LSST Exposure Time Calculator version 4.1
	new version with sky levels near solar min(click here for original sky levels)

In the four sections of this form, select the appropriate astronomical source, instrument, telescope, observing condition and observation parameters. Click on the calculate button () at the bottom of any section to submit the parameters from all the sections to the server. The results are reported in a separate web page that can be resized and printed.

General guidance on use of the Exposure Time Calculator (ETC) is available; specific help on each section of the form is available by following the more info and other (blue highlighted) links. Note: at this time Netscape 6 and 6.01 do not work with web forms. Changes, enhancements and bugs within the ETC are listed chronologically.

Astronomical source definition

Spatial profile and brightness:(more info) Choose one of point, extended or user-defined source profile and the brightness in any filter/wavelength
	Point source (nominal PSF) with spatially integrated brightness mag AB mag Jy W/m^2/um ergs/s/cm^2/A ergs/s/cm^2/Hz (e.g. 19.3 mag or 2e-17 W/m^2/um)
	Extended source having ...
		Gaussian profile with full width half maximum of arcsec and spatially integrated brightness of mag AB mag Jy W/m^2/um ergs/s/cm^2/A ergs/s/cm^2/Hz (e.g. 19.3 mag or 2e-17 W/m^2/um)
		Uniform surface brightness mag / sq arcsec AB mag / sq arcsec Jy / sq arcsec W/m^2/um / sq arcsec ergs/s/cm^2/A / sq arcsec ergs/s/cm^2/Hz / sq arcsec (e.g. 21.6 mag / sq arcsec)
		Exponential profile with spatially integrated brightness mag AB mag Jy W/m^2/um ergs/s/cm^2/A ergs/s/cm^2/Hz (e.g. 19.3 mag or 2e-17 W/m^2/um) and half-light radius of arcsec (disabled)
		Elliptical r^(1/4) profile with spatially integrated brightness mag AB mag Jy W/m^2/um ergs/s/cm^2/A ergs/s/cm^2/Hz (e.g. 19.3 mag or 2e-17 W/m^2/um) and half-light radius of arcsec (disabled)
	User-defined 2D image read from file (disabled)
with the above brightness normalization applied in filter u (0.35um) g (0.48um) r (0.62um) i (0.75um) z (0.87um) y (1.0um) band or at a wavelength micron (latter option disabled)
Spectral distribution: (more info) Choose one SED, the redshift and extinction
	Library spectrum of a non-stellar object elliptical galaxy spiral galaxy (Sc) QSO HII region (Orion) Planetary nebula (NGC7009)
	Library spectrum of a star with spectral type O5V O8III B0V B5-7V B5III B5I A0V A0III A0I A5V A5III F0V F0III F0I F5V F5V-w F6V-r F5III F5I G0V G0V-w G0V-r G0III G0I G2V G5V G5V-w G5V-r G5III G5III-w G5III-r G5I K0V K0V-r K0III K0III-w K0III-r K0-1II K4V K4III K4III-w K4III-r K4I M0V M0III M3V M3III M6V M6III M9III
	Single emission line at wavelength micron with line flux W/m^2 ergs/s/cm^2 and line width km/s on a flat (in wavelength) continuum of flux density W/m^2/um ergs/s/cm^2/A
	Model black body spectrum with temperature K
	Model power-law spectrum (S_lambda = lambda ^ )
	User-defined spectrum read from file (size < 1MB)
with the spectrum mapped to a redshift z = or a radial velocity v = km/s
...and subject to dust reddening by a foreground screen (see more info on the extinction law) having a visual extinction of Av = mag (disabled)

Instrument (LSST) and telescope configuration

Instrument optical properties:(more info)

Color filter:   u (0.35um) g (0.48um) r (0.62um) i (0.75um) z (0.87um) y (1.0um)

Detector properties:(more info)

CCD readout noise of 5 e-

CCD dark current of .0015 e-/s

pixel size of 10 microns

No CCD binning; camera plate scale is 0.20 arcsec/pixel

Telescope configuration:(more info)

Mirror coating: aluminium  silver (not yet implemented)

Observing condition constraints

Note: you should read the explanatory notes for the meaning of the various settings and percentiles.
Seeing (fwhm):	arcsecs
Sky transparency:	average, no humidity correction
Cloud cover (transmittance):	photometric	patchy	cloudy	usable
Sky background (lunar phase):	3 day	7 day	11 day	14 day
Typical air mass during observation:	<1.2	1.5	2.0

Details of observation

Calculation method:(more info) Select the calculation method

Total S/N ratio resulting from exposures each having an exposure time of secs and with a fraction of exposures that observe the source

Total integration time to achieve a S/N ratio of using an exposure time for each exposure of secs and with a fraction of exposures that observe the source

Analysis method: (more info)

Software aperture that gives 'optimum' S/N ratio and with a sky aperture times the target aperture

Software aperture of diameter (or slit length) arcsec and with a sky aperture times the target aperture

Optimal Filter: (more info)

psf-weighted filter

not weighted

Last update September 30, 2005; Perry Gee