Herbig Ae stars generally show emission in the H line (outside of the spectral range of the spectra used in this atlas), and quite often emission in H and even H . Many Ae stars are still contracting to the main sequence, and are thus either still surrounded by remnants of their stellar cocoons, or have developed massive stellar winds.
Recently, Gray & Corbally (1998 AJ 116, 2530) have devised an extension of the MK Classification System to the Herbig Ae-type stars. This system, in addition to the usual MK-type, utilizes indices to indicate emission or stronger than normal absorption in lines of the Fe II (42) multiplet, the strength of the Balmer decrement, and characteristics of the emission in the H line. The three stars illustrated here demonstrate that system. The extended spectral type consists of a normal MK type along with an indication of the nature of the Balmer line emission. An "e" indicates strong emission in the H line, (e) indicates marginal or weak emission, and an "r" or "b" indicates whether this emission is shifted to the red or blue of the photospheric line. The strength of the Balmer decrement is indicated by the symbols <, , =, , > for weak, somewhat weak, normal, somewhat strong, and strong. The nature of the emission and/or absorption, plus the strength relative to the normal absorption strength of the relevant standard of the lines of the Fe II (42) multiplet are indicated with the N index. Nem indicates these lines are in emission, Nab that they are in stronger than normal absorption, and Npc and Nipc indicate P Cygni and inverse P Cygni profiles in these lines.
The spectral types of these Herbig Ae stars can change quite dramatically on time scales of a few days. As a consequence, the spectral types of these stars should always be accompanied by a date.