The Interfromtre deux tlescopes Genesis of I2T

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The  Interféromètre à deux télescopes  Genesis
of I2T

Antoine Labeyrie Collège de France
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Influences received from pioneers

• Michelson Pease, Hanbury Brown Twiss
• Shao Staehlin
• Discussions with radio-astronomers at Meudon
  Blum, Lequeux  limited to small sub-apertures
  by  seeing  ?  yes, but  speckle
  interferometry  
• M.Cagnet (Professor at Institut dOptique)
• Visit of Linniks Michelson-type interferometer
  at Pulkovo ( 1965 ?)

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Prototypes at Meudon

• I2T precursor built with D.Bonneau,L.Koechlin,
  A.Blazit, never worked ( manual guiding)
• Back from a year at Stony Brook, and speckle
  observing at Palomar
• I2T rebuilt with alt-alt mounts, instead of
  equatorial
• delivered at Nice spring 1974
• Support of F.Roddier and group fringes in
  August
• Controlled without computer
• I had to do the mechanical design and
  construction, welding , pier with moving table,
  primitive star tracker

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Camera

• Built photon-counting camera image intensifier
  e-bombarded silicon vidicon
• Same as used for speckle interferometry

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Operation at Nice

• Warm welcome and moral support of F. C.Roddier
  and group fringes in 3 months
• Some support of local workshops ( thanks
  Mugnier , Jeansaume)
• Quick progress because driven without computer
  cam for optical path

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Simple optics

• Fixed 12 meter baseline

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Initial installation at Nice Observatory

• 12 meters baseline, first fringes on Vega

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Beam combiner and fringe tracker

• Moving table, pushed by transverse motorized
  screw
• and cam for cosine H law

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I2T fringes in Nice

• Photon-counting camera
• Video rate ( 20 ms exposure)
• Filtered about 10 nm with field grating (
  Courtès scheme)

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Operation at Nice Vega

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Visit of R.Hanbury-Brown J.Davis

• Then planning a larger intensity interferometer
• Saw the I2T fringes, recorded on video tape
• you guys have lots of signal/noise !
• Dropped their project to build SUSI

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I2T moved to Calern, on tracks

• Reasons for moving
• longer baseline and better seeing needed
• support of director J.Kovalevsky
• Lab in 3 mobile cabins, pending a building
• D.Bonneau, L.Koechlin, J.L.Oneto, built tracks
  and observed
• Infra-red observing by O.Citterio and P. di
  Benedetto J.M.Mariotti

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I2T moved to Calern with team

• D.Bonneau, L.Koechlin, A.Blazit, J.L.Oneto
• Tracks built
• Then came F.Vakili, R. F.Foy, G..Schumacher, D.
  Mourard, I.Bosc M.Tallon

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I2T moved to Calern , on tracks Capella

• Newton said If I have seen further, it is by
  standing on the shoulders of giants
• He could have seen even further by standing at
  the eye-piece of giant interferometers

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I2T at Calern
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I2T catching fire (courtesy L.Koechlin)

• Ho

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Capella A and B measured

• 5,2 4,0 arc-milliseconds how correct ?

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Dreamt in 1974 ( Ap.J. 1975)

• No mention of delay lines or moving telescopes
  then

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Dreams of Optical Very Large Arrays

• Fixed 12 meter baseline

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GI2T at Calern

• Pair of 1.5 m telescopes ( one built in part by
  F.Vakili and P.Assus)
• Intended objects ( QSO 3C 273, etc)
• And infra-red for larger r0

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GI2T

• Fixed 12 meter baseline

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GI2T Fringed spectrum of gamma Cass ( Mourard
et al. , Nature, 1989)

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A faster route towards many apertures ?

• Depends on crater sites usable
• Limited to 1500 - 2000 m effective aperture

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Exo-Earth images ?
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Conclusion

• Interferometry is complicated
• .. but should eventually bloom
• and greatly improve mans understanding of the
  universe