Optical Spectroscopic Monitoring Observations of a Young Binary Z CMa

Abstract

The results of optical spectroscopic monitoring observations of a young binary system, Z CMa, are presented in this study. Z CMa consists of a Herbig Be star and an FU Orionis object, and it shows irregular light variation in the quiescent phase and exploding brightening in the outburst phase. Medium-resolution spectra were obtained on 21 nights between 2015 and 2019 using the Nayuta telescope in Japan. We also used five high-resolution spectra, obtained between 2008 and 2011, with the Keck Telescope. During the outburst phase, the intensity of the He I absorption line increased with an increase in the luminosity of the system. Because the He I absorption line is a characteristic feature of an early-type star, we considered that the outbursts were caused by the Herbig Be star. The equivalent widths of the [O I] line decreased with an increase in the luminosity of the system. We claim steady mass loss at the rate of The intensities of the Hα and Fe II emission lines did not change during the outbursts. However, the line intensities increased with an increase in the luminosity of the system in the quiescent phase. We consider that those lines are attributed to the FU Orionis object and the light variations in the quiescent phase were caused by the FU Orionis object.