Transcript targets - siamois

Ground-based
Doppler asteroseismology
after CoRoT and Kepler
Benoît Mosser, for the SIAMOIS team
http://siamois.obspm.fr/
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Asteroseismology
What do we need after CoRoT, that Kepler, and hopefully
PLATO, will not provide?
Doppler velocity
(Space-borne observations are photometric)
Provide additional information
More precise for structure inversion
Ground-based
High duty cycle, continuous measurements
Dome C in Antarctica provide excellent observation conditions
Scientific objectives require the observation of a few bright targets
for convergence of very precise measurements
observed with a small collector
Asteroseismic program at Dome C
simple, robust, with an easy setup
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Spectrometry
/ Photometry
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Granulation noise
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HD 49933 CoRoT/HARPS data
Mosser et al 2005
Appourchaux et al 2008, in press
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Additional Information
l =3 modes
Granulation
noise at low
frequency
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not visible in
photometry
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Large and small separations
Small separation
Dn1-3
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Low low-frequency noise
+
l=3 modes

Courtesy Thierry Appourchaux
Doppler / photometry on the Sun
Inversion 4 times
more precise with
Doppler data
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High duty cycle,
long duration time series
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Clear sky fraction at Dome C
Clear sky fraction (naked eye, Eric Aristidi, 2006 winter)
Clear sky fraction > 90% during 84% of the time
Average number of consecutive clear days: 6.8 days
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Duty cycle: h_sun = -4°
Mosser & Aristidi 2007
Bad weather
Operations:
telescope
derotation…
Sky brightness
Resulting duty cycle (bright targets) > 90% during 90 days
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Duty cycle: h_sun = -8°
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Duty cycle: h_sun = -13°
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Duty cycle at Dome C
[GONG data]
Performance at Dome C compared to a 6-site network as GONG
(Mosser & Aristidi 2007, PASP)
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Scientific
program
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Scientific program
High-precision determination of the interior structure of nearby stars
• Age determination
~ a few %
• Stellar radii (impact for exoplanet radii)
~ a few %
• Composition
Comparative study: photometry / Doppler
• Convection, damping, excitation mechanisms
• Diagnostic of convective cores; depth of convection and of
second Helium ionization zones
Classical pulsators
• Non-linear physics, saturation effects, mode coupling
• Stochastically excited modes
Slowly rotating targets
• Rotation
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Simulations
l= 2
0
3
1
F6V star, mV = 4, vsini = 5 km/s, 90-day long run
Modelling: stochastic excitation + intrinsic damping
+ SIAMOIS characteristics and performance
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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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Targets with a 40-cm telescope
Observable solar-like
stars with p-mode
oscillations for a
dedicated 40-cm
telescope
[for all selected targets
SNR > 6 in 5 nights]
• 40-cm telescope:
- 7 bright targets, type: F, G, K class: IV & V
- many red giants; d Scuti (v sin i < 20 km/s)
 Enough targets for completing the scientific program in 3 to 6 winterings
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Targets with a 40-cm telescope
Long duration observation
 dedicated collector
Observable targets (solarlike stars with solar-like
oscillations) with SIAMOIS
and a 40-cm telescope
dedicated to the project
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With a 2-m telescope
• dimmer solar-like targets (e.g. star with exoplanets;
Sylvie Vauclair’s cancelled talk)
• ro Ap
+ any target with
• g doradus
vsini < 20 km/s
• d scuti
mV < 10.5
• red giants
Out of the scope of SIAMOIS: white dwarfs and subdwarf B stars
(too faint magnitude (1319), with a limited number of too broad
spectral lines)
Don Kurtz’talk; Gerard Vauclair’s cancelled presentation
 For bright targets, dedicated small telescope
 For dimmer targets, shared larger telescope
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Conclusion
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Space / Ground
space
ground
Observation
photometry
spectrometry
Max. degree
2
Targets magnitude
faint
3
bright
v sin i
-
< 20 km/s
Inversion
4 times more precise
Photometry on faint targets, without any other precise measurements
 Statistical approach
Precise Doppler measurements on nearby bright targets
+ convergent measurements (interferometry, high resolution spectrometry…)
 Determination of a sample of stellar standards
 Insights into the physical laws governing stellar interiors
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Comparison
CoRoT
Kepler
PLATO
SONG
SIAMOIS
2 eyes
diam = 12°
10° x 10°
(Cygnus-Lyra)
20° x 20°
|d| < 30°
4 sites full sky
d < -45°
Duty cycle
92%
~ 100%
~ 100% (L2)
~ 85%
~ 90%
5-day perf.
0.6 ppm
~ ppm
~ ppm
Max obs.
5 months
< 4 years
> 4 years
3 months
3 months
Magnitude
>6
>9
< 13
<7
<7
# targets
28
Up to 40 : 4 yr
Up to 160 : 1 yr
Up to 1000 : 90 d
100 000
>100
> 30
# solar-like
4
~ few 100
In operation
Launch
= 04/ 2009
Status
Instrument
cost
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65 M€
2-20 cm/s
7
Assessment study
at ESA
Phase A funded
Prototype > 2011
Network > 2014
Phase A is OK
2013 at Dome C
Class M project
> 12 M€ (6 tel)
0.86 M€ (1 tel)
1.02 M€ (2 tel)
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Doppler asteroseismology
Space-borne observations = photometric observations
MOST, CoRoT, Kepler, Brite, PLATO…
Ground-based observations = Doppler observations
- less noise at low frequency
- measurement of modes up to degree l= 3
- observation of bright stars
 very precise inversion and modelling
Next talk
- looking in great detail into nearby stars
- identifying the physical processes
Dome C = unique site for asteroseismology
3-month continuous observation with duty cycle ~ 90%
* High performance with a 40-cm collector
* Scientific program with 40-cm and 2-m collectors
http://siamois.obspm.fr
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Granada:16
- 18/04/ 08
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Additional
material
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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
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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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Photometry / activity
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Bright targets
Solar-like targets with solar-like oscillations [A scaled to (L/M)0.7]
- d Scuti
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- g Dor
- PMS
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- Red giants
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An example
Mosser et al 2008
HD 203608, F8V, mV = 4.2
Observations with HARPS:
- 5 nights
- duty cycle ~ 40 %
- SNR = 5
Precision of interior structure
parameters improved by a
factor 3 to 10
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