Spectra of Planetary Nebulae

This Java program reads a file containing a list of emission line wavelengths and their corresponding strengths then simulates the appearance of the spectrum in a good visual spectroscope.

Note: This program generates deep 24 bit color plots, therefore you may need to increase the color depth of your system to view subtle details in these spectra.

Warning: There may be a small delay as the Applet loads its element emission line file and computes the spectra...

• Click on the nebula in the first column of the table below to launch the spectra viewer

There is a comprehensive description for each emission line found in these tables from Meinel et al. (1975) and Acker et al. (1989). The element, wavelength range and line width are all controlled by applet parameter (PARAM) tags in the HTML source for this page. There are other options such as width and height of spectra in pixels and contrast which can also be controlled. There are also options to overlay a continuous blackbody spectrum of varying strength and to limit the wavelength range.
For example here are the parameters for Neon :

<APPLET CODE=discharge.class WIDTH=784 HEIGHT=64>
<PARAM NAME=element VALUE=NGC2440.txt>
<PARAM NAME=startWavelength VALUE=4000>
<PARAM NAME=endWavelength VALUE=7000>
<PARAM NAME=lineWidth VALUE=2.5>
<PARAM NAME=contrast VALUE=20>
<PARAM NAME=continuum VALUE=0.3>
</APPLET>

• Contrast:
  • Range: 1 to 10000 (the upper limit comes from intensity of the weakest line)
  • Default: 1 (maximum of strongest line assigned to maximum intensity, no distortion of line profile)
  • Should be adjusted to 'burn out' the strongest lines and boost the intensity of the weaker lines. Should not be too high or some line blending may occur, also the relative difference between the various emission line strengths is lost. A compromise should be reached.
• Line Width:
  • Range: 0 to 100
  • Default: 3
  • The width of emission lines is user controlled and should be adjusted so that the line profile covers at least one pixel; too small a width causes undersampling to occur and some lines may 'disappear'! However too broad a line will cause blending of lines that are closer together. Again, a compromise must be reached.
• Continuum:
  • Range: 0 to 1
  • Default: 0.3
  • Physics: In many plasma environments some residual broadband background light 'pollutes' the spectrum, either by scattering from an external white source or internal transitions involving the ion continuum. This causes a smooth background to appear as weak 'rainbow' below the level of most of the emission lines. This creates a 'pleasing' colored background which 'fills' in the empty gap between the emission lines. Here is an example of the Continuum parameter set to maximum : Continuum=1 (white light).

• NetScape Navigator 3.01
• NetScape Communicator 4.01, 4.03, 4.04
• HotJava 1.0
• Microsoft Internet Explorer v3.01

This Applet was created by John Talbot. Source code is available : discharge.java (Currently limited to 200 emission lines, however this limit can easily be removed by changing the source code and recompiling. There are more details on the color encoding subroutine)

I am also working on several other Java Applets.

Physics Background

• Instrumental Broadening
  • The first is due to finite spectroscopic resolution and can be controlled by the researcher. Often higher resolution can be achieved by larger gratings or coarse gratings operated in higher order or longer path lengths for fourier transform spectrometers.
• Intrinsic Broadening
  • The second is fundamental line broadening which can be caused by at least three factors:
    1. Doppler Broadening
       • Related to special relativity: Motion components of a particle along the line of sight causes a shift in radiation frequency. Since particles generally have a distribution of velocities, this creates a gaussian blurring in the spectral lines.
    2. Lifetime Broadening
       • Quantum mechanical in origin : Allowed transitions have a short lifetime and this translates to some uncertainty in the frequency of atomic oscillators creating a Lorentzian line profile.
    3. Density Broadening
       • Combination of quantum mechanical and electromagnetic effects: Ions are bombarded by transient electric and magnetic fields of high speed electrons zipping nearby, these electric fields split and shift the energy levels. This constant perturbation within the plasma environment depends most strongly on density and causes strong line broadening in higher density plasmas. Temperature, ionization level and the particular quantum transition involved also plays a role.

References

• Links to stellar spectra data
• Lines identified in planetary nebula from Meinel et al. (1975) and Acker et al. (1989).
• False color planetary nebula images
• Color spectra of the abundant elements [Java]