Ram-pressure stripping (RPS) is a process known to remove gas from satellite galaxies. Recent observational studies have found an increased ratio of active galactic nuclei (AGN) among the population of RPS galaxies compared to regular galaxies in the field. To test whether ram pressure (RP) can trigger an AGN, we perform a suite of hydrodynamical wind-tunnel simulations of a massive (Mstar = 1011 Mȯ) galaxy, with inclusion of star formation, stellar feedback and high resolution up to 39 pc. We find that RP increases the inflow of gas to the galaxy centre, which in turn can result in the enhanced BH accretion, as measured by the Bondi-Hoyle model. We also estimate pressure of outflows from our accretion rates and show that AGN feedback would play an important role on the early stages of stripping, while RP itself is not so strong.

We present a study of the evolution of two types of coronal holes (CHs) in the solar minimum of 24/25, which was preceded by a prolonged minimum of 23/24 and a weak 24 solar cycle. The goal of the study is to clarify whether the behavior of CHs during this period is also unusual? The study is based on the material of observations obtained by SDO/AIA/193. The Heliophysics Events Knowledgebase was used to localize the CHs and calculate their areas. Analysis of the evolution of the areas of polar and non-polar CHs in solar minimum 24/25 revealed a number of features. The hemispheric asymmetry is evident both in solar activity indices and in the localization of maxima of polar and non-polar CH areas. The hemispheric area imbalance is minimal for polar CHs and pronounced in the regions of non-polar CHs and sunspots. This is consistent with the general concept of polar CHs as the main source of the Sun’s dipole magnetic field. The areas of polar CHs significantly exceed the areas of non-polar CHs and make a significant contribution to the total area of all CHs in the solar disk. It is concluded that the dynamics of polar and nonpolar CHs suggests that the 24/25 minimum is rather close to earlier minima than to the 23/24 minimum.

A striking feature of the solar cycle is that at the beginning, sunspots appear around mid-latitudes, and over time the latitudes of emergences migrate towards the equator. The maximum level of activity varies from cycle to cycle. For strong cycles, the activity begins early and at higher latitudes with wider sunspot distributions than for weak cycles. The activity and the width of sunspot belts increase rapidly and begin to decline when the belts are still at high latitudes. However, in the late stages of the cycles, the level of activity, and properties of the butterfly wings all have the same statistical properties independent of the peak strength of the cycles. We have modelled these features using Babcock–Leighton type dynamo model and shown that the toroidal flux loss from the solar interior due to magnetic buoyancy is an essential nonlinearity that leads to all the cycles decline in the same way.

Feedback and outflows associated with a quasar phase are expected to be critical in quenching the most massive galaxies at high-z. Observations targeting the cool molecular and atomic phases, which dominate the mass and momentum budget of massive galaxy outflows and remove the direct fuel for star formation are, however, severely limited in high-z QSO hosts. We discuss two recent ALMA programs: one targeting molecular outflows in 3 z ∼ 6 QSO hosts using the OH 119 μm absorption line and another targeting the diffuse, predominantly atomic gas in the halos surrounding 5 QSO host between z ∼ 2 – 4 using the OH+(11 – 10) absorption line. Outflows are successfully detected in both samples and compared with outflows driven by high-z star-forming galaxies observed in the same lines. Both studies indicate that observing QSOs during the blow-out phase is crucial for studying the impact of the active nucleus on the ejection of gas from the host galaxy.

In this contribution, I present a selected overview of optical interferometry imaging results that brought insights on stellar activity and mass loss in evolved stars. I briefly introduce the STELLIM project that aims to characterize stellar surfaces and circumstellar environments by producing fast and reliable interferometric images.

This study analyzed the Doppler shift in the solar spectrum using the Interface Region Imaging Spectrograph (IRIS). Two types of oscillations were investigated: long period damp and short period damp. The researchers observed periodic perturbations in the Doppler velocity oscillations of bright points (BPs) in the chromosphere and transition region (TR). Deep learning techniques were used to examine the statistical properties of damping in different solar regions. The results showed variations in damping rates, with higher damping in coronal hole areas. The study provided insights into the damping behavior of BPs and contributed to our understanding of energy dissipation processes in the solar chromosphere and TR.

Babcock–Leighton process, in which the poloidal field is generated through the decay and dispersal of tilted bipolar magnetic regions (BMRs), is observed to be the major process behind the generating poloidal field in the Sun. Based on this process, the Babcock–Leighton dynamo models have been a promising tool for explaining various aspects of solar and stellar magnetic cycles. In recent years, in the toroidal to poloidal part of this dynamo loop, various nonlinear mechanisms, namely the flux loss through the magnetic buoyancy in the formation of BMRs, latitude quenching, tilt quenching, and inflows around BMRs, have been identified. While these nonlinearities tend to produce a stable magnetic cycle, the irregular properties of BMR, mainly the scatter around Joy’s law tilt, make a considerable variation in the solar cycle, including grand minima and maxima. After reviewing recent developments in these topics, I end the presentation by discussing the recent progress in making the early prediction of the solar cycle.

Just like the Sun, other stars also exhibit differential rotation. Currently, the rotation profile of a star that hosts a transiting planet can be estimated if during a transits, the planet occults a spot on the photosphere of the star, causing slight variations in its light curve. By detecting the same spot during a later transit, the stellar rotation period at that latitude is determined. Here, we present the results of differential rotation for 48 stars, 13 from the spot transit mapping method, while the remaining 35 stars from other techniques. The results show that the differential rotation is correlated with the stellar mean rotation period for fast rotating stars and strongly anti-correlated for slow rotators. The transition occuring at rotation period of 5 days. On the other hand, the differential shear increases with effective temperature for fast rotating stars, but the correlation is lost for the slow rotators.

. Post-starburst galaxies (PSBs) have quenched (significant decline in star formation rate) both recently and rapidly (≲Gyr). They are thus promising in providing insights into activities that are happening at the early stage of quenching. While studies have suggested that black hole feedback in the form of active galactic nuclei (AGN) and outflows play important roles in quenching, the details of how they impact the host galaxies and their interplay with other quenching mechanisms are still not fully understood. We find that PSBs commonly show signatures of AGN activity but they appear to be weak and/or heavily obscured. These AGN might be able to drive outflows but they are likely not strong enough to remove gas from the host galaxy. Direct evidence of AGN quenching the star formation of the host galaxy is still missing and AGN likely quench by disturbing rather than expelling the gas.

The induction and momentum equations of solar dynamo are simplified to a dynamic system for the convective Root-Mean-Square (rms) velocity and the rms magnetic field in the solar convection zone. The study of stable stationary points of this system gives a minor excess of the critical level of the dynamo and, accordingly, moderate magnetic field typically about 1 T (10 kG). A significantly lower rms magnetic field may be possible at some parameters of the system. The stable rms velocity is about 100 m/sec, and the characteristic magnetic times are about the half-period of solar rotation or about an average lifetime of sunspots. Relative magnetic energy is of order 5 kJ/kg that is about the kinetic energy. The unstable stationary points could be near zero magnetic fields as in periods of very lower solar activity similar to the Maunder minimum.

The tilt of the bipolar magnetic region (BMR) is crucial in the Babcock-Leighton process for the generation of the poloidal magnetic field in the Sun. We extend the work of Jha et al. (2020) and analyze the recently reported tracked BMR catalogue based on AutoTAB (Sreedevi et al. 2023) from Michelson Doppler Imager (1996–2011) and Helioseismic and Magnetic Imager (2010–2018). Using the tracked information of BMRs based on AutoTAB, we confirm that the distribution of Bmax reported by Jha et al. (2020) is not because of the BMRs are picked multiple times at the different phases of their evolution instead it is also present if we consider each BMRs only once. Moreover, we find that the slope of Joy’s law (〈γ0〉) initially increases slowly with the increase of Bmax. However, when Bmax >2.5 kG, γ0 decreases. The decrease of observed γ0 with Bmax provides a hint to a nonlinear tilt quenching in the Babcock-Leighton process.

Observations of super flare occurrence (with energy 1033–1036 erg)s in low mass stars like M dwarfs still remains as a puzzle. In this paper we have inferred the typical sizes and characteristics of magnetic fields associated with active regions in M dwarfs responsible for these super flares. This is done by extrapolation of physical conditions associated with largest solar flares. The average poloidal and toroidal magnetic fields near the surface of selected M dwarfs will be also inferred in this context.

In this article, the physical processes occurring in the convective layer and the photosphere of the Sun and their connection to the formation of active regions (ARs) and the development of the corresponding magnetic field are explored. Specifically, we test the magnetic flux emergence hypothesis and based on the line-of-sight magnetic field and Doppler shift data obtained from the Global Oscillation Network Group (GONG) observations. The study encompasses the analysis of 24 ARs observed during the period from 2011 to 2022. We find a strong correlation between the magnetic flux and the imbalance of radial velocity fluxes. The results indicate that the magnetic flux emergence hypothesis cannot fully explain the evolution of ARs during their early stages of development.

Historical sunspot records provide piece by piece more information on solar variability on a centennial scale. In this work, we analyze sunspot observations from the archives of Georg Christoph Eimmart, which is the second-richest data set of the Maunder minimum after the archives of the Paris observatory. Comparing the dates of the blank solar disk from the database by Hoyt & Schatten (1998) with dates of observations at the Eimmart observatory, we find that spotless days reports originate from astrometric observations. A comparison of the observations by La Hire and Müller of 1719 suggests that the observations by La Hire were for astrometric purposes as well, rather than aimed at sunspot counting.

During the last decade, our understanding of stellar physics and evolution has undergone a tremendous revolution thanks to asteroseismology. Space missions such as CoRoT, Kepler, K2, and TESS have already been observing millions of stars providing high-precision photometric data. With these data, it is possible to study the convection of stars through the convective background in the power spectrum density of the light curves. The properties of the convective background or granulation has been shown to be correlated to the surface gravity of the stars. In addition, when we have enough resolution (so long enough observations) and a high signal-to-noise ratio (SNR), the individual modes can be characterized in particular to study the internal rotational splittings and magnetic field of stars. Finally, the surface magnetic activity also impacts the amplitude and hence detection of the acoustic modes. This effect can be seen as a double-edged sword. Indeed, modes can be studied to look for magnetic activity changes. However, this also means that for stars too magnetically active, modes can be suppressed, preventing us from detecting them.

In this talk, I will present some highlights on what asteroseismology has allowed us to better understand the convection, rotation, and magnetism of solar-like stars while opening doors to many more questions.

The formation of highly structured, spatially localized complex structures during solar flux emergence facilitates adaptation of topological methods, extending the research of emerging macroscopic MHD fluxes into knots, links and braids. Combining mathematical considerations, remote images and in situ satellite observations at solar vicinity, we construct new characteristics of those braided/knotted magnetic structures, applying Braid and Knot Theory to physical configurations, deducing their topological invariants, constraining the evolution and stability while delineating the relaxation path to magnetized equilibria.

The fast rotating solar analogs show a decrease of the dynamo period with an increase of the rotation rate for the moderate stellar rotation periods in the range between 10 and 25 days. Simultaneously, observations indicate two branches: the “in-active” branch stars shows short dynamo cycles and the active branch stars show the relatively long magnetic cycles. We suggest that this phenomenon can be produced by effect of the doubling frequency of the dynamo waves, which is due to excitation of the second harmonic. It is generated because of the nonlinear B2 effects in the large-scale dynamo.

We correlate the annual Wolf numbers W and their time derivatives Wʹ by shifting time fragments of W and Wʹ relative to each other. The most significant (up to 0.874) correlation is with 3 years shifts for fragments covering 14 years. For longer and shorter periods, the correlation coefficients 0.771–0.855 with 2–3 years shift. The most significant 9 years shift corresponds to -0.852/-0.824 anti-correlation coefficient for 14/11 years period. The other periods are less significant. To evaluate predictive estimates, we use the times series fragments of W shifted back into the past. A forecast can be made using the leading graphs based upon the derived calibration factor. Test calculations show that the most effective is the calibration factor calculated for changing the phase of the cycle. The best linear pairwise correlation coefficient of the approximation is 0.94.

Statistical study of 3047 active regions (ARs) from 1996 to 2021 was performed using the catalog of the magneto-morphological classes (MMC) of ARs CrAO. According to the magneto-morphological classification of ARs proposed earlier, all ARs, except for unipolar spots, were sorted out between two categories: regular (bipolar groups obeying the Hale’s polarity law, the Joy’s law, etc.) and irregular ARs (all the rest). We analyzed the number and fluxes of ARs depending on their location in different (relative to the equator) hemispheres. We found that the trends for fluxes are more pronounced. For ARs of both MMC types, they demonstrate signs of both a multi-peak and double-peak structure. Some peaks coincide with the main maxima of the cycle. The second main maximum is mainly formed by the irregular ARs in the S-hemisphere. This might be due to the interaction of the dipole and quadrupole components of the global magnetic field.

Stellar activity depends on multiple parameters one of which is the age of the star. The members of open clusters are good targets to observe the activity at a given age of the stars since their ages are more precisely determined than that of field stars. Choosing multiple clusters, each with different age, gives us insight to the change in activity during the lifetime of stars. With the analysis of these stars we can also refine the parameters of gyrochronology (Barnes 2003), which is a method for estimating the age of low-mass, main sequence stars from their rotation periods.