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Large Binocular Telescope Interferometer
LBTI/NOMIC data analysisB. Mennesson, D. Defrère, P. Hinz, B. Hoffmann, O.
Absil, B. Danchi, R. Millan-Gabet, and A. Skemer
Instrument Status ReviewTucson AZ Sep 4 2013
Large Binocular Telescope Interferometer
Group activities
• Detector and background characterization
• Noise mitigation strategies
• Optimization of chopping/nodding frequency
• Definition of data acquisition sequence
• Computation of key instrument performance indicators
• Adaptation of statistical reduction technique
Large Binocular Telescope Interferometer
Group activities
• Detector and background characterization
• Noise mitigation strategies
• Optimization of chopping/nodding frequency
• Definition of data acquisition sequence
• Computation of key instrument performance indicators
• Adaptation of statistical reduction technique
✓
Large Binocular Telescope Interferometer
Group activities
• Detector and background characterization
• Noise mitigation strategies
• Optimization of chopping/nodding frequency
• Definition of data acquisition sequence
• Computation of key instrument performance indicators
• Adaptation of statistical reduction technique
✓✓
Large Binocular Telescope Interferometer
Group activities
• Detector and background characterization
• Noise mitigation strategies
• Optimization of chopping/nodding frequency
• Definition of data acquisition sequence
• Computation of key instrument performance indicators
• Adaptation of statistical reduction technique
✓✓✓
Large Binocular Telescope Interferometer
Group activities
• Detector and background characterization
• Noise mitigation strategies
• Optimization of chopping/nodding frequency
• Definition of data acquisition sequence
• Computation of key instrument performance indicators
• Adaptation of statistical reduction technique
✓✓✓✓
Large Binocular Telescope Interferometer
Group activities
• Detector and background characterization
• Noise mitigation strategies
• Optimization of chopping/nodding frequency
• Definition of data acquisition sequence
• Computation of key instrument performance indicators
• Adaptation of statistical reduction technique
✓✓✓✓✓
Large Binocular Telescope Interferometer
Group activities
• Detector and background characterization
• Noise mitigation strategies
• Optimization of chopping/nodding frequency
• Definition of data acquisition sequence
• Computation of key instrument performance indicators
• Adaptation of statistical reduction technique
✓✓✓✓✓✗
Large Binocular Telescope Interferometer
Detector and background
• Complex spatiotemporal fluctuations
• Flux-dependent detector behavior
• Temporal and spatial noise correlation
• Must be corrected for accurate null measurements
Background Detector
Large Binocular Telescope Interferometer
Noise mitigation strategies
Concentric Vertical offset Horizontal offset
OBVIOUS DRIFT
Time series of residual background (DARK frames, June 27th 2013 – 55ms)
• Investigated various strategies:
Large Binocular Telescope Interferometer
Noise mitigation strategiesDetector frame
Photometric apertureBackground regions
(optimized for r=0.64l/D)
Corrected
Raw
DIT=21ms
DARKS
Large Binocular Telescope Interferometer
Noise mitigation strategiesDetector frame
Photometric apertureBackground regions
(optimized for r=0.64l/D)
Corrected
Raw
chopping/nodding
DIT=55ms
BACKGROUND
Large Binocular Telescope Interferometer
Noise mitigation strategies
WITHOUT NODDING SUBTRACTION
• 40-min of sky data nodding every ~1min30 (June 27th 2013)
• Offset reduced to ~8 ADU/PSF (+ Gaussian noise)
WITH NODDING SUBTRACTION
DIT=55msDIT=55ms
Large Binocular Telescope Interferometer
Noise mitigation strategies
WITHOUT NODDING SUBTRACTION
• 40-min of sky data nodding every ~1min30 (June 27th 2013)
• Offset reduced to ~8 ADU/PSF (+ Gaussian noise)
WITH NODDING SUBTRACTION
DIT=55msDIT=55ms
Large Binocular Telescope Interferometer
Noise mitigation strategies
Vega on June 27th (40 min of integration)
• Measured Vega’s flux ~ 2.2*105 ADU/PSF in 55ms (optimum
aperture)
• Background noise is ~0.2% in 55ms (i.e., 0.07 Jy)
• Background bias is ~0.004% (i.e., 0.001 Jy)
= bias= noise
DIT=55ms
Large Binocular Telescope Interferometer
Background
Minimum integration time necessary to achieve 3-zodi sensitivity (assuming 1 zodi = 5.10-5).
Comparing shot noise on constant background (ideal non realistic case) withcurrent measured background uncertainty (after spatio/temporal correction of
fluctuations)
Vega ~ 0.6 sec
b Leo ~ 10 sec
Altair ~ 1 sec
Large Binocular Telescope Interferometer
Chopping/nodding frequency
• Nodding frequency:
• Remove quasi-static offsets between photometric aperture and
background regions
• Can be slow (a few minutes or more)
• Chopping frequency:
• Relaxed thanks to simultaneous background subtraction
technique
• Will be constrained by photometric calibration (more data
needed)
• Likely to be slow
• Still needed in conjunction of nodding for accurate background
removal
Large Binocular Telescope Interferometer
Data acquisition sequence
1
PHOTOMETRIC FRAME- Chop positions: (1,2)- Nod positions: (0,0)
L
R
2
INTERFEROMETRIC FRAME
- Chop positions: (2,2)- Nod positions: (0,0)
R+L
REF
3
PHOTOMETRIC FRAME- Chop positions: (2,1)- Nod positions: (0,0)
R
L
4
INTERFEROMETRIC FRAME
- Chop positions: (1,1)- Nod positions: (0,0)
R+L
REF
5
PHOTOMETRIC FRAME- Chop positions: (1,2)- Nod positions: (1,1)
L
R
6
INTERFEROMETRIC FRAME
- Chop positions: (2,2)- Nod positions: (1,1)
R+L
REF
7
PHOTOMETRIC FRAME- Chop positions: (2,1)- Nod positions: (1,1)
R
L
8
INTERFEROMETRIC FRAME
- Chop positions: (1,1)- Nod positions: (1,1)
R+L
REF
NO
D 0
NO
D 1
Large Binocular Telescope Interferometer
• Statistical reduction technique. Adaptation from NIR Palomar Fiber
Nuller not straightforward:
1D to 2D data
Higher background at 10microns
No single-mode fibers used -> higher phase orders than piston
• Computation of chopping frequency (photometric calibration)
• Determination of OPD reset frequency
- How long does the NIR OPD target remain valid in the MIR ?
- Transverse atm dispersion
- Other chromatic effects?
Ongoing and future analysis