摘要
本文利用列于IRAS Point Source Catalog上的Be星资料,讨论了利用IRAS的三个流量(12μm、25μm、60μm)区分红外色余是自由-自由跃迁还是由星周尘埃再发射所产生。前者被认为是经典的Be星,而后者则可能是处于主序前的Herbig Ae/Be星。但是有16个一般认为是经典Be星的,却也显示出部分红外色余来自尘埃的再发射。它们的物理状态显然值得进一步研究。
Infrared excess is one of the important characters of Be stars. The free-free radiation due to the interaction between the high temperature stellar wind and the low temperature gas disc is used to explain infrared excess of Be stars. If it is true, Be stars on the infrared color-color diagram should be distributed in a small special area as shown in Fig. 1.All Be stars listed in Jaschek and Egret (1982) and those with available IRAS flux densities at 12, 25, and 60 μm are plotted in Fig. 1. It is easy to distinguish all 64 Be stars in two groups: the first group consists of Be stars, whose infrared excess can be explained as the radiation from free-free transition of gas disc, and they are listed in Table 1. The Be stars listed in Table 2 are of the second group. They are located outside the special area in the infrared color-color diagram. This result means that their infrared excess is not only due to the free-free radiation. The reasonable explanation is the thermal reradiation of circumstel-lar dust grains caused by absorption of UV and visual photons from the central stars. It should be pointed out that there are 16 Be stars in Table 2, which are studied by Sletteback (1982) and generally considered as classical Be stars.In Fig. 2 the Be stars are plotted according to their characters, i.e. the classical Be stars, the Be stars associated with star forming region (HII regions, dark clouds and so on), the Be stars, in which IRAS LRS show silicates or Sic features. As Hu, The and de Winter (1988) have pointed out the Be stars in the last group are the candidates of Herbig Ae/Be stars. In Fig. 3 the Be stars are plotted with the mark of their (V -[25] ), except the classical Be stars in the special area. From Fig. 2 and Fig. 3 we found the criteria of Be stars based on the IRAS data.1) Classical Be stars: (V-[25] )≤5;2) Be stars associated with star forming regions: (V-[25])≥7, and F12<F25<F60 ;3) Be stars as candidates of Herbig Ae/Be stars: (V-[25] )≥7, and with 9.7 or 11.3 μm features in IRAS LRS.
