What is spectrograph test?

Answer 1

The procedure that has been adopted for the processing of the data includes the following stages:

• The spectrum of a reference star is obtained.
• The sky is removed from the raw spectral star image.
• The columns perpendiclar to the spectral image are added to obtain the stella spectrum.

These tasks have been performed in IRIS. The sky removal and optimal addition options within IRIS both seem to give excellent results.

The output from IRIS has had the local sky effects removed but is still dependant on the spectral response of the optical system. To calibrate the spectrum we do the following:

• Divide our spectrum by a library spectrum for the same spectral type.
• The resulting curve is smoothed.
• This is then used to calibrate the other spectra... We divide our other spectra by the calibration curve.

These tasks are performed in Visual Spec. The library spectra are supplied as part of that package. These appear to be from the Pickles catalogue and are normalised with to 550nm (V-Band) to equal a relative flux value of 1.

It is clear that errors could be included at each step in the procedure. It would also be very complex to calculate these individual errors. However, the differences between the different spectra of the same star taken over the course of a number of nights would give us a good idea of the overall accuracy of our results.

So.... If we.....

• Take the spectrum of a reference star, process it to obtain a spectral response curve.
• Take the spectrum of another star with a different spectral type, use the response curve to calibrate it.
• Repeat this same procedure a number of times over a number of different nights.
• Compare the data sets and calculate an error value for each wavelength and hopefully a percentage error.
• Convert this to an average error across the B, V & R bands if this is possible.

This could then provide some level of quality assurance for the spectra obtained.

I hope it help you... :)