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ESO 1.52m + B&C Exposure Meter

This form will help you plan your observations at the ESO 1.52m telescope using the B&C spectrograph by allowing you to produce a graph of S/N against exposure time for a star or an extended object of given magnitude. The output is produced as gif, encapsulated PS and ASCII (a table) files. Fill in the form below (help is available for all the fields via the hypertext links) and then click on `Submit'.

grating #
diff. order
Wavelengths 1 (nm)		2 (nm)
3 (nm)
AB Magnitude
Exp. Time: Min (s)		Max (s)
N. of columns

General Description

This exposure time estimator uses an HTML form to submit data to a PERL script via the Common Gateway Interface. The PERL script processes the parameters, and calls a FORTRAN program. The FORTRAN program generates the plot in GIF and PostScript formats using SuperMongo library routines, as well as a table containing the data points. To avoid problems with caching, each of the files generated has its own id number, and to avoid disk overload the (n-5)th files are deleted when the n'th files are generated (Note: not all browsers support Pragma: no cache). The PERL script generates the page returned to the user.

Diffraction order

Type here the diffraction order you are using

Wavelengths

Enter here 3 wavelengths in nm at which the S/N will be computed. The computation is done assuming the same AB magnitude at each wavelength. The S/N v exposure time curves are shown in different colors for the different wavelengths.

AB Magnitude

Type here the AB magnitude of the object. The S/N will be computed assuming the object to have this magnitude at all the 3 wavelength specified in the form

Exposure Time

Type here the minimum and the maximum exposure time in seconds for which you want plots and table to be computed. The S/N is computed on 100 points going from Exp.Time Min to Exp.Time Max with a logaritmic step

N. of Columns

Type here how many columns the spectrum will cover. For a stellar source, this is generally 3 or 4. If you are observing an extended object, you can put N. of column = 1. In this case the input magnitude will be the magnitude falling on 1 column of the CCD, that is the surface brightness of the object times 0.82 x slit width (in arcsecs). For a 2" slit is therefore magnitude = surface brightness x 1.64.