Vspec+frequency+calibration

Vspec calibration for frequency

The screen shots below are a click by click method to calibrate a strip image from IRIS.

The first step is to load the image and then display the graph by clicking on the icon shown below.

The graph will then need to be trimmed to remove the source star and the background sky. Click, hold and drag the mouse. A dotted line a the start and end of the section required will be shown as in the image below.

The icon to crop the graph is shown in the image below.

When cropped, the data can be calibrated for frequency. This may be done in a number of different ways. The method below is to select 'Calibration 2 lines' as can be seen by the icon slected within the image. The default in Vspec is for H alpha and H beta. Other elements may be selected, but this will be detailed in another section.

When you click 'Calibration 2 lines' you are presented with a check box. Click Yes.

This is the tricky part. Unless you are farmiliar with looking at these graphs, it would not be obviouse as to which 'dip' would be H alpha. Hydrogen shows up strongly in certain stars, and is used as the default reference points for calibration. Unless you manualy change this.

6563 Angstroms is H-Alpha (656 Nano meters), Hydrogen-Beta is 4861 Angstroms (486 Nano meters) Balmer series.

It appears that these graphs become farmiliar over time and you 'get to know' what the dips mean and where the elements are!

Click, hold and drag the mouse over the Hydrogen Alpha 'dip' to right (Red, longer wavelengths are to the right, shorter to the left) and then release the mouse. A number will appear. This should be 6563. If not type it in.

You can if you wish select the desired frequency from the Medeleiev table. Click 'Tools/Elements' from the tool bar. The small 'Calander' looking icon when clicked will bring up the table. Selecting the element will change the number to what you require.

When Hydrogen Alpha is selected, press enter.

Then you will need to select Hydrogen-Beta which is 4861 Angstroms (486 Nano meters) Balmer series.

Again, click, hold and drag the mouse over the Hydrogen Beta 'dip' to left and then release the mouse.

A number will appear. This should be 4861. If not type it in. Hit the return key to complete the procedure.



When complete you can then click the 'Graduations' icon to the right of the graph This is the small yellow square outlined with black outline and small black marks.



Bring up the elements table by clicking 'Tools/Elements' and then bring up the Medeleiev table. Click on Hydrogen. This will then show all the Hydrogen lines within the graph. They should corolate with the dips within the graph.



The image below shows Hydrogen aligned with the calibrated graph.



The next phase is to calibrate the graph for CCD/system response. Click Vspec ccd response calibration to follow this procedure