Chemical evolution of the Galactic disk(s)

Abundance trends in the inner and outer Galactic disk

Based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan telescopes we present detailed elemental abundances for 64 red giant stars in the inner and outer Galactic disk. For the inner disk sample (4-7 kpc from the Galactic centre) we find that stars with both thin and thick disk abundance patterns are present while for Galactocentric distances beyond 10 kpc, we only find chemical patterns associated with the local thin disk, even for stars far above the Galactic plane. Our results show that the relative densities of the thick and thin disks are dramatically differen…

Effect of finite disk-thickness on swing amplification of non-axisymmetric perturbations in a sheared galactic disk

A typical galactic disk is observed to have a finite thickness. Here, we present the study of the physical effect of introduction of finite thickness on the generation of small-scale spiral arms by swing amplification in a differentially rotating galactic disk. The galactic disk is modelled first as a one-fluid system, and then as a gravitationally-coupled two-fluid (stars and gas) system where each fluid is taken as isothermal, and corotating with each other. We derived the equations governing the evolution of growth of the non-axisymmetric perturbations in a sheared frame of reference while …

The Galactic thin and thick disk

The ongoing large spectroscopic surveys of the Milky Way such as SEGUE and RAVE have enabled us to take a fresh look at the structure of the Galactic thin and thick disks, and how their structure fits within the framework of structure formation via hierarchical clustering. In this article I will summarize some recent results mainly based in the RAVE survey with respect to the structure of the Galactic disks, their possible origin as well as indications of substructure and asymmetries.

A Search for a Globular Cluster whose Passage through the Galactic Disk Could Induce the Formation of the Gould Belt

The distribution of sites where globular clusters have crossed the Galactic disk during the last 100 million years has been analyzed using the most recent kinematic data for 133 globular clusters (GCs). Three GCs (NGC 6341, NGC 7078, and $ω$ Cen) whose distances between the positions where they crossed the Galactic disk and trajectories of the Gould Belt are less than 20\% of their heliocentric distances at the crossing time (82, 98, and 96 million years ago, respectively) have been identified. For each of the clusters, this was their next to last, rather than their last, crossing of the Galac…

通过贫金属星揭示银盘的起源与演化

Unraveling the Origins and Development of the Galactic Disk through Metal-Poor Stars

本研究利用光度金属丰度估计和盖亚早期数据发布3的天体测量，筛选纯净的最古老贫金属星样本，以揭示银河系银盘的起源与演化。

Chemical history of molecules in circumstellar disks

The chemical composition of a protoplanetary disk is determined not only by in situ chemical processes during the disk phase, but also by the history of the gas and dust before it accreted from the natal envelope. In order to understand the disk's chemical composition at the time of planet formation, especially in the midplane, one has to go back in time and retrace the chemistry to the molecular cloud that collapsed to form the disk and the central star. Here we present a new astrochemical model that aims to do just that. The model follows the core collapse and disk formation in two dimension…

Measuring the Matter Density of the Galactic Disk Using Stellar Streams

We present a novel method for determining the total matter surface density of the Galactic disk by analysing the kinematics of a dynamically cold stellar stream that passes through or close to the Galactic plane. The method relies on the fact that the vertical component of energy for such stream stars is approximately constant, such that their vertical positions and vertical velocities are interrelated via the matter density of the Galactic disk. By testing our method on mock data stellar streams, with realistic phase-space dispersions and Gaia uncertainties, we demonstrate that it is applicab…

Pulsar Rotation Measures and Large-scale Magnetic Field Reversals in the Galactic Disk

We present the measurements of Faraday rotation for 477 pulsars observed by the Parkes 64-m radio telescope and the Green Bank 100-m radio telescope. Using these results along with previous measurements for pulsars and extra-galactic sources, we analyse the structure of the large-scale magnetic field in the Galactic disk. Comparison of rotation measures of pulsars in the disk at different distances as well as with rotation measures of background radio sources beyond the disk reveals large-scale reversals of the field directions between spiral arms and interarm regions. We develop a model for t…

Could the Galactic disk heating be due to Globular Cluster impacts?

So far, six mechanisms have been proposed to account for the Galactic disk heating. Of these, the most important appear to be a combination of scattering of stars by molecular clouds and by spiral arms. We study a further mechanism, namely, the repeated disk impact of the original Galactic Globular Cluster population up to the present. We find that Globular Clusters could have contributed at most a small fraction of the current vertical energy of the disk, as they could heat the whole disk to {$σ$}$_{z}$ = 5.5kms$^{{\rm -} {\rm 1}}$ (c.f. the observed 18 and 39 kms$^{{\rm -} {\rm 1}}$ for the …

Origin of chemical and dynamical properties of the Galactic thick disk

We adopt a scenario in which the Galactic thick disk was formed by minor merging between the first generation of the Galactic thin disk (FGTD) and a dwarf galaxy about 9 Gyr ago and thereby investigate chemical and dynamical properties of the Galactic thick disk. In this scenario, the dynamical properties of the thick disk have long been influenced both by the mass growth of the second generation of the Galactic thin disk (i.e., the present thin disk) and by its non-axisymmetric structures. On the other hand, the early star formation history and chemical evolution of the thin disk was influenc…

Angular Momentum Transport in Extended Galactic Disks

We demonstrate a significant difference in the angular momentum transport properties of galactic disks between regions in which the interstellar medium is single phase or two phase. Our study is motivated by observations of HI in extended galactic disks which indicate velocity dispersions of nonthermal origin, suggesting that turbulence in the gas may be contributing significantly to the observed dispersion. To address this, we have implemented a shearing-box framework within the FLASH code. The new code was used to perform local simulations of galactic disks that incorporate differential rota…

The radial metallicity gradients in the Milky Way thick disk as fossil signatures of a primordial chemical distribution

In this letter we examine the evolution of the radial metallicity gradient induced by secular processes, in the disk of an $N$-body Milky Way-like galaxy. We assign a [Fe/H] value to each particle of the simulation according to an initial, cosmologically motivated, radial chemical distribution and let the disk dynamically evolve for 6 Gyr. This direct approach allows us to take into account only the effects of dynamical evolution and to gauge how and to what extent they affect the initial chemical conditions. The initial [Fe/H] distribution increases with R in the inner disk up to R ~ 10 kpc a…

Bending and Breathing Modes of the Galactic Disk

We explore the hypothesis that a passing satellite or dark matter subhalo has excited coherent oscillations of the Milky Way's stellar disk in the direction perpendicular to the Galactic midplane. This work is motivated by recent observations of spatially dependent bulk vertical motions within ~ kpc of the Sun. A satellite can transfer a fraction of its orbital energy to the disk stars as it plunges through the Galactic midplane thereby heating and thickening the disk. Bulk motions arise during the early stages of such an event when the disk is still in an unrelaxed state. We present simple to…

Models for the 3-D axisymmetric gravitational potential of the Milky Way Galaxy - A detailed modelling of the Galactic disk

Aims. Galaxy mass models based on simple and analytical functions for the density and potential pairs have been widely proposed in the literature. Disk models constrained by kinematic data alone give information on the global disk structure only very near the Galactic plane. We attempt to circumvent this issue by constructing disk mass models whose three-dimensional structures are constrained by a recent Galactic star counts model in the near-infrared and also by observations of the hydrogen distribution in the disk. Our main aim is to provide models for the gravitational potential of the Gala…

JINA-NuGrid Galactic Chemical Evolution Pipeline

Galactic chemical evolution is a topic that involves nuclear physics, stellar evolution, galaxy evolution, observation, and cosmology. Continuous communication and feedback between these fields is a key component in improving our understanding of how galaxies form and how elements are created and recycled in galaxies and intergalactic space. In this proceedings, we present the current state of the JINA-NuGrid chemical evolution pipeline. It is designed to probe the impact of nuclear astrophysics uncertainties on galactic chemical evolution, to improve our knowledges regarding the origin of the…

Weighing the Galactic disk using phase-space spirals III. Probing distant regions of the disk using the Gaia EDR3 proper motion sample

We have applied our method for weighing the Galactic disk using phase-space spirals to the Gaia EDR3 proper motion sample. For stars in distant regions of the Galactic disk, the latitudinal proper motion has a close projection with vertical velocity, such that the phase-space spiral in the plane of vertical position and vertical velocity can be observed without requiring that all stars have available radial velocity information. We divided the Galactic plane into 360 separate data samples, each corresponding to an area cell in the Galactic plane in the distance range of 1.4-3.4 kpc, with an ap…

Characterisation of the Galactic thick disk

Thick disks appear to be common in external large spiral galaxies and our own Milky Way also hosts one. The existence of a thick disk is possibly directly linked to the formation history of the host galaxy and if its properties is known it can constrain models of galaxy formation and help us to better understand galaxy formation and evolution. This brief review attempts to highlight some of the characteristics of the Galactic thick disk and how it relates to other stellar populations such as the thin disk and the Galactic bulge. Focus has been put on results from high-resolution spectroscopic …

Role of galactic gaseous halos in recycling enriched winds from bulges to disks: A new bulge-disk chemical connection

We demonstrate for the first time that gaseous halos of disk galaxies can play a vital role in recycling metal-rich gas ejected from the bulges and thus in promoting chemical evolution of disks. Our numerical simulations show that metal-rich stellar winds from bulges in disk galaxies can be accreted onto the thin disks owing to hydrodynamical interaction between the gaseous ejecta and the gaseous halos, if the mean densities of the halos (rho_ hg) are as high as 10^{-5} cm^{-3}. The total amount of gas that is ejected from a bulge through a stellar wind and then accreted onto the disk depends …

The chemical history of molecules in circumstellar disks. II. Gas-phase species

Context: The chemical composition of a molecular cloud changes dramatically as it collapses to form a low-mass protostar and circumstellar disk. Two-dimensional (2D) chemodynamical models are required to properly study this process. Aims: The goal of this work is to follow, for the first time, the chemical evolution in two dimensions all the way from a pre-stellar core into a circumstellar disk. Of special interest is the question whether the chemical composition of the disk is a result of chemical processing during the collapse phase, or whether it is determined by in situ processing after th…

Excitation of coupled stellar motions in the Galactic Disk by orbiting satellites

We use a set of high-resolution N-body simulations of the Galactic disk to study its interactions with the population of satellites predicted cosmologically. One simulation illustrates that multiple passages of massive satellites with different velocities through the disk generate a wobble, having the appearance of rings in face-on projections of the stellar disk. They also produce flares in the disk outer parts and gradually heat the disk through bending waves. A different numerical experiment shows that an individual satellite as massive as the Sagittarius dwarf galaxy passing through the di…

Galactoseismology: Discovery of Vertical Waves in the Galactic Disk

We present evidence for a Galactic North-South asymmetry in the number density and bulk velocity of solar neighborhood stars. The number density profile, which is derived from main-sequence stars in the Sloan Digital Sky Survey, shows a (North - South)/(North + South) deficit at |z| ~ 400 pc and an excess at |z| ~ 800 pc. The bulk velocity profile, which is derived from the Sloan Extension for Galactic Understanding and Exploration, shows a gradual trend across the Galactic midplane as well as smaller-scale features. We speculate that the North-South asymmetry, which has the appearance of a wa…

Collisions between Dark Matter Confined High Velocity Clouds and Magnetized Galactic Disks: The Smith Cloud

The Galaxy's population of High Velocity Clouds (HVCs) may include a subpopulation that is confined by dark matter minihalos and falling toward the Galactic disk. We present the first magnetohydrodynamic simulational study of dark matter-dominated HVCs colliding with a weakly magnetized galactic disk. Our HVCs have baryonic masses of $5 \times 10^6\,$M$_{\odot}$ and dark matter minihalo masses of 0, $3 \times 10^8$, or $1 \times 10^9\,$M$_{\odot}$. They are modeled on the Smith Cloud, which is said to have collided with the disk 70 Myr ago. We find that, in all cases, the cloud's collision wit…

Rotation Curve Anomaly and Galactic Warp in M51

We revisit the anomaly of rotation curve in the nearly face-on galaxy M51 that shows an apparently faster decrease of rotation velocity than the Keplerian law in the outer disk, further showing apparent counter rotation in the outermost HI disk. We interpret this anomaly as due to warping of the galactic disk, and determined the warping structure of M51's disk using the tilted-ring method, assuming that the intrinsic rotation curve is normal. It is shown that the disk is nearly flat in the inner disk at a constant inclination angle, but the disk suddenly bends at radius 7.5 kpc by about 27$°$.…

Milky Way Tomography with K and M Dwarf Stars: the Vertical Structure of the Galactic Disk

We use the number density distributions of K and M dwarf stars with vertical height from the Galactic disk, determined using observations from the Sloan Digital Sky Survey, to probe the structure of the Milky Way disk across the survey's footprint. Using photometric parallax as a distance estimator we analyze a sample of several million disk stars in matching footprints above and below the Galactic plane, and we determine the location and extent of vertical asymmetries in the number counts in a variety of thin- and thick-disk subsamples in regions of some 200 square degrees within 2 kpc in ver…

Effects of Galactic fountains and delayed mixing in the chemical evolution of the Milky Way

The majority of galactic chemical evolution models assumes the instantaneous mixing approximation (IMA). This assumption is probably not realistic as indicated by the existence of chemical inhomogeneities, although current chemical evolution models of the Milky Way can reproduce the majority of the observational constraints under the IMA. The aim of this paper is to test whether relaxing this approximation in a detailed chemical evolution model can improve or worsen the agreement with observations. To do that, we investigated two possible causes for relaxing of the instantaneous mixing: i) the…

Modeling the Galactic Magnetic Field using Rotation Measure Observations in the Galactic Disk from the CGPS, SGPS, and the VLA

Interstellar magnetic fields play critical roles in many astrophysical processes. Yet despite their importance, our knowledge about magnetic fields in our Galaxy remains limited. For the field within the Milky Way, much of what we do know comes from observations of polarisation and Faraday rotation measures (RMs) of extragalactic sources and pulsars. A high angular density of RM measurements in several critical areas of the Galaxy is needed to clarify the Galactic magnetic field structure. Using observations made with the VLA, we have determined RMs for sources in regions of the Galactic plane…

Interaction of HVCs with the Outskirts of Galactic Disks: Turbulence

There exist many physical processes that may contribute to the driving of turbulence in galactic disks. Some of them could drive turbulence even in the absence of star formation. For example, hydrodynamic (HD) or magnetohydrodynamic (MHD) instabilities, frequent mergers of small satellite clumps, ram pressure, or infalling gas clouds. In this work we present numerical simulations to study the interaction of compact high velocity clouds (CHVC) with the outskirts of magnetized gaseous disks. With our numerical simulations we show that the rain of small HVCs onto the disk is a potential source of…

Evidence of Early Enrichment of the Galactic Disk by Large-Scale Winds

Large-scale homogeneous surveys of Galactic stars may indicate that the elemental abundance gradient evolves with cosmic time, a phenomenon that was not foreseen in existing models of Galactic chemical evolution (GCE). If the phenomenon is confirmed in future studies, we show that this effect, at least in part, is due to large-scale winds that once enriched the disk. These set up the steep abundance gradient in the inner disk (R <14 kpc). At the close of the wind phase, chemical enrichment through accretion of metal-poor material from the halo onto the disk gradually reduced the metallicity of…

星系盘低密度区域的恒星形成

Star formation in low-density regions of galactic disks

本文论证了LSB星系盘与正常旋涡星系XUV盘外缘在极低密度、引力稳定条件下的恒星形成具有相似性，其效率均依赖于盘亮度，并简要探讨了激发该过程的机制。

The Origin of Parsec-Scale Gaseous and Stellar Disks in the Galactic Center and AGNs

The Galactic center stellar disk and the circumnuclear ring provide a unique opportunity to study in detail the dynamics and physical conditions of distant molecular disks in the nuclei of galaxies. One of the key questions is how these disks form so close to their host black holes and under what condition they form stars in a tidally stressed environment. We argue that disk formation around a massive black hole is due to partial accretion of extended molecular clouds that temporarily pass through the central region of the Galaxy. The cancellation of angular momentum of the gravitationally foc…

3D test particle simulations of the Galactic disks. The kinematical effects of the bar

Aims: To study the imprints of a rotating bar on the kinematics of stars in the thin and thick disks throughout the Galaxy. Methods: We perform test particle numerical simulations of the thin and thick disks in a 3D Galactic potential that includes a halo, a bulge, thin and thick disks, and a Ferrers bar. We analyze the resulting velocity distributions of populations corresponding to both disks, for different positions in the Galaxy and for different structural parameters of the bar. Results: We find that the velocity distributions of the disks are affected by the bar, and that strong transien…

Vertical Structure and Kinematics of the Galactic Outer Disk

We report measurements of parallax and proper motion for four 22 GHz water maser sources as part of VERA Outer Rotation Curve project. All sources show Galactic latitudes of $>$ 2$^{\circ}$ and Galactocentric distances of $>$ 11 kpc at the Galactic longitude range of 95$^{\circ}$ $< l <$ 126$^{\circ}$. The sources trace the Galactic warp reaching to 200$\sim$400 pc, and indicate the signature of the warp to 600 pc toward the north Galactic pole. The new results along with previous results in the literature show the maximum height of the Galactic warp is increased with Galactocentric distance. …

Kinematical and chemical vertical structure of the Galactic thick disk I. Thick disk kinematics

The variation of the kinematical properties of the Galactic thick disk with Galactic height Z are studied by means of 412 red giants observed in the direction of the south Galactic pole up to 4.5 kpc from the plane. We confirm the non-null mean radial motion toward the Galactic anticenter found by other authors, but we find that it changes sign at |Z|=3 kpc, and the proposed inward motion of the LSR alone cannot explain these observations. The rotational velocity decreases with |Z| by -30 km/s/kpc, but the data are better represented by a power-law with index 1.25, similar to that proposed fro…

利用LAMOST和Gaia红团簇样本绘制银盘：VIII：利用单年龄和单丰度恒星族群绘制银盘运动学

Mapping the Galactic disk with the LAMOST and Gaia Red clump sample: VIII: Mapping the kinematics of the Galactic disk using mono-age and mono-abundance stellar populations

基于LAMOST-Gaia红团簇恒星，按年龄与[α/Fe]族群测绘银盘运动学，揭示整体运动、旋臂、扰动及不同加热机制。

An Analysis of HCN Observations of The Galactic Centre's Circumnuclear Disk

The Circumnuclear Disk (CND) is a torus of dust and moleular gas rotating about the galactic centre and extends from 1.6 to 7pc from the central massive black hole SgrA*. Large Velocity Gradient modelling of selected transitions of HCN rotational collisions with molecular hydrogen is used to infer Hydrogen density and HCN opacities. The analysis concludes that the predicted hydrogen number density of CND clumps is about 10^6 which is insufficiently dense to withstand the tidal shear forces generated by SgrA* and the stellar group in the cavity between the galactic centre and the CND.

银河系盘金属丰度的南北不对称性可能是盘翘曲的新示踪器

The Galactic Disk North-south Asymmetry in Metallicity May Be A New Tracer for the Disk Warp

本研究利用LAMOST和APOGEE的17万颗红团簇恒星，首次发现金属丰度南北不对称性可示踪银河系盘翘曲，并精确拟合其形态与节线方向。

Estimation of the Vertical Disk Scale Height Using Young Galactic Objects

We have collected literature data on young Galactic objects such as masers with VLBI-measured trigonometric parallaxes, OB associations, HII regions and Cepheids. We have recently established that vertical disk scale height is strongly influenced by the objects of the Local arm. In the present work we used samples that do not contain objects in this arm. Based on the model of a self-gravitating isothermal disk for the density distribution, we have found the following vertical disk scale heights: h=46+/-5 pc from 69 masers with trigonometric parallaxes, h=36+/-3 pc from 59 OB associations, h=35…

An Intermediate Velocity HI Cloud Falling to the Galactic Disk; Possible Evidence for Low Metallicity HI Gas Originated Outside the Galactic Disk

We found that an intermediate velocity cloud (IVC) IVC 86-36 in HI 21 cm emission shows a head-tail distribution toward the Galactic plane with marked parallel filamentary streamers, which is extended over 40 degrees in the sky. The distance of IVC 86-36 is constrained to be less than ~3 kpc from absorption of a background star as determined from opticalspectroscopy. There is a bridge feature in velocity between the IVC and the local ISM with velocity separation of ~50 km s-1, which may indicate dynamical interaction of the IVC with the disk. If the interaction is correct, the distance estimat…

Kinematics of the Galactic disk from LAMOST Dwarf sample

Based on the LAMOST survey and Sloan Digital Sky Survey (SDSS), we use low-resolution spectra of 130,043 F/G-type dwarf stars to study the kinematics and metallicity properties of the Galactic disk. Our study shows that the stars with poorer metallicity and larger vertical distance from Galactic plane tend to have larger eccentricity and velocity dispersion. After separating the sample stars into likely thin-disk and thick-disk sub-sample, we find that there exits a negative gradient of rotation velocity $V_ϕ$ with metallicity [Fe/H] for the likely thin-disk sub-sample, and the thick-disk sub-…

Impacts of Radial Mixing on the Galactic Thick and Thin Disks

Using N-body simulations of the Galactic disks, we qualitatively study how the metallicity distributions of the thick and thin disk stars are modified by radial mixing induced by the bar and spiral arms. We show that radial mixing drives a positive vertical metallicity gradient in the mono-age disk population whose initial scale-height is constant and initial radial metallicity gradient is tight and negative. On the other hand, if the initial disk is flaring, with scale-height increasing with galactocentric radius, radial mixing leads to a negative vertical metallicity gradient, which is consi…

Galactic chemical evolution: the observational side

In this review I outline some ideas in chemical evolution, necessary for understanding the evolution of galaxies from measured elemental abundance ratios. I then discuss abundance results from studies of Local Group dwarf galaxies and the globular cluster Omega Cen. I present a qualitative scenario of prolonged chemical enrichment in a leaky box that can explain the observed abundance ratios in these systems. Space limitations prevent a comprehensive review of this vast field, so I have restricted the discussion to dwarf systems.

Estimating the Fuel Supply Rate on the Galactic Disk from High Velocity Clouds (HVCs) Infall

Previous studies suggest that the estimated maximum accretion rate from approaching high velocity clouds (HVCs) on the Galactic disk can be up to ~ 0.4 solar mass per year. In this study, we point out that the hydrodynamic interaction between the HVCs and the Galactic disk is not considered in the traditional method of estimating the infall rate and therefore the true supply rate of fuel from HVCs can be different from the suggested value depending on the physical configurations of HVCs including density, velocity, and distance. We choose 11 HVC complexes and construct 4 different infall model…

A test of the failed disk wind scenario for the origin of the broad line region in active galactic nuclei

It has been recently proposed that the broad line region in active galactic nuclei originates from dusty clouds driven from the accretion disk by radiation pressure, at a distance from the black hole where the disk is cooler than the dust sublimation temperature. We test this scenario by checking the consistency of independent broad line region and accretion disk reverberation measurements, for a sample of 11 well studied active galactic nuclei. We show that independent disk and broad line region reverberation mapping measurements are compatible with a universal disk temperature at the Hβ radi…

The circum-galactic gas around cosmologically simulated disks

We analyze the physical properties and infall rates of the circum-galactic gas around disks obtained in multi-resolved, cosmological, AMR simulations. At intermediate and low redshifts, disks are embedded into an extended, hot, tenuous corona that contributes largely in fueling the disk with non-enriched gas whereas the accretion of enriched gas from tidal streams occurs throughout episodic events. We derive an infall rate close to the disk of the same value as the one of the star formation rate in the disk and its temporal evolution as a function of galacto-centric radius nicely shows that th…

The Galactic Thick Disk: An Observational Perspective

In this review, we present a brief description of observational efforts to understand the Galactic thick disk and its relation to the other Galactic components. This review primarily focused on elemental abundance patterns of the thick disk population to pin down the process or processes that were responsible for its existence and evolution. Kinematic and chemical properties of disk stars establish that the thick disk is a distinct component in the Milky Way. The chemical enrichment and star formation histories hold clues to the bigger picture of understanding the Galaxy formation.

The population of planetary nebulae near the Galactic centre: chemical abundances

Planetary nebulae (PNe) constitute an important tool to study the chemical evolution of the Milky Way and other galaxies, probing the nucleosynthesis processes, abundance gradients and the chemical enrichment of the interstellar medium. In particular, Galactic bulge PNe (GBPNe) have been extensively used in the literature to study the chemical properties of this Galactic structure. However, the presently available GBPNe chemical composition studies are strongly biased, since they were focused on brighter objects, predominantly located in Galactic regions of low interstellar reddening. In this …

On the Size Evolution of a Galactic Disk in Hierarchical Merging of Cold Dark Matter Halos

We investigate the dynamical effects of dark matter subhalos on the structure and evolution of a galactic disk, using semi-analytic method that includes approximated and empirical relations as achieved in detailed numerical simulations of the cold dark matter model. We calculate the upper limit for the size of a galactic disk at a specific redshift $z$, based on the orbital properties of subhalos characterized by their pericentric distances from the center of a host halo. We find that this possibly largest size of a disk as determined by the smallest pericentric distances of subhalos shows the…

Galactic chemical evolution]{Galactic chemical evolution of the solar neighborhood, solar twins and exoplanet indicators

Galactic chemical evolution (GCE), solar analogues or twins, and peculiarities of the solar composition with respect to the twins are inextricably related. We examine GCE parameters from the literature and present newly derived values using a quadratic fit that gives zero for a Solar age (i.e., 4.6 Gyr). We show how the GCE parameters may be used not only to "correct" abundances to the solar age, but to predict relative elemental abundances as a function of age. We address the question of whether the solar abundances are depleted in refractories and enhanced in volatiles and find that the answ…

The Abundance of Fluorine in Normal G and K Stars of the Galactic Thin Disk

The abundance of fluorine is determined from the (2-0) R9 2.3358 micron feature of the molecule HF for several dozen normal G and K stars in the Galactic thin disk from spectra obtained with the Phoenix IR spectrometer on the 2.1-m telescope at Kitt Peak. The abundances are analyzed in the context of Galactic chemical evolution to explore the contributions of supernovae and asymptotic giant branch (AGB) stars to the abundance of fluorine in the thin disk. The average abundance of fluorine in the thin disk is found to be [F/Fe] = +0.23 +/- 0.03, and the [F/Fe] ratio is flat or declines slowly w…

Chemical evolution of a protoplanetary disk

In this paper we review recent progress in our understanding of the chemical evolution of protoplanetary disks. Current observational constraints and theoretical modeling on the chemical composition of gas and dust in these systems are presented. Strong variations of temperature, density, high-energy radiation intensities in these disks, both radially and vertically, result in a peculiar disk chemical structure, where a variety of processes are active. In hot, dilute and heavily irradiated atmosphere only the most photostable simple radicals and atoms and atomic ions exist, formed by gas-phase…

On the vertical equilibrium of the local Galactic disk and the search for disk dark matter

Estimates of the dynamical surface mass density at the solar Galactocentric distance are commonly derived assuming that the disk is in vertical equilibrium with the Galactic potential. This assumption has recently been called into question, based on the claim that the ratio between the kinetic and the gravitational energy in such solutions is a factor of 3 larger than required if Virial equilibrium is to hold. Here we show that this ratio between energies was overerestimated and that the disk solutions are likely to be in Virial equilibrium after all. We additionally demonstrate, using one-dim…

Galactic bar: normal mode of the stellar disk or superposition of transient spirals?

Several mechanisms of bar formation in stellar galactic disks are considered, including Toomre swing amplification and normal mode approach. On example of the well-known model of Kuzmin--Toomre using N-body simulations it was shown that the stellar bar is developed as a result of the evolution of an unstable normal mode. The pattern speed and the growth rate found agree well with linear perturbation theory. Nonlinear evolution of the bar is followed. Role of the growing transient spirals in bar formation is discussed.

On the Metallicity Gradient in the Galactic Disk

The problem of the chemical composition gradient in the galactic disk is studied based on a sample of metallicity estimates of open star clusters, using Gaia DR2-improved distance estimates. A clearly non-monotonic variation was observed in the average metallicity of clusters with increasing galactocentric distance. One can clearly see the metallicity jump of 0.22 in [Fe/H] at a Galactocentric distance of about 9.5 kpc, which appears to be linked to the outer boundary of the thinnest and youngest component of the galactic disk. The absence of a significant metallicity gradient in the internal …

Impact of the Galactic Disk and Large Magellanic Cloud on the Trajectories of Hypervelocity Stars Ejected from the Galactic Center

We consider how the gravity of the Galactic disk and the Large Magellanic Cloud (LMC) modifies the radial motions of hypervelocity stars (HVSs) ejected from the Galactic Center. For typical HVSs ejected towards low (high) Galactic latitudes, the disk bends trajectories by up to 30 degrees (3-10 deg). For many lines-of-sight through the Galaxy, the LMC produces similar and sometimes larger deflections. Bound HVSs suffer larger deflections than unbound HVSs. Gravitational focusing by the LMC also generates a factor of two overdensity along the line-of-sight towards the LMC. With large enough sam…