Does%20Transparent%20Hidden%20Matter%20Generate%20Optical%20Scintillation?

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Projet Optical Scintillation
by Extraterrestrial Refractors
La matière cachée Fait-elle scintiller Les
étoiles?
Moriond 2006 20/03/2006
Marc MONIEZ, IN2P3
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Where are the hidden baryons?

• Compact Objects? gt NO (microlensing)
• Gas?
• Atomic H well known (21cm hyperfine emission)
• Poorly known contribution molecular H2 (25 He)
• Cold (10K) gt 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).

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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) _at_ l500nm
• Corresponding to a column of 300 m H2(normal P
  and T)

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Scintillation through a strongly diffusive screen
Propagation of distorted wave surface driven
byFresnel diffraction global  refraction
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Scintillation through a strongly diffusive screen
Pattern moves at thespeed of the screen
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Scintillation through a strongly diffusive screen
Pattern moves at the speed of the screen
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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)

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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
Diffractive B and R NOT correlated Diffractive B and R NOT correlated Refractive B and R correlated Refractive B and R correlated
Source Screen position tscint Contrast scale with l1/2 tscint contrast
LMC A5 stars rS1.7rSun, mv20.5 OR SNIa_at_max (z0.2) Thin disc (300pc) Minute 10 Hour or more Few
LMC A5 stars rS1.7rSun, mv20.5 OR SNIa_at_max (z0.2) Thick disc (1kpc) Minute 5 Hour or more Few
LMC A5 stars rS1.7rSun, mv20.5 OR SNIa_at_max (z0.2) Gal. halo (10kpc) Minute 2 Hour or more Few
LMC B8V stars rS3 rSun, mv18.5 Thin disc (300pc) 10 min. 5 Hour or more Few
LMC B8V stars rS3 rSun, mv18.5 Thick disc (1kpc) 10 min. 2 Hour or more Few
LMC B8V stars rS3 rSun, mv18.5 Gal. halo (10kpc) 10 min. 1 Hour or more Few
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Simulation of a turbulent cloud gt Phase screen
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Illumination on earth from a LMC A5V star behind
a screen_at_1kpc

• Simulation modulation index of the light
  received on Earth, as a function of Rdiff
  (l500nm)

Rdiff separation such that sd(rRdiff)-d(r)l/2
p
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Refractive scintillation simulation B8V  big 
star in LMC, screen _at_ 1kpc
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Fraction of scintillating stars
Looking for clumpuscules with d(Nl)10-7 in 1000km

• Let a the fraction ofhalo into molecular gas
• Optical depth t
• Max for all modes
• t lt a.10-2
• Min for diffractive mode(better signature)
• t gt a.10-7

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 Event  rate

• G t/Dt
• Diffractive mode phases of few fluctuation at
  the minute scale, during a few minutes
• G gt1 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 fluctuationsgt continuity of
  observations is NOT criticalAny event is fully
  included in an observation session

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Detection requirements on Earth

• Diffractive mode gt small stars (105/deg2)
• Smaller than A5 type in LMC gt MV20.5
• Characteristic time 1 min. gt few sec.
  exposures
• Photometric precision required 1
• Dead-time lt few sec. gt
• B and R fringes not correlated gt
• 106/a starxhour for one event gt

• Refractive mode
• Slower, detectable with the same setup. Signature
  not as strong (B and R variations correlated).

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Possible experimental setup
tip/tilt compensation

• 2-4m telescope
• few 100s hours

2 cameras Wide field
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Fore and back-grounds

• Atmospheric turbulence
• Prism effects, image dispersion, BUT DI/I lt 1 at
  any time scale in a big telescope
• BECAUSE speckle with 3cm length scale is
  averaged in a gt1m 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

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Expected difficulties, cures

• Blending (crowded field)gt 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 gt complementary
  observations (large telescope photometry,
  spectroscopy, synchronized telescopes)

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What could we learn from detection or
non-detection?

• Expect 1000a events after monitoring 105 stars
  during 100 hours if column density fluctuations
  gt 10-7 within 1000km
• If detection
• Get details on the clumpuscule (structure, column
  density -gt 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)

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Test towards Bok globule B68NTT IR (2 nights in
2004 2 coming in 2006)
4 fluctating stars (other than known artifacts)
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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 100s hours, 2-4m)

Biblio AA 412, 105-120 (2003) Proc. 21rst IAP
Colloquium (2005)
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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
• gt positions and dynamics of the clouds
• Plus structuration of the clouds (inverse problem)