, G, F, class IV V targets
• Red giants
• 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
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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 lt 20 km/s)
• Scientific program for more than 6 winterings

• Program complementary to CoRoT

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Clear sky fraction at Dome C
Clear sky fraction gt 90 during 84 of the time
Average number of consecutive clear days 6.8 days
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Duty cycle
Better performance at Dome C compared to a 6-site
network (Mosser Aristidi 2007, PASP)
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SIAMOIS

• 40-cm telescope small size, low cost,
  easy antarctization, dedicated to the project

• 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 lt 100 kb/day

Phase A completed, April 2007
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Simulations
l 2 0 3 1
F6V star, mV 4.5, vsini 5 km/s, 90-day long
run Modelling stochastic excitation intrinsic
damping ? Lorentzian profiles (Anderson et al
1990)
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Simulations
Longer lifetimes at low frequency ? clear
multiplets
l 2 0 3 1
F6V star, mV 4.5, vsini 5 km/s, 90-day long
run Precision on the eigenfrequency measurement
0.10 0.25 mHz (Libbrecht 1992)
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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
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Planning budget

• lt 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 ltlt budget for an equivalent
6-site network
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Perspectives

• Asteroseismology requires uninterrupted
  long-duration time series !
• 1 dedicated 40-cm telescope
• first season observation
• fiber FOV 5 (gtgt seeing)
• stellar magnitude lt 5 for solar-like
  oscillations
• lt 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 lt 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

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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 gt 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.

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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

gtgt 2012
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Comparison
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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 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