2. Projet O ptical S cintillation by E xtraterrestrial R efractors Moriond 2006 20/03/2006 La matière cachée Fait-elle scintiller Les étoiles? Marc MONIEZ, IN2P3

3. Compact Objects? ===> NO (microlensing) Gas? –Atomic H well known (21cm hyperfine emission) –Poorly known contribution: molecular H 2 (+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 ). Where are the hidden baryons?

4. These clouds refract light Elementary process involved: polarizability  –far from resonance Extra optical path due to H 2 medium – ~80,000 (on 1% of the sky) @ =500nm –Corresponding to a column of ~300 m H 2 (normal P and T)

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

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

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

8. 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 )

9. scintillation modes and characteristics Diffractive B and R NOT correlated Refractive B and R correlated Source Screen position t scint Contrast scale with 1/2 t scint contrast LMC A5 stars r S =1.7r Sun, m v =20.5 OR SNIa@max (z=0.2) Thin disc (300pc) Minute ~10% Hour or more Few % Thick disc (1kpc)~ 5% Gal. halo (10kpc)~ 2% LMC B8V stars r S =3 r Sun, m v =18.5 Thin disc (300pc) 10 min. ~5% Thick disc (1kpc)~ 2% Gal. halo (10kpc)~ 1% for a star seen through a clumpuscule with column density fluctuations of 10 -6 in a few 10 3 km at  = 500nm

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

11. Simulation : modulation index of the light received on Earth, as a function of R diff ( =500nm) Illumination on earth from a LMC A5V star behind a screen@1kpc R diff separation such that:  [  (r+R diff )-  (r)]= /2 

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

13. Fraction of scintillating stars Let  the fraction of halo into molecular gas Optical depth  –Max for all modes .10 -2 –Min for diffractive mode (better signature) .10 -7 Looking for clumpuscules with  (Nl)~10 -7 in 1000km

14. « Event » rate  =  t Diffractive mode : phases of few % fluctuation at the minute scale, during a few minutes  >1 event per 10 6 /  star x hour All modes : assumed quasi-permanent, few % fluctuations at the hour scale 1 scintillating star per ~ 100/  *Short time scale fluctuations => continuity of observations is NOT critical Any event is fully included in an observation session

15. Telescope > 2 meters Fast readout Camera 2 cameras Wide field Detection requirements on Earth Refractive mode Slower, detectable with the same setup. Signature not as strong (B and R variations correlated). Diffractive mode => small stars (10 5 /deg 2 ) Smaller than A5 type in LMC => M V ~20.5 Characteristic time ~ 1 min.=> few sec. exposures Photometric precision required ~1% Dead-time B and R fringes not correlated => 10 6 /  star x hour for one event =>

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

17. Fore and back-grounds Atmospheric turbulence Prism effects, image dispersion, BUT  I/I < 1% at any time scale in a big telescope BECAUSE s peckle 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

18. 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 => complementary observations (large telescope photometry, spectroscopy, synchronized telescopes…)

19. What could we learn from detection or non-detection? Expect 1000  events after monitoring 10 5 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 R diff (fluctuations of column density)

20. Test towards Bok globule B68 NTT IR (2 nights in 2004 + 2 coming in 2006) 4 fluctating stars (other than known artifacts)

21. 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 (10 17 molecules/cm 2 ) 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)

22. 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 R diff and V T measurements => positions and dynamics of the clouds Plus structuration of the clouds (inverse problem)