scholarly journals Seeding the second star – II. CEMP star formation enriched from faint supernovae

2020 ◽  
Vol 497 (3) ◽  
pp. 3149-3165 ◽  
Author(s):  
Gen Chiaki ◽  
John H Wise ◽  
Stefania Marassi ◽  
Raffaella Schneider ◽  
Marco Limongi ◽  
...  
Keyword(s):  
First Generation ◽  
Dust Grains ◽  
Low Mass Stars ◽  
Chemical Enrichment ◽  
Living Fossils ◽  
Normal Core ◽  
Iron Abundance ◽  
Gas Cooling ◽  
Low Mass ◽  
First Time

ABSTRACT Carbon-enhanced metal-poor (CEMP) stars are the living fossils holding records of chemical enrichment from early generations of stars. In this work, we perform a set of numerical simulations of the enrichment from a supernova (SN) of a first generation of metal-free (Pop III) star and the gravitational collapse of the enriched cloud, considering all relevant cooling/heating processes and chemical reactions as well as the growth of dust grains. We adopt faint SN models for the first time with progenitor masses MPopIII = 13–$80 \ {\rm M_{\bigodot }}$, which yield C-enhanced abundance patterns ([C/Fe] = 4.57–4.75) through mixing and fallback of innermost layers of the ejecta. This model also considers the formation and destruction of dust grains. We find that the metals ejected by the SN can be partly re-accreted by the same dark matter minihalo, and carbon abundance of the enriched cloud A(C) = 3.80–5.06 is lower than the abundance range of observed CEMP stars (A(C) ≳ 6) because the mass of the metals ejected by faint SNe is smaller than normal core-collapse SNe due to extensive fallback. We also find that cloud fragmentation is induced by gas cooling from carbonaceous grains for $M_{\rm Pop III}= 13 \ {\rm M_{\bigodot }}$ even with the lowest iron abundance [Fe/H] ∼ −9. This leads to the formation of low-mass stars, and these ‘giga metal-poor’ stars can survive until the present-day Universe and may be found by future observations.

scholarly journals On producers of cosmic organic compounds: exploring the boron abundance in lithium-rich K giant stars

2017 ◽  
Vol 13 (S332) ◽  
pp. 237-241 ◽  
Author(s):  
N. A. Drake ◽  
R. de la Reza ◽  
V. V. Smith ◽  
K. Cunha
Keyword(s):  
Organic Compounds ◽  
Organic Material ◽  
Emission Lines ◽  
Low Mass Stars ◽  
Strong Emission ◽  
Giant Stars ◽  
First Approximation ◽  
Low Mass ◽  
Stellar Interiors ◽  
First Time

AbstractThe element boron belongs, together with lithium and beryllium, to a known trio of important elements for the study of evolutionary processes in low mass stars. Because B is the least fragile of this trio to be destroyed in the stellar interiors, it can be used to test if the Li enrichment is of planetary origin. Here, for the first time, boron lines are examined in the UV for four giants with different degrees of large Li enrichment by means of observations with the Hubble telescope. Two main results are found in our study. One is that to first approximation B abundances appear not to be in excess, invalidating the planet engulfment mechanism. The second one is that the two stars with very large Li abundances present emission lines indicating that quite strong active chromospheres are acting in these very Li-rich giants. These new results obtained from the UV complement our recent studies in the mid-IR (de la Rezaet al.2015) where strong emission-line features of organic material were found in the spectra of some Li-rich stars.

scholarly journals Correlation between mass segregation and structural concentration in relaxed stellar clusters

2019 ◽  
Vol 485 (4) ◽  
pp. 5752-5760 ◽  
Author(s):  
Ruggero de Vita ◽  
Michele Trenti ◽  
Morgan MacLeod
Keyword(s):  
Globular Clusters ◽  
Initial Conditions ◽  
Hubble Space Telescope ◽  
Stellar Clusters ◽  
Low Mass Stars ◽  
Best Fitting ◽  
Low Mass ◽  
The Difference ◽  
Mass Segregation ◽  
First Time

Abstract The level of mass segregation in the core of globular clusters has been previously proposed as a potential indicator of the dynamical constituents of the system, such as presence of a significant population of stellar-mass black holes (BHs), or even a central intermediate-mass black hole (IMBH). However, its measurement is limited to clusters with high-quality Hubble Space Telescope data. Thanks to a set of state-of-the-art direct N-body simulations with up to 200k particles inclusive of stellar evolution, primordial binaries, and varying BH/neutron stars, we highlight for the first time the existence of a clear and tight linear relation between the degree of mass segregation and the cluster structural concentration index. The latter is defined as the ratio of the radii containing 5 per cent and 50 per cent of the integrated light (R5/R50), making it robustly measurable without the need to individually resolve low-mass stars. Our simulations indicate that given R5/R50, the mass segregation Δm (defined as the difference in main-sequence median mass between centre and half-light radius) is expressed as Δm/M⊙ = −1.166R5/R50 + 0.3246, with a root-mean-square error of 0.0148. In addition, we can explain its physical origin and the values of the fitted parameters through basic analytical modelling. Such correlation is remarkably robust against a variety of initial conditions (including presence of primordial binaries and IMBHs) and cluster ages, with a slight dependence in best-fitting parameters on the prescriptions used to measure the quantities involved. Therefore, this study highlights the potential to develop a new observational tool to gain insight on the dynamical status of globular clusters and on its dark remnants.

The First Proto-Brown Dwarf Binary Candidate Identified through Dynamics of Jets

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Tien-Hao Hsieh ◽  
Shih-Ping Lai ◽  
Arnaud Belloche ◽  
Friedrich Wyrowski
Keyword(s):  
Binary System ◽  
Orbital Motion ◽  
Brown Dwarf ◽  
Low Mass Stars ◽  
Core Mass ◽  
Substellar Objects ◽  
Current Mass ◽  
Low Mass ◽  
Dynamical Features ◽  
First Time

AbstractThe formation mechanism of brown dwarfs (BDs) is one of the long-standing problems in star formation because the typical Jeans mass in molecular clouds is too large to form these substellar objects. To answer this question, it is crucial to study a BD at the embedded phase (proto-brown dwarf). IRAS16253 is classified as a Very Low Luminosity Object (VeLLO, Lint < 0.1L⊙), which is considered as a proto-brown dwarf candidate. We use the IRAM 30m, APEX telescopes and the SMA to probe the molecular jet/outflow driven by IRAS 16253 in CO (2–1), (6–5), and (7–6) and study its dynamical features and physical properties. We detect a wiggling pattern in the position-velocity diagrams of the jets. Assuming that this pattern is due to the orbital motion of a binary system, we obtain the current mass of the binary is ~0.026 M⊙. Together with the low parent core mass, IRAS16253 will likely form one or two proto-BD in the future. This is the first time that the current mass of a proto-BD binary system is identified through the dynamics of the jets. Since IRAS16253 is located in an isolated environment, we suggest that BDs can form through fragmentation and collapse like low mass stars.

scholarly journals The first galactic stars and chemical enrichment in the halo

2009 ◽  
Vol 5 (S265) ◽  
pp. 81-89
Author(s):  
Piercarlo Bonifacio
Keyword(s):  
Chemical Composition ◽  
High Mass ◽  
Mass Star ◽  
Low Mass Stars ◽  
Chemical Enrichment ◽  
The Galaxy ◽  
Low Metallicity ◽  
Low Mass ◽  
Indirect Information ◽  
The Universe

AbstractThe cosmic microwave background and the cosmic expansion can be interpreted as evidence that the Universe underwent an extremely hot and dense phase about 14 Gyr ago. The nucleosynthesis computations tell us that the Universe emerged from this state with a very simple chemical composition: H, 2H, 3He, 4He, and traces of 7Li. All other nuclei where synthesised at later times. Our stellar evolution models tell us that, if a low-mass star with this composition had been created (a “zero-metal” star) at that time, it would still be shining on the Main Sequence today. Over the last 40 years there have been many efforts to detect such primordial stars but none has so-far been found. The lowest metallicity stars known have a metal content, Z, which is of the order of 10−4Z⊙. These are also the lowest metallicity objects known in the Universe. This seems to support the theories of star formation which predict that only high mass stars could form with a primordial composition and require a minimum metallicity to allow the formation of low-mass stars. Yet, since absence of evidence is not evidence of absence, we cannot exclude the existence of such low-mass zero-metal stars, at present. If we have not found the first Galactic stars, as a by product of our searches we have found their direct descendants, stars of extremely low metallicity (Z ≤ 10−3Z⊙). The chemical composition of such stars contains indirect information on the nature of the stars responsible for the nucleosynthesis of the metals. Such a fossil record allows us a glimpse of the Galaxy at a look-back time equivalent to redshift z = 10, or larger. The last ten years have been full of exciting discoveries in this field, which I will try to review in this contribution.

scholarly journals Formation of globular clusters with multiple populations

2015 ◽  
Vol 12 (S316) ◽  
pp. 281-286
Author(s):  
T. Decressin
Keyword(s):  
Chemical Composition ◽  
Globular Clusters ◽  
First Generation ◽  
Outer Part ◽  
Rotation Velocity ◽  
Early Evolution ◽  
Rotating Stars ◽  
Low Mass Stars ◽  
Low Mass ◽  
Intracluster Gas

AbstractSpectroscopic and photometric evidences have led to a complete revision of our understanding of globular clusters with the discovery of multiple stellar populations which differ chemically. Whereas some stars have a chemical composition similar to fields stars, others show large star-to-star variations in light elements (Li to Al) while their composition in iron and heavy elements stay constant. This peculiar chemical pattern can be explained by self-pollution of the intracluster gas occurring in the early evolution of clusters. Here the possible impact from a first generation of fast rotating stars to the early evolution of globular clusters is presented. The high rotation velocity will allow the stars to rotate at the break-up velocity and release matter enrich in H-burning which in turn will produce new stars with a chemical composition in agreement with observations. The massive stars have also an important role to clear the cluster from the remaining gas left after the star formation episodes. If the gas expulsion is fast enough, the strong change in the potential well will lead to the loss of stars occupying the outer part of the cluster. As second generation stars are preferentially born in the cluster centre, the ratio of second to first generation stars will increase over time to match the present ratio determined by observations. Considerations on the properties of low-mass stars still present in globular clusters will also be presented.

scholarly journals The K2-HERMES Survey: age and metallicity of the thick disc

2019 ◽  
Vol 490 (4) ◽  
pp. 5335-5352 ◽  
Author(s):  
Sanjib Sharma ◽  
Dennis Stello ◽  
Joss Bland-Hawthorn ◽  
Michael R Hayden ◽  
Joel C Zinn ◽  
...  
Keyword(s):  
Selection Function ◽  
Population Synthesis ◽  
Low Mass Stars ◽  
Mass Scaling ◽  
Elemental Abundances ◽  
Thick Disc ◽  
Promising Tool ◽  
Low Mass ◽  
The Mean ◽  
First Time

ABSTRACT Asteroseismology is a promising tool to study Galactic structure and evolution because it can probe the ages of stars. Earlier attempts comparing seismic data from the Kepler satellite with predictions from Galaxy models found that the models predicted more low-mass stars compared to the observed distribution of masses. It was unclear if the mismatch was due to inaccuracies in the Galactic models, or the unknown aspects of the selection function of the stars. Using new data from the K2 mission, which has a well-defined selection function, we find that an old metal-poor thick disc, as used in previous Galactic models, is incompatible with the asteroseismic information. We use an importance-sampling framework, which takes the selection function into account, to fit for the metallicities of a population synthesis model using spectroscopic data. We show that spectroscopic measurements of [Fe/H] and [α/Fe] elemental abundances from the GALAH survey indicate a mean metallicity of log (Z/Z⊙) = −0.16 for the thick disc. Here Z is the effective solar-scaled metallicity, which is a function of [Fe/H] and [α/Fe]. With the revised disc metallicities, for the first time, the theoretically predicted distribution of seismic masses show excellent agreement with the observed distribution of masses. This indirectly verifies that the asteroseismic mass scaling relation is good to within five per cent. Assuming the asteroseismic scaling relations are correct, we estimate the mean age of the thick disc to be about 10 Gyr, in agreement with the traditional idea of an old α-enhanced thick disc.

scholarly journals Models of very-low-mass stars, brown dwarfs and exoplanets

2012 ◽  
Vol 370 (1968) ◽  
pp. 2765-2777 ◽  
Author(s):  
F. Allard ◽  
D. Homeier ◽  
B. Freytag
Keyword(s):  
Extrasolar Planets ◽  
Cloud Model ◽  
Brown Dwarfs ◽  
Spectroscopic Properties ◽  
Model Atmosphere ◽  
Low Mass Stars ◽  
Hot Jupiters ◽  
Solar Type ◽  
Low Mass ◽  
First Time

Within the next few years, GAIA and several instruments aiming to image extrasolar planets will be ready. In parallel, low-mass planets are being sought around red dwarfs, which offer more favourable conditions, for both radial velocity detection and transit studies, than solar-type stars. In this paper, the authors of a model atmosphere code that has allowed the detection of water vapour in the atmosphere of hot Jupiters review recent advances in modelling the stellar to substellar transition. The revised solar oxygen abundances and cloud model allow the photometric and spectroscopic properties of this transition to be reproduced for the first time. Also presented are highlight results of a model atmosphere grid for stars, brown dwarfs and extrasolar planets.

scholarly journals Bipolar molecular outflow of the very low-mass star Par-Lup3-4

2020 ◽  
Vol 640 ◽  
pp. A13
Author(s):  
A. Santamaría-Miranda ◽  
I. de Gregorio-Monsalvo ◽  
N. Huélamo ◽  
A. L. Plunkett ◽  
Á. Ribas ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Spectral Energy ◽  
Molecular Gas ◽  
Mass Star ◽  
Low Mass Stars ◽  
Molecular Outflow ◽  
Outflow Rate ◽  
Low Mass ◽  
First Time ◽  
Mass Sources

Context. Very low-mass stars are known to have jets and outflows, which is indicative of a scaled-down version of low-mass star formation. However, only very few outflows in very low-mass sources are well characterized. Aims. We characterize the bipolar molecular outflow of the very low-mass star Par-Lup3-4, a 0.12 M⊙ object known to power an optical jet. Methods. We observed Par-Lup3-4 with ALMA in Bands 6 and 7, detecting both the continuum and CO molecular gas. In particular, we studied three main emission lines: CO(2–1), CO(3–2), and 13CO(3–2). Results. Our observations reveal for the first time the base of a bipolar molecular outflow in a very low-mass star, as well as a stream of material moving perpendicular to the primary outflow of this source. The primary outflow morphology is consistent with the previously determined jet orientation and disk inclination. The outflow mass is 9.5 × 10−7 M⊙, with an outflow rate of 4.3 × 10−9 M⊙ yr−1. A new fitting to the spectral energy distribution suggests that Par-Lup3-4 may be a binary system. Conclusions. We have characterized Par-Lup3-4 in detail, and its properties are consistent with those reported in other very low-mass sources. This source provides further evidence that very low-mass sources form as a scaled-down version of low-mass stars.

scholarly journals Stellar Luminosity and Mass Functions of Globular Clusters

1996 ◽  
Vol 174 ◽  
pp. 71-80 ◽  
Author(s):  
Giampaolo Piotto ◽  
Adrienne M. Cool ◽  
Ivan R. King
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Mass Range ◽  
Theoretical Limit ◽  
Low Mass Stars ◽  
Luminosity Functions ◽  
Hydrogen Ignition ◽  
Low Mass ◽  
First Time ◽  
Mass Functions

HST makes it possible for the first time to study nearly the entire mass range of globular-cluster main sequences, from the turnoff down almost to the theoretical limit for hydrogen ignition. We present main-sequence luminosity functions (LFs) for four clusters that include stars with M < 0.15M⊙ in all cases. We compare these and other LFs that have been obtained with HST for a total of five globulars to date. Two of the three clusters in the sample that have similar metallicities have nearly identical LFs, while the third is relatively deficient in low mass stars. Possible implications of this finding are briefly discussed. Inferred mass functions vary significantly depending on the mass-luminosity relations that are adopted.

scholarly journals Planetary Nebulae and the Chemical Evolution of Galaxies

1983 ◽  
Vol 103 ◽  
pp. 463-472 ◽  
Author(s):  
Alfonso Serrano
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Planetary Nebulae ◽  
Low Mass Stars ◽  
Chemical Enrichment ◽  
The Past ◽  
The Galaxy ◽  
History Of ◽  
Low Mass

Tinsley (1978) has done an excellent review that illustrates the methods and concepts that can be developed to assess the effects of planetary nebulae (PN) on the long-term history of the galaxy. Tinsley concluded that research in PN could put constraints on the past rate of star formation and provide information on chemical enrichment by low mass stars.

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