Change page style: 

Michelle ITC

Home » Sciops » Instruments » Integration Time Calculators

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

General guidance on use of the Integration Time Calculators (ITCs) 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 ITC 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 (e.g. 19.3 mag or 2e-17 W/m^2/um)
Extended source having ...(When this option is selected the image quality selection in section 3 of the ITC is disabled.)
  Gaussian profile with full width half maximum of arcsec and spatially integrated brightness of (e.g. 19.3 mag or 2e-17 W/m^2/um)
  Uniform surface brightness (e.g. 21.6 mag / sq arcsec)
  disabled Exponential profile with spatially integrated brightness (e.g. 19.3 mag or 2e-17 W/m^2/um) and half-light radius of arcsec (disabled)
  disabled Elliptical r^(1/4) profile with spatially integrated brightness (e.g. 19.3 mag or 2e-17 W/m^2/um) and half-light radius of arcsec (disabled)
disabled User-defined 2D image read from file
with the above brightness normalisation applied in filter band or disabled 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
option disabled Library spectrum of a star with spectral type
Single emission line at wavelength micron with line flux and line width km/s on a flat (in wavelength) continuum of flux density
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) disabled

 


Instrument (Michelle) and telescope configuration

Instrument optical properties:
Filter: Focal plane unit:
Grating: Spectrum central wavelength: um
Polarimetry: disabled  enabled
Detector properties:
Read noise and dark current have not yet been measured for the new Michelle science array but should not be significant for background-limited observations. Following are the values assumed by the ITC:
Read noise of 4,000 e- per pixel
Dark current of 270,000 e-/s per pixel
Telescope configuration:(more info)
Mirror coating: aluminium  silver
Instrument port: up-looking (2 reflections)  side-looking (3 reflections)
Wavefront sensor for tip-tilt compensation: PWFS   (no OIWFS)

 


Observing condition constraints

Note: you should read the explanatory notes for the meaning of the percentiles and to ensure that your selected conditions are appropriate for the observing wavelength. Further details are available on the observing condition constraints pages.
Image quality: best 20%-ile 70%-ile 85%-ile any
Sky transparency (cloud cover): best 20%-ile 50%-ile 70%-ile disabled 90%-ile disabled any
Sky transparency (water vapour): best 20%-ile 50%-ile 80%-ile any
Sky background: Any (see explanatory notes)
Typical air mass during observation: <1.2 1.5 2.0

 


Details of observation

Calculation method:(more info)
Select imaging or spectroscopy and the calculation method (note: second method is not available for spectroscopy)
Imaging or  spectroscopy ...
  Total S/N ratio resulting from a total time of secs and with a fraction of exposures that observe the source (number of individual exposures will be calculated from assumed frame time)
  Total integration time to achieve a S/N ratio of 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
Output:
For spectroscopy, autoscale or specify limits for plotted spectra (lower wavelength um and upper wavelength um)

 

Last update May 24, 2007; Brian Walls