Be B[e stars

- It becomes more and more clear that, although the majority of Be stars are photometrically variable, not all of them could be properly called GCAS variables. Quite a number of them show small-scale variations not necessarily related to shell events; in some cases the variations are quasi-periodic. By now we are not able to present an elaborated system of classification for Be variables, but we adopt a decision that in the cases when a Be variable cannot be readily described as a GCAS star we give simply Be for the type of variability. GCVS

B[e] stars have often been called y Cas stars4 or even y Eri stars5 although the y Cas variable stars are a distinct group of stars recognized within the GCVS and must be considered as a separate group. Carefully

'Gamma Cassiopeia variables, named for the bright, BOIVe star, y Cas.

sGamma Eridanus variables, named for the bright, MllUb star, y Eri.

distinguishing between these two similar groups of variable stars requires patience and care. The name y Eri stars is not longer used.

Within the GCVS, you will find more than 220 B[e] stars as well as almost 50 listed as uncertain (i.e. B[e]:). A handful of these stars are being observed as part of several long-term projects and amateur participation is encouraged (e.g. Dr. John Percy of AAVSO).

The B[e] stars did not become an interesting group of variable stars until after the spectrograph was developed and became a tool used by astrophysicists. An interesting phenomenon that occurs within the spectra of these stars is that both emission and shell lines can disappear completely and when this occurs, a B[e] star is indistinguishable from a normal B-type star. For unknown reasons, perhaps several years later, emission and shell spectra may again form within the normal B absorption spectrum.

The long-term variability of these stars is not strictly periodic, though it may be cyclic, meaning that the variability repeats but not in a completely predictable manner. In order to understand the nature of the variations of B[e] stars, it will be necessary to patiently observe a large number of them over the course of many years. Long-term observing campaigns are necessary for disclosing the nature of long-term variations and instruments are recommended.

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