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Large Binocular Telescope Interferometer Status and Requirements on AO

Large Binocular Telescope Interferometer Status and Requirements on AO. Outline:. Phil Hinz. Goals of LBTI. Provide sensitive nulling interferometric observations of nearby solar-like stars.

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Large Binocular Telescope Interferometer Status and Requirements on AO

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  1. Large Binocular Telescope Interferometer StatusandRequirements on AO Outline: Phil Hinz

  2. Goals of LBTI • Provide sensitive nulling interferometric observations of nearby solar-like stars. • Provide beam combination compatible with wide-field Fizeau (imaging) interferometry in the thermal infrared.

  3. UBC=Universal Beam Combiner NIL=Nulling Interferometer for the LBT NOMIC=Nulling-Optimized Mid-Infrared Camera The LBT Interferometer (LBTI)

  4. Fringe Sensing with the LBTI • LBTI will overlap the two pupils from the LBT and use brightness variations to track phase changes. • Images of the overlapped pupils are formed to allow measurement of phase variations at each point in the pupil. • Phase and tip-tilt errors will be corrected by an internal corrector. • Modal amplitudes errors can also be sensed. Slow feedback of these errors will be sent through the TCS? Fast feedback would also be useful.

  5. LBTI metering structure

  6. Reimaging Mirror LBTI Parts 07/04 vacuum bellows rough cryostat housing Mirror being polished cryostat housing machined center metering structure metering structure edge-on

  7. LBTI Components 02/05 Fast Pathlength Corrector SiC Mirror Left UBC Cryostat 4 K Mech. Cooler

  8. AO for LBTI • Wavefront sensing for LBTI will be done with facility “W” units. • The AGW enclosure will NOT be used to house the wavefront sensors. Instead the units will be rigidly connected to the LBTI structure. • The bright stars available for nulling observations will allow use of fast (1 kHz) wavefront sensing correcting many modes. • Acquisition of off-axis guide stars will be useful for longer wavelength imaging. Dichroics are designed to deliver 140” diameter FOV to “W” units.

  9. “W” units on LBTI

  10. LBTI requirements(chopping) • Chopping capability of 5” at 10 Hz is needed. Chopping should be in elevation direction. • Science camera will provide TTL level signal to synchronize chop. • Need closed loop operation in BOTH beams of chop. Need dual pyramid in “W” units.

  11. LBTI requirements (AO performance) • Strehls of 60-90% in K will be required to achieve a good nulling level. Nulling will take advantage of “extreme AO” capability of system if it is available. • Need to be able to lock on the brightest stars in the sky (Sirius, Arcturus, etc.) • Sky derotation for off-axis guide stars will be done by X-Y translation stages: need ~3-10 mas ( 2-6 um) precision

  12. LBTI requests • Accelerometers integrated into the deformable mirror’s position loop will help alleviate telescope vibration problems. We would like to see this implemented as soon as possible. • We would like to keep the possibility open to have LBTI provide a separate feedback signal to the mirrors at speeds up to 1 kHz.

  13. Conclusion • Main unique requirement of LBTI is the chopping. • Need to get to get together with Arcetri and work out details of dedicated LBTI “W” units.

  14. BACKUP SLIDES

  15. The LBTI on the Telescope

  16. Synchronized Feedback example Left W senses a focus error of 1 unit Right W senses a focus error of 1 unit Fringe tracker senses a delta focus error of 3 units

  17. Science Results using a prototype nuller on the MMT HD 100546 (Liu et al. 2003, (ApJL 598, 111)) Constructive Null • Disk approximately 25 AU in diameter. • Disk similar in size at 11 microns and 24.5 microns. • Consistent with an inner hole? (Bouwman et al. 2003) ε Mus HD 100546 AB Aur and V892 Tau (Liu et al. ApJL accepted) • AB Aur Disk ~32 AU. • Disk inclined at 45 degrees. • V892 Tau size ~22 AU. Vega (Liu et al. 2004, (ApJL 610, 125)) • Upper limit to zodiacal dust is <2% (3 σ) of the stellar flux on Vega, ~3 times more sensitive than best photometric measurements. • Corresponds to a limit of a zodiacal dust disk <650 times our own.

  18. LBTI Accommodates Anticipated Fizeau Imaging • The requirements for nulling interferometry with the LBT are consistent with the design requirements for wide-field imaging (or Fizeau) interferometry. • This technique allows high resolution (0.01-0.05”) imaging of even faint objects over wide (30-40”) fields of view. • The LBTI design preserves this capability over a broad range of wavelengths in the near and mid infrared (1-20 microns). • Fizeau imagers and phase sensing to take advantage of this are not within the scope of the LBTI program.

  19. Sky Background N M photons/s/m 2/μm/arcsec 2 Telescope Background L' Wavelength (μm) LBTI Imaging Sensitivity

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