Astron. Astrophys. 344, 614-616 (1999)

4. Discussion and conclusions

A B[e] stars is a Be star exhibiting forbidden lines in emission (Jaschek & Jaschek, 1987). The most frequently found forbidden emission lines in B[e] stars are those of [Fe II] and [O I]. The spectroscopic characteristics of 3G71 indicate that it must be a B[e] star. Since B[e] stars are defined by spectroscopic criteria alone, a certain superposition exists between B[e] stars and Herbig Ae/Be stars. Finkenzeller and Mundt (1984) noted that among the some 60 Herbig Ae/Be stars discovered at that time, about 30 are B[e] stars, so we wonder whether 3G71 is also a Herbig Ae/Be star.

As a kind of special stars, an important criterion of Herbig Ae/Be stars is that there must exist nebulosity around the star, as Herbig (1960) first suggested. To confirm our suspicion, we have made a search for a nebulosity in the immediate vicinity of 3G71 by consulting Palomar Sky Survey map and actually found a bright nebula with a diameter about 1 arc-minute, at whose center 3G71 is just located.

Be stars with peculiar infrared excess can be divided into three classes (Hu and Zhou, 1990), that is, classical Be stars, Be stars associated with star formation region, and Herbig Ae/Be stars. Hu and Zhou (1990) found that for classical Be stars the difference between visual magnitude V and 25 µm infrared magnitude [25] of a star is equal to or less than 5, while for Be stars associated with star formation region and Herbig Ae/Be stars the difference V - [25] is equal to or larger than 7. Furthermore, they pointed out that, one can distinguish stars associated with star formation region from Herbig Ae/Be star candidates, only by judging whether the criterion of flux densities is satisfied or not. In the infrared color-color diagram, these three types occupy different parts (Hu and Zhou, 1990). Observations demonstrated two stars (HD 100546 and HD 104237), falling in the Herbig Ae/Be stars region in the infrared color-color diagram, turned out to be good candidates (Hu, The, & de Winter, 1989), and are now accepted as Herbig Ae/Be stars (van den Ancker et al. 1997). 3G71 is largely deviated from the classical Be-star region in both Cote & Waters' (1987) and Hu & Zhou's (1990) color-color diagrams, and its V - [25] equals 12.47, which means that it is not a classical Be star. Moreover, the flux densities do not satisfy the criteria given by Hu and Zhou (1990), and from its position in infrared color-color diagram one can predict that 3G71 should be a Herbig Ae/Be star, so the characteristics in infrared region of the star further illustrate that it is a Herbig Ae/Be star candidate.

According to the analyses mentioned above, the fundamental characteristics of 3G71 coincide completely with the criteria for membership of Herbig Ae/Be stars (The et al. 1994), so we can conclude that 3G71 is a Herbig Ae/Be star candidate.

This result implies that 3G71 might not be the optical counterpart of the hard X-ray source 1H2214+589. Previous identification may be wrong and a further identification is needed. So far, none of about 30 Be/X-ray binaries identified has been found to be Herbig Ae/Be stars or B[e] stars.

© European Southern Observatory (ESO) 1999

Online publication: March 18, 1999
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