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

Abstract

Abstract. We present the results of low-and highresolution 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] ≥ 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:−6 M yr −1 . The photometric and new spectroscopic data indicate that the star's T 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 Send offprint requests to: A.S. Miroshnichenko, e-mail: anatoly@physics.utoledo.edu Table 9 is only available in electronic form at the CDS via anonymous ftp (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html containing a B-type intermediate-luminosity star and a gaseous disk around the less luminous component.

TOWARD UNDERSTANDING THE B[e] PHENOMENON. III. PROPERTIES OF THE OPTICAL COUNTERPART OF IRAS 00470+6429

“…Second, their average radial velocity is ∼ −100 km s −1 versus ∼ +20 km s −1 for the emission components of the Balmer lines and ∼ −25 km s −1 for those of the Fe II lines. A similar phenomenon was found in several other FS CMa type objects, such as MWC 657 (Miroshnichenko et al 2000) and AS 160 (Miroshnichenko, Klochkova, & Bjorkman 2003). Finally, they appear to exhibit a long-term (∼ 1200 days), probably cyclic, variation (Figure 12).…”

“…The presence of P Cyg profiles in the spectrum of IRAS 00470+6429 is unusual for the FS CMa star group, the majority of whose members exhibit single-or double-peaked profiles that are typical for disk-like CS gaseous envelopes. There are only two other objects in the entire group with P Cyg type profiles: AS 78 (Miroshnichenko et al 2000) and HD 85567 (Miroshnichenko et al 2001). However, this type of a line profile does not exclude a disk-like geometry, which is natural in a binary system (our working hypothesis for explaining properties of FS CMa stars, .…”

“…Our previous studies of some FS CMa type objects (see, e.g., Miroshnichenko et al 2000Miroshnichenko et al , 2002 did not take into account the entire variety of the CS effects on their parameters, because we had very sparse data at that time. Over the last few years we obtained multiple spectroscopic and photometric observations for a large fraction of the group members.…”

Fundamental parameters and evolutionary state of the Herbig Ae star candidate HD 35929

“…Studies of the IR excess evolution show that the near-IR excess usually disappears first as the star evolves toward the main sequence (e.g., Miroshnichenko et al 1996;Malfait et al 1998). The shape of the IR excess is more consistent with a steady-state mass loss than with accretion.…”

Toward Understanding the B[e] Phenomenon. I. Definition of the Galactic FS CMa Stars

“…PreYmain-sequence stars exhibit much stronger far-IR excesses (due to cold preexisting dust) and retain them much longer than the near-IR ones ( Miroshnichenko et al 1996;Malfait et al 1998). The only possibility for a preYmain-sequence star to lose the cold dust first is to be exposed to stellar winds from nearby stars in dense star-forming regions (Hollenbach & Adams 2004).…”