scholarly journals The Metal Pre-Enrichment of the Galactic Disk: Solving the G-Dwarf Problem

1996 ◽  
Vol 169 ◽  
pp. 395-401
Author(s):  
M. Samland ◽  
G. Hensler
Keyword(s):  
Chemical Evolution ◽  
Galactic Disk ◽  
Evolutionary Models ◽  
Low Mass Stars ◽  
Low Mass ◽  
Stringent Test ◽  
Metallicity Distribution

The stellar metallicity distribution of low-mass stars is one of the major touchstones for models describing the chemical evolution of our Galaxy. In contrast to the gaseous components, the abundances of the stellar components also reflect the temporal enrichment. Hence, the stellar metallicity distribution is a stringent test for evolutionary models of galaxies.

scholarly journals The Evolution of 3He, 4He and D in the Galaxy

2000 ◽  
Vol 198 ◽  
pp. 540-546 ◽  
Author(s):  
Cristina Chiappini ◽  
Francesca Matteucci
Keyword(s):  
Chemical Evolution ◽  
Present Model ◽  
Galactic Disk ◽  
The Sun ◽  
Mixing Process ◽  
Low Mass Stars ◽  
A Value ◽  
The Galaxy ◽  
Low Mass ◽  
Standing Problem

In this work we present the predictions of a modified version of the ‘two-infall model’ (Chiappini et al. 1997 - CMG) for the evolution of 3He, 4He and D in the solar vicinity, as well as their distributions along the Galactic disk. In particular, we show that when allowing for extra-mixing process in low mass stars (M < 2.5 M⊙), as predicted by Charbonnel and do Nascimento (1998), a long standing problem in chemical evolution is solved, namely: the overproduction of 3He by the chemical evolution models as compared to the observed values in the sun and in the interstellar medium. Moreover, we show that chemical evolution models can constrain the primordial value of the deuterium abundance and that a value of (D/H)p < 3 × 10—5 is suggested by the present model. Finally, adopting the primordial 4He abundance suggested by Viegas et al. (1999), we obtain a value for ΔY/ΔZ ≃ 2 and a better agreement with the solar 4He abundance.

scholarly journals The Bologna Open Cluster Chemical Evolution project: a large, homogeneous sample of Galactic open clusters

2008 ◽  
Vol 4 (S258) ◽  
pp. 153-160
Author(s):  
Angela Bragaglia
Keyword(s):  
Chemical Evolution ◽  
Galactic Disk ◽  
Open Cluster ◽  
Open Clusters ◽  
Photometric Data ◽  
Homogeneous Sample ◽  
Metallicity Distribution

AbstractThe Bologna Open Cluster Chemical Evolution (BOCCE) project is a photometric and spectroscopic survey of open clusters, to be used as tracers of the Galactic disk properties and evolution. The clusters parameters (age, distance, reddening, metallicity, and detailed abundances) are derived in a precise and homogeneous way. This will contribute to a solid, reliable description of the disk: the clusters parameters will be used, for instance, to determine the metallicity distribution in the Galactic disk and how it has evolved with time. We have concentrated on old open clusters and we have presently in our hands data for about 40 open clusters; we have fully analyzed the photometric data for about one half of them and the spectra for one quarter of them.

scholarly journals Abundance gradients from Planetary Nebulae in the galactic disk

1997 ◽  
Vol 180 ◽  
pp. 397-404 ◽  
Author(s):  
W.J. Maciel
Keyword(s):  
Chemical Evolution ◽  
Spiral Galaxies ◽  
Galactic Disk ◽  
Chemical Elements ◽  
Planetary Nebulae ◽  
Hii Regions ◽  
Additional Constraint ◽  
Established Fact ◽  
Metallicity Distribution

Radial abundance gradients in the disks of spiral galaxies are made evident from observations of ionized nebulae (HII regions, planetary nebulae, and SNRs) and stars. They have been observed for several chemical elements, and their presence is an established fact, despite some inconsistencies in the results. Therefore, these gradients can be considered as an additional constraint to the chemical evolution models, as the age-metallicity relation or the metallicity distribution of the G-dwarfs.

scholarly journals The early evolution of low mass stars and brown dwarfs

2009 ◽  
Vol 5 (H15) ◽  
pp. 755-755
Author(s):  
Isabelle Baraffe
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Brown Dwarfs ◽  
Early Evolution ◽  
Evolutionary Models ◽  
Low Mass Stars ◽  
Low Mass ◽  
Effects Of Rotation ◽  
Star Formation Regions

My talk will focus on the early evolution of low mass objects. I will discuss the main uncertainties on current evolutionary models and the effects of rotation, magnetic field and early accretion history on young object's structure. I will also present possible solutions to the well known spread in HRD observed in star formation regions for objects of a few Myr old.

scholarly journals Peter Pan discs: finding Neverland’s parameters

2020 ◽  
Vol 496 (1) ◽  
pp. L111-L115
Author(s):  
Gavin A L Coleman ◽  
Thomas J Haworth
Keyword(s):  
Initial Conditions ◽  
Mass Star ◽  
Evolutionary Models ◽  
Peter Pan ◽  
Low Mass Stars ◽  
Star Forming ◽  
Star Forming Regions ◽  
Accretion Rates ◽  
Order Of Magnitude ◽  
Low Mass

ABSTRACT Peter Pan discs are a recently discovered class of long-lived discs around low-mass stars that survive for an order of magnitude longer than typical discs. In this paper, we use disc evolutionary models to determine the required balance between initial conditions and the magnitude of dispersal processes for Peter Pan discs to be primordial. We find that we require low transport (α ∼ 10−4), extremely low external photoevaporation (${\le}10^{-9}\, {\rm M}_{\odot }\, {\rm yr^{-1}}$), and relatively high disc masses (&gt;0.25M*) to produce discs with ages and accretion rates consistent with Peter Pan discs. Higher transport (α = 10−3) results in disc lifetimes that are too short and even lower transport (α = 10−5) leads to accretion rates smaller than those observed. The required external photoevaporation rates are so low that primordial Peter Pan discs will have formed in rare environments on the periphery of low-mass star-forming regions, or deeply embedded, and as such have never subsequently been exposed to higher amounts of UV radiation. Given that such an external photoevaporation scenario is rare, the required disc parameters and accretion properties may reflect the initial conditions and accretion rates of a much larger fraction of the discs around low-mass stars.

scholarly journals A Relative Age Test of Pre-Main Sequence Evolutionary Models Based on the Young Quadruple System GG Tauri

2001 ◽  
Vol 200 ◽  
pp. 464-467
Author(s):  
Russel J. White
Keyword(s):  
Spectral Type ◽  
Temperature Scale ◽  
Main Sequence ◽  
Evolutionary Models ◽  
Low Mass Stars ◽  
Relative Age ◽  
Wide Range ◽  
Quadruple System ◽  
Low Mass

The components of the young hierarchical quadruple GG Tau, which span a wide range in spectral type (K7 – M7.5), are used to test both evolutionary models and the temperature scale for very young, low mass stars under the assumption of coeval formation. Of the evolutionary models tested which extend into the substellar regime, those of Baraffe et al. yield the most consistent ages when combined with a temperature scale intermediate between that of dwarfs and giants. The Palla & Stahler and Siess et al. models are also capable of yielding a coeval age down to their lowest mass (0.1 M⊙). These latter two models, which extend to much higher masses than the Baraffe et al. models, agree reasonably well with the Baraffe et al. models at 1.0 M⊙ and thus could be combined to construct a set evolutionary models that extends from Substellar to several solar masses.

scholarly journals Abundances and Chemical Evolution of the Galactic Center

1977 ◽  
Vol 45 ◽  
pp. 79-101
Author(s):  
Jean Audouze
Keyword(s):  
Chemical Evolution ◽  
Gamma Rays ◽  
Molecular Clouds ◽  
Galactic Center ◽  
Solar Neighbourhood ◽  
Interstellar Matter ◽  
Low Mass Stars ◽  
Element Abundances ◽  
The Galaxy ◽  
Low Mass

AbstractFrom observations of the galactic center using various techniques radioastronomy, millimeter waves (molecules) – infrared and gamma rays, the interstellar matter of this region* appears to have been strongly processed into stars : the gas density is much lower than in the solar neighbourhood. From CO measurements one knows that there are many molecular clouds such as SgrB2 where stars are forming now. From IR measurements, there are some indication that low mass stars are relatively more numerous in such regions than in the external regions of the galaxy. Finally the heavy element abundances show three important features (i) the possibility of strong enhancements in elements such as N and in a less extent 0 and Ne (the so called abundance gradients), (ii) Some specific enhancements of isotopes such43C,44N and also47O relative to42C,45N and43O (iii) Deuterium seems to have a lower abundance than in other parts of the galaxy such as the solar neighbourhood. Simple models of chemical evolution have been designed to account for such features and are rewiewed here.

scholarly journals Evolutionary properties of stellar standard candles: Red clump, AGB clump and white dwarfs

2012 ◽  
Vol 8 (S289) ◽  
pp. 145-152
Author(s):  
Maurizio Salaris
Keyword(s):  
Galactic Disk ◽  
Absolute Magnitude ◽  
Asymptotic Giant Branch ◽  
Low Mass Stars ◽  
Empirical Calibration ◽  
Magnitude Diagram ◽  
Low Mass ◽  
Red Clump ◽  
Semi Empirical ◽  
Distance Indicators

AbstractThe location of the white dwarf cooling sequence in the colour–magnitude diagram of simple stellar populations, the magnitude of the red clump and the magnitude of the asymptotic giant branch clump are three stellar distance indicators based on advanced evolutionary phases of low-mass stars. With the present observational capabilities, they can be applied to reach distances ranging from the Galactic disk and halo populations, to galaxies within the Local Group. Techniques devised to exploit these distance indicators are presented, together with a discussion of their calibration and the main sources of systematic errors. A first semi-empirical calibration of the asymptotic giant branch absolute magnitude in both the I and K bands is also derived.

scholarly journals Evolutionary models for two hyper-iron-poor low-mass stars

2007 ◽  
Vol 377 (4) ◽  
pp. 1520-1530
Author(s):  
G. J. Harris ◽  
R. Porter ◽  
A. E. Lynas-Gray ◽  
J. Tennyson
Keyword(s):  
Evolutionary Models ◽  
Low Mass Stars ◽  
Low Mass

scholarly journals THE LUMINOSITY AND MASS FUNCTIONS OF LOW-MASS STARS IN THE GALACTIC DISK. II. THE FIELD

2010 ◽  
Vol 139 (6) ◽  
pp. 2679-2699 ◽  
Author(s):  
John J. Bochanski ◽  
Suzanne L. Hawley ◽  
Kevin R. Covey ◽  
Andrew A. West ◽  
I. Neill Reid ◽  
...  
Keyword(s):  
Galactic Disk ◽  
Low Mass Stars ◽  
Low Mass ◽  
Mass Functions
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