Take a look at Deneb, which is an A21a star (luminosity classes are also further subdivided): The "code" tells you it's a white supergiant, and you'll find it in the upper left of the supergiant branch in the HR diagram.
Spectral Classes Luminosity Classes Spectral Class Characteristics Luminosity Type Class O Hottest; blue I Supergiant B Blue-white II Bright giant A White III Giant F Yellow-White IV Subgiant G Yellow V Dwarf K Orange M Coolest; red Caption: CELESTIAL MILEPOSTS Most of the distances to the stars of the Winter ' Hexagon can be used as markers for moments in a human life.
Without improved photometric colour data, or better, spectroscopic data to determine spectral and luminosity classes
, it cannot be assumed that our model is unique, although it is astrophysically plausible and in good company with other systems.
Based on the relative populations of different stellar luminosity classes
, Stern finds it "statistically likely that all comets in the Oort cloud have been [heated] to 27 kelvins [-246|C] at least once, and that 20 to 40 percent of all Oort comets have experienced at least one episode of surface heating to 50 K [-223|C].' As few as 50 to 100 stars with 10,000 times the sun's luminosity may ever have been through the cloud, he says.
As Schaaf points out in his introduction, if you include the dwarf companions of these bright stars, then you'll have "a nearly complete representation of the basic different spectral types, luminosity classes
, and special categories (double stars, variable stars) of stellar bodies."
Precise measurements of stars of all spectral and luminosity classes
will greatly improve our understanding of stellar physics and evolution.
Stars are assigned to luminosity classes
by Roman numerals: I for supergiants (often subdivided into classes Ia-0, Ia, Iab, and Ib in order of decreasing luminosity), II for bright giants, III for normal giants, IV for subgiants, V for dwarfs on the main sequence, and occasionally VI for subdwarfs.