About half of the objects listed in Table 1 (click here) show neither small nebulosities (their images are comparable with those of stars), nor large envelopes. Around three objects small nebulosities and around the standard nebula Hb 6 a halo were discovered. Besides, at four further emission-line objects the presence of very small nebulae is possible, but questionable.
The above method with the relation given in Sect. 3 requires nebulosities with Gauss profiles. This is of course not valid for large nebulae, but it may be accepted for
very small nebulosities (in the range of 1 arcsec or below). Perhaps this is the reason why the somewhat larger standard nebulae Hb 6 and IC 4997, with a ringlike structure, appear smaller when using the Gauss approximation.