Long-Term Variations in the Spectrum of Boss 1985.
Anne Pyne Cowley · The Astronomical Journal · 1964
In many respects the over-all spectrum of Boss 1985 is similar to VV Cephei. Bidelman had classified the red component as an M2 lab. In the blue region there are numerous emission lines of permitted and forbidden Fe II superimposed on the absorption spectrum. At wavelengths shorter than He the composite spectrum is dominated by the continuum and some absorption features of a B-type star. Many emissions of [Ni II,~ [Cr IIj, and [Fe ii~ appear in the ultraviolet. Well over 100 spectral plates from Michigan, Lick, Mt. Wilson, McDonald, and the Cape Observatory have been included in this study. The earliest slit spectra were taken in 1918. Measurement of the absorption spectrum of the M star reveals a velocity variation with a period of approximately 27 years. Preliminary orbital elements are: P=9900days "`=2120 K=18 km/sec T=JD2431990 e=0.4 a, sini=2.25X109 km = +33 km/sec =15.0 a.u. The forbidden Fe II emission shows no conspicuous variations in either intensity or velocity throughout the orbital cycle. The mean velocity, on the basis of 83 plates, of the [Fe IIJ lines in the blue region is + 34 km/sec with a scatter of about 15 km/sec. This value is remarkably close to the center of mass velocity of the system. Both the permitted Fe II and hydrogen emission lines vary considerably in intensity. They are present with great strength for about one third of the orbit, reaching maximum intensity near the time of periastron passage. Small intensity variations may occur in less than a year. Like VV Cephei, the hydrogen lines usually show a reversed P Cygni profile. In VV Cephei, however, the hydrogen emission lines disappear as the B star is eclipsed by the supergiant M star. In striking contrast to that conclusion we find in Boss 1985 that the hydrogen and Fe II emission lines are exceedingly strong at the time when the B star is most distant, this is, at the time when an eclipse would occur if the inclination were suitable. An ultraviolet shell-like absorption spectrum was noted by McLaughlin, Swings, and others between 1947 and 1949. Although it appeared at approximately the phase one would expect if it were due to an atmospheric eclipse of the B star by the M star (like that of VV Cephei) its interpretation is ambiguous, since this time closely coincides with the periastron passage of the stars in their quite eccentric orbits. Thus the shell spectrum may be associated with the close approach of the two stars. The shell spectrum appears to be weaker than that of VV Cephei.