The planned outburst of the recurrent nova T CrB has still not occurred. There are, however, plenty of interesting phenomena in the sky and likewise many activities by the members of the common Section of Variable Stars and Exoplanets of the Slovak Astronomical Society at the Slovak Academy of Sciences and the Slovak Astronomical Union (hereafter the Section). As usual, I will divide the report into a part dealing with events in the sky and a part summarizing the efforts of astronomers on Earth to understand what the signals from the Universe are telling us.
In the universe
Improving observational techniques is bringing many discoveries, transient phenomena, high-quality light curves, and surprising observations. What follows is only a modest selection based on the author’s subjective choice.
BG CMi in a low state
Low states in intermediate polars are, unlike in classical polars, rare. But as observations become denser, they are gradually appearing. Known cases include V1223 Sgr, FO Aqr, MU Cam, DW Cnc, V515 And, RX J2133+5107, DO Dra, V1323 Her, V1025 Cen, and most recently BG CMi. The drop in brightness is associated with a change in the mode of mass transfer between the components. Instead of disk-fed accretion, direct transfer from the secondary to the white dwarf (stream-fed accretion) takes over. From the observer’s point of view, this effect is accompanied by a change in the periodogram. Instead of the frequency ω corresponding to the white dwarf rotation, aliases with the orbital period Ω appear. The low state of BG CMi, which began at the beginning of 2025, is a textbook example of the described process. In Fig. 1, the long-term light curve of BG CMi from AAVSO data (left) is shown. The lower panel illustrates the drop at the beginning of the year. Periodograms from nightly time series, also from AAVSO data (right), taken from a forthcoming paper by A. W. Shaw et al., “A multi-wavelength study of the 2025 low state of the intermediate polar BG CMi”, show that during the low state, the dominant frequencies became ω − 2Ω and ω − Ω.
The reduced brightness of an intermediate polar is most likely caused by a lower mass transfer rate. However, the cause of this lower rate is not clear. A commonly accepted explanation is that a cool spot on the surface of the secondary star reaches the L1 point from which matter flows. Proving this hypothesis will not be easy. It will be necessary to map spots on the surface of the red dwarf, whose contribution to the total light is minute.
RW Sex — disappeared flickering
RW Sextantis represents nova-like stars, a group of cataclysmic variables with the highest mass transfer rates. The accretion disk is therefore constantly in a hot state, and no classical eruptions occur; other activity manifestations are observed instead — for example, flickering, but also long-term brightness changes. A group led by Andrej Dobrotka studies flickering. RW Sex was observed as part of a campaign aimed at detecting a break frequency around 1 mHz. As a by-product, it turned out that a small brightness drop of 0.2 mag was accompanied by a significant reduction in the amplitude of flickering, which is demonstrated in Fig. 2.
This raises the question whether low states in intermediate polars and in nova-like stars may have the same origin, and whether modeling spots on the surface of the secondary star might be more appropriate for some nova-like stars.
T CrB is again in an active stage
The recurrent symbiotic nova T CrB (1786?, 1866, 1946, ?) can erupt at any time. All previous predictions have failed. The active phase that began in 2015 ended in April 2023. Brightness dropped, emission lines practically disappeared, leaving only a weak Balmer series. Activity resumed in 2025. A rough impression can be obtained by measuring the equivalent width of the H-alpha line (Fig. 3).
EG And and a “ghost” planetary nebula
A revolution in astronomical photography was recently brought about by the discovery of the Drechsler–Strottner–Sainty object (SDSO1) near the galaxy M31 (Drechsler et al. 2023). Ogle et al. 2025 offered an explanation that does not associate the object with the galaxy but with the well-known symbiotic star in our Galaxy — EG And. According to the authors, EG And is responsible for the creation of a “ghost planetary nebula”. This new term describes the final stage of a planetary nebula’s evolution when it interacts with the interstellar medium (ISM) and shines thanks to shocks produced in the interaction. For such a phenomenon to occur, the planetary nebula’s gas must move relative to the ISM at hypersonic speed. Thanks to measurements from the GAIA satellite, we know that EG And indeed moves relative to the local ISM at 107 km/s (Mach 7.1).
The story of SDSO1 also lies behind the formation of the collaboration between our Section and the Section of Astronomical Photography. It demonstrates how astrophotographic techniques can be useful in studying stellar evolution.
The eclipse of EE Cep
The long-period eclipsing binary EE Cep is among systems whose eclipsing object is a dusty disk or torus around the secondary. With a period of 5.61 years and an eclipse duration of 57 days, it may be considered a younger sibling of the record-holder ε Aurigae (period 27.08 years and eclipse lasting ~2 years). In 2025, the eclipse was predicted to begin on 15 October (JD 2,460,964), the midpoint on 13 November (JD 2,460,993), and the end on 11 December (JD 2,461,021). This was essentially confirmed. Fig. 5 shows a significant difference in the shape of the light curve compared with the previous eclipse in 2020. This year’s curve is smoother apart from a short halt on the descending part of the light curve. At the same time, the last minimum is substantially deeper than the previous ones. This only confirms that the eclipsing object is not an ordinary star but an inhomogeneous structure.
The eclipse of V1413 Aql
V1413 Aql is an eclipsing symbiotic binary. The orbital period is 434 days. Eclipses are therefore not rare, but each one is different. The last eclipse occurred at the end of 2025 during an outburst of the symbiotic system, while in the previous year the eclipse occurred during a quiet phase. Fig. 6 shows that the difference is reflected in the shape of the light curve as well as in the profile of the H-alpha emission line. It seems that during the outburst, the accretion disk is larger and therefore not completely eclipsed. This could explain the minimum without a flat bottom and the broad wings in the spectral line profile.
On Earth
Publication activity of Section members
Twenty-eight papers with co-authorship by our members were published. In five cases, a Section member was the first author. The most productive was Jaroslav Merc with 16 publications. Among them, the review paper “
Symbiotic Stars in the Era of Modern Ground and Space-Based Surveys” deserves special mention. Undoubtedly, the work by J. Budaj et al., “
A swarm of dusty objects in orbit around the central star of planetary nebula WeSb 1”, attracted the most attention. It offers a view into the life of a planetary system destroyed by a star that reached the asymptotic giant branch.
Events
The main event of previous years used to be the Variable astrocamp, which was held at the Astronomical Observatory on Kolonické sedlo. Unfortunately, this year it was not possible to hold it. Its future is unclear. Either we will reach an agreement with the management of the Vihorlat Observatory in Humenné, or the event will take place elsewhere.
The traditional Kolos conference was held on 4–6 December 2025. More information, including links to individual contributions, is available at https://www.astrokolonica.sk/2025/12/09/konferencia-kolos-2025-a-15-vyrocie-zalozenia-pto-poloniny/. Four Section members actively participated (R. Galis, T. Pribulla, M. Kamenec, P. Gajdoš).
Another regular meeting where Section members gather is the Bezovec conference. This year, it took place from 2 to 8 June 2025 as a conference of young astronomers. Five Section members actively participated (P. Dubovský, R. Galis, M. Kamenec, P. Mártonfi, K. Petrík).
The Czech equivalent of our variable-star meetings is the Conference on Research of Variable Stars, organized by the Section of Variable Stars and Exoplanets of the Czech Astronomical Society. This year, it took place right next to the largest telescope in the Czech Republic, in the new seminar room of the Astronomical Institute of the Czech Academy of Sciences in Ondřejov. Two members attended on behalf of the Section (P. Dubovský and M. Vrašťák).
Workshop Astrorob25 in Almería, Spain — another in the series of workshops on robotic telescopes — was also represented by our Section. P. Dubovský and K. Petrík presented the aion of the observatories in Hlohovec and Kolonica and the campaign to search for supernova remnants after novae. Participation in the workshop was also possible thanks to financial support approved by the Council of the Slovak Astronomical Association.
Projects
A considerable part of the observational and publishing activities concerning variable stars and exoplanets took place as part of the grant APVV-20-0128 “From interacting binaries to exoplanets”. The project was implemented from 2021 to 2025. The principal investigator was T. Pribulla.
At the same time, a new grant for the period 2025–2029 was approved: “Revealing the nature of special stellar systems and exoplanets” — project leader: T. Pribulla (APVV-24-0160).
Equipment
- At the Astronomical Institute of the Slovak Academy of Sciences on Skalnaté pleso, the main mirror of the 1.3 m telescope was re-coated.
- At the Astronomical Observatory on Kolonické sedlo two observing domes were aed. One is intended for spectroscopy, the other for photometry and astrophotography. Due to changes in personnel, the equipment is currently not in use.
- Our member M. Vrašťák completed the construction of his new telescope Newton 508/1900, entirely made at home.
Collaboration
The campaign to search for nova super-remnants, which began in 2024, was carried out as a joint activity of the Section of Variable Stars and Exoplanets and the Section of Astronomical Photography. The pilot phase — deep imaging around Z Camelopardalis and image processing from various instruments — was completed. The result is shown in Fig. 7. The tested methodology can now be used to search for unknown remnants. A suitable field is being selected for truly very deep imaging — around 1,000 hours of accumulated exposure time. The start of the “real” phase of the campaign should be in March 2026.
One of the main lessons from the ongoing campaign is that carrying it out in Central European conditions is practically impossible. The weather does not provide enough time. Hence, a private initiative arose to build our own telescope hosting facility that would provide a place for telescopes of Slovak amateurs as well as professionals. Details are on the website www.bombol.space.
