Radiation Lab and Demo

This applet is experimental (in particular, an excuse to learn Java). It's possibly too technical for 100-level astronomy, and too elementary for science majors. However, hopefully elements will suggest themselves as useful for abstraction and further development for either of those tracks. Comments, suggestions, and requests welcome. Background and instructions follow the applet.

HINT: Sliders rarely slide smoothly; try clicking on the slide bar or arrows.

Choice Buttons

The line of buttons at top enables the user to choose a continuum, absorber and filter. The Applet starts by default with BlackBody continuum (6000K), no absorber, no filter. The current options are:

Continuum

BlackBody: 2000 - 10,000 K, shown 0.38 - 0.78 microns
Synchrotron: peak frequency 0.05 - 22 GHz, shown 0.1 - 14.5 GHz; the optically thin spectral slope is 0.5. (NB. "peak" frequency is the frequency of unit optical depth in the comoving frame.)
X-ray cluster: 5 - 200 MK, shown 0.1 - 10.0 keV (NB. the low energy (E<<kT) Gaunt factor is kludged to match the high energy form at E=kT -- introducing an error of about x2 for E<<kT: who cares!)
OB Stars: 30,000 - 90,000 K, shown 0.01 - 3.4 (L-Band) microns; this is essentially the same as the BlackBody, but is displayed logarithmically (magnitude-LIKE scale) over a much larger range of wavelength to admit demonstrating dust absorption, particularly in the UV.

NB. The plot is logarithmic if that is normal practice for the waveband.

Absorber

Absorbers take effect only for the continua for which they make sense -- optical lines for the BlackBody, HII for the synchrotron, etc. In particular, both line and dust absorption may be used with both "regular" and OB-star BlackBody continua; however, because of the logarithmic scale used for the latter, and the arbitrary line depths used, invoking line absorption on the OB-star continuum is not very illuminating.

None
H gas -- main Lyman, Balmer and Paschen lines
FeI/II -- lines of neutral and singly ionized Fe from 2084 to 9000A. The strong UV lines may be seen by redshifting the absorber. These data kindly supplied by Prof. Charles Cowley .
HII plasma -- parameters are for T=10⁴K, and with density and size appropriate for a substantial Galactic HII region (10⁸ m^-3, 20pc) or an elongated ISM fluctuation such as might cause an Extreme Scattering Event (10¹¹ m^-3, 2.5x10^-4pc).
ISM gas -- solar neighborhood abundance with HI column depth = 10²¹cm^-2 using Wisconsin cross sections; as shifting the absorber can lead to energies < 0.1keV, a nominal plateau is inserted at shifted energies below the value covered by the interpolation coefficients.
Dust -- parameters are R_v=3.1, typical of the diffuse ISM, and A(V)=2.65, corresponding to a Hydrogen column of approximately 5x10²¹ cm^-2. The values for interstellar extinction are from Cardelli et al. (1989) down to a wavelength of 0.1 microns, below which two polynomial fits to the data tabulated in AQ(4th Ed)-21.2.1 are used.

NOTE: There is no attempt to show the true line width; this would be unresolved for all but things like BAL spectra on this scale.

Filter

Filters take effect only for the continua for which they make sense -- U, B and V for the BlackBody etc. Note that they cannot be invoked for the OB-star continuum, because of its logarithmic scale.

None
U-band; these are currently approximated by skewed exponentials
V-band
B-band

NOTE: when reselecting a continuum, the absorber and filter are reset to none.

Guide Strip

Below these buttons a graphic representation shows from left to right: the continuum, the absorber, the filter and a telescope. Use this as a visual guide to the current selections.

Plot Area

The spectrum is plotted in the main part of the Applet area, and adjusts immediately in response to any user changes. NOTE: The vertical axis is in arbitrary units, and rescales upon adjustment. In general, changes make such a large difference to the peak (e.g., T=2000K to T=10,000K for the BlackBody) that absolute scaling is not viable.

Visual Spectrum

If, and only if, the continuum is a BlackBody, a strip below the plot area gives a visual representation of the continuum and lines. This is depicted as realistically as is practical: CIE Color Matching Functions and Chromaticity Coordinates for the XYZ to RGB vector transformation have been taken from Bruton, 1996.

Continuum Slider

Enables the user to adjust one parameter associated with the continuum.

Continuum Doppler Slider

Enables the user to change the redshift (-0.95<z<4.9) of the continuum.

Absorber Doppler Slider

Enables the user to change the redshift (-0.95<z<4.9) of the absorber.

Memos to Self

Add more line absorbers / Use proper line strength parameters?
More accurate U/B/V filters, and extend to IR?
Smarten up plot graphics..... NO resize on plot, colors, better gifs?

Unit increment on ScrollBars seems system dependent; true?
No Y label, bug of appletviewer alone? (Does appear with NN/Solaris & WNT.)
IE/W95 gives Security Exception. (No problem with NN/Solaris & WNT; function of flakey IE on my LT?)

The main plot is done with Leigh Brookshaw's Graph2D, with the following changes:

Graph2D was subclassed as Graph2De to allow an override of
public Dimension getPreferredSize() and
public synchronized Dimension getMinimumSize();
otherwise the layout manager produces a plot of zero size.
Axis.java was modified and rebuilt to add
int dot = label_string[i].indexOf(".");
label_string[i] = label_string[i].substring(0,dot+2);
to protected void calculateGridLabels(); otherwise because of rounding some labels have double precision number of digits, greatly distorting plot. Could not see an easy way to avoid this through subclassing/override.

P. A. Hughes. Last changed 29 March 2000. Email: phughes@umich.edu