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VISIR Exposure Time Calculator

Infrared Long Wavelength Spectroscopy Mode Version 6.0.0
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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
Single 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
Target coordinates (J2000) and radial velocity
Coordinates (J2000) alpha:  hr min sec
delta:   deg min sec
Radial velocity
(relative to the barycenter of the Solar System)
km/s (Note: The velocity is negative for an approaching target)
Date of observation:       This information is used with the target coordinates to compute the doppler shift due to the orbital and rotational movement of the Earth (barycentric correction).
Time of observation UT:

Sky Conditions

PWV: mm Probability 55% for a PWV smaller or equal to the requested value
Seeing: arcsec FWHM in V-band at zenith (use this value in the proposal). The seeing is irrelevant for extended sources.
Probability 60% for a seeing smaller or equal to the requested value
For point sources, the resulting Image Quality FWHM is modeled by the ETC considering the transfer functions of the atmosphere, telescope and instrument. See the helpfile for details.

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 = 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 setting 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
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)
Details of Image Quality Calculations (only for pointsources)
Detailed S/N info

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