LAMOST-Subaru exploration of chemical relics of first stars

2017 ◽  
Vol 13 (S334) ◽  
pp. 21-24
Author(s):  
Haining Li ◽  
Wako Aoki ◽  
Gang Zhao ◽  
Takuma Suda ◽  
Satoshi Honda ◽  
...  
Keyword(s):  
Mass Star ◽  
Chemical Abundances ◽  
Homogeneous Sample ◽  
First Stars ◽  
Joint Project ◽  
Stellar Spectra ◽  
Chemical Enrichment ◽  
Chemical Signatures ◽  
Wide Range ◽  
Low Mass

AbstractVery metal-poor (VMP) stars preserve chemical signatures of early generations of stars, and are crutial to understand the early nucleosynthesis and first stars. Millions of stellar spectra obtained by LAMOST provide an unprecedented chance to enlarge the currently limited VMP star sample. Since 2014, a joint project on searching for VMP stars has been conducted based on the LAMOST survey and Subaru follow-up observations. So far, the project has obtained chemical abundances for about 250 VMP stars and a number of chemically interesting objects, e.g., three ultra metal-poor stars with [Fe/H] ~ − 4.0, a dozen Li-rich VMP stars distributed in a wide range of evolutionary stages. Statistics of the large homogeneous sample of VMP stars will be of great interest and importance to probe the chemical enrichment in the early Galaxy and low-mass star evolution.

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 First core properties: from low- to high-mass star formation

2018 ◽  
Vol 618 ◽  
pp. A95 ◽  
Author(s):  
Asmita Bhandare ◽  
Rolf Kuiper ◽  
Thomas Henning ◽  
Christian Fendt ◽  
Gabriel-Dominique Marleau ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Star Formation ◽  
Molecular Cloud ◽  
Radiation Transport ◽  
High Mass ◽  
Mass Star ◽  
Intermediate Mass ◽  
Wide Range ◽  
Low Mass ◽  
Cloud Core

Aims. In this study, the main goal is to understand the molecular cloud core collapse through the stages of first and second hydrostatic core formation. We investigate the properties of Larsons first and second cores following the evolution of the molecular cloud core until the formation of Larson’s cores. We expand these collapse studies for the first time to span a wide range of initial cloud masses from 0.5 to 100 M⊙. Methods. Understanding the complexity of the numerous physical processes involved in the very early stages of star formation requires detailed thermodynamical modelling in terms of radiation transport and phase transitions. For this we used a realistic gas equation of state via a density- and temperature-dependent adiabatic index and mean molecular weight to model the phase transitions. We used a grey treatment of radiative transfer coupled with hydrodynamics to simulate Larsons collapse in spherical symmetry. Results. We reveal a dependence of a variety of first core properties on the initial cloud mass. The first core radius and mass increase from the low-mass to intermediate-mass regime and decrease from the intermediate-mass to high-mass regime. The lifetime of first cores strongly decreases towards the intermediate- and high-mass regimes. Conclusions. Our studies show the presence of a transition region in the intermediate-mass regime. Low-mass protostars tend to evolve through two distinct stages of formation that are related to the first and second hydrostatic cores. In contrast, in the high-mass star formation regime, collapsing cloud cores rapidly evolve through the first collapse phase and essentially immediately form Larson’s second cores.

scholarly journals Assessing the performance of LTE and NLTE synthetic stellar spectra in a machine learning framework

2020 ◽  
Vol 498 (3) ◽  
pp. 3817-3834 ◽  
Author(s):  
Spencer Bialek ◽  
Sébastien Fabbro ◽  
Kim A Venn ◽  
Nripesh Kumar ◽  
Teaghan O’Briain ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Rotational Velocity ◽  
Chemical Abundances ◽  
Stellar Spectra ◽  
Learning Framework ◽  
Accuracy And Precision ◽  
Wide Range ◽  
Parameter Ranges ◽  
Spectral Libraries ◽  
Temperature Surface

ABSTRACT In the current era of stellar spectroscopic surveys, synthetic spectral libraries are the basis for the derivation of stellar parameters and chemical abundances. In this paper, we compare the stellar parameters determined using five popular synthetic spectral grids (INTRIGOSS, FERRE, AMBRE, PHOENIX, and MPIA/1DNLTE) with our convolutional neural network (CNN, StarNet). The stellar parameters are determined for six physical properties (effective temperature, surface gravity, metallicity, [α/Fe], radial velocity, and rotational velocity) given the spectral resolution, signal-to-noise ratio, and wavelength range of optical FLAMES-UVES spectra from the Gaia-ESO Survey. Both CNN modelling and epistemic uncertainties are incorporated through training an ensemble of networks. StarNet training was also adapted to mitigate differences between the synthetic grids and observed spectra by augmenting with realistic observational signatures (i.e. resolution matching, wavelength sampling, Gaussian noise, zeroing flux values, rotational and radial velocities, continuum removal, and masking telluric regions). Using the FLAMES-UVES spectra for FGK-type dwarfs and giants as a test set, we quantify the accuracy and precision of the stellar label predictions from StarNet. We find excellent results over a wide range of parameters when StarNet is trained on the MPIA/1DNLTE synthetic grid, and acceptable results over smaller parameter ranges when trained on the 1DLTE grids. These tests also show that our CNN pipeline is highly adaptable to multiple simulation grids.

scholarly journals The Nucleosynthetic Imprint of 15 - 40 M⊙ Primordial Supernovae on Metal-Poor Stars

2009 ◽  
Vol 5 (S265) ◽  
pp. 42-45
Author(s):  
Daniel J. Whalen ◽  
Candace C. Joggerst
Keyword(s):  
Black Holes ◽  
Galactic Halo ◽  
Numerical Models ◽  
Two Dimensional ◽  
Chemical Abundances ◽  
First Stars ◽  
Indirect Measures ◽  
Low Mass ◽  
Population Iii Stars ◽  
Good Agreement

AbstractThe first stars are key to the formation of primeval galaxies, early cosmological reionization, and the assembly of supermassive black holes. Although Population III stars lie beyond the reach of direct observation, their chemical imprint on long-lived second generation stars may yield indirect measures of their masses. While numerical models of primordial SN nucleosynthetic yields have steadily improved in recent years, they have not accounted for the chemical abundances of ancient metal-poor stars in the Galactic halo. We present new two-dimensional models of 15 - 40 M⊙ primordial SNe that capture the effect of progenitor rotation, mass, metallicity, and explosion energy on elemental yields. Rotation dramatically alter the structure of zero-metallicity stars, expanding them to much larger radii. This promotes mixing between elemental shells by the SN shock and fallback onto the central remnant, both of which govern which elements escape the star. We find that a Salpeter IMF average of our yields for Z=0 models with explosion energies of 2.4 × 1051 ergs or less is in good agreement with the abundances measured in extremely metal-poor stars. Because these stars were likely enriched by early SNe from a well-defined IMF, our models indicate that the bulk of the metals in the early universe were synthesized by low-mass primordial stars.

scholarly journals Star Formation as Seen by Low Mass Stars

2014 ◽  
Vol 1 (1) ◽  
pp. 113-117
Author(s):  
Nino Panagia ◽  
Guido De Marchi
Keyword(s):  
Star Formation ◽  
Physical Properties ◽  
Main Sequence ◽  
Hubble Space Telescope ◽  
Ongoing Study ◽  
Low Mass Stars ◽  
Homogeneous Sample ◽  
Wide Range ◽  
Low Mass ◽  
Pms Stars

Using the Hubble Space Telescope (HST) we have characterised and compared the physical properties of a large sample of pre-main sequence (PMS) stars spanning a wide range of masses (0:5 - 4M<sub>ʘ</sub>), metallicities (0:1 - 1 Z<sub>ʘ</sub>) and ages (0:5 - 30 Myr). This is presently the largest and most homogeneous sample of PMS objects with known physical properties. The main results of this ongoing study are briefly summarised here.

scholarly journals Abundance patterns and the chemical enrichment of nearby dwarf galaxies

2009 ◽  
Vol 5 (S265) ◽  
pp. 219-226 ◽  
Author(s):  
Vanessa Hill
Keyword(s):  
Star Formation ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
First Stars ◽  
Potential Wells ◽  
Dwarf Spheroidal Galaxies ◽  
Massive Galaxies ◽  
Chemical Enrichment ◽  
Abundance Patterns ◽  
Spheroidal Galaxies

AbstractAs the least massive galaxies we know, dwarf spheroidal galaxies (dSph) allow to probe chemical enrichement on the smallest scales, and perhaps in its simplest expression. Particularly interesting are the issues concerning the efficency with which metals are retained or lost in these shallow potential wells (supernovae feedback), and the effect of this on star formation itself. Another fundamental issue concerns the earliest epochs of star formation: are first stars formed in similar ways and proportions in all halos ? Finally, as the smallest galaxies know, dSph have been suggested to be the surviving cousins of galaxy building blocs that (in λ-CDM) assemble to make larger galaxies. This parenthood would not necessarily hold at all late times, when survivors have lived their own differentiated life, but is expected at least at the earliest epochs.I review here the chemical abundances of individual stars in the nearest dwarf spheroidal galaxies, that have become available in increasing numbers (sample size and galaxies probed) in the last decade. Special emphasis is given to: a) recent results obtain with FLAMES on VLT, highlighting the power of detailed chemical abundance patterns of large samples of stars to unravel the various evolutionnary paths followed by dSph; b) the oldest and most metal-poor populations in dSph.

Low‐Mass Star Formation and the Initial Mass Function in IC 348

1998 ◽  
Vol 508 (1) ◽  
pp. 347-369 ◽  
Author(s):  
K. L. Luhman ◽  
G. H. Rieke ◽  
C. J. Lada ◽  
E. A. Lada
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Mass Star ◽  
Low Mass

scholarly journals Dust Production around Carbon-Rich Stars: The Role of Metallicity

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 233
Author(s):  
Ambra Nanni ◽  
Sergio Cristallo ◽  
Jacco Th. van Loon ◽  
Martin A. T. Groenewegen
Keyword(s):  
Wind Speed ◽  
Galactic Halo ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Chemical Enrichment ◽  
Wide Range ◽  
The Universe

Background: Most of the stars in the Universe will end their evolution by losing their envelope during the thermally pulsing asymptotic giant branch (TP-AGB) phase, enriching the interstellar medium of galaxies with heavy elements, partially condensed into dust grains formed in their extended circumstellar envelopes. Among these stars, carbon-rich TP-AGB stars (C-stars) are particularly relevant for the chemical enrichment of galaxies. We here investigated the role of the metallicity in the dust formation process from a theoretical viewpoint. Methods: We coupled an up-to-date description of dust growth and dust-driven wind, which included the time-averaged effect of shocks, with FRUITY stellar evolutionary tracks. We compared our predictions with observations of C-stars in our Galaxy, in the Magellanic Clouds (LMC and SMC) and in the Galactic Halo, characterised by metallicity between solar and 1/10 of solar. Results: Our models explained the variation of the gas and dust content around C-stars derived from the IRS Spitzer spectra. The wind speed of the C-stars at varying metallicity was well reproduced by our description. We predicted the wind speed at metallicity down to 1/10 of solar in a wide range of mass-loss rates.

scholarly journals Modelling H2 and its effects on star formation using a joint implementation of gadget-3 and KROME

2021 ◽  
Vol 504 (2) ◽  
pp. 2325-2345
Author(s):  
Emanuel Sillero ◽  
Patricia B Tissera ◽  
Diego G Lambas ◽  
Stefano Bovino ◽  
Dominik R Schleicher ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Physical Parameters ◽  
Density Profiles ◽  
Star Forming ◽  
Chemical Enrichment ◽  
Numerical Resolution ◽  
Stellar Radiation ◽  
Wide Range ◽  
The Impact

ABSTRACT We present p-gadget3-k, an updated version of gadget-3, that incorporates the chemistry package krome. p-gadget3-k follows the hydrodynamical and chemical evolution of cosmic structures, incorporating the chemistry and cooling of H2 and metal cooling in non-equilibrium. We performed different runs of the same ICs to assess the impact of various physical parameters and prescriptions, namely gas metallicity, molecular hydrogen formation on dust, star formation recipes including or not H2 dependence, and the effects of numerical resolution. We find that the characteristics of the simulated systems, both globally and at kpc-scales, are in good agreement with several observable properties of molecular gas in star-forming galaxies. The surface density profiles of star formation rate (SFR) and H2 are found to vary with the clumping factor and resolution. In agreement with previous results, the chemical enrichment of the gas component is found to be a key ingredient to model the formation and distribution of H2 as a function of gas density and temperature. A star formation algorithm that takes into account the H2 fraction together with a treatment for the local stellar radiation field improves the agreement with observed H2 abundances over a wide range of gas densities and with the molecular Kennicutt–Schmidt law, implying a more realistic modelling of the star formation process.

scholarly journals Chemical Enrichment and Central Star Properties

1993 ◽  
Vol 155 ◽  
pp. 572-572
Author(s):  
C.Y. Zhang
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Agb Stars ◽  
Physical Processes ◽  
Chemical Abundances ◽  
Core Mass ◽  
Chemical Enrichment ◽  
The Core ◽  
Stellar Temperature ◽  
Independent Parameters

We have selected a sample of planetary nebulae, for which the core masses are determined using distance-independent parameters (Zhang and Kwok 1992). The chemical abundances of He, N, O, and C are taken from the literature for them. Relationships of the ratios of He/H, N/O, and C/O with various stellar parameters of planetary nebulae (PN), such as the core mass, the mass of the core plus the ionized nebular gas, the stellar age and temperature, are examined. It is found that the N/O increases with increasing mass, while the C/O first increases and then decreases with the core mass. No strong correlation seems to exist between the He/H and the core mass. A correlation of the N/O and He/H with the stellar temperature exists. The current dredge-up theory for the progenitor AGB stars cannot satisfactorily account for these patterns of chemical enrichment in PN. Furthermore, the correlations of the N/O and He/H with the stellar age and temperature indicate that besides the dredge-ups in the RG and AGB stages, physical processes that happen in the planetary nebula stage may also play a role in forming the observed patterns of chemical enrichment in the planetary nebulae.

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