Astronomy & Astrophysics

Table 5: Contrast degradation factors and allocations derived in the K-band with a 35 spectral resolution. $l_{\rm c}$ is the coherence length and Airy the Airy disk size.
Allocations $\rho$ Contrast Requirement

noise rms

OPD equality 0.995 $l_{\rm c}$ /19 (4 $\mu$ m)

OPD vibration (rms) 10^-3 $\lambda$ /140 (16 nm)

Image overlapping 0.99 Airy/10 (3'')

Overlapping jitters 10^-3 Airy/12 (3'')

Wavefront quality 0.95 $\lambda$ /16 (140 nm)

Defocus 0.99 $\approx$ 10 mm

Phase delay 0.99 17 $^\circ$

Differential rotation of

polarization frames 0.99 16 $^\circ$

Unequal intensity 0.999 I₁/I₂ $\approx$ 0.9

Total $\approx$ 0.89 $\approx$ 10^-3

**Table 5:** Contrast degradation factors and allocations derived in the K-band with a 35 spectral resolution. $l_{\rm c}$ is the coherence length and *Airy* the Airy disk size.
Allocations	$\rho$	Contrast	Requirement
		noise	rms
OPD equality	0.995		$l_{\rm c}$ /19 (4 $\mu$ m)
OPD vibration (rms)		10^-3	$\lambda$ /140 (16 nm)
Image overlapping	0.99		Airy/10 (3'')
Overlapping jitters		10^-3	Airy/12 (3'')
Wavefront quality	0.95		$\lambda$ /16 (140 nm)
Defocus	0.99		$\approx$ 10 mm
Phase delay	0.99		17 $^\circ$
Differential rotation of
polarization frames	0.99		16 $^\circ$
Unequal intensity	0.999		I₁/I₂ $\approx$ 0.9
Total	$\approx$ 0.89	$\approx$ 10^-3

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