Spectroscopy and photometry of the emission-line B-type stars AS 78 and MWC 657

We present the results of low- and high-resolution spectroscopic and multic olour photometric observations of two early-type emission-line stars, AS 78 and MWC 657. They were identified by Dong & Hu (1991) with the IRAS source s 03549+5602 and 22407+6008, respectively, among many other sources display ing a very strong infrared excess, V - [25] greater than or equal to 8 mag AS 78 is recognized as a photometric variable for the first time. A large n ear-IR excess radiation is detected in AS 78 and confirmed by new, higher-q uality, data for MWC 657. Significant variations in the Balmer line profile s are detected for both objects. Modelling of the Balmer line profiles of A S 78 obtained in 1994 yields the following parameters of the star and its w ind: T-eff similar to 17000 K, log L-bol/L. similar to 4.0, (M) over dot 10 (-6) M. yr(-1). The photometric and new spectroscopic data indicate that th e star's T-eff increases with time, while the stellar wind changes its stru cture. Distances towards both objects are estimated on the basis of their r adial velocities and the galactic rotation curve. Consideration of differen t options about the nature and evolutionary state of both objects leads us to suggest that they are binary systems containing a B-type intermediate-lu minosity star and a gaseous disk around the less luminous component.