large binocular telescope interferometer lbti/nomic data analysis b. mennesson, d. defrère, p....

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


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


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Detector and background

• Complex spatiotemporal fluctuations

• Flux-dependent detector behavior

• Temporal and spatial noise correlation

• Must be corrected for accurate null measurements

Background Detector


Noise mitigation strategies

Concentric Vertical offset Horizontal offset

OBVIOUS DRIFT

Time series of residual background (DARK frames, June 27th 2013 – 55ms)

• Investigated various strategies:


Noise mitigation strategiesDetector frame

Photometric apertureBackground regions

(optimized for r=0.64l/D)

Corrected

Raw

DIT=21ms

DARKS


Noise mitigation strategiesDetector frame

Photometric apertureBackground regions

(optimized for r=0.64l/D)

Corrected

Raw

chopping/nodding

DIT=55ms

BACKGROUND



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



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


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


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


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


R

L

4



R+L

REF

5


L

R

6



R+L

REF

7


R

L

8



R+L

REF

NO

D 0

NO

D 1


• 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

large binocular telescope interferometer lbti/nomic data analysis b. mennesson, d. defrère, p....

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