Institut für Astronomie und Astrophysik Abteilung Astronomie Sand 1, D-72076 Tübingen, Germany
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Spectrum

Click into this spectrum!  X:  Y:  Order:  Wavelength:  nm Remark:

If you click into the image the following information is filled out at the right side of the image:

• X and Y: the coordinates of the clicked position
• Order: the Echelle order, which is identified for the clicked position
• Wavelength: the wavelength for this position, calculated from the X-coordinate and the Echelle order.

The intensity during these measurements was low, for this image about 270 Photons per second were registered, the integration time was 34 minutes. Gas discharge lamps produce light with many emission lines, but there is practically no continuum. Further below there is a table containing several identified emission lines.

You will see that several lines, especially in the higher orders, appear in two adjacent orders. This is due to the fact, that the wavelength ranges of the individual orders overlap for a certain range, which is the larger, the higher the Echelle order is.

The entrance aperture of the spectrometer is a 20 arcsecond diaphragm, i.e. during the astronomical observations this diaphragm shows a circle of 20 arcseconds of the sky. This is a relative large area as compared to the pointing accuracy of the ASTRO-SPAS satellite. As the diaphragm is completely illuminated during these laboratory measurements the emission lines apear much more blurred than they were later during the astronomical observations.

At the bottom left and the upper right corners there are bright spots visible. These spots are produced by electronical test pulses, which are recorded during all measurements. These test pulses will allow to record changes of the electronics (e.g. caused by temperature drifts), which could therefore be corrected later.

The wavelength calibration used for this page is based on a simple linear calculation, its accuracy is about 0.2nm (depending on the accuracy which can be achieved by placing the hand cursor of the browser). The final wavelength calibration is much more detailed and thus much more accurate.

The image shwon has a format of 512 x 512 pixels. During the mission the images were recorded with 1024 pixels in horizontal (main dispersion) direction.
 

Cut along the 45^th order

This graphics shows the intensity of the 45^th Echelle order. Note that the wavelength scale runs in the reverse direction than the pixel numbers, i.e. from right to left!

For extraction a stripe of 9 pixels was used, so that the complete Echelle order was covered by this stripe. For each horizontal pixel the intensity values (number of registered photons) of the 9 vertical pixels were added and the corresponding wavelength was calculated for each horizontal pixel. The result is the picture shown above, which shows the number of registered photons (counts) against the wavelength. The wavelength unit is given in Angstrom: 10 Å = 1 nm. This unit is no longer an official unit, but it is still preferred as a unit for the wavelength of light.

In the final data reduction of the measured spectra the counted photons are converted to the flux unit "photons/second/cm²". For this conversion the effective area of the instrument has to be considered together with the integration time. Another common unit is "ergs/second/cm²", for which the energy of a photon is converted to the energy unit erg.

This is the original plot to order 45 of the spectrum files given below.
 

Table of some identified lines

FUV test at IABG

This image shows the upper part of the telescope with the echelle spectrometer hanging downward in a vacuum chamber at the company IABG in Ottobrunn. In the center of the telescope the spider pot is visible, which will contain later the Berkeley spectrometer. The closed telescope cover is located at the back side.

Main task of the FUV tests was the verification of the optical adjustment and the focussing of the detector. As there is no active focussing of the Echelle Spectrometer, the best focal position of the detector had to be found by trial and error. The detector was then mounted with the optimized focus position found during these tests.
 

Individual Echelle Orders as spectrum files

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| Impressum Last modified 16 Feb 2005