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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

New paper on rho Cas and its recent outburst in 2013

A new outburst of the yellow hypergiant star Rho Cas

Michaela Kraus, Indrek Kolka, Anna Aret, Dieter H. Nickeler, Grigoris Maravelias, Tõnis Eenmäe, Alex Lobel, Valentina G. Klochkova

Yellow hypergiants are evolved massive stars that were suggested to be in post-red supergiant stage. Post-red supergiants that evolve back to the blue, hot side of the Hertzsprung-Russell diagram can intersect a temperature domain in which their atmospheres become unstable against pulsations (the Yellow Void or Yellow Wall), and the stars can experience outbursts with short, but violent mass eruptions. The yellow hypergiant Rho Cas is famous for its historical and recent outbursts, during which the star develops a cool, optically thick wind with a very brief but high mass-loss rate, causing a sudden drop in the light curve. Here we report on a new outburst of Rho Cas which occurred in 2013, accompanied by a temperature decrease of ~3000 K and a brightness drop of 0.6 mag. During the outburst TiO bands appear, together with many low excitation metallic atmospheric lines characteristic for a later spectral type. With this new outburst, it appears that the time interval between individual events decreases, which might indicate that Rho Cas is preparing for a major eruption that could help the star to pass through the Yellow Void. We also analysed the emission features that appear during phases of maximum brightness and find that they vary synchronous with the emission in the prominent [CaII] lines. We conclude that the occasionally detected emission in the spectra of Rho Cas, as well as certain asymmetries seen in the absorption lines of low to medium-excitation potential, are circumstellar in nature, and we discuss the possible origin of this material.

arXiv.org: 1812.03065

AAVSO top visual observers

I just stumbled upon an interesting article about Rod Stubbings, a visual observer who made more than 200,000th variable star observations! This, as Mike Simonsen says, places him in top five visual observers in the history of variable star astronomy.

An interesting image of the persons and their corresponding number of observations (through the year 2009-2010) is the following one.