Infrared Exposure Time Calculator

VISIR Exposure Time Calculator

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Infrared Long Wavelength Spectroscopy Mode Version 3.1.0

Description.

F.A.Q

Performance

Input 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).

Magnitudes and line flux are given per arcsec² for extended sources.

Spatial Distribution: Point Source Extended Source

Target Doppler Shift

No Doppler Shift

Doppler:

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:

h m s

Sky Conditions

Airmass :
Seeing :	arcsec

Instrument Setup

Grating:

Low res	setting :
Medium res	central wavelength: nm
High res, long slit
High res, cross-dispersed Offset from main order:

Slit width: arcsecs

Results

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.

On submission the model can generate the following graphs:
(input parameters are replicated in the output page)

Resulting spectrum (object + sky)

Object Spectrum only

Sky Emission Spectrum

S/N as a function of wavelength

Input spectrum in physical units