Asteroseismology with A-STEP

The sun from the South Pole Grec, Fossat & Pomerantz, 1980, Nature, 288, 541

3D oscillations – stars radial modes Cepheids P 1 /P 0 = 0.7 P 1 /P 0 = 0.33

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 l=1, m=0 l=1, m=+1

l=2, m=-1 l=2, m=-2l=2, m=0 Quadrupole modes

Rotation of the sun

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

The sun as a star - GOLF large separationsmall 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 = V836 Cen 20-yr multicolour photometry Core overshooting with a OV = 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 stars - sdBV

PG

 Dor – mixed-mode pulsators

HD 49434

White dwarfs – g-mode pulsators

BPM 37093

A giant solar-like oscillator

COROT Field of view Adaptation of COROTLUX software for variables Input sample: Besançon model ~ stars

Pulsation in EXO FoV  Cep : 2 SPB : 29  Sct : 2500  Dor : 3200 Hyb : 2200 Ceph : 1 LP : 46 Fraction of variables: 30%?

Simulation of CCD photometry of a Cen A and B Such simulations are useful for study of the different noise contributions: smearing, guiding read-out noise, cosmic,...

Stellar limitation Photon noise< up to M=15 Stellar noiselow frequencies Activitysee S. Aigrain Instrumental limitation Read-out noiseLower than photon noise for M<16 Thermal noisenegligible Guiding noise PRNU~1%, Cosmic raysTBE Gain variationno data. Global/pixel Shutter noise1- 2 ms -> Ti > 30 s

The amplitude of the oscillations changes with the wavelength VIRGO data

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

A few words about atmospheric turbulence and scintillation From Dravins et al, 1997

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)  0 (ms) 7.0  0 (arcs) AASTINO 2004 data 0.27 ‘’ ‘’ s Interferometric coherence times    = 0.31 r 0 / v ~7 ms    = 0.31 L 0 / v ~775 ms L 0 = 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)  0 (ms) 7.0  0 (arcs) AASTINO 2004 data 0.27 ‘’ ‘’ s Interferometric coherence times    = 0.31 r 0 / v ~7 ms    = 0.31 L 0 / v ~775 ms L 0 = 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