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

A giant solar-like oscillator

http://www.lcse.umn.edu/

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