Solar coronal dimmings have been observed extensively in the past two decades and are believed to have close association with coronal mass ejections (CMEs). Recent study found that coronal dimming is the only signature that could differentiate powerful flares that have CMEs from those that do not. Therefore, dimming might be one of the best candidates to observe the stellar CMEs on distant Sun-like stars. In this study, we investigate the possibility of using coronal dimming as a proxy to diagnose stellar CMEs. By simulating a realistic solar CME event and corresponding coronal dimming using a global magnetohydrodynamics model (AWSoM: Alfvén-wave Solar Model), we first demonstrate the capability of the model to reproduce solar observations. We then extend the model for simulating stellar CMEs by modifying the input magnetic flux density as well as the initial magnetic energy of the CME flux rope. Our result suggests that with improved instrument sensitivity, it is possible to detect the coronal dimming signals induced by the stellar CMEs.

Resolved observations of star-forming galaxies at cosmic noon with the Hubble Space Telescope and large ground-based facilities provide a view on the spatial distribution of stars, gas and dust, and probe gaseous motions revealing the central gravitational potential and local feedback processes at play. In this paper, we review recent insights gained from such observations, with an emphasis on results obtained through optical/near-infrared imaging and imaging spectroscopy. Their context and implications are documented more fully in a forthcoming review article by Förster Schreiber & Wuyts (in prep).

Since past few decades, observations have improved so strongly that when modelling Milky Way (MW) dynamics it is required to include small perturbations to the modelling process. It is difficult task that we try to solve by selecting regions to model so small that the perturbation can be considered to give nearly constant effect. We use Solar Neighbourhood (SN) as our test sample and assume that the bar effects show more or less constant contribution to SN. By extrapolating and smoothing observed stars on their orbits, and requiring that smoothed and observed phase space are consistent we were able to deduce acceleration vector. We conclude from non-radial acceleration component that the bar must cause about one third of total acceleration near SN.

We present new constraints on the cosmic cold molecular gas evolution out to redshift 6 based on systematic mining of the public ALMA archive in the COSMOS field (A3 COSMOS). Our A3 COSMOS dataset contains ∼ 700 galaxies (0.3 ≲ z ≲ 6) with high-confidence ALMA detection and multi-wavelength SEDs. Combining with ∼ 1,200 CO-observed galaxies at 0 ≲ z ≲ 4 (75% at z < 0.1) in the literature, we parameterize galaxies’ molecular gas depletion time and gas fraction each as a function of stellar mass, offset from the star-forming main-sequence and cosmic age. We propose a new functional form which provides a better fit and implies a “downsizing” effect and “mass-quenching”. By adopting galaxy stellar mass functions and applying our gas fraction function, we obtain a cosmic cold molecular gas density evolution in agreement with recent CO blind field surveys as well as semi-analytic modeling. These together provide us a coherent picture of galaxy cold molecular gas, SFR and stellar mass evolution.

Signs of stellar activity such as large surface spots and radio flares are often related to binarity. UX Arietis is one of the most active members of the RS CVn class of binaries in which spin-up of a sub-giant/giant star by a close companion leads to the creation of magnetic fields. UX Arietis exhibits these signs of activity, originating mostly on the K0 sub-giant primary component. We measured the orbit with the CHARA interferometer and made images of a single large spot rotating in and out of view over a month in 2012. The rotation of the stars is synchronous with the orbit, and long-term photometric observations show that the spot or spots do not move much during intervals of a year. Our aim is to relate the positions of the stars and the spots on the primary to astrometry of the radio components observed during outbursts.

Several scenarios have been proposed to describe the physical connection between galaxies and their central active galactic nuclei (AGN). This connection could act on a range of spatial scales and vary across cosmic time. In these proceedings, we consider black hole and galaxy growth and whether that growth is affected by AGN feedback both based on statistical approaches – which reveal general population trends – and based on an individual case study – which gives us a more detailed insight on the physical processes at play. For the statistical approach, we showcase a low-redshift (0.04 < z < 0.2) SDSS sample with AGN classification based on a combination of emission-line diagnostic diagrams, and for which we account for sample selection by using a V/Vmax approach. The trends on the star formation rate - stellar mass (SFR – M*) plane suggest that the most likely connection is a common gas reservoir for star formation and AGN, and that they both decline as the gas reservoir is consumed. The trends established at low-redshift could act as a local benchmark against which to compare higher redshift studies. As a complementary approach, we use a detailed case study of a nearby AGN host with integral field spectroscopy from the VLT/MUSE instrument in order to spatially resolve the interplay between AGN feedback and the host galaxy. We find that the galaxy substructure likely plays a role by collimating and/or obscuring the outflows and radiation from the central engine. Ongoing and future work with 3D spectroscopy will enable us to learn more about galaxy and black hole coevolution. Lastly, we briefly discuss lessons learnt from both approaches.

We report on our project to study the activity in both the Sun and low mass stars. Utilising high cadence, Hα observations of a filament eruption made using the CRISP spectropolarimeter mounted on the Swedish Solar Telescope has allowed us to determine 3D velocity maps of the event. To gain insight into the physical mechanism which drives the event we have qualitatively compared our observation to a 3D MHD reconnection model. Solar-type and low mass stars can be highly active producing flares with energies exceeding erg. Using K2 and TESS data we find no correlation between the number of flares and the rotation phase which is surprising. Our solar flare model can be used to aid our understanding of the origin of flares in other stars. By scaling up our solar model to replicate observed stellar flare energies, we investigate the conditions needed for such high energy flares.

We describe an algorithm that can fit the properties of the dwarf galaxy progenitor of a tidal stream, given the properties of that stream. We show that under ideal conditions (the Milky Way potential, the orbit of the dwarf galaxy progenitor, and the functional form of the dwarf galaxy progenitor are known exactly), the density and angular width of stars along the stream can be used to constrain the mass and radial profile of both the stellar and dark matter components of the progenitor dwarf galaxy that was ripped apart to create the stream. Our provisional fit for the parameters of the dwarf galaxy progenitor of the Orphan Stream indicates that it is less massive and has fewer stars than previous works have indicated.

The dynamo mechanism, responsible for the solar magnetic activity, is still an open problem in astrophysics. Different theories proposed to explain such phenomena have failed in reproducing the observational properties of the solar magnetism. Thus, ab-initio computational modeling of the convective dynamo in a spherical shell turns out as the best alternative to tackle this problem. In this work we review the efforts performed in global simulations over the past decades. Regarding the development and sustain of mean-flows, as well as mean magnetic field, we discuss the points of agreement and divergence between the different modeling strategies. Special attention is given to the implicit large-eddy simulations performed with the EULAG-MHD code.

Spectral line intensities observed by the Extreme Ultraviolet Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO) during 2012 March 9 M6.3 flare were used to diagnose a presence of a non-thermal electron distribution represented by a κ-distribution. The diagnosed electron densities ($\approx 2 \times {10^{11}}{\rm{c}}{{\rm{m}}^{ - 3}}$) are affected only a little by the presence of the non-thermal distribution, and are within the uncertainties of observation. On the other hand, the temperature diagnostics based on the line ratios involving different ionization degrees is strongly affected by the type of the electron distribution. The distribution functions diagnosed from relative Fe line intensities demonstrate the presence of strongly non-thermal distributions during the impulsive phase of the flare and later their gradual thermalization.

Density profiles of galaxy groups can provide an insight on how large-scale structure in the Universe formed and evolved, since galaxy groups bridge the gap between individual galaxies and galaxy clusters. Studying the galaxy group that is gravitational lensing HELMS18, a submillimeter galaxy at z = 2.39 from the Herschel’s HerMES Large Mode Survey (HELMS), we aim to probe the total density profile by combining strong gravitational lensing with kinematics of the centrally-located galaxies and kinematics of the group members. We have high-resolution data of HELMS18 obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) and multi-object spectroscopic data of the group members from Gemini-GMOS. Our main goal is to match these observations to probe the DM and stellar density profiles and to establish a complete description of this galaxy group.

A recently discovered young, high-velocity giant star J01020100-7122208 is a good candidate of hypervelocity star ejected from the Galactic center, although it has a bound orbit. If we assume that this star was ejected from the Galactic center, it can be used to constrain the Galactic potential, because the deviation of its orbit from a purely radial orbit informs us of the torque that this star has received. Based on this assumption, we estimate the flattening of the Galactic dark matter halo by using the Gaia DR2 data and the circular velocity data. Our Bayesian analysis shows that the orbit of J01020100-7122208 favors a prolate halo within ~ 10 kpc from the Galactic center. The posterior distribution of the density flattening q shows a broad distribution at q ≳ 1 and peaks at q ≃ 1.5. Also, 98.5% of the posterior distribution is located at q > 1, highly disfavoring an oblate halo.

HST and integral-field spectroscopic observations of star-forming galaxies at cosmic noon provide a view on the spatial distribution of stars, gas and dust, and probe gaseous motions revealing the central gravitational potential and local feedback processes at play. In this paper, we review recent insights gained from such observations, with an emphasis on results obtained through near-infrared imaging spectroscopy. Their context and implications are documented more fully in a forthcoming review article by Förster Schreiber & Wuyts (in prep).

Based on our modern 4D-var data assimilation pipeline Solar Predict we present in this short proceeding paper our prediction for the next solar cycle 25. As requested by the Solar Cycle 25 panel call issued on January 2019 by NOAA/SWPC and NASA, we predict the timing of next minimum and maximum as well as their amplitude. Our results are the following: the minimum should have occured within the first semester of year 2019. The maximum should occur in year 2024.4 ± 6 months, with a value of the sunspot number equal to 92±10. This is in agreement with the NOAA/NASA consensus published in April 2019. Note that our prediction errors are based on 1-σ measure and do not consider all the systematics, so they are likely underestimated. We will update our prediction and error analysis regularly as more data becomes available and we improve our prediction pipeline.

A key outstanding issue in galaxy evolution studies is how galaxies quench their star formation. I will present new results from our VLT/X-Shooter, ALMA and VLA campaign of a pilot sample of lensed quiescent massive galaxies at z > 1.5. Lensing magnification enables us to spatially resolve the stellar structure and kinematics of these compact galaxies, that are otherwise barely resolvable even with HST. Our deep X-Shooter spectra provided multiple absorption lines enabling strong constraints on their stellar populations, namely their star formation rates, ages, dispersions, and in some cases metallicities. Our complementary ALMA+VLA programme probes their molecular gas content through CO emission. All these observations provide unparalleled constraints on their quenching mechanisms. Our results indicate that quiescent galaxies at z ∼ 2 (1) have short star formation timescales of a few hundred Myrs; (2) have a variety of stellar morphology from exponential disks to bulges; (3) are devoid of molecular gas; and (4) host low-luminosity active galactic nuclei which may be responsible for suppressing star formation. In addition to discussing the insights gained on quenching, I will highlight how these findings bring about new questions that can be addressed with future JWST and ALMA studies.

The Milky Way’s stellar halo preserves a fossil record of smaller dwarf galaxies that merged with the Milky Way throughout its formation history. Currently, though, we lack reliable ways to identify which halo stars originated in which dwarf galaxies or even which stars were definitively accreted. Selecting stars with specific chemical signatures may provide a way forward. We investigate this theoretically and observationally for stars with r-process nucleosynthesis signatures. Theoretically, we combine high-resolution cosmological simulations with an empirically-motivated treatment of r-process enhancement. We find that around half of highly r-process-enhanced metal-poor halo stars may have originated in early ultra-faint dwarf galaxies that merged into the Milky Way during its formation. Observationally, we use Gaia DR2 to compare the kinematics of highly r-process-enhanced halo stars with those of normal halo stars. R-process-enhanced stars have higher galactocentric velocities than normal halo stars, suggesting an accretion origin. If r-process-enhanced stars largely originated in accreted ultra-faint dwarf galaxies, halo stars we observe today could play a key role in understanding the smallest building blocks of the Milky Way via this novel approach of chemical tagging

Coronal holes can be identified as the darkest regions in EUV or soft X-ray images with predominantly unipolar magnetic fields (LIRs) or as the regions with open magnetic fields (OMF). Our study reveals that only 12% of OMF regions are coincident with LIRs. The aim of this study is to investigate the conditions that affect the EUV intensity of OMF regions. Our results indicate that the EUV intensity and the magnetic field expansion factor of the OMF regions are weakly positively correlated when plotted in logarithmic scale, and that the bright OMF regions are likely to locate inside or next to the regions with closed field lines. We empirically determined a linear relationship between the expansion factor and the EUV intensity. The relationship is demonstrated to improve the consistency from 12% to 23%. The results have been published in Astrophysical Journal (Huang et al. 2019).

We present the case of hot semi-detached Algols showing photometric cycles longer than the orbital period. The evidence indicating that this long cycle might be due to a magnetic dynamo operating in the rapidly rotating donor star is examined.

We investigate the minor interactions of two disk galaxies with mass ratio of 10:1 in fly-by encounters that do not lead to the merging of the galaxies. In our N-body simulations, we vary only the pericenter distances to see the effect of the fly-by on the bulge of the major galaxy over the course of the trajectory. At different time steps of the evolution, we did two-dimensional fittings of disk, bulge and bar to trace the variation in the sersic index of the bulge. Our results suggest that galaxy bulges can become boxy/disky through flyby interactions of galaxies.