Gravitational Instability of Gas-Dust Circumnuclear Disks in Galaxies

We numerically study the origin of the multi-armed spiral structure observed in the circumnuclear gaseous mini-disks of nearby galaxies. We show that the presence of dust in such disks and its interaction with the gravitationally stable gaseous component leads to the development of a multi-armed spiral structure. As a particular example, we study the formation of the multi-armed spiral pattern in the mini-disk of the galaxy NGC 4736, for which the observational data for the rotation and the density distribution are available. We find that the multi-armed spiral structure grows in the stable gaseous mini-disk of NGC 4736 if the gas-to-dust ratio is about 5-20 percent. We also demonstrate that together with the dust concentration, the important factor for the development of instability is the size of the dust grains. A nonlinear multi-armed spiral pattern develops in the stable gaseous disk with sizes of grains larger than one micron. If future observations confirm the presence of a large amount of dust in the mini-disks of galaxies, this will pinpoint the mechanism of the formation of the multi-armed spiral structure in them.Comment: 15 pages, 6 figures; https://www.mdpi.com/2075-4434/11/2/4

The Influence of the Galactic Bar on the Dynamics of Globular Clusters

We make use of recent estimates for the parameters of the Milky Way's halo globular clusters and study the influence of the galactic bar on the dynamics of these clusters by computing their orbits. We use both an axisymmetric and non-axisymmetric galactic potentials, which include the rotating elongated bar/bulge structure. We account for observational errors both in the positions and in the velocities of the globular clusters and explore the influence of the bar on cluster's evolution. This is contained in the angular momentum-total energy plane, (Lz,E), which is widely exploited as an indicator of the groups of globular clusters that originated from the same accretion event. Particular attention is devoted to the Gaia-Sausage/Enceladus and Pontus structures identified recently as two independent accretion events. Our study shows that it is not possible to identify GSE and Pontus as different merger events.Comment: 17 pages, 9 figure

Prospects for utilizing secondary resources in the construction of facilities for various purposes

The objective of this research is to explore potential opportunities for utilizing secondary resources in the road construction, and construction of agricultural facilities, considering the changes in their technical and consumer attributes over the lifespan of used materials and their ecological impact. This study examines the challenges associated with implementing innovative materials, such as fiber-reinforced concrete and low carbon materials in the road and agricultural industry. Taking into account generally accepted indicators for assessing the properties of materials, a method based on a separate analysis of regulatory and methodological support for the construction preparation process was applied. The main tool for influencing the design process is the formalization of requirements for preparing design documentation, which involves the use of innovative building materials. These requirements need to be consolidated in the form of an improved mechanism for introducing innovations, providing for the expansion of possible areas of application of innovative materials, taking into account their technical and cost characteristics. The article is recommended to a wide range of specialists in civil, agricultural and road construction, as well as environmental engineering

The origin of globular cluster FSR 1758

Context. Globular clusters in the Milky Way are thought to have either an in situ origin, or to have been deposited in the Galaxy by past accretion events, like the spectacular Sagittarius dwarf galaxy merger.Aims. We probe the origin of the recently discovered globular cluster FSR 1758, often associated with some past merger event and which happens to be projected toward the Galactic bulge. We performed a detailed study of its Galactic orbit, and assign it to the most suitable Galactic component.Methods. We employed three different analytical time-independent potential models to calculate the orbit of the cluster by using the Gauss Radau spacings integration method. In addition, a time-dependent bar potential model is added to account for the influence of the Galactic bar. We ran a large suite of simulations via a Montecarlo method to account for the uncertainties in the initial conditions.Results. We confirm previous indications that the globular cluster FSR 1758 possesses a retrograde orbit with high eccentricity. The comparative analysis of the orbital parameters of star clusters in the Milky Way, in tandem with recent metallicity estimates, allows us to conclude that FSR 1758 is indeed a Galactic bulge intruder. The cluster can therefore be considered an old metal-poor halo globular cluster formed in situ that is passing right now in the bulge region. Its properties, however, can be roughly accounted for by also assuming that the cluster is part of some stream of extra-Galactic origin.Conclusions. We conclude that assessing the origin, either Galactic or extra-galactic, of globular clusters is surely a tantalising task. In any case, by using an Occam's razor argument, we tend to prefer an in situ origin for FSR 1758

A Capture Scenario for Globular Cluster Omega Centauri

We explore an accretion origin for Omega Cen by N-body modeling of the orbital decay and disruption of a Milky-Way dwarf satellite. This work is focused on studying a particular satellite model that aims to reproduce the present orbit of Omega Cen, as recently determined from absolute proper motions. The model satellite is launched from 58 kpc from the Galactic Center, on a radial, low-inclination orbit. We find that a capture scenario can produce an Omega Cen-like object with the current low-energy orbit of the cluster. Our best model is a nucleated galaxy with a Hernquist density profile that has a mass of 8 10**8 Msun, and a half-mass radius of 1.4 kpc.Comment: 15 pages, 5 figures, accepted by ApJ

In-Situ Star Formation in the Outskirts of the Large Magellanic Cloud: Gaia DR2 Confirmation

We explore the Gaia DR2 proper motions of six young, main-sequence stars, members of the Large Magellanic Cloud (LMC) reported by Moni Bidin et al. (2017). These stars are located in the outskirts of the disk, between 7 and 13 degrees from the LMC's center where there is very low H I content. Gaia DR2 proper motions confirm that four stars formed locally, in situ, while two are consistent with being expelled via dynamical interactions from inner, more gas-rich regions of the LMC. This finding establishes that recent star formation occurred in the periphery of the LMC, where thus far only old populations are known.Comment: Accepted for publication in Astrophysical Journal Letter

The Origins of Young Stars in the Direction of the Leading Arm of the Magellanic Stream: Abundances, Kinematics, and Orbits

We explore the origins of the young B-type stars found by Casetti-Dinescu et al.(2014) at the outskirts of the Milky-Way disk in the sky region of Leading Arm of the Magellanic Stream. High-resolution spectroscopic observations made with the MIKE instrument on the Magellan Clay 6.5m telescope for nine stars are added to the previous sample analyzed by Zhang et al. (2017). We compile a sample of fifteen young stars with well-determined stellar types, ages, abundances and kinematics. With proper motions from Gaia DR2 we also derive orbits in a realistic Milky-Way potential. We find that our previous radial-velocity selected LA candidates have substantial orbital angular momentum. The substantial amount of rotational component for these stars is in contrast with the near-polar Magellanic orbit, thus rendering these stars unlikely members of the LA. There are four large orbital-energy stars in our sample. The highest orbital-energy one has an age shorter than the time to disk crossing, with a birthplace $z=2.5$~kpc and $R_{\rm GC}\sim 28$~kpc. Therefore, the origin of this star is uncertain. The remaining three stars have disk runaway origin with birthplaces between 12 and 25 kpc from the Galactic center. Also, the most energetic stars are more metal poor ([Mg/H] =$-0.50\pm0.07$) and with larger He scatter ($\sigma_{\rm [He/H]} = 0.72$) than the inner disk ones ([Mg/H] $=0.12\pm0.36$, $\sigma_{\rm [He/H]} = 0.15$). While the former group's abundance is compatible with that of the Large Magellanic Cloud, it could also reflect the metallicity gradient of the MW disk and their runaway status via different runaway mechanisms.Comment: 58 pages, 17 figures, 7 tables. Accepted for publication in Ap

Chemical Composition of Young Stars in the Leading Arm of the Magellanic System

Chemical abundances of eight O- and B-type stars are determined from high-resolution spectra obtained with the MIKE instrument on the Magellan 6.5m Clay telescope. The sample is selected from 42 candidates of membership in the Leading Arm of the Magellanic System. Stellar parameters are measured by two independent grids of model atmospheres and analysis procedures, confirming the consistency of the stellar parameter results. Abundances of seven elements (He, C, N, O, Mg, Si, and S) are determined for the stars, as are their radial velocities and estimates of distances and ages. Among the seven B-type stars analyzed, the five that have radial velocities compatible with membership to the LA have an average [Mg/H] of $-0.42\pm0.16$, significantly lower than the average of the remaining two [Mg/H] = $-0.07\pm0.06$ that are kinematical members of the Galactic disk. Among the five LA members, four have individual [Mg/H] abundance compatible with that in the LMC. Within errors, we can not exclude the possibility that one of these stars has a [Mg/H] consistent with the more metal-poor, SMC-like material. The remaining fifth star has a [Mg/H] close to MW values. Distances to the LA members indicate that they are at the edge of the Galactic disk, while ages are of the order of $\sim 50-70$ Myr, lower than the dynamical age of the LA, suggesting a single star-forming episode in the LA. V$_{\rm LSR}$ the LA members decreases with decreasing Magellanic longitude, confirming the results of previous LA gas studies.Comment: 61 pages, 18 figures, 5 tables. Accepted for publication in Ap