This is another in a series of reports that I began preparing on my own initiative in 2021. It has become a good custom to divide it into two parts: one celestial, about the interesting behavior of stars, and one earthly, about the activities of the members of the Section of Variable Stars and Exoplanets of SAS at SAV and SZA (hereafter “the Section”). Thus, this article may also be regarded as a report on the activities of the Section.
From the novae that erupted in 2021, attention was still drawn by the slowest one, V1405 Cas, and, paradoxically, also by the fastest nova ever, V1674 Her.
V1405 Cas
V1405 Cas is a very slow nova with multiple maxima and variations in brightness. In 2023, it was in the nebular stage and continued to show short-period variations with large amplitude. Figure 1 shows the result of a simple period analysis. The longer wave matches well with the orbital period of 4.52138 hours. The faster variations do not have a stable period and change from night to night. Both of these periodic changes leave plenty of room for deeper research. We have collected a large amount of data.
V1674 Her
V1674 Her is the fastest of all novae known to date. In addition, it is also an intermediate polar. In Kolonica and Hlohovec we monitor this object just like the other selected intermediate polars in order to determine the evolution of the white dwarf’s rotational period in the system. The most recent results were presented at the conference Observing techniques, instrumentation and science for metre-class telescopes III in the Tatras in September 2023. The relevant O-C diagram is shown in Figure 2. In addition to the extraordinarily rapid spin-up, we also have information on the evolution of the orbital period. However, it is still too early to draw any conclusions.
V808 Aur
V808 Aur is our favorite polar with deep eclipses. We have been observing it since its discovery in 2009 using the 1 m telescope at the Astronomical Observatory at Kolonica Saddle. It would already be possible to study the evolution of its orbital period, when suddenly the polar surprised us with an unusually deep low state. As with all polars, this one has so far alternated between high and low states. However, this decline is significantly deeper, as documented in Figure 3.
Supernova in M101 – SN 2023ixf
A supernova only 20 million light-years away is the event of the year in the world of variable stars. The eruption in galaxy M101 was well covered by many observatories worldwide and did not require special efforts from us in Slovakia. At Kolonica Saddle it was monitored by astrophotographer Karel Kolomazník. We are awaiting the results of a photometric analysis of his color images, prepared by our member Matúš Kamenec. In the meantime, he has become a PhD student in astronomy at UPJŠ in Košice and is therefore quite busy. For now, we can look at the light curve obtained by Ian Sharp, a member of the Variable Star Section of the British Astronomical Association (VSS BAA). The decline in brightness after the 180th day post-explosion is not easy to explain. On the other hand, it shows how interesting it is to monitor supernovae (and novae) long after maximum.
Among global advances, I draw attention to the review by E. Aydi et al. on classical novae: “Revisiting the classics: On the evolutionary origin of the ‘Fe II’ and ‘He/N’ spectral classes of novae”. In brief, the classification of novae by spectrum into Fe II and He/N types is affected by selection bias. It seems that all novae pass through both stages, though our observational methods do not always capture them.
Activities of the Section
Let us smoothly move on to the second part of the report focused on the Section’s activities. First of all, congratulations to Matúš Kamenec, who is formally joining the professionals.
The year 2023 was the third year of the Section’s existence. The official number of members is 20. Each of them carried out individual observational or publication activities. In peer-reviewed journals, 15 papers on variable stars and exoplanets were published with Section members as co-authors, and in eight cases, a Section member was the first author. It is not my place to assess their importance, but I will highlight two articles to illustrate how Slovak astronomy contributes to global knowledge:
– BU Canis Minoris – the most compact known flat doubly eclipsing quadruple system (Pribulla et al., 2023, MNRAS 524, 4220P)
– Chaos in multiplanetary extrasolar systems (Gajdoš & Vaňko, 2023, MNRAS 518 2068G)
The main event where Section members could personally participate was the Variable summer school, held in July at the Astronomical Observatory at Kolonica Saddle, again under the professional guidance of Theodor Pribulla. This time, it focused on an advanced course in photometry using the IRAF software package. Over the long term, we can state that a well-prepared event mainly attracts Ukrainian and Polish participants, with only a few Slovak participants.
In September, an important conference took place in the Tatras: the third edition of the conference on observing techniques, instrumentation, and research with small telescopes. Five Section members actively participated. Alongside it, the traditional Kolos conference was also held, organized under the leadership of the Vihorlatská Observatory in Humenné.
Looking Ahead to 2024
We must be on alert in 2024. The eruption of the recurrent nova T CrB is approaching. At maximum, it can reach a magnitude 2. This is a challenge, especially for photometric monitoring. Usually, we strive to push the limiting magnitude of our instruments toward the faintest objects. Here, however, the task is exactly the opposite. It is an opportunity for low-cost, wide-field amateur setups. Spectroscopy with both low and high resolution is already prepared in Slovakia—in the Tatras, Kolonica, Liptovská Štiavnica, and Hlohovec. The previous eruption occurred in 1946.
Traditional events will also take place. Please note the dates:
– Variable: 26 July – 3 August 2024
– Kolos: 24–26 October 2024
Kolonica, 1 January 2024
Pavol A. Dubovský
Chairman of the Section