The behavior of the OI line 7772 in Be and related stars.

We describe the spectra of more than sixty stars in the 7570-7980 region. We find that O I 7772 is always in emission in Be stars: in the earliest types it is seen in clear emission whereas in the later types it fills in the observed absorption line. We find a good correlation of the line intensity of O I 8446 with O I 7772, the former being about four times stronger than the latter. We confirm the correlation with Fe II 7712. We also derive the outer radii of the line emission forming regions and find that O I 7772 is formed very close to the stars surface, whereas Fe II is formed farther away. We also provide criteria to distinguish, at this wavelength range, the classical Be, Herbig Ae-Be and B(e) stars.