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In our sample selection, we chose optically visible stars which had previously been identified on the temperature and luminosity scales of the revised MK system (Keenan 1987). [^1] The majority of the stars were drawn from the following fundamental lists: i) Morgan, Abt, and Tapscott (1978) for 29 stars O6–G0; ii) Keenan and McNeil (1989) for 45 stars G0–K5; and iii) Kirkpatrick, Henry, and McCarthy (1991) for 5 late–type dwarfs K5–M3. We supplemented these primary standards with an additional 5 secondary standards from the compilation of Jaschek, Conde, and de Sierra (1964) and one late–type dwarf classified by Henry, Kirkpatrick, and Simons (1994).

In order to cover as complete a range of stellar temperature and luminosity as possible, we defined a two-dimensional grid with 26 bins of spectral type and three bins of luminosity class. Our temperature grid is binned $\times 2$ more coarsely in spectral subclass than the revised MK system, so that we typically sample only every other MK subclass. The three luminosity bins are divided into supergiants (I–II), giants (III), and subgiants/dwarf stars (IV–V). A full sampling of this grid would have resulted in 78 distinct temperature/luminosity pairs. Our atlas includes a total of 85 sources 