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

A.S. Miroshnichenko^1,2 - E.L. Chentsov^3,4 - V.G. Klochkova^3,4 - K.S. Kuratov⁵ - T.A. Sheikina⁵ - D.B. Mukanov⁶ - K.S. Bjorkman¹ - R.O. Gray⁷ - R.J. Rudy⁸ - D.K. Lynch⁸ - S. Mazuk⁸ - R. Puetter⁹ - P. García-Lario¹⁰ - J.V. Perea¹¹ - Yu.K. Bergner²

1 - Ritter Observatory, Dept. of Physics & Astronomy, University of Toledo, Toledo, OH 43606, U.S.A.
2 - Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo, 196140, Saint-Petersburg, Russia
3 - Special Astrophysical Observatory of the Russian Academy of Sciences, Karachai-Cirkassian Republic, Nizhnij Arkhyz, 357147, Russia
4 - Isaak Newton Institute of Chile, SAO branch, Chile
5 - Fesenkov Astrophysical Institute of the National Academy of Sciences, Kamenskoe plato, Almaty, 480068, Kazakhstan
6 - Al-Farabi Kazakh National State University, Almaty, 480000, Kazakhstan
7 - Dept. of Physics and Astronomy, Appalachian State University, Boone, NC 28608, U.S.A.
8 - Aerospace Corp. M2/266, P.O. Box 92957, Los Angeles, CA 90009, U.S.A.
9 - Center for Astrophysics and Space Sciences, University of California, San Diego, C-0111, La Jolla, CA 92093, U.S.A.
10 - ISO Data Centre, Astrophysics Division, Space Science Department of ESA, Villafranca del Castillo, Apartado de Correos 50727, E-28080 Madrid, Spain
11 - INSA S.A., Villafranca del Castillo, Apartado de Correos 50727, E-28080 Madrid, Spain

Abstract:

We present the results of low- and high-resolution spectroscopic and multicolour photometric observations of two early-type emission-line stars, AS 78 and MWC 657. They were identified by Dong & Hu (1991) with the IRAS sources 03549+5602 and 22407+6008, respectively, among many other sources displaying a very strong infrared excess, $V-[25] \ge$ 8 mag AS 78 is recognized as a photometric variable for the first time. A large near-IR excess radiation is detected in AS 78 and confirmed by new, higher-quality, data for MWC 657. Significant variations in the Balmer line profiles are detected for both objects. Modelling of the Balmer line profiles of AS 78 obtained in 1994 yields the following parameters of the star and its wind: $T_{\rm eff} \sim$ $17\, 000$ K, log $L_{\rm bol}$ / $L_{\odot} \sim$ 4.0, $\dot M$ $\sim$ 10^-6 $M_{\odot }$ yr^-1. The photometric and new spectroscopic data indicate that the star's $T_{\rm eff}$ increases with time, while the stellar wind changes its structure. Distances towards both objects are estimated on the basis of their radial velocities and the galactic rotation curve. Consideration of different options about the nature and evolutionary state of both objects leads us to suggest that they are binary systems containing a B-type intermediate-luminosity star and a gaseous disk around the less luminous component.

Key words: techniques: photometric -- techniques: spectroscopic -- stars: emission-line -- stars: circumstellar matter -- stars: individual (AS 78, MWC 657)