Astrophysics (Index)About

color-magnitude diagram

(graph plotting stars' color to luminosity)

A color-magnitude diagram (CMD or CM) is a graph analogous to an H-R diagram, but plotting a color index against absolute magnitude (luminosity). It is often used for galaxies and groups of stars such as globular clusters.

A hardness-intensity diagram (HID) is an X-ray variant on the concept: hardness generally short for hardness ratio, which is a color index within the X-ray spectral band, and intensity measured as photons received by an instrument during an observation. HIDs are typically used for variable X-ray sources such as an X-ray binary, the plotted points representing separate measurements each representing a time interval observation of the same source, e.g., a plot of a few hours with each plotted point being count of photons collected over one minute.

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