The Spectral Energy Distribution (SED) of a source refers to the measured flux, flux density, or luminosity of the source per unit wavelength, frequency, or energy. An aggregate SED can be built by combining photometric points and/or spectroscopic segments from various observatories across a wide spectral range; this is one of the functions of the Iris SED analysis tool. Iris fully supports photometric data, and provides partial support for spectroscopic data. The distinction between a photometric point and a spectroscopic segment is explained below:

Photometric points

A photometric point is defined by three numbers (s, f(s), t), namely a spectral coordinate s (either a wavelength, frequency, or energy), a flux f(s) (or flux density, or luminosity) measured at that spectral coordinate, and the time t of the observation.

Spectroscopic segments

A spectroscopic segment consists of a relatively tightly spaced collection of adjacent spectral coordinates and corresponding fluxes (or luminosities): (s_i, f(s_i)).

Iris is mainly a photometric SED analysis tool, but does provide support for short spectroscopic segments (< ~1000 points); larger segments may take a long time to display and analyze.

Note: While the time coordinate associated to a photometric or spectroscopic measurement is a fundamental piece of information, we ignore the explicit dependence in the context of SED analysis in Iris.