Asteroseismology with A-STEP
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Asteroseismology with A-STEP
The sun from the South Pole
Grec, Fossat & Pomerantz, 1980, Nature, 288, 541
Asteroseismology
Angular structure of the modes
• n = number of radial nodes
= total number of surface nodes
• m = number of surface nodes that are lines of longitude
– m = number of surface nodes that are lines of latitude
Dipole modes immm ePY cos, 11
l=1, m=0 l=1, m=+1
immm ePY cos, 22
l=2, m=-1 l=2, m=-2l=2, m=0
Quadrupole modes
p modes and g modes
p modes (n,) = (8,100), (8,2)
g mode (n,) = (10,5)
Gough et al., 1996, Science, 272, 1281
p modes and g modes
J. P. Cox, 1980, Theory of Stellar Pulsation, Princeton University Press.
The sun as a star - BiSON
0 2n n
The sun as a star - GOLF
large separation small separation
An asteroseismic HR diagram
Solar-like Oscillations in Centauri
• UVES & UCLES• 42 oscillation frequencies
• ℓ = 1-3
• Mode lifetimes only 1-2 days
• Noise level = 2 cm s-1!
Bedding, T., et al. 2004, ApJ, 614, 380
From G. Houdek
Amplitudes in velocity between 10 to 250 cm/s
Amplitudes in intensity are of the order of 1-10 ppm
roAp
HR 1217 WET Xcov20
Kurtz et al., 2005, MNRAS, 358, 651
HR 1217 WET Xcov20
Kurtz et al., 2005, MNRAS, 358, 651
p modes: Cephei stars
HD 129929 = V836 Cen 20-yr multicolour photometry
Core overshooting with aOV = 0.1
Non-rigid rotation: 4 times faster near core
Aerts et al., 2003, Science, 300, 926 Asteroseismology of HD129929: Core overshooting and nonrigid rotation
p modes: EC 14026 stars - sdBV
PG 1336 + 018
Dor – mixed-mode pulsators
HD 49434
White dwarfs – g-mode pulsators
BPM 37093
COROT Field of view
Adaptation of COROTLUX software for variables
Input sample: Besançon model ~ 25000 stars
Pulsation in EXO FoV
Cep : 2SPB : 29 Sct : 2500 Dor : 3200Hyb : 2200Ceph : 1LP : 46
Fraction of variables:
30%?
Stellar limitation
• Photon noise < 10-4 up to M=15 • Stellar noise low frequencies• Activity see S. Aigrain
Instrumental limitation
• Read-out noise Lower than photon noise for M<16• Thermal noise negligible• Guiding noise PRNU~1%, • Cosmic rays TBE• Gain variation no data. Global/pixel• Shutter noise 1- 2 ms -> Ti > 30 s
3
43 10.5
2 S
pI
Atmospheric limitations of photometric observations
• Transparency fluctuations• Interruptions (clouds)• Scintillation
•Diffused light
These values are still uncertain: A-STEP will contribute to the site qualification
No dust, low humidity, snow< 15 %
Few auroras, moon
Better than anywhere else, but still limiting
hD(h)dh hChD.
hD(h)dh hCh.
(h)dh hC.r
nI
nI
n
223372
265
611
672
5
3
22
0
Zsec1219
Zsec1219
Zsec2
420
A few words about atmospheric turbulence and scintillation
From Dravins et al, 1997
IzK 3/46/50 cos
Optical/interferometric parameters
Integrated from h=8m
Balloons
Seeing (arcs) 0.4
0 (ms) 11.2
0 (arcs) 5.3
Integrated from h =30m
Balloons (10)
Dimms (March- May 05)
Seeing (arcs) 1.6 1.2
0 (ms) 7.0
0 (arcs) 5.3 3.6
AASTINO 2004 data
0.27 ‘’
7.9
5.7 ‘’
s
Interferometric coherence times
= 0.31 r0/ v ~7 ms
= 0.31 L0/ v ~775 ms
L0 = 10 m
GSM h=3.5m
1 h > 30 m
3 h > 0 m
opd
Optical/interferometric parameters
Integrated from h=8m
Balloons
Seeing (arcs) 0.4
0 (ms) 11.2
0 (arcs) 5.3
Integrated from h =30m
Balloons (10)
Dimms (March- May 05)
Seeing (arcs) 1.6 1.2
0 (ms) 7.0
0 (arcs) 5.3 3.6
AASTINO 2004 data
0.27 ‘’
7.9
5.7 ‘’
s
Interferometric coherence times
= 0.31 r0/ v ~7 ms
= 0.31 L0/ v ~775 ms
L0 = 10 m
GSM h=3.5m
1 h > 30 m
3 h > 0 m
opd
Conclusion
• Asteroseismology benefits a lot from continuity
• A-STEP very similar to COROT EXO Field
• Unlike COROT, the full dataset can be recovered
• roAp, Dor are top-priority programs• PMS Scuti, Red Giants to be
investigated• Solar-type stars ?
Requirements
• 30 – 60 s integration time
• 90 days continuous observations
• Good guiding
• Precise timing
• Best telescope height still unknown
• Color photometry allow mode identification
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