The Distance to the Pleiades

A. Table 1 is a list of several stars from the Pleiades cluster and their colors (mB – mV, or equivalently B-V) and their apparent visual magnitudes (mV, or equivalently V). Since B-V is a color, and color is related to temperature through Wein’s law, the B-V axis is a measure of temperature. Since all of the cluster members are at approximately the same distance, plotting apparent visual magnitude is like absolute magnitude plus a constant. This is because

 mV - MV = 5logd - 5,

where d is the distance in parsecs and MV is the absolute magnitude. This means that, for a cluster, a plot of B-V vs. V is similar to a plot of temperature vs. absolute magnitude (with a vertical offset) or luminosity. Recall that temperature vs. luminosity is an H-R diagram

Sample Solution

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