Stellar Spectra

Begin by choosing a star from the pop-up menu. An image of the star will be displayed and, for most stars, the measured annual parallax angle and absolute error in that measurement will be displayed in the text box to the right of the image.

Note that the image is not, except in the case of Sol, an image of the stellar surface. It is actually a diffraction pattern with a strong, wide central maximum (the central circular "image") and in most cases indiscernible secondary maxima. In some cases, the image is a negative exposure (which sometimes makes it easier to identify the position of the star).

For all stars, the text box will also contain the minimum and maximum flux values over the range of the displayed spectrum, along with the total flux over that range.

Below this is another pop-up menu which selects an element (or ion or molecule) for spectral line identification, followed by a button and scroll bar enabling a black body temperature fit to the spectrum. Beneath those are three displays. The top display shows the spectral lines associated with the element selected (they are displayed as emission lines, that is, bright against a black background). Below that is a reconstructed color image of the actual spectra (wavelengths in the ultraviolet and infrared are displayed in shades of gray). Finally there is a graph of the flux as a function of wavelength:

You need a Java-capable browser to be able to use the applets. If they do not work with your Windows system, download the Java VM (Virtual Machine) for your version of Windows at the download section at java.sun.com.

You may click on either the spectrum image or graph to mark a central wavelength value on which to focus for detailed inquiries. The "Zoom In" and "Zoom Out" buttons allow you to quickly change the range of wavelengths displayed about that central value, and the values of the wavelength at the left and right edges of the graphs are displayed to the right of those buttons. The scroll bar labeled "Central lambda" allows you to smoothly vary the central value, and the value of the flux at the central wavelength is displayed to the right of the central lambda value. Finally, the "Gaussian Fit" button draws a Gaussian fit to the spectrum graph centered on the central lambda value, with a standard deviation as specified by the scroll bar to the right.

A few notes about the spectra:

The spectra are a mixture of low (i.e. 108 Virginis) and high (i.e. 94 Ceti) resolutions, coming from different spectrographs.

The spectra of Alpha Lyrae is a combination of a high-res ultraviolet spectrogram and a low-res visible spectrogram.

Some spectra (i.e. G93-48) exhibit flares: bright emission peaks instead of absorption dips.

Please send comments or suggestions to the author.