scholarly journals Evolution of Abundance Gradients along the Galactic Disk

2001 ◽  
Vol 204 ◽  
pp. 419-419
Author(s):  
J. L. Hou ◽  
Nikos Prantzos ◽  
Samuel Boissier
Keyword(s):  
Milky Way ◽  
Galactic Disk ◽  
Current Data ◽  
Solar Neighborhood ◽  
Observational Constraints ◽  
Type I ◽  
Intermediate Mass Stars ◽  
Abundance Profile ◽  
Gradient Evolution ◽  
Inside Out

A detailed investigation of the abundance gradients and their evolution along the Galactic disk has recently appeared (Hou, J. L., Prantzos, N., & Boissier, S. 2000, A&A, in press; astro-ph/0007164). A chemical evolution model of S. Boissier & N. Pranzos (1999, MNRAS, 307, 857) was quite successful in reproducing the main observational constraints both in the solar neighborhood and the entire Milky Way disk. Studied elements include He, C, N, O, Ne, Mg, Al, Si, S, Ar and Fe. We use metallicity dependent yields for massive stars with and without mass loss. We find that most observed abundance profiles are correctly reproduced by massive star yields, but C and N require supplementary sources. We argue that massive, mass losing stars can totally account for the abundance profile of C, while intermediate mass stars are the main source of N. We also find that the adopted “inside-out” formation scheme for the Milky Way disk produces abundance profiles steeper in the past. Using current data on planetary nebulae of type I, II, and III, on N, Ne, S, Ar as observational constraints for gradient evolution, we find that it is difficult to conclude whether the gradient steepens or flattens with time. However, for a given interval of Galactic age, our model predicts that the corresponding abundance scatter is smaller in the inner disk than in the outer regions.

scholarly journals Extended stellar systems in the solar neighborhood

2019 ◽  
Vol 622 ◽  
pp. L13 ◽  
Author(s):  
Stefan Meingast ◽  
João Alves ◽  
Verena Fürnkranz
Keyword(s):  
Wavelet Decomposition ◽  
Stellar Population ◽  
Main Sequence ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Galactic Disk ◽  
Mass Function ◽  
Solar Neighborhood ◽  
Giant Stars ◽  
Stellar Streams

We report the discovery of a large, dynamically cold, coeval stellar stream that is currently traversing the immediate solar neighborhood at a distance of only 100 pc. The structure was identified in a wavelet decomposition of the 3D velocity space of all stars within 300 pc of the Sun. Its members form a highly elongated structure with a length of at least 400 pc, while its vertical extent measures only about 50 pc. Stars in the stream are not isotropically distributed but instead form two parallel lanes with individual local overdensities, that may correspond to a remnant core of a tidally disrupted cluster or OB association. Its members follow a very well-defined main sequence in the observational Hertzsprung–Russel diagram and also show a remarkably low 3D velocity dispersion of only 1.3 km s−1. These findings strongly suggest a common origin as a single coeval stellar population. An extrapolation of the present-day mass function indicates a total mass of at least 2000 M⊙, making it larger than most currently known clusters or associations in the solar neighborhood. We estimated the age of the stream to be around 1 Gyr based on a comparison with a set of isochrones and giant stars in our member selection and find a mean metallicity of [Fe/H] = −0.04. This structure may very well represent the Galactic disk counterpart to the prominent stellar streams observed in the Milky Way halo. As such, it constitutes a new valuable probe to constrain the Galaxy’s mass distribution.

scholarly journals Interstellar Objects Follow the Collapse of Molecular Clouds

2021 ◽  
Vol 921 (2) ◽  
pp. 168
Author(s):  
Susanne Pfalzner ◽  
Dylan Paterson ◽  
Michele T. Bannister ◽  
Simon Portegies Zwart
Keyword(s):  
Interstellar Medium ◽  
Molecular Cloud ◽  
Gas Dynamics ◽  
Molecular Clouds ◽  
Milky Way ◽  
Solar Neighborhood ◽  
Observational Constraints ◽  
Parent Population ◽  
Test Particles ◽  
Relevant Component

Abstract Interstellar objects (ISOs), the parent population of 1i/‘Oumuamua and 2i/Borisov, are abundant in the interstellar medium of the Milky Way. This means that the interstellar medium, including molecular-cloud regions, has three components: gas, dust, and ISOs. From observational constraints of the field density of ISOs drifting in the solar neighborhood, we infer that a typical molecular cloud of 10 pc diameter contains some 1018 ISOs. At typical sizes ranging from hundreds of meters to tens of kilometers, ISOs are entirely decoupled from the gas dynamics in these molecular clouds. Here we address the question of whether ISOs can follow the collapse of molecular clouds. We perform low-resolution simulations of the collapse of molecular clouds containing initially static ISO populations toward the point where stars form. In this proof-of-principle study, we find that the interstellar objects definitely follow the collapse of the gas—and many become bound to the new-forming numerical approximations to future stars (sinks). At minimum, 40% of all sinks have one or more ISO test particles gravitationally bound to them for the initial ISO distributions tested here. This value corresponds to at least 1010 actual ISOs being bound after three initial freefall times. Thus, ISOs are a relevant component of star formation. We find that more massive sinks bind disproportionately large fractions of the initial ISO population, implying competitive capture of ISOs. Sinks can also be solitary, as their ISOs can become unbound again—particularly if sinks are ejected from the system. Emerging planetary systems will thus develop in remarkably varied environments, ranging from solitary to richly populated with bound ISOs.

Galactic archaeology: Understanding the metallicity gradients with chemo-dynamical models

2018 ◽  
Vol 14 (A30) ◽  
pp. 253-254
Author(s):  
I. Minchev ◽  
F. Anders ◽  
C. Chiappini
Keyword(s):  
Interstellar Medium ◽  
Milky Way ◽  
Cosmic Time ◽  
Dynamical Evolution ◽  
Disk Galaxies ◽  
Dynamical Models ◽  
Disk Formation ◽  
Recent Method ◽  
Gradient Evolution ◽  
Inside Out

AbstractRadial metallicity gradients measured today in the interstellar medium (ISM) and stellar components of disk galaxies are the result of chemo-dynamical evolution since the beginning of disk formation. This makes it difficult to infer the disk past without knowledge of the ISM metallicity gradient evolution with cosmic time. We show that abundance gradients are meaningful only if stellar age information is available. The observed gradient inversion with distance from the disk mid-plane seen in the Milky Way can be explained as the effect of inside-out disk formation and disk flaring of mono-age populations. A novel recent method is presented for constraining the evolution of the Galactic ISM metallicity with radius and time directly from the observations, while at the same time recovering the birth radii of any stellar sample with precise metallicity and age measurements.

scholarly journals Inside Out and Upside-Down: The Roles of Gas Cooling and Dynamical Heating in Shaping the Stellar Age-Velocity Relation

2021 ◽  
Author(s):  
Jonathan C Bird ◽  
Sarah R Loebman ◽  
David H Weinberg ◽  
Alyson M Brooks ◽  
Thomas R Quinn ◽  
...  
Keyword(s):  
Milky Way ◽  
Velocity Dispersion ◽  
Solar Neighborhood ◽  
Disk Galaxies ◽  
Low Velocity ◽  
Velocity Relationship ◽  
Gas Cooling ◽  
Multi Phase ◽  
Inside Out ◽  
Over Time

Abstract Kinematic studies of disk galaxies, using individual stars in the Milky Way or statistical studies of global disk kinematics over time, provide insight into how disks form and evolve. We use a high-resolution, cosmological zoom-simulation of a Milky Way-mass disk galaxy (h277) to tie together local disk kinematics and the evolution of the disk over time. The present-day stellar age-velocity relationship (AVR) of h277 is nearly identical to that of the analogous solar-neighborhood measurement in the Milky Way. A crucial element of this success is the simulation’s dynamically cold multi-phase ISM, which allows young stars to form with a low velocity dispersion (σbirth∼6 − 8 km s−1) at late times. Older stars are born kinematically hotter (i.e., the disk settles over time in an “upside-down” formation scenario), and are subsequently heated after birth. The disk also grows “inside-out”, and many of the older stars in the present-day solar neighborhood are present because of radial mixing. We demonstrate that the evolution of σbirth in h277 can be explained by the same model used to describe the general decrease in velocity dispersion observed in disk galaxies from z ∼ 2 − 3 to the present-day, in which the disk evolves in quasi-stable equilibrium and the ISM velocity dispersion decreases over time due to a decreasing gas fraction. Thus, our results tie together local observations of the Milky Way’s AVR with observed kinematics of high z disk galaxies.

scholarly journals Tracing the Origin of Moving Groups. III. Detecting Moving Groups in LAMOST DR7

2021 ◽  
Vol 922 (2) ◽  
pp. 105
Author(s):  
Yong Yang ◽  
Jingkun Zhao ◽  
Jiajun Zhang ◽  
Xianhao Ye ◽  
Gang Zhao
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Milky Way ◽  
Galactic Disk ◽  
Solar Neighborhood ◽  
The Other ◽  
Spiral Arms ◽  
Nearby Stars ◽  
Moving Groups ◽  
Wavelet Technique

Abstract We revisit the moving groups (MGs) in the solar neighborhood with a sample of 91,969 nearby stars constructed from LAMOST DR7. Using the wavelet technique and Monte Carlo simulations, five MGs together with a new candidate located at V≃−130 km s−1 are detected simultaneously in V − U 2 + 2 V 2 space. Taking into account the other known MGs, we conclude that MGs in the Galactic disk are spaced by approximately 15–25 km s−1 along V velocity. The origin of detected MGs is analyzed through the distributions of [Fe/H]−[Mg/Fe] and ages. Our results support attributing the origin to the continuous resonant mechanisms probably induced by the bar or spiral arms of the Milky Way.

scholarly journals The Stellar Population of the Thin Disk

2009 ◽  
Vol 5 (S265) ◽  
pp. 304-312
Author(s):  
Carlos Allende Prieto
Keyword(s):  
Galaxy Formation ◽  
Stellar Population ◽  
Milky Way ◽  
Galactic Disk ◽  
Symmetry Plane ◽  
Thin Disk ◽  
Solar Neighborhood ◽  
Galaxy Formation And Evolution ◽  
The Galaxy ◽  
Formation And Evolution

AbstractWe discuss recent observations of stars located close to the symmetry plane of the Milky Way, and examine them in the context of theories of Galaxy formation and evolution. The kinematics, ages, and compositions of thin disk stars in the solar neighborhood display complex patterns, and interesting correlations. The Galactic disk does not seem to pose any unsurmountable obstacles to hierarchical galaxy formation theories, but a model of the Milky Way able to reproduce the complexity found in the data will likely require a meticulous study of a significant fraction of the stars in the Galaxy. Making such an observational effort seems necessary in order to make a physics laboratory out of our own galaxy, and ultimately ensure that the most relevant processes are properly understood.

scholarly journals Inflow of Neutral Gas toward the Galactic Disk

1989 ◽  
Vol 120 ◽  
pp. 396-407 ◽  
Author(s):  
I.F. Mirabel
Keyword(s):  
Atomic Hydrogen ◽  
Large Scale ◽  
Milky Way ◽  
Accretion Rate ◽  
Galactic Disk ◽  
Solar Neighborhood ◽  
Milky Way Galaxy ◽  
Neutral Gas ◽  
The Galaxy ◽  
Very High

Summary:I highlight the evidence for inflow of neutral gas toward the disk of the Galaxy. The Milky Way is accreting 0.2-0.5 M⊙/yr of extragalactic atomic hydrogen at very high velocities. The interaction of infalling clouds with galactic material produces large-scale disturbances in the interstellar medium. Although the injection of energy into the galactic disk by infalling neutral gas is only 1% of the energy from supernovae, the impinging of high velocity neutral gas may be a relatively important source of energy in localized regions of the outer Galaxy.In the solar neighborhood the downfall rate of HI at intermediate velocities is 2.72 x 10-8 z-1(kpc) M⊙ pc-2 yr-1, which if representative of the whole galactic disk, is at least 10 times more massive than the estimated accretion rate of extragalactic HI at very high velocities. This implies that most of the neutral gas that is infalling in the solar vicinity has originated in the galactic disk. It is concluded that in the Milky Way galaxy there is a moderate inflow of extragalactic neutral gas on top of a more intensive disk-halo circulation.

scholarly journals Contribution of White Dwarfs to Cluster Masses

1998 ◽  
Vol 11 (1) ◽  
pp. 430-432
Author(s):  
Ted Von Hippel
Keyword(s):  
Stellar Evolution ◽  
Mass Fraction ◽  
Globular Clusters ◽  
White Dwarfs ◽  
Literature Search ◽  
Galactic Disk ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Solar Neighborhood ◽  
Current Evidence

The study of cluster white dwarfs (WDs) has been invigorated recently bythe Hubble Space Telescope (HST). Recent WD studies have been motivated by the new and independent cluster distance (Renzini et al. 1996), age (von Hippel et al. 1995; Richer et al. 1997), and stellar evolution (Koester & Reimers 1996) information that cluster WDs can provide. An important byproduct of these studies has been an estimate of the WD mass contribution in open and globular clusters. The cluster WD mass fraction is of importance for understanding the dynamical state and history of star clusters. It also bears an important connection to the WD mass fractions of the Galactic disk and halo. Current evidence indicates that the open clusters (e.g. von Hippel et al. 1996; Reid this volume) have essentially the same luminosity function (LF) as the solar neighborhood population. The case for the halo is less clear, despite the number of very good globular cluster LFs down to nearly 0.1 solar masses (e.g. Cool et al. 1996; Piotto, this volume), as the field halo LF is poorly known. For most clusters dynamical evolution should cause evaporation of the lowest mass members, biasing clusters to have flatter present-day mass functions (PDMFs) than the disk and halo field populations. Dynamical evolution should also allow cluster WDs to escape, though not in the same numbers as the much lower mass main sequence stars. The detailed connection between cluster PDMFs and the field IMF awaits elucidation from observations and the new combined N-body and stellar evolution models (Tout, this volume). Nevertheless, the WD mass fraction of clusters already provides an estimate for the WD mass fraction of the disk and halo field populations. A literature search to collect cluster WDs and a simple interpretive model follow. This is a work in progress and the full details of the literature search and the model will be published elsewhere.

scholarly journals Remarkable Symmetries in the Milky Way Disc's Magnetic Field

2011 ◽  
Vol 28 (2) ◽  
pp. 171-176 ◽  
Author(s):  
P. P. Kronberg ◽  
K. J. Newton-McGee
Keyword(s):  
Magnetic Structure ◽  
Large Scale ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Field Structure ◽  
Field Pattern ◽  
Close Coupling ◽  
Sign Change

AbstractWe apply a new, expanded compilation of extragalactic source Faraday rotation measures (RM) to investigate the broad underlying magnetic structure of the Galactic disk at latitudes ∣b∣ ≲15° over all longitudes l, where our total number of RMs is comparable to those in the combined Canadian Galactic Plane Survey (CGPS) at ∣b∣ < 4° and the Southern Galactic Plane (SGPS) ∣b∣<1.5°. We report newly revealed, remarkably coherent patterns of RM at ∣b∣≲15° from l∼270° to ∼90° and RM(l) features of unprecedented clarity that replicate in l with opposite sign on opposite sides of the Galactic center. They confirm a highly patterned bisymmetric field structure toward the inner disc, an axisymmetic pattern toward the outer disc, and a very close coupling between the CGPS/SGPS RMs at ∣b∣≲3° (‘mid-plane’) and our new RMs up to ∣b∣∼15° (‘near-plane’). Our analysis also shows the vertical height of the coherent component of the disc field above the Galactic disc's mid-plane—to be ∼1.5 kpc out to ∼6 kpc from the Sun. This identifies the approximate height of a transition layer to the halo field structure. We find no RM sign change across the plane within ∣b∣∼15° in any longitude range. The prevailing disc field pattern and its striking degree of large-scale ordering confirm that our side of the Milky Way has a very organized underlying magnetic structure, for which the inward spiral pitch angle is 5.5°±1° at all ∣b∣ up to ∼12° in the inner semicircle of Galactic longitudes. It decreases to ∼0° toward the anticentre.

Comprehensive Review on Neuro-Degenerative Type 3DM

2021 ◽  
Vol 18 ◽  
Author(s):  
Chandani V. Chandarana ◽  
Salona Roy
Keyword(s):  
Type 2 Diabetes ◽  
Insulin Signaling ◽  
Insulin Signalling ◽  
Amyloid Β ◽  
Diabetes Mellitus Type 1 ◽  
Current Data ◽  
The Body ◽  
Type I ◽  
Therapeutic Benefits

: Alzheimer disease (AD) is thought to be the metabolic illness raised by defective insulin signaling, insulin resistance, and low insulin levels in the brain, according to a growing body of research. The "Type 3 diabetes" has been postulated for AD because reduced insulin signalling has molecular and physiological consequences that are comparable to Type I and Type 2 diabetes mellitus (Type 1 DM and Type 2 DM, respectively). The similarities between type 2 diabetes and Alzheimer's disease suggest that these clinical trials might yield therapeutic benefits. However, it's important to note that lowering your risk of Alzheimer's dementia, whether you have diabetes or not, is still a multidimensional process involving factors like exercise, smoking, alcohol, food, and mental challenge. The current aim is to show the relationship between T3D and AD being based on both the processing of amyloid-β (Aβ) precursor protein toxicity and the clearance of Aβ are the result of an impaired insulin signaling. The brain's metabolism with its high lipid content and energy needs, places excess demands on mitochondria and appears more susceptible to oxidative damage than the rest of the body. Current data suggests that increased oxidative stress relates to amyloid-β (Aβ) pathology and onset of AD.

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