Thanks to a fortunate time-space configuration, signals about several interesting phenomena in our Galaxy reached Earth during 2022. In this post I will summarize the basic information about some of them.
First of all, novae that exploded in the period of 2020, 2021 were still active. Of them, I will mention two completely opposite objects. V1405 Cas is a very slow nova with multiple maxima and brightness variations. By the end of 2022, it was already in the nebular stage, but still brighter than 12 mag. And short-period variations with a characteristic time similar to the orbital period also appeared. However, there is no stable signal corresponding to the orbital period. In the world of cataclysmic variable stars, such behavior is usually called quasi-periodic oscillations. It will require a detailed periodic analysis. Fig. 1 shows the last few light curves.
V1674 Her, on the other hand, is one of the fastest nova. However, it is also interesting because archival observations revealed that it was caused by an intermediate polar. This created a unique opportunity to measure the effect of the explosion on the rotation of the white dwarf. It actually succeeded. Patterson and others reported in the paper “The Periodic Signals of Nova V1674 Herculis (2021)” that the period had increased by 71 milliseconds. But then there was a dramatic acceleration of rotation, unseen in any known intermediate polar. In 2021 by 182 milliseconds. That doesn’t seem like a big number. But one turn of the white dwarf lasts only about 501 seconds. So it can happen that in a year it makes 5 turns more than expected according to the original period. It is therefore important to have the course densely covered by observations so that we do not count the turns incorrectly. The theory explains that the white dwarf is accelerated by the accretion of a large amount of mass with a larger angular momentum. It should gradually stop. From the observations in Hlohovec and Kolonica, it was possible to construct an O-C diagram of the times of the maximum light pulses caused by the rotation of the white dwarf. In Fig. 2 shows a quadratic fit describing the rate of acceleration. On the residuals obtained after subtracting this fit, it can be seen that “acceleration deceleration” has already occurred recently.
The June outburst of the recurrent nova U Scorpii came at an ideal time. Excellent photometric and spectroscopic coverage was achieved. In the world also in various fields of electromagnetic radiation from radio waves to X-rays. So far, there have been no theoretical works evaluating these observations.
The end of the year was further enlivened by nova Persei 1901, which today is an intermediate polar showing flares and has the designation GK Per. It is a completely unique object. For example, just because it has the longest orbital period, almost 2 days, among the known intermediate polars. The year-end outburst seems to be one of the weaker ones. It reached 11.2 mag in the V band.
Among the R-CrB stars that are characterized by deep unpredictable decreases in brightness, V482 Cyg should be mentioned. After twenty-six years of no activity, the decline finally occurred. From the usual 11th magnitude to 15.8 V. By the end of the year, it had already returned to the 12th magnitude level, but that may not be the end of the event. On this object, we can illustrate what problems observers encounter. It is known that 7 arcseconds southeast of V482 Cyg lies a star of magnitude 13.7. It must be ensured that the measurements are not contaminated by the light of this star. Under good conditions, this is not a problem for both visual and CCD observers. You still need to avoid confusing the stars. With V482 Cyg at maximum it is clear. But as it fades, caution is in order. However, there was one more problem that nobody knew about until now. 3 arcseconds northeast of V482 Cyg lies another 15-mag star that only became apparent when the variable weakened. It is only found in the GAIA DR3 catalog. It is possible to distinguish these two objects only with really good seeing. The whole situation is shown in Fig. 3.
It must be said that astrophysical research is not only based on the spectacular phenomena mentioned above. Knowledge also advances thanks to observations of cataclysmic binaries in a quiescence, measurement of regular pulsations of pulsating stars, accurate measurement of transits of exoplanets, modeling of eclipsing binaries, etc. The mentioned phenomena are just the icing on the cake, which will delight the heart of every variable stars observer.