SIAMOIS : asteroseismic observations after CoRoT: the need for spectroscopic measurements

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)


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


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)


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


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%


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


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)


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


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


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


• 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


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


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


Doppler / photometry on the Sun

Solar granulation noise: photometric observations 50 times noisier at low frequency than Doppler measurements


Granulation noise


l=3 modes

l=3 modes have higher visibility in spectroscopy

Small separation


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


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


Fourier transformSeismometry:The Doppler signal is retrieved from the interferogram of the stellar spectrum

Fourier Transform Seismometry


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


(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


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


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


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


• 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


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


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


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


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


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)


Duty cycle

Better performance at Dome C compared to a 6-site network(Mosser & Aristidi 2007, PASP)


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


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


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


Fourier tachometer

• Another advantage: multi-object advantage simultaneous observations of several targets

First step: small telescope + FTThen: multi-targets observation = small telescopes + 1 FT


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


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


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.


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


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)


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

SIAMOIS : asteroseismic observations after CoRoT: the need for spectroscopic measurements

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