We discuss the possibility of the realization of the plasma generation mechanism in the source of decameter radio emission associated with Ganymede and the explanation of the formation of quasi-periodic sequences of bursts of this radiation based on this mechanism. According to the model being discussed, the recorded quasi-periodic sequences of radiation pulses are a consequence of the realization of a pulsating regime of plasma wave conversion into extraordinary electromagnetic waves with a small refractive index in the source. The negative radiation frequency drift observed in the frequency–time spectrogram is due to the group delay of waves with a small refractive index and the dispersion of the medium. Based on the plasma model, we have estimated the plasma parameters in the generation region, which are in agreement with the data obtained through satellite measurements.

We have identified the radio and gamma-ray pulsars known in the eastern half of the sky in the soft X-ray band using data from the all-sky X-ray survey performed by the eROSITA telescope onboard the Spectrum–Roentgen–Gamma observatory. As a result, we have found new candidate counterparts for 12 pulsars of different ages and types at a confidence level $${\gtrsim}3\sigma$$ . A comparable number has been previously identified in the western half of the sky. In total, this accounts for about 12 $$\%$$ of the number of known pulsars that have already been detected in X-rays. We give estimates of the X-ray fluxes from the new counterparts, preliminary characteristics of their X-ray spectra, and brief descriptions of the properties of the pulsars themselves. The telescope has also detected 56 pulsars in the eastern half of the sky previously identified in X-rays by other observatories.

The influence of the dust component of a magnetocentrifugal disk wind on the circumstellar extinction and the infrared thermal radiation of T Tauri stars is investigated. The wind models from Safier’s papers, which are analytical approximations of the solutions for a magnetocentrifugal dusty disk wind, are taken as a basis. An accretion spot whose luminosity is scaled in accordance with the accretion rate and stellar parameters is added to the stellar spectrum. The radiative transfer in the wind and the circumstellar disk has been simulated by the Monte Carlo method using the RADMC3D code. The results of our simulations are applied to T Tauri stars with UX Ori-type variability. We show that when such stars are observed at a small angle to the disk plane, an increase in the accretion rate can cause an optical fading of the stars and, simultaneously, an enhancement of their infrared radiation. We also show that the results of our simulations are sensitive to the magnetic field topology in the disk in the wind formation zone. The results of our calculations are discussed in connection with the observations of deep minima in the T Tauri stars V1184 Tau and RW Aur accompanied by an enhancement of their radiation in the near-infrared spectral range. In the Conclusions we briefly discuss alternative mechanisms for the uplift of dust above the disk capable of causing an enhancement of the infrared radiation from young stars.

Emission of water molecules cannot be observed from Earth, less abundant isotopologues, such as H $${}_{2}^{18}$$ O and HDO, are used to trace water in star-forming regions. The main aim of this study is to determine HDO abundance in the hot core RCW 120 S2. We performed observations of the hot core in the 200–255 GHz range using the nFLASH230 receiver on the APEX telescope. Two HDO lines were detected toward RCW 120 S2. Their intensities are described by excitation temperature $${\approx}290$$ K and gas number density $${\geq}10^{9}$$ cm $${}^{-3}$$ . The emission originates from the hot core rather than the warm dense envelope surrounding a central young stellar object. The HDO column density ranges from $$(3.9{-}7.9)\times 10^{13}$$ cm $${}^{-3}$$ with the best-fit model value of $$5.6\times 10^{13}$$ cm $${}^{-3}$$ . The HDO abundance relative to hydrogen is $$1.7\times 10^{-9}$$ . This HDO abundance value is among the lowest reported for hot cores. Combined with the non-detection of the H $${}_{2}^{18}$$ O line, we conclude that protostellar heating in RCW 120 S2 is still in its early stages.

We study the $$f(Q,C)$$ gravity model by finding a power-law solution for the Hubble parameter $$H(z)=H_{0}(1+z)^{{3}/{2n}}$$ and examine its consequences using a variety of cosmological datasets. Our approach involves the fitting of the model parameters to datasets from Hubble, BAO and Phantom that are in good agreement with observations. Upon analyzing the energy density $$\rho(z)$$ , we discover that it provides evidence for a dynamic dark energy theory. The $$Om(z)$$ diagnostic and the statefinder parameters $$r$$ and $$s$$ show the behaviours that is compatible with quintessence models. According to our findings, the $$f(Q,C)$$ gravity model offers a feasible substitute for the conventional $$\Lambda$$ CDM model and offer a valuable understanding into the dynamic characteristics of dark energy and cosmic expansion.

The method for estimating the spatial period of energy release in solar flares based on the application of a Fourier analysis to the difference images of flare arcades in the far ultraviolet is applied to the observations of the large solar flare on November 4, 2003. The flare occurred at the solar limb; the flare arcade extending along the solar limb was imaged in detail in the ultraviolet 195 Å channel of the TRACE satellite. The Fourier analysis of its difference images has shown the presence of a series of harmonics in the spatial distribution of the regions of flare energy release with characteristic periods lying in the range from 3.3 to 18.6 Mm. Such periodization may result from the decay of the preflare current layer accumulating the solar flare energy in coronal magnetic fields due to some instability of thermal, plasma, or other nature.

The source OGLE-BLG-DN-0064 (hereafter OGLE64) was classified as a potential dwarf nova based on its regular outburst activity revealed by the OGLE optical survey. In this paper we investigate the X-ray and optical emissions from the source OGLE64 based on archival Chandra and Swift X-ray data and our optical observations with the 6-m BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences. OGLE64 shows an X-ray luminosity $$L_{X}\approx 1.6\times 10^{32}$$ erg s $${}^{-1}$$ and a high X-ray-to-optical flux ratio $$F_{X}/F_{\textrm{opt}}\approx 1.5$$ typical for accreting white dwarfs. The X-ray spectrum of OGLE64 is better fitted by the models of a power law with a photon index $$\Gamma\approx 1.9$$ and an optically thin plasma with a temperature $$kT\approx 6.4$$ keV. The optical spectrum shows hydrogen and neutral helium emission lines in some of which a double-peaked structure is observed. An analysis of the outburst activity of OGLE64 based on data from the OGLE, ZTF, ATLAS, and ASAS-SN optical surveys has revealed superoutbursts with a characteristic supercycle $$P_{\textrm{super}}\approx 400$$ days. We found no significant variability in either the X-ray or optical light curves of OGLE64 that could be associated with the change in the visibility conditions for the emitting regions at different orbital phases. Our estimates of the orbital period of the system by indirect methods show that the period probably lies in the range $$P_{\textrm{orb}}\sim 1.5{-}3.5$$ h. The properties of the X-ray and optical emissions from OGLE64 lead us to conclude that the system is an SU UMa-type dwarf nova.

Based on low-resolution ( $$R\approx 3000$$ ) spectra, we have determined some parameters of the star Gaia DR3 5877303483506681472 ( $$G=19.4$$ mag), the closest object to the X-ray source [GV2003]N toward the supernova remnant G315.4–2.30: its effective temperature $$T_{\textrm{eff}}=4830$$ K, surface gravity log $$g=4.3$$ , and metallicity $$\textrm{[Fe/H]}=-0.05$$ . We have analyzed its radial velocity for variability and found no variations within the error limits ( $$\sigma V_{\textrm{rad}}\approx 5$$ km s $${}^{-1}$$ ). An overabundance of the elements Ca, Ti, V, and Mn has been revealed. The color excess of the star has been estimated from the intensity of diffuse interstellar bands to be $$E(B-V)=0.68\pm 0.08$$ . Our estimate of the photometric distance $$d=2.5\pm 0.9$$ kpc points to a possible connection with the supernova remnant.

We studied rotational modulation of the radial velocities of narrow emission lines in four classical T Tauri stars. We found that the previously declared shift of the mean velocity of neutral and ionized helium lines relative to the mean radial velocity of the star is not associated with the inflow of accreted gas into the hotspot, since the radial velocity curves for lines with different velocity shifts should exhibit phase shifts relative to each other, while the observed phase shifts are absent within their uncertainties and do not correspond to the observed line velocity shifts. This means that the line shifts are not caused by the actual gas motion. For neutral helium lines, the shifts can be explained by the large optical thickness of the lines and the Stark effect at plasma parameters expected at the base of the accretion column of T Tauri stars.

Greenwich type 0 sunspot groups, i.e., single sunspots, are considered. It is shown that in addition to the previously noted properties of sunspot groups separating into two populations, large long-lived (LLG) and small short-lived (SSG) ones, such groups, i.e., single sunspots, differ by the relationship between the total sunspot area $$S$$ and the umbra area $$U$$ . The ratio $$S/U$$ for the entire LLG population of this class may be deemed constant and is $$Q_{\textrm{LLG}}=5.756\pm 0.039$$ . The ratio of $$S$$ and $$U$$ for the SSG population is determined by a power law, $$S=(5.569\pm 0.093)U^{0.8957\pm 0.0040}$$ . The difference of the structural properties of sunspots in the populations, along with other previously found differences of their physical properties, is consistent with the hypothesis about the formation of the magnetic flux of two different sunspot populations in different zones: the deep tachocline and the near-surface leptocline.