Spectra and Elements

You will need to be ON line for this one as the applet referenced below is not on this CDROM but the main one is.

Using this applet do the following and record your answers. referenced above.

1. Determine the wavelengths of the lines in the Hydrogen spectrum. Clicking on the spectrum part of the applet will show a vertical white line with the wavelength, in angstroms indicated. Use this to measure the wavelengths of the Hydrogen lines.

2. What is the wavelength of the Sodium (Na) line that is in the yellow part of the spectrum?

3. What is the wavelength of the strongest (eg darkest or brightest if you select emission) line in the spectrum of Magnesium (Mg).

Now use the applet below and answer the following questions:

Two digital spectra are displayed above (they are the same star).

Select Hydrogen (H) as the Element by clicking on the button labelled No Element. You should see 4 dark lines that line up precisely with the digital spectrum. So the Hydrogen lines are strong in this star. What about other stars?

Using the top of the two buttons labeled A1--3V, select a star of type: G1-2V (this is what our sun is):

4. Are the hydrogen lines weaker or stronger than in the A star?

5. Try other types of stars. Identify a type of star that has no hydrogen lines.

6. Now return to the selection of G1-2V. Notice that there are two features just to the left of the hydrogen line in the violet part of the spectrum. Determine if these lines come from Helium (He), Carbon (C), Neon (Ne), Calcium (Ca), or Magnesium (Mg).

7. Now remember that sodium line in the yellow part of the spectrum? Identify which kinds of stars have strong sodium.

There is one important parameter tag here:

With the value of false, as is the case here, there are no confusing lines that are used in the actual measurment of the equivalent width.

If you want the student to measure equivalent width then set this value = "true". That will bring up two green lines and a blue line. The green lines should be place on either side of the absorption feature. Yellow boxes between the green lines indicate where the integration is to being done. The blue line represents the continuum reference point and a little rectangle and the bottom of the blue line shows you visually the equivalent width. The equivalent width is also listed in the read out box. Place the blue line on either side of the continuum and average the measurements.

Finally note that one can use integrated spectra of galaxies and measure redshifts, etc, in this applet by selecting galaxies. I don't have time at the moment to document and show how this is used. Check the web page update later.