VISIR Exposure Time Calculator

Infrared Long Wavelength Spectroscopy Mode Version P105
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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:
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 only
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)

Debug text output
Show execution time details