Short-term H{\alpha} line variations in Classical Be stars: 59 Cyg and OT Gem

TL;DR

This study analyzes short-term Hα line variations in two Classical Be stars, revealing rare emission features, disk size changes, and rotational properties, enhancing understanding of their circumstellar disk dynamics.

Contribution

First detailed optical spectroscopic monitoring of 59 Cyg and OT Gem revealing rare triple-peak emission and disk evolution patterns in Classical Be stars.

Findings

59 Cyg exhibits a rare triple-peak Hα emission phase.

OT Gem shows significant disk loss over three months.

59 Cyg likely a rapid rotator with a large circumstellar disk.

Abstract

We present the optical spectroscopic study of two Classical Be stars, 59 Cyg and OT Gem obtained over a period of few months in 2009. We detected a rare triple-peak H$\alpha$ emission phase in 59 Cyg and a rapid decrease in the emission strength of H$\alpha$ in OT Gem, which are used to understand their circumstellar disks. We find that 59 Cyg is likely to be rapid rotator, rotating at a fractional critical rotation of $\sim$ 0.80. The radius of the H$\alpha$ emission region for 59 Cyg is estimated to be $R_d/R_*$ $\sim$ 10.0, assuming a Keplerian disk, suggesting that it has a large disk. We classify stars which have shown triple-peaks into two groups and find that the triple-peak emission in 59 Cyg is similar to $\zeta$ Tau. OT Gem is found to have a fractional critical rotation of $\sim$ 0.30, suggesting that it is either a slow rotator or viewed in low inclination. In OT Gem, we observed a large reduction in the radius of the H$\alpha$ emission region from $\sim$ 6.9 to $\sim$ 1.7 in a period of three months, along with the reduction in the emission strength. Our observations suggest that the disk is lost from outside to inside during this disk loss phase in OT Gem.