Anatoly Miroshnichenko

Hot star candidates with recently formed dust

We have identified a distinct group of hot stars with IRAS fluxes suggestive of a recent CS dust formation process (Miroshnichenko et al. 2002). These objects (19 B[e] stars; tentatively called B[e] stars with Warm Dust or B[e]WD hereafter) have a wide range of luminosities (log L/Lo=2.5-5). Their existence suggests that new dust can be formed near intermediate- and even low-luminosity stars. However, no systematic study of this process has been carried out yet.  B[e]WD occupy a well-defined region of the IRAS color-color diagram (Fig. 1); however, cool stars with CS dust are also found in this region. The latter can be identified from other color-color diagrams.

We found ~4500 IRAS sources with colors within the B[e]WD box, and kept identifying B[e]WD candidates in the 2MASS near-IR catalog and the astrometric optical USNO-B1.0 catalog (Monet et al. 2003). So far we separated ~40 objects with IRAS fluxes of good quality at 12, 25, and 60 microns, whose color-indices imply the presence of a hot star (Fig. 2). They are definitely not young stars, because of the lack of far-IR flux. Near-IR low-resolution spectroscopy of 2 of them (IRAS00470+6429 and IRAS02155+6410) shows that are indeed early-type emission-line stars.  The B[e]WD group, which currently contains ~60 objects, becomes the largest among the family of dust making early-type stars.

Evolved hot stars are significant contributors of gas to the IS medium (comparable to supernovae). Similarly, they could supply a large amount of dust. However, the scale of this process is not clear, as only a few dozen dust-forming hot stars are currently known. Our findings of intermediate-luminosity B[e]WD suggest that existing IR catalogs may contain many more of them. We will continue to search for new B[e]WD candidates using the results of this project to sharpen the search criteria. Extending the B[e]WD group may lead to a completely new view of CS dust formation, stimulate studies of mass loss from intermediate-mass and luminosity single stars and various binary systems, and suggest new research directions for the forthcoming space missions (e.g., Spitzer, SIM, Herschel).

References

Miroshnichenko, A.S., Bjorkman, K.S., Chentsov, E.L., & Klochkova, V.G. 2002, ASP Conf. Ser., 279, 303
Monet, D.G., et al. 2003, AJ, 125, 984

Last updated: 2004 October 28