Maravelias & Kraus 2022: Bouncing against the Yellow Void — exploring the outbursts of ρ Cas from visual observations

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

Grigoris Maravelias and Michaela Kraus

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.

Figure 3.The duration of each outburst (dots) with time(using the minimum dates as identified from the fitting process). There is a trend of shorter outbursts with time (linear model indicated with the violet dashed line). They also seem to occur more frequently, as it is indicated by the time difference between the outbursts (violet arrows).

arXiv: 2112.13158

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