Bouncing against the Yellow Void – exploring the outbursts of ρ Cas from visual observations

Michaela Kraus from the ASU Stellar department together with Grigoris Maravelias from Greece studied the episodes of dimming connected with a mass loos of the ρ Cas star observed both visually or with digital technology. In their work, they show that for the study of significant brightness variations of stars, visual techniques are sufficient and, due to the length of the time series, irreplaceable. The studied star probably shifts to the edge of the yellow gap in the Hertzsprung-Russell diagram in current phase of its life.


Massive stars are rare but of paramount importance for their immediate environment and their host galaxies. They lose mass from their birth through strong stellar winds up to their spectacular end of their lives as supernovae. The mass loss changes as they evolve and in some phases it becomes episodic or displays outburst activity. One such phase is the Yellow Hypergiants, in which they experience outbursts due to their pulsations and atmosphere instabilities. This is depicted in photometry as a decrease in their apparent magnitude. The object ρ Cassiopeia (Cas) is a bright and well known variable star that has experienced four major outbursts over the last century, with the most recent one detected in 2013. We derived the light curves from both visual and digital observations and we show that with some processing and a small correction (∼ 0.2 mag) for the visual the two curves match. This highlights the importance of visual observations both because of the accuracy we can obtain and because they fully cover the historic activity (only the last two of the four outbursts are well covered by digital observations) with a homogeneous approach. By fitting the outburst profiles from visual observations we derive the duration of each outburst. We notice a decreasing trend in the duration, as well as shorter intervals between the outbursts. This activity indicates that ρ Cas may be preparing to pass to the next evolutionary phase.

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