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New paper: exploring the outbursts of ρ Cas from visual observations

This is a paper that I finally managed to complete. Starting back in 2016 we looked into the light curves for ρ Cas to identify potential correlations with its latest outburst in 2013, but not all data made it through the final paper (Kraus et al. 2019). Given this first analysis and the fact that visual observations cover almost a century of star’s behavior, we continued the study and we looked into the four distinct outbursts. The result is even more interesting as there is a clear trend of shorter and more frequent outbursts, as if ρ Cas is bouncing against the Yellow Void.

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

Digitizing (some) older observations of rho Cassiopeia

In the old days observations were not coming in such convenient formats like machine readable tables or though Vizier catalogs. There were written in text within the papers. So, for today’s standards it is a bit frustrating to find data in this format when you need them. The way to digitize them can be automated today but still some manual treatment may be needed.

Anyways…this whole introduction was made to justify somehow this post. I found myself trying to include some data to build a light curve for rho Cassiopeia, and in particular V measurements around its outburst in 1986. Zsoldos & Percy (1991) and Leiker & Hoff (1987) are two papers with about 70-80 observations each. The V magnitudes were given either directly or as a difference with a standard star. I have done all the necessary … eye processing to “copy” all the observations form the two papers to two separate simple ascii files each one containing the Julian Data, the magnitude, and its error (if available).

So, if you ever (..!) find yourself trying to do the same thing, just use the following files ! Enjoy!

Zsoldos & Percy (1991) data | Leiker & Hoff (1987) data