MgH lines in the spectrum of Arcturus

The synthetic spectra of MgH lines was computed for the grid of the model atmospheres and compared with observed spectrum of Arcturus. The parameters of the atmosphere of Arcturus log g=1.5 for Teff=4300 K were found by using the minimization procedure of differences between observed and computed spectra and compared our results of other studies.Comment: Work was presented at YSC'20 and will appear in AAS

Tidal debris from Omega Centauri discovered with unsupervised machine learning

The gravitational interactions between the Milky Way and in-falling satellites offer a wealth of information about the formation and evolution of our Galaxy. In this paper, we explore the high-dimensionality of the GALAH DR3 plus Gaia eDR3 data set to identify new tidally stripped candidate stars of the nearby star cluster Omega Centauri ($\omega\,\mathrm{Cen}$). We investigate both the chemical and dynamical parameter space simultaneously, and identify cluster candidates that are spatially separated from the main cluster body, in regions where contamination by halo field stars is high. Most notably, we find candidates for $\omega\,\mathrm{Cen}$ scattered in the halo extending to more than $50^{\circ}$ away from the main body of the cluster. Using a grid of simulated stellar streams generated with $\omega\,\mathrm{Cen}$ like orbital properties, we then compare the on sky distribution of these candidates to the models. The results suggest that if $\omega\,\mathrm{Cen}$ had a similar initial mass as its present day mass, then we can place a lower limit on its time of accretion at t$_{\mathrm{acc}} > 7$ Gyr ago. Alternatively, if the initial stellar mass was significantly larger, as would be expected if $\omega\,\mathrm{Cen}$ is the remnant core of a dwarf Galaxy, then we can constrain the accretion time to t$_{\mathrm{acc}} > 4$ Gyr ago. Taken together, these results are consistent with the scenario that $\omega\,\mathrm{Cen}$ is the remnant core of a disrupted dwarf galaxy.Comment: 22 pages, 19 figures, 2 tables, accepted for publication in MNRA

The HR 1614 moving group is not a dissolving cluster

The HR 1614 overdensity in velocity space and has for a long time been known as an old (~2 Gyr) and metal-rich ([Fe/H]~0.2) nearby moving group that has a dissolving cluster origin. The existence of such old and metal-rich groups in the solar vicinity is quite unexpected since the vast majority of nearby moving groups are known to be young. In the light of new and significantly larger data sets we aim to re-investigate the properties and origin of the HR 1614 moving group. To identify and characterise the HR 1614 moving group we use astrometric data from Gaia DR2; distances, extinction, and reddening corrections from the StarHorse code; elemental abundances from the GALAH and APOGEE spectroscopic surveys; and photometric metallicities from the SkyMapper survey. Bayesian ages were estimated for the SkyMapper stars. Since the Hercules stream is the closest kinematical structure to the HR 1614 moving group in velocity space, we use it for comparison purposes. Stars that are likely to be members of the two groups were selected based on their space velocities. The HR 1614 moving group is located mainly at negative U velocities, does not form an arch of constant energy in the U-V space and is tilted in V. The overdensity is not chemically homogeneous but that its stars exist at a wide range of both metallicities, ages, and elemental abundance ratios. They are essentially similar to what is observed in the Galactic thin and thick disks, a younger population (~3 Gyr) that is metal-rich (-0.2<[Fe/H]<0.4) and alpha-poor. It should therefore not be considered as a dissolving open cluster, or an accreted population. We suggest that HR 1614 has a complex origin that could be explained by combining several different mechanisms such as resonances with the Galactic bar and spiral structure, phase-mixing of dissolving spiral structure, and phase-mixing due to an external perturbation.Comment: Accepted for publication in A&

The nature of kinematic structures in the Galactic disc

The velocity distribution of stars in the Galactic disc is complex and consists of a vast number of kinematic structures, that is, stars that share similar velocity components. The reasons why some stars move together may be different and are related to dynamical processes connected to the Galaxy, both internal as well as external ones, such as resonances with the Galactic bar or the Galactic spiral arm structure, dissolution of open clusters, or merger events with other galaxies. Therefore, studies of kinematic structures of the Galactic disc may provide information about the formation and evolution history of the Milky Way. In this thesis we focus on detecting and chemo-dynamical characterisation of kinematic structures of the Galactic disc using the most recent and up-to-date astrometric, spectroscopic, and photometric surveys. In Paper I we studied kinematic structures in the solar neighbourhood with the wavelet transform method. In Paper II and Paper III we studied origin of the Arcturus stream and HR 1614 moving group respectively by studying chemo-dynamical properties of the structures.The result of Paper I is the detection of old and well-known kinematic groups together with three new velocity structures. The results of Paper II and Paper III show that both the Arcturus and the HR 1614 structures are composed of thin and thick disc stars and are not dissolved open clusters or accreted stellar populations. We conclude that the origin of kinematic structures is complex and might be a combination of several dynamical processes such as resonances and phase mixing

Disentangling the Arcturus stream

Context. The Arcturus stream is an over-density of stars in velocity space and its origin has been much debated recently without any clear conclusion. The (classical) dissolved open cluster origin is essentially refuted; instead the discussions try to distinguish between an accretion, a resonant, or an external-perturbation origin for the stream. As kinematic structures are observational footprints of ongoing and past dynamical processes in disc galaxies, resolving the nature of the Arcturus stream may provide clues to the formation history of the Milky Way and its stellar populations. Aims. We aim to characterise the kinematical and chemical properties of the Arcturus stream in order to resolve its origin. Methods. The space velocities, angular momenta, and actions for a sample of more than 5.8 million stars, composed from Gaia DR2 were analysed with a wavelet transform method to characterise kinematic over-densities in the Galactic disc. The kinematic characteristics of each identified group is used to select possible members of the groups from the GALAH and APOGEE spectroscopic surveys to further study and constrain their chemical properties. Results. In the velocity and angular momentum spaces the already known Sirius, Pleiades, Hyades, Hercules, AF06, Arcturus and KFR08 streams are clearly identified. The Hercules stream appears to be a mixture of thin and thick disc stars. The Arcturus stream, as well as the AF06 and KFR08 streams, are high-velocity and low-angular momentum structures with chemical compositions similar to the thick disc. These three groups extend further from the Galactic plane compared to the Hercules stream. The detections of all the groups were spaced by approximately 20 - 30 km s-1 in azimuthal velocity. Conclusions. A wide spread of chemical abundances within the Arcturus stream indicates that the group is not a dissolved open cluster. Instead the Arcturus stream, together with the AF06 and KFR08 streams, are more likely to be part of a phase-space wave, that could have been caused by a merger event. This conclusion is based on that the different structures are detected in steps of 20 - 30 km s-1 in azimuthal velocity, that the kinematic and chemical features are different from what is expected for bar-originated structures, and that the higher-velocity streams extend further from the disc than bar-originated structures

Methodology of the environmental efficiency assessment of spatial organization of rural areas

The article features and substantiates the methodology of the environmental efficiency assessment of the spatial organization of rural areas. This methodology is based on a comprehensive analysis of key indicators to take reasoned decisions on land use arrangement and organization of agrolandscapes. At the same time, the research found that it is impossible to achieve sustainable land use without a comprehensive understanding of the situation on the spatial structure of territories, therefore, the initial stage of the model implementation is to analyze the current state and level of the research object. The methodology provides for taking into account the integral indicator of the spatial organization of rural areas, which is defined as the sum of normalized values of indicators (relative to their optimal level), with reference to the corresponding weighing coefficients. The advantage of the proposed approach is that it can determine the level of efficiency of optimization of the spatial structure of rural areas in the context of the region, which ensures the relative comparability of the calculated environmental indicators. Testing of the proposed assessment methodology on the example of Lviv region of Ukraine has proven its practical ability to optimize management decisions

4MOST Scientific Operations

The 4MOST instrument is a multi-object spectrograph that will address Galactic and extragalactic science cases simultaneously by observing targets from a large number of different surveys within each science exposure. This parallel mode of operation and the survey nature of 4MOST require some distinct 4MOST- specific operational features within the overall operations model of ESO. The main feature is that the 4MOST Consortium will deliver, not only the instrument, but also contractual services to the user community, which is why 4MOST is also described as a facility. This white paper concentrates on information particularly useful to answering the forthcoming Call for Letters of Intent