The study of radial metallicity gradients in the disc of the Milky Way is a powerful tool to understand the mechamisms that have been acting in the formation and evolution of the Galactic disc. In this proceeding, I will put the eye on some problems that should be carefully addressed to obtain precise determinations of the metallicity gradients.

We present the NLTE abundances of 10 chemical species in 65 very metal-poor stars in eight dSphs and the Milky Way halo. The classical dSphs Sculptor, Ursa Minor, Sextans, and Fornax reveal a similar plateau at [α/Fe] = 0.3 for each of Mg, Ca, and Ti, similarly to the MW halo. We provide the evidence for a decline in α/Fe in the Boötes I UFD, that is probably due to the ejecta of SNeIa. The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical dSphs, similarly to the MW halo, calling for two different nucleosynthesis channels for Sr. The Boötes I and UMa II UFDs reveal very similar ratios of [Sr/Mg] = −1.3 and [Ba/Mg] = –1. The stars in the Coma Berenices and Leo IV UFDs are even poorer in Sr and Ba. The subsolar Sr/Ba ratios of Boötes I and UMa II indicate a common r-process origin of their n-capture elements.

Using high resolution 3D hydrodynamical simulations we quantify the amount of mass accreted onto the secondary star of the binary system η Carinae during periastron passage on its highly eccentric orbit. The accreted mass is responsible for the spectroscopic event occurring every orbit close to periastron passage, during which many lines vary and the x-ray emission associated with the destruction wind collision structure declines. The system is mainly known for its giant eruptions that occurred in the nineteenth century. The high mass model of the system, M1=170M⊙ and M2=80M⊙, gives Macc≍ 3×10−6M⊙ compatible with the amount required for explaining the reduction in secondary ionization photons during the spectroscopic event, and also matches its observed duration. As accretion occurs now, it surely occurred during the giant eruptions. This implies that mass transfer can have a huge influence on the evolution of massive stars.

The first detection of gravitational waves from a merging double neutron star (DNS) binary implies a much higher rate of DNS coalescences in the local Universe than typically estimated on theoretical grounds. The recent study by Chruslinska et al. (2018) shows that apart from being particularly sensitive to the common envelope treatment, DNS merger rates appear rather robust against variations of several factors probed in their study (e.g. conservativeness of the mass transfer, angular momentum loss, and natal kicks), unless extreme assumptions are made. Confrontation with the improving observational limits may allow to rule out some of the extreme models. To correctly compare model predictions with observational limits one has to account for the other factors that affect the rates. One of those factors relates to the assumed history of star formation and chemical evolution of the Universe and its impact on the final results needs to be better constrained.

We explore the Milky Way supershell GS242-03+37. We argue that the observed HI distribution can be explained as an expanding structure about 100 Myr old powered with a modest energy released by an OB association. The formation of star clusters has been triggered less than 30 Myr ago when the ISM density in the supershell increased due to the galactic differential rotation. The observed age sequence of young star clusters is related to the evolution of the column density during the supershell expansion.

The U.S. National Optical Astronomy Observatory’s Education and Public Outreach group has produced a Quality Lighting Teaching Kit. The kits are designed around problem-based learning scenarios. The kit’s six activities allow students to address real lighting problems that relate to wildlife, sky glow, aging eyes, energy consumption, safety, and light trespass. The activities are optimized for 11-16 year olds. As part of the IAU100 celebration, the kits will be manufactured and made available to observatories and communities around the world.

In order to determine the true impact of stellar multiplicity on the formation and evolution of planets, we initiated direct imaging surveys to search for (sub)stellar companions of exoplanet host stars on close orbits, as their gravitational impact on the planet bearing disk at first and on formed planets afterwards is expected to be maximal. According to theory these are the most challenging environments for planet formation and evolution but might occur quite frequently in the milky way, due to the large number of multiple stars within our galaxy. On this poster we showed results, obtained so far in the course of our AO and Lucky-imaging campaigns of exoplanet host stars, conducted with NACO/ESO-VLT for southern and with AstraLux/CAHA2.2m for northern targets, respectively. In addition, we introduced our new high contrast imaging survey with SPHERE/ESO-VLT to search for close companions of southern exoplanet host stars, and presented some first results.

We analyze the data from the 6 gravitational waves signals detected by LIGO through the lens of multifractal formalism using the MFDMA method, as well as shuffled and surrogate procedures. We identified two regimes of multifractality in the strain measure of the time series by examining long memory and the presence of nonlinearities. The moment used to divide the series into two parts separates these two regimes and can be interpreted as the moment of collision between the black holes. An empirical relationship between the variation in left side diversity and the chirp mass of each event was also determined.

Because the number of asteroids in the IMB with absolute magnitude H<16.5 is effectively complete, the distributions of the sizes and the orbital elements of these asteroids must be devoid of observational selection effects. This allows us to state that the observed size-frequency distributions (SFDs) of the five major asteroid families in the IMB, defined by Nesvorný (2015) using the Hierarchical Clustering Method (Zappala et al. 1990), are distinctly different and deviate significantly from the linear log-log relation described by Dohnanyi (1969). The existence of these differences in the SFDs, and the fact that the precursor bodies of the major families have distinctly different eccentricities and inclinations, provides a simple explanation for the observations that the mean sizes of the family asteroids, taken as a whole, are correlated with their mean proper eccentricities and anti-correlated with their mean proper inclinations. While the latter observations do have a simple explanation, we observe that the mean sizes of the non-family asteroids in the IMB are also correlated with their mean proper eccentricities and anti-correlated with their mean proper inclinations. We deduce from this, and from the fact that the SFDs of the non-family and the family asteroids (again taken as a whole) are almost identical, that the family and most of the non-family and asteroids have a common origin. We estimate that ~85% of all the asteroids in the IMB with H<16.5 originate from the Flora, Vesta, Nysa, Polana and Eulalia families with the remaining ~15% originating from either the same families or, more likely, a few ghost families (Dermott et al. 2018).

It is well-known that there are two types of gamma-ray bursts (GRBs): short/hard and long/soft ones, respectively. The long GRBs are coupled to supernovae, but the short ones are associated with the so called macronovae (also known as kilonovae), which can serve as the sources of gravitational waves as well. The kilonovae can arise from the merging of two neutron-stars. The neutron stars can be substituded by more massive black holes as well. Hence, the topic of gamma-ray bursts (mainly the topic of short ones) and the topic of massive binaries, are strongly connected.

In this contribution, the redshifts of GRBs are studied. The surprising result - namely that the apparently fainter GRBs can be in average at smaller distances - is discussed again. In essence, the results of Mészáros et al. (2011) are studied again using newer samples of GRBs. The former result is confirmed by the newer data.

We present the status of an ongoing project to map the detailed chemical abundances of stars across the main body of the Sagittarius dwarf Spheroidal galaxy (Sgr dSph). The Sgr dSph is the closest known dwarf galaxy, and is being tidally destroyed by its interaction with the Milky Way (MW), leaving behind a massive stellar stream. Sgr dSph is a chemically outstanding object, with peculiar abundance ratios, clear center-outskirts abundance gradients, and spanning more than 3 orders of magnitude in metallicity. We present here detailed abundances from UVES@VLT spectra for more than 50 giants across 8 fields along the major and minor axes of Sgr dSph, and 5 more outside the galaxy main body, but possibly associated to its stellar stream.

VLT instruments and ALMA have revolutionized in the past five years our view and understanding of how disks turn into planetary systems. They provide exquisite insights into non-axisymmetric structures likely closely related to ongoing planet formation processes. The following cannot be a complete review of the physical and chemical properties of disks; instead I focus on a few selected aspects. I will review our current understanding of the physical properties (e.g. solid and gas mass content, snow and ice lines) and chemical composition of planet forming disks at ages of 1-few Myr, especially in the context of the planetary systems that are forming inside them. I will highlight recent advances achieved by means of consistent multi-wavelength studies of gas AND dust in protoplanetary disks.

We show the results of global 3D magnetohydrodynamics simulations of an accretion disk with a rotating, weakly magnetized central star (Takasao et al. 2018). The disk is threaded by a weak large-scale poloidal magnetic field. The central star has no strong stellar magnetosphere initially and is only weakly magnetized. We investigate the structure of the accretion flows from a turbulent accretion disk onto the star. Our simulations reveal that fast accretion onto the star at high latitudes is established even without a stellar magnetosphere. We find that the failed disk wind becomes the fast, high-latitude accretion as a result of angular momentum exchange mediated by magnetic fields. The rapid angular momentum exchange occurs well above the disk, where the Lorentz force that decelerates the rotational motion of gas can be comparable to the centrifugal force. Unlike the classical magnetospheric accretion model, fast accretion streams are not guided by magnetic fields of the stellar magnetosphere. Nevertheless, the accretion velocity reaches the free-fall velocity at the stellar surface owing to the efficient angular momentum loss at a distant place from the star. Our model can be applied to Herbig Ae/Be stars whose magnetic fields are generally not strong enough to form magnetospheres, and also provides a possible explanation why Herbig Ae/Be stars show indications of fast accretion.

We have combined data of the DustPedia project with observations of gas components of the interstellar medium (ISM) and metallicity abundances for late-type DustPedia galaxies to definitively characterize the ISM scaling relations in the Local Universe. In particular, we have focused on the comparison of the dust-to-gas mass ratio with gas phase metallicities.

The medium-band Vilnius photometric system with the mean wavelengths at 345 (U), 374 (P), 405 (X), 466 (Y), 516 (Z), 544 (V), and 656 (S) nm for many years was an important tool to determine interstellar reddenings and distances of single stars due to its ability to classify stars of all temperatures in spectral classes and luminosity classes in the presence of different interstellar reddenings. At present, Gaia DR2 presents distances to stars with an unprecedented accuracy at least up to 3 kpc. However, multicolor photometry, which allows the classification of stars as well as the preliminary determination of stellar temperatures, gravities, metallicities and interstellar reddenings, remains an important method for distant stars. Here we present an empirical calibration of the intrinsic color indices of the Vilnius system in terms of physical parameters of stars for dwarf and giant stars of spectral classes F-G-K-M. In any attempted photometric determination of physical parameters of stars it is important to have an extensive and homogeneous sample of spectroscopically determined parameters for stars for which there are also accurate photometric data. As a source catalogue for the Vilnius photometry the latest updated version of the Catalogue of Photoelectric Observations in the Vilnius System was used, which contains compilations from the published photometry for about 11 000 stars. The stars which had both the Gaia DR2 parallaxes and the determinations of stellar parameters from high-dispersion spectra were extracted from this catalogue. The final sample contains more than 1500 stars of spectral classes F-M. The majority of these stars (ca 70%) are not reddened, for others the values of interstellar reddening AV were determined using the regular techniques of photometric classification in the Vilnius system. The absolute magnitudes MV and consequently the luminosity classes were determined using Gaia DR2 parallaxes. We present the analytical expressions for the effective temperature Teff and surface gravity logg and evaluate the errors of solutions for dwarf and giant stars. To test the accuracy of the proposed method, we have compared our results with the stars observed by Gaia and with the stellar parameters available from the large spectroscopic surveys: APOGEE, Gaia-ESO, GALAH, LAMOST, RAVE and SEGUE. The results of comparison contain 5-6 % outliers.

The proposed method allows the fast and straightforward evaluation of stellar physical parameters for the stars observed in the Vilnius photometric system. Despite the fact, that the accuracy of determination is significantly lower than in the case of spectroscopic methods, the method described may be useful for distant faint stars, which are still inaccessible for spectroscopic observations.

The Small Magellanic Cloud (SMC) presents us with a unique opportunity to study in detail the effect of environmental processes (interaction with the LMC and the Milky Way) on its star formation history. With the 6.5m Magellan Telescope at the Las Campanas Observatory in Chile we have acquired deep B and I images in four 0.44 degree fields covering a large part of the main body of the SMC, yielding accurate photometry for 1,068,893 stars down to ~24th magnitude, with a spatial resolution of 0.201 arcsec/pixel. Colour-magnitude diagrams and luminosity functions (corrected for completeness) have been constructed, yielding significant new results that indicate at least two discrete star formation events around 2.7 and 4-5 Gyr ago.

Using a hybrid binary population synthesis approach, we modelled the formation and evolution of populations of accreting white dwarfs (WDs) for differing star formation histories. We found that the delay time distribution of SNe Ia in the single degenerate scenario is inconsistent with observations. Additionally, we found that our predicted X-ray and UV emission of populations of accreting WDs are consistent with the X-ray luminosities of early-type galaxies observed by Chandra and the HeII 4686 Å/Hβ line ratio measured in stacked SDSS spectra of passively evolving galaxies. Moreover, we found that the majority of current novae in elliptical-like galaxies have low-mass WDs, long decay times, long recurrence periods and are relatively faint. In contrast, the majority of current novae in spiral-like galaxies have massive WDs, short decay times, short recurrence periods and are relatively bright. Our predicted distribution of mass-loss timescales in an M31-like galaxy is consistent with observations for Andromeda.

. We continue our study of spectral and photometric variability of Cyg X-1 on the basis of the 45-year long series of multicolor photometric observations and many-year-long series of spectral observations we have accumulated up to now. The mean level of star brightness continues to decrease since 1999 with the variations on smaller time scales superimposed. There is a connection between X-ray and optical changes. The chaotic variations of X-ray flux sometimes reaching to “hard” - “soft” state irregular changes switch on when U brightness decrease and He I λ 4713 Å absorption line depth increase. And inversely - they switch off during U brightness increasing and He I λ 4713 Å absorption line depth decreasing. This may be connected with star size variations, causing outflow gas instability. It is concluded that the fundamental parameters of the supergiant in the system of Cyg X-1 continue to vary on the time scales of years - decades.

We present an analysis of a sample of clusters of young stars in order to investigate the inherent properties of clustering and dynamic evolution of stellar components, based on fractal statistics. In addition, we present the application of new mathematical and numerical techniques with potentiality for use in models of filamentary structures.