Dust envelopes around the secondary components of BM Ori and V1016 Ori

We explore the question of whether dust envelopes can survive around the secondary components of the B stars BM Ori and V1016 Ori. The assumption that such envelopes exist is shown to be unavoidable. Two alternative compositions of these envelopes are considered: graphite and alpha-cristobalite (alpha-SiO2, the refractory modification of quartz). For the graphite envelope around the secondary of BM Ori, we have failed to unambigously solve the question of its survival. The mean grain temperature is below the graphite sublimation temperature. In the case of intense mixing, the envelope does not evaporate. If, however, the envelope is static (the case of corotation), then the dust temperature turns out to be lower than the sublimation temperature in 67% of the envelope and high in its remaining part (33%). The envelope then evaporates. Model calculations show that 98% of the envelope does not evaporate in: the case of grains coagulation, and, accordingly, it survives. Since the temperature of the entire quartz envelope is below the quartz melting temperature, such an envelope can exist. An envelope made up of graphite dust grains definitely cannot exist around the secondary of V1016 Ori-such dust evaporates. However, an envelope composed of quartz grains can exist. In this case, quartz remains in a solid phase. We propose an observational check on the derived temperature distribution in the envelopes. To this end, we compare the temperatures and radii of the envelopes that we determined by analyzing the stars' continuum in the bands from to M with those estimated from the dust-envelope models. The JHKL observations of deep minima in BM Ori also lend support to the dust-envelope model. In the Appendix, we solve the light curve of V1016 Ori by assuming that the primary star is eclipsed both by the secondary and by the dust envelope. This solution is in satisfactory agreement with the observations.