Reaching micro-arcsecond astrometry with long baseline optical interferometry - Application to the GRAVITY instrument

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Volume 567 (July 2014)

A&A, 567 (2014) A75

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Table 1

GRAVITY astrometric error budget (between UTs, for a single baseline).

Error label	Cause	Amplitude considered	Consequence	μas^a

	B_NAB Error
in terrestrial coordinates	Physical pointing of the telescope	± 10″	Baseline error 0.5 mm	5
B_WAB stability	Paranal structural stability	0.5 mm	Baseline error 0.5 mm	5
Terrestrial to sidereal reference frame	LST time during observation	1/15 s	Baseline error 0.5 mm	5

	Pupil Error
Lateral pupil		10 mas – 4 cm	OPD error of 2 nm	4
Longitudinal pupil		10 mas – 10 km	OPD error of 10 pm	0.02

	Dispersion Error
Dispersion of air		1 mm – 8 × 10^-8	OPD error of 80 pm	0.16
Differential length of fiber		10 μm – 2 × 10^-4	OPD error of 2 nm	4

	High order terms Error
Non-common path aberrations	Details in Table 2		OPD error of 3.7 nm	7.4
Common path aberrations	Details in Table 3		OPD error of 0.9 nm	1.8

TOTAL				16.5^b

Notes.

^(a)

Accuracy obtained between two targets separated by 1 arcsec, projected on a 100 m baseline.

^(b)

Using all six baselines, and needing astrometry on the two coordinate axis, the final accuracy would reach as.

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