NACO Exposure Time Calculator

Infrared Adaptive Optics Imaging Mode Version P100.2
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NOTE: Tests on the NACO ETC v6.0.0 in JHKs for standard stars S860-D and P565-C indicate that the ETC is over-predicting the observed counts by approximately 35% in H and Ks and 50% in J. No tests at longer wavelengths have been possible. The ETC will be updated after a major intervention in NACO programmed for October-November 2015. Note that the throughput of NACO was essentially unchanged after the move from UT4 to UT1.

Target Input Flux Distribution

Template Spectrum: Spectral Type: (only JHK)
Blackbody: Temperature : K

Target Magnitude : =

Magnitudes are given per square arcsec for extended sources.

Spatial Distribution: Point Source     Extended Source

Adaptive Optics Mode:

LGSLaser Guide Star

Natural Guide Star

Target / Reference Source
Separation: arcsec
Reference Source
V mag: Spectral Type

Sky Conditions

Airmass: range:[1, 3]
Seeing/Image Quality:
A model of the AO-corrected PSF is used to define the S/N reference area. See the helpfile for details.
Seeing: arcsec FWHM in V-band at zenith (use this value in the proposal)
              Probability ---% of realising the seeing ≤ 1.00 arcsec
IQ: arcsec FWHM at the airmass and wavelength of observation (to be used for the OB constraint set)
              The corresponding seeing and probability will be indicated in the ETC output page
Image Quality is not a parameter in AO modes

Instrument Setup

Neutral Density Filter: Out       In
Wollaston Prism System: Out       In
NAOS WFS/Dichroic:
Dichroic Name Reflected light to the WFS
Transmitted light to CONICA
Conditions of use
VIS V,R,I [0.45 - 0.95] microns
J,H,K,L,M [1.05 - 5.0] microns
Near-IR observations
with optical WF sensing
N20C80 V,R,I,J,K [0.45 - 2.55] microns
V,R,I,J,H,K [1.05 - 5.0] microns
WF sensing and
observing in the IR
N90C10 V,R,I,J,K [0.45 - 2.55] microns
V,R,I,J,H,K [1.05 - 5.0] microns
WF sensing and
observing in the IR
JHK I,J,H,K [0.8 - 2.55] microns
L,M [2.8 - 5.5] microns
Thermal-IR observations
with WF sensing in the near-IR
K K [1.9 - 2.55] microns
V,R,I,J,H [0.45 - 1.8] microns
J,H observations
with WF sensing in K
FREE The NAOS-PS will try to find an optimal Dicroic/WFS combination. Note
Instrument mode:


Aperture radius:  ×λ/D = arcsec

The two dynamic input fields are mutually updated when one of the values changes. The value in the "arcsec" field is updated if the filter is changed. The upper limit of the aperture radius is half of the camera FOV.
To revert to the default aperture for the current filter, press here:

S/N ratio: S/N = DIT = s Please note the relevant minimum DIT in the NACO manual.
Exposure Time: Non-chopping: NDIT =
Chopping: Total Exposure Time = min

The total exposure time is the product of DIT (Detector Integration Time) by NDIT (number of DITs). Instrument and telescope overheads are not taken into account.

Plots: Toggle All / No Plots

2-D PSF image (jpg and FITS ) (point source only)
Encircled Energy as a function of Aperture Radius (point source only)
S/N as a function of Exposure Time