VISIR Exposure Time Calculator

Infrared Long Wavelength Spectroscopy Mode Version P114
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Target Flux Distribution

Uniform (constant with wavelength)
Blackbody: Temperature: K
Greybody: Temperature: K, Exponent:
Object Flux scaled to: mJy   at the central wavelength of the selected configuration
Emission line: Wavelength: The emission line is centered on the (doppler-shifted, if applied) central wavelength specified below.
  Flux: 10-16 W/m2
  FWHM: nm   (the minimal width is set by the sampling)

Target Geometry

Spatial Distribution: Point Source
Extended Source   Magnitudes and line flux are given per arcsec2 for extended sources

Target Doppler Shift

No Doppler Shift
Coordinates (J2000) alpha:  hr min sec
delta:   deg min sec
Radial velocity: km/s relative to the Solar System barycenter. The velocity is negative for an approaching target.
Date of observation:      
UT time of observation:

Sky Conditions

Moon FLI: Airmass:
Time step forward/back

Target coordinates Name or ID:  
α      δ     
UT rise
Hour Angle azimuth altitude zenith distance airmass FLI moon/sun
phase angle
An advanced almanac is available in the ESO SkyCalc sky model calculator
PWV:     mm     Probability % of realising the PWV ≤ 10.00 mm
Seeing/Image Quality:
Turbulence Category:   (FWHM of the atmospheric PSF outside the telescope at zenith at 500 nm)
IQ: arcsec FWHM at the airmass and reference wavelength
              The corresponding seeing and turbulence category will be indicated in the output page
Image Quality is not a parameter in AO modes

Instrument Setup

Low res N band, [ 9700 - 13300 ] nm, center=10500 nm
High res, long slit central wavelength: nm
High res, cross-dispersed
      Offset from main order:

Slit width: arcsec


S/N ratio: S/N = The total integration time (without overheads) INT=NDIT*DIT. In reality, the optimal DIT depends on the atmospheric conditions at the time of observation - the actual partition of NDIT is done on-the-fly. In this model, a DIT typical for the chosen filter is assigned, and NDIT is computed according to the S/N or INT requested by the user.
Exposure Time: INT = s

In spectroscopy, the calculations correspond to the sensitivity obtained with chopping and nodding in parallel direction, such that all 3 beams appear on the detector

Plots: Toggle All / No Plots

Resulting Observed spectrum (object + sky)
Resulting Object Spectrum in reference area
Resulting Sky Emission Spectrum only (use this plot for the Finding Chart for the High-res modes)
Sky Transmission Spectrum
Sky Radiance Spectrum in physical units (ph/s/m2/micron/arcsec2)
S/N as a function of wavelength
Total Efficiency and Wavelength Range
Input spectrum in physical units
Target PSF and Slitwidth (point source only)
Enslitted Energy for the Target (point source only)