Spectral Types of Stars
The Java applet below allows you to plot observed spectra of stars of several
spectral types. You can then compare them with blackbody spectra of
adjustable temperature.
This applet is part of some sample notes from
"Life in the Universe", a distance learning course
in astronomy offered by the
Jodrell Bank Observatory of
The University of
Manchester. More information on these courses
is available here.
The applet has the following features:
- Selecting observed data: At bottom left of the graph there is a
choice button which initially says "O5V". The blue line on the graph
is th spectrum of a star of spectral type O%, luminosity class V.
By clicking on the
button at the right of the "O5V" text you can select another type
from the pop-up list.
-
Changing the temperature of the blackbody: At the bottom of the applet is a slider allowing you to click and drag the
temperature between 1 and 30,000K. It is initially set at 8,000K. Clicking on
the arrows at either end of the slider will change the temperature by 1K. The text field
at the left of the slider shows you the current temperature. You can also click in this
field and change the temperature to any value you like.
-
Fiducial wavelength: The program automatically scales the blackbody spectrum
so it passes through the observed spectrum at the fiducial wavelength. This is
initially 5000 Angstroms. You can change this to any point you like by clicking on
the observed spectrum at the point you would like the blackbody curve to pass through.
- Zooming in and out: You can zoom in on any region of the
graph by clicking on the graph and dragging out a rectangular region.
Start at the upper left corner of the region
you wish to view in more detail, and drag downwards and to the
right. [Dragging upwards instead allows you to zoom out - when zooming
out, a reference box is drawn that will represent the current view,
and dragging will cause a box to be displayed that represents the
new view.] Clicking on the "fill" button at the upper right brings all
data back within range.
Work through the following exercises:
1. Select spectral type G5V. Choose a fiducial wavelength around 7000 Angstroms by clicking on the spectrum of the star at about that wavelength. Adjust the blackbody temperature until you get the best fit to the observed spectrum on the right side of the plot i.e. where the flux is declining towards higher wavelengths. Is this temperature consistent with what you expected? |
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2. Suggest why the blackbody curves seem to fit best to the long wavelength end of the
observed spectra?
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Return to Life in the Universe
Properties of Stars web pages.
The graph plotting in this applet is achieved using the
Ptplot package.