Projet O ptical S cintillation by E xtraterrestrial R efractors

1. ProjetOpticalScintillationbyExtraterrestrialRefractors La matière cachée Fait-elle scintiller Les étoiles? Marc MONIEZ, IN2P3 Moriond 2006 20/03/2006

2. Where are the hidden baryons? • Compact Objects?===> NO (microlensing) • Gas? • Atomic H well known (21cm hyperfine emission) • Poorly known contribution: molecular H2(+25% He) • Cold (10K) => no emission. Very transparent medium. • In fractal structure covering 1% of the sky. Clumpuscules ~10 AU (Pfenniger & Combes 1994) • In the thick disc or/and in the halo • Thermal stability with a liquid/solid hydrogen core • Detection of molecular clouds with quasars (Jenkins et al. 2003, Richter et al. 2003) and indication of the fractal structure with clumpuscules from CO lines in the galactic plane (Heithausen, 2004).

3. These clouds refract light • Elementary process involved: polarizability a • far from resonance • Extra optical path due to H2 medium • ~80,000l (on 1% of the sky) @ l=500nm • Corresponding to a column of ~300 m H2(normal P and T)

4. Scintillation through a strongly diffusive screen Propagation of distorted wave surface driven by:Fresnel diffraction+« global » refraction

5. Scintillation through a strongly diffusive screen Pattern moves at thespeed of the screen

6. Scintillation through a strongly diffusive screen Pattern moves at the speed of the screen

7. Fresnel diffraction on pulsars and stars have been detected before • In radioastronomy Classical technique to study interstellar medium • In optics • diffraction during lunar occultations • effects from the upper atmosphere of Saturn (Cooray & Elliot 2003)

8. scintillation modes and characteristics for a star seen through a clumpuscule with column density fluctuations of 10-6 in a few 103km at l = 500nm

9. Diffraction image ofa point-like sourcethrough this cloud @1 kpc Light-curve of an A5V-LMC star (integral in the sliding disk) Simulation of a turbulent cloud => Phase screen

10. Illumination on earth from a LMC A5V star behind a screen@1kpc Simulation: modulation index of the light received on Earth, as a function of Rdiff (l=500nm) Rdiff separation such that: s[d(r+Rdiff)-d(r)]=l/2p

11. Refractive scintillation simulation B8V « big » star in LMC, screen @ 1kpc

12. Fraction of scintillating stars Looking for clumpuscules with d(Nl)~10-7 in 1000km • Let a the fraction ofhalo into molecular gas • Optical deptht • Max for all modes t < a.10-2 • Min for diffractive mode(better signature) t > a.10-7

13. « Event » rate G = t/Dt • Diffractive mode : phases of few % fluctuation at the minute scale, during a few minutes G >1 event per 106/a starxhour • All modes : assumed quasi-permanent, few % fluctuations at the hour scale 1 scintillating star per ~ 100/a • Short time scale fluctuations=> continuity of observations is NOT criticalAny event is fully included in an observation session

14. Telescope > 2 meters Fast readout Camera 2 cameras Wide field Detection requirements on Earth • Diffractive mode => small stars (105/deg2) • Smaller than A5 type in LMC => MV~20.5 • Characteristic time ~ 1 min. => few sec. exposures • Photometric precision required ~1% • Dead-time < few sec. => • B and R fringes not correlated => • 106/a starxhour for one event => • Refractive mode • Slower, detectable with the same setup. Signature not as strong (B and R variations correlated).

15. Focal plane Mosaic of frame-tranfert CCDs 10cm Dichroic separator Possible experimental setup tip/tilt compensation 2-4m telescope few 100’s hours 2 cameras Wide field

16. Atmospheric turbulence Prism effects, image dispersion, BUT DI/I < 1% at any time scale in a big telescope BECAUSE speckle with 3cm length scale is averaged in a >1m aperture High altitude cirruses Would induce easy-to-detect collective absorption on neighbour stars. Gas at ~10pc Scintillation would also occur on the biggest stars Intrinsic variability Rare at this time scale and only with special stars Fore and back-grounds

17. Expected difficulties, cures • Blending(crowded field)=> differential photometry • Delicate analysis • Detect and Subtract collective effects • Search for a not well defined signal • VIRGO robust filtering techniques (short duration signal) • Autocorrelation function (long duration signal) • Time power spectrum, essential tool for the inversion problem(as in radio-astronomy) • If interesting event => complementaryobservations (large telescope photometry, spectroscopy, synchronized telescopes…)

18. What could we learn from detection or non-detection? • Expect 1000a events after monitoring 105 stars during 100 hours if column density fluctuations > 10-7 within 1000km • If detection • Get details on the clumpuscule (structure, column density -> mass) through modelling (reverse problem) • Measure contribution to galactic hidden matter • If no detection • Get max. contribution of clumpuscules as a function of their structuration parameter Rdiff (fluctuations of column density)

19. Test towards Bok globule B68NTT IR (2 nights in 2004 + 2 coming in 2006) 4 fluctating stars (other than known artifacts)

20. Conclusions - perspectives • Opportunity to search for hidden transparent matter is technically accessible right now • Risky project but not worse than many others • Need clumpuscules with a structuration that induce column density fluctuations ≥ 10-7 (1017 molecules/cm2) per 1000 km • Alternatives to OSER: GAIA, LSSC. But much longer time scale • Call for telescope (few 100’s hours, 2-4m) Biblio : A&A 412, 105-120 (2003); Proc. 21rst IAP Colloquium (2005)

21. And for the future… A network of distant telescopes • Would allow to decorrelate scintillations from atmosphere and interstellar clouds • Snapshot of interferometric pattern + follow-up • Simultaneous Rdiff and VT measurements • => positions and dynamics of the clouds • Plus structuration of the clouds (inverse problem)