We present a chemo-dynamical analysis of low-resolution ($R \sim 1300$) spectroscopy of stars from the AAOmega Evolution of Galactic Structure (AEGIS) survey, focusing on two key populations of carbon-enhanced metal-poor (CEMP) stars within the disk system of the Milky Way: a mildly prograde population ($L_z < 1000\,$kpc$\,$km$\,$s$^{-1}$) and a strongly prograde ($L_z > 1000\,$kpc$\,$km$\,$s$^{-1}$) population. Based on their chemical and kinematic characteristics, and on comparisons with similar populations found in the recent literature, we tentatively associate the former with an ex-situ inner-halo population originating from either the $Gaia$ Sausage or $Gaia$-Enceladus. The latter population is linked to the metal-weak thick-disk (MWTD). We discuss their implications in the context of the formation history of the Milky Way.
Demers and Battinelli published, in 2007 the rotation curve of the Milky Way based on the radial velocity of carbon stars outside the Solar circle. Since then we have established a new list of candidates for spectroscopy. The goal of this paper is to determine the rotation curve of the galaxy, as far as possible from the galactic center, using N type carbon stars. The stars were selected from their dereddened 2MASS colours, then the spectra were obtained with the Dominion Astrophysical Observatory and Asiago 1.8 meter telescopes. This publication adds radial velocities and Galactrocentric dist…
We assemble 121 spectroscopically-confirmed halo carbon stars, drawn from the literature, exhibiting measurable variability in the Catalina Surveys. We present their periods and amplitudes, which are used to estimate distances from period-luminosity relationships. The location of the carbon stars - and their velocities when available - allow us to trace the streams of the Sagittarius (Sgr) dwarf spheroidal galaxy. These are compared to a canonical numerical simulation of the accretion of Sgr. We find that the data match this model well for heliocentric distances of 15-50 kpc, except for a virt…
We use Gaia DR2 astrometric and photometric data, published radial velocities and MESA models to infer distances, orbits, surface gravities, and effective temperatures for all ultra metal-poor stars ($\FeH<-4.0$ dex) available in the literature. Assuming that these stars are old ($>11\Gyr$) and that they are expected to belong to the Milky Way halo, we find that these 42 stars (18 dwarf stars and 24 giants or sub-giants) are currently within $\sim20\kpc$ of the Sun and that they map a wide variety of orbits. A large fraction of those stars remains confined to the inner parts of the halo and wa…
We report photometric estimates of effective temperature, $T_{\rm eff}$, metallicity, [Fe/H], carbonicity, [C/Fe], and absolute carbon abundances, $A{\rm (C)}$, for over 700,000 stars from the Southern Photometric Local Universe Survey (S-PLUS) Data Release 2, covering a substantial fraction of the equatorial Sloan Digital Sky Survey Stripe 82. We present an analysis for two stellar populations: 1) halo main-sequence turnoff stars and 2) K-dwarf stars of mass $0.58 < M/M_{\odot} <0.75$ in the Solar Neighborhood. Application of the Stellar Photometric Index Network Explorer (SPHINX) to the mixe…
The evolution of C and O abundances in the Milky Way can impose strong constraints on stellar nucleosynthesis and help understanding the formation and evolution of our Galaxy. The aim is to review the measured C and O abundances in the disk and bulge of the Galaxy and compare them with model predictions. We adopt two successful chemical evolution models for the bulge and the disk, which assume the same nucleosynthesis prescriptions but different histories of star formation. The data show a clear distinction between the trend of [C/O] in the thick and thin Galactic disks, while the thick disk a…
The first stars are predicted to have formed within 200 million years after the Big Bang, initiating the cosmic dawn. A true first star has not yet been discovered, although stars with tiny amounts of elements heavier than helium ('metals') have been found in the outer regions ('halo') of the Milky Way. The first stars and their immediate successors should, however, preferentially be found today in the central regions ('bulges') of galaxies, because they formed in the largest over-densities that grew gravitationally with time. The Milky Way bulge underwent a rapid chemical enrichment during th…
We explore the origin of a population of stars recently detected in the inner parsec of the Milky Way Nuclear Cluster (NC), which exhibit sub-solar metallicity and a higher rotation compared to the dominant population. Using state-of-the-art $N$-body simulations, we model the infall of a massive stellar system into the Galactic center, both of Galactic and extra-galactic origin. We show that the newly discovered population can either be the remnant of a massive star cluster formed a few kpc away from the Galactic center (Galactic scenario) or be accreted from a dwarf galaxy originally located …
Carbon-enhanced metal poor stars (CEMP) form a significant proportion of the metal-poor stars, their origin is not well understood. Three very metal-poor C-rich turnoff stars were selected from the SDSS survey, observed with the ESO VLT (UVES) to precisely determine the element abundances. In turnoff stars (unlike giants) the carbon abundance has not been affected by mixing with deep layers and is therefore easier to interpret. The analysis was performed with 1D LTE static model atmospheres. When available, non-LTE corrections were applied to the classical LTE abundances. The 3D effects on the…
The carbon-enhanced metal-poor (CEMP) stars constitute approximately one fifth of the metal-poor ([Fe/H] ~< -2) population but their origin is not well understood. The most widely accepted formation scenario, invokes mass-transfer of carbon-rich material from a thermally-pulsing asymptotic giant branch (TPAGB) primary star to a less massive main-sequence companion which is seen today. Recent studies explore the possibility that an initial mass function biased toward intermediate-mass stars is required to reproduce the observed CEMP fraction in stars with metallicity [Fe/H] < -2.5. These models…
The Hipparcos orbiting observatory has revealed a large number of helium-core-burning "clump" stars in the Galactic field. These low-mass stars exhibit signatures of extra-mixing processes that require modeling beyond the first dredge-up of standard models. The 12C/13C ratio is the most robust diagnostic of deep mixing, because it is insensitive to the adopted stellar parameters. In this work we present 12C/13C determinations in a sample of 34 Galactic clump stars as well as abundances of nitrogen, carbon and oxygen. Abundances of carbon were studied using the C2 Swan (0,1) band head at 5635.5…
A substantial fraction of the lowest metallicity stars show very high enhancements in carbon. It is debated whether these enhancements reflect the stars' birth composition, or if their atmospheres were subsequently polluted, most likely by accretion from an AGB binary companion. Here we investigate and compare the binary properties of three carbon-enhanced sub-classes: The metal-poor CEMP-s stars that are additionally enhanced in barium; the higher metallicity (sg)CH- and Ba II stars also enhanced in barium; and the metal-poor CEMP-no stars, not enhanced in barium. Through comparison with simu…
We present the results of a detailed abundance analysis of one of the confirmed building blocks of the Milky Way stellar halo, a kinematically-coherent metal-poor stellar stream. We have obtained high resolution and high S/N spectra of 12 probable stream members using the MIKE spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the 2dCoude spectrograph on the Smith Telescope at McDonald Observatory. We have derived abundances or upper limits for 51 species of 46 elements in each of these stars. The stream members show a range of metallicity (-3.4 < [Fe/H] < -1.5) but ar…
The carbon-enhanced metal-poor star BD+44 493 ([Fe/H]=-3.9) has been proposed as a candidate second-generation star enriched by metals from a single Pop III star. We report the first detections of P and S and the second detection of Zn in any extremely metal-poor carbon-enhanced star, using new spectra of BD+44 493 collected by the Cosmic Origins Spectrograph on the Hubble Space Telescope. We derive [P/Fe]=-0.34 +/- 0.21, [S/Fe]=+0.07 +/- 0.41, and [Zn/Fe]=-0.10 +/- 0.24. We increase by ten-fold the number of Si I lines detected in BD+44 493, yielding [Si/Fe]=+0.15 +/- 0.22. The solar [S/Fe] a…
The chemical abundances of a galaxy's metal-poor stellar population can be used to investigate the earliest stages of its formation and chemical evolution. The Magellanic Clouds are the most massive of the Milky Way's satellite galaxies and are thought to have evolved in isolation until their recent accretion by the Milky Way. Unlike the Milky Way's less massive satellites, little is know about the Magellanic Clouds' metal-poor stars. We have used the mid-infrared metal-poor star selection of Schlaufman & Casey (2014) and archival data to target nine LMC and four SMC giants for high-resolution…
LTE abundances of light elements in extremely metal-poor (EMP) stars have been previously derived from high quality spectra. New derivations, free from the NLTE effects, will better constrain the models of the Galactic chemical evolution and the yields of the very first supernovae. The NLTE profiles of the magnesium and potassium lines have been computed in a sample of 53 extremely metal-poor stars with a modified version of the program MULTI and adjusted to the observed lines in order to derive the abundances of these elements. The NLTE corrections for magnesium and potassium are in good agre…
Detailed spectroscopic studies of metal-poor halo stars have highlighted the important role of carbon-enhanced metal-poor (CEMP) stars in understanding the early production and ejection of carbon in the Galaxy and in identifying the progenitors of the CEMP stars among the first stars formed after the Big Bang. Recent work has also classified the CEMP stars by absolute carbon abundance, A(C), into high- and low-C bands, mostly populated by binary and single stars, respectively. Our aim is to determine the frequency and orbital parameters of binary systems among the CEMP-s stars, which exhibit s…
(Abridged) Carbon-enhanced metal-poor (CEMP) stars in the halo components of the Milky Way are explored, based on accurate determinations of the carbon-to-iron ([C/Fe]) abundance ratios and kinematic quantities for over 30000 calibration stars from the Sloan Digital Sky Survey (SDSS). Using our present criterion that low-metallicity stars exhibiting [C/Fe] ratios ("carbonicity") in excess of [C/Fe]$ = +0.7$ are considered CEMP stars, the global frequency of CEMP stars in the halo system for \feh\ $< -1.5$ is 8%; for \feh\ $< -2.0$ it is 12%; for \feh\ $<-2.5$ it is 20%. We also confirm a signi…
We explore the kinematics and orbital properties of a sample of 323 very metal-poor stars in the halo system of the Milky Way, selected from the high-resolution spectroscopic follow-up studies of Aoki et al. and Yong et al. The combined sample contains a significant fraction of carbon-enhanced metal-poor (CEMP) stars (22% or 29%, depending on whether a strict or relaxed criterion is applied for this definition). Barium abundances (or upper limits) are available for the great majority of the CEMP stars, allowing for their separation into the CEMP-$s$ and CEMP-no sub-classes. A new method to ass…
Metal-poor stars are important tools for tracing the early history of the Milky Way, and for learning about the first generations of stars. Simulations suggest that the oldest metal-poor stars are to be found in the inner Galaxy. Typical bulge surveys, however, lack low metallicity ([Fe/H] < -1.0) stars because the inner Galaxy is predominantly metal-rich. The aim of the Pristine Inner Galaxy Survey (PIGS) is to study the metal-poor and very metal-poor (VMP, [Fe/H] < -2.0) stars in this region. In PIGS, metal-poor targets for spectroscopic follow-up are selected from metallicity-sensitive CaHK…
Exploring the Milky Way stellar disk. Carbon, nitrogen, oxygen, sulphur, potassium, and copper abundances for 714 F- and G-type dwarf stars in the solar neighbourhood
Metal-poor stars in the Milky Way are local relics of the epoch of the first stars and the first galaxies. However, a low metallicity does not prove that a star formed in this ancient era, as metal-poor stars form over a range of redshift in different environments. Theoretical models of Milky Way formation have shown that at constant metallicity, the oldest stars are those closest to the center of the Galaxy on the most tightly-bound orbits. For that reason, the most metal-poor stars in the bulge of the Milky Way provide excellent tracers of the chemistry of the high-redshift universe. We repo…
Mapping the Distant and Metal-Poor Milky Way with SDSS-V
Department of Astronomy & Astrophysics, University of Chicago（芝加哥大学天文与天体物理系）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理学研究所）；NSF-Simons AI Institute for the Sky (SkAI)（NSF-Simons 天空人工智能研究所 (SkAI)）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Department of Astronomy, Columbia University（哥伦比亚大学天文学系）；Department of Astronomy, Boston University（波士顿大学天文学系）；Instituto de Astrofísica, Departamento de Física y Astronomía, Facultad de Ciencias Exactas, Universidad Andres Bello（安第斯贝尔托大学精确科学学院物理与天文学系天体物理研究所）；LIRA
The Pristine Inner Galaxy Survey (PIGS) V: a chemo-dynamical investigation of the early assembly of the Milky Way with the most metal-poor stars in the bulge
HE0144-4657: A Carbon-Enhanced Ultra Metal-Poor Star ([Fe/H] ~ -4.1) from the Helmi Stream Disrupted Dwarf Galaxy
NSF NOIRLab（美国国家光学红外天文科学实验室）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理学研究所）；Department of Astronomy & Astrophysics, University of Chicago（芝加哥大学天文与天体物理系）；Randolph School（兰道夫学校）；Zentrum für Astronomie der Universität Heidelberg, Landessternwarte（海德堡大学天文中心，州立天文台）
Mixing and fallback models in faint supernova models are supposed to reproduce the abundance patterns of observed carbon-enhanced metal-poor (CEMP) stars in the Galactic halo. A fine tuning of the model parameters for individual stars is required to reproduce the observed ratios of carbon to iron. We focus on extremely metal-poor stars formed out of the ejecta from the mixing and fallback models using a chemical evolution model. Our chemical evolution models take into account the contribution of individual stars to chemical enrichment in host halos together with their evolution in the context …
The detailed composition of most metal-poor halo stars has been found to be very uniform. However, a fraction of 20-70% (increasing with decreasing metallicity) exhibit dramatic enhancements in their abundances of carbon - the so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic chemical evolution models is whether this non-standard composition reflects that of the stellar natal clouds, or is due to local, post-birth mass transfer of chemically processed material from a binary companion; CEMP stars should then all be members of binary systems. Our aim is to determine …
Recent discoveries of carbon-enhanced metal-poor stars like SMSS J031300.36-670839.3 provide increasing observational insights into the formation conditions of the first second-generation stars in the Universe, reflecting the chemical conditions after the first supernova explosion. Here, we present the first cosmological simulations with a detailed chemical network including primordial species as well as C, C$^+$, O, O$^+$, Si, Si$^+$, and Si$^{2+}$ following the formation of carbon-enhanced metal poor stars. The presence of background UV flux delays the collapse from $z=21$ to $z=15$ and cool…
We show that the low ratios of $α$ elements (Mg, Si, and Ca) to Fe recently found for a small fraction of extremely metal-poor stars can be naturally explained with the nucleosynthesis yields of core-collapse supernovae, i.e., $13-25M_\odot$ supernovae, or hypernovae. For the case without carbon enhancement, the ejected iron mass is normal, consistent with observed light curves and spectra of nearby supernovae. On the other hand, the carbon enhancement requires much smaller iron production, and the low [$α$/Fe] of carbon enhanced metal-poor stars can also be reproduced with $13-25M_\odot$ fain…
This work presents the medium-resolution ($R \sim 1,500$) spectroscopic follow-up of 522 low-metallicity star candidates from the Southern Photometric Local Universe Survey (S-PLUS). The objects were selected from narrow-band photometry, taking advantage of the metallicity-sensitive S-PLUS colors. The follow-up observations were conducted with the Blanco and Gemini South telescopes, using the COSMOS and GMOS spectrographs, respectively. The stellar atmospheric parameters (T$_{\rm eff}$, log$g$, and [Fe/H]), as well as carbon and $α$-element abundances, were calculated for the program stars in …
We present a low metallicity map of the Milky Way consisting of $\sim$111,000 giants with $-3.5 \lesssim$ [Fe/H] $\lesssim -$0.75, based on public photometry from the second data release of the SkyMapper survey. These stars extend out to $\sim$7kpc from the solar neighborhood and cover the main Galactic stellar populations, including the thick disk and the inner halo. Notably, this map can reliably differentiate metallicities down to [Fe/H] $\sim -3.0$, and thus provides an unprecedented view into the ancient, metal-poor Milky Way. Among the more metal-rich stars in our sample ([Fe/H] $> -2.0$…
We present a comparison of the frequencies of carbon-enhanced metal-poor (CEMP) giant and main-sequence turnoff stars, selected from the Sloan Digital Sky Survey and the Sloan Extension for Galactic Understanding and Exploration, with predictions from asymptotic giant-branch (AGB) mass-transfer models. We consider two initial mass functions (IMFs)-a Salpeter IMF, and a mass function with a characteristic mass of 10 solar mass. These comparisons indicate good agreement between the observed CEMP frequencies for stars with [Fe/H] > -1.5 and a Salpeter IMF, but not with an IMF having a higher char…
We have observed a sample of 19 carbon stars in the Sculptor, Carina, Fornax, and Leo I dwarf spheroidal galaxies with the Infrared Spectrograph on the Spitzer Space Telescope. The spectra show significant quantities of dust around the carbon stars in Sculptor, Fornax, and Leo I, but little in Carina. Previous comparisons of carbon stars with similar pulsation properties in the Galaxy and the Magellanic Clouds revealed no evidence that metallicity affected the production of dust by carbon stars. However, the more metal-poor stars in the current sample appear to be generating less dust. These d…
From detailed abundance analysis of >100 Hamburg/ESO candidate extremely metal-poor (EMP) stars we find 45 with [Fe/H] < -3.0 dex. We identify a heretofore unidentified group: Ca-deficient stars, with sub-solar [Ca/Fe] ratios and the lowest neutron-capture abundances; the Ca-deficient group comprises ~ 10% of the sample, excluding Carbon stars. Our radial velocity distribution shows that the carbon-enhanced stars with no s-process enhancements, CEMP-no, and which do not show C2 bands are not preferentially binary systems. Ignoring Carbon stars, approximately 15% of our sample are strong (> 5 s…
The origin of carbon-enhanced metal-poor (CEMP) stars and their possible connections with the chemical elements produced by the first stellar generations is still highly debated. We briefly review observations of CEMP stars in different environments (Galactic stellar halo, ultra-faint and classical dwarf galaxies) and interpret their properties using cosmological chemical-evolution models for the formation of the Local Group. We discuss the implications of current observations for the properties of the first stars, clarify why the fraction of carbon-enhanced to carbon-normal stars varies in dw…
Star formation models predict that the metal-poor initial mass function (IMF) can be substantially different from that observed in the metal-rich Milky Way. This changeover occurs because metal-poor gas clouds cool inefficiently due to their lower abundance of metals and dust. However, predictions for the metal-poor IMF to date rely on assuming Solar-scaled abundances, that is, [X/O] = 0 at all [O/H]. There is now growing evidence that elements such as C and O that dominate metal line cooling in the ISM do not follow Solar scaling at low metallicities. In this work, we extend models that predi…
Elemental abundances of extrinsic carbon stars provide insight into the poorly understood origin and evolution of elements in the early Galaxy. In this work, we present the results of a detailed spectroscopic analysis of four potential carbon star candidates from the Hamburg/ESO Survey (HES) HE~0457$-$1805, HE~0920$-$0506, HE~1241$-$0337, and HE~1327$-$2116. This analysis is based on the high-resolution spectra obtained with Mercator/HERMES (R$\sim$86,000) and SUBARU/HDS (R$\sim$50,000). Although the abundances of a few elements, such as, Fe, C, and O are available from medium-resolution spect…
In this work we present the main atmospheric parameters, carbon, nitrogen and oxygen abundances, and 12C/13C ratios determined in a sample of 28 Galactic clump stars. Abundances of carbon were studied using the C2 band at 5086.2 Å. The wavelength interval 7980-8130 Å with strong CN features was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 Å. The mean abundances of C, N and O abundances in the investigated clump stars support our previous estimations that, compared to the Sun and dwarf stars of t…
Abundances of planetary nebulae and evolved stars: Iron and sulfur depletion, and carbon and nitrogen enrichment, in low- and intermediate-mass stellar populations in the Milky Way
We identify six new CEMP stars ([C/Fe]>+0.7 and [Fe/H]< -1.8) and another seven likely candidates within the APOGEE database following Data Release 12. These stars have chemical compositions typical of metal-poor halo stars, e.g., mean [$α$/Fe] = +0.24$\pm$0.24, based on the ASPCAP pipeline results. A lack of heavy element spectral lines impedes further sub-classification of these CEMP stars, however, based on radial velocity scatter, we predict most are not CEMP-s stars which are typically found in binary systems. Only one object, 2M15312547+4220551, may be in a binary since it exhibits a sca…
Massive disk galaxies like our Milky Way should host an ancient, metal-poor, and centrally concentrated stellar population. This population reflects the star formation and enrichment in the few most massive progenitor components that coalesced at high redshift to form the proto-Galaxy. While metal-poor stars are known to reside in the inner few kiloparsecs of our Galaxy, current data do not yet provide a comprehensive picture of such a metal-poor "heart" of the Milky Way. We use information from Gaia DR3, especially the XP spectra, to construct a sample of 2 million bright (BP $<15.5$ mag) gia…
Dwarf spheroidal galaxies (dSph) orbiting the Milky Way are complex objects often with complicated star formation histories and internal dynamics. In this work, we search for stellar substructures in four of the classical dSph satellites of the Milky Way: Sextans, Carina, Leo I, and Leo II. We apply two methods to search for stellar substructure: the minimum spanning tree method, which helps us to find and quantify spatially connected structures, and the "brute-force" method, which is able to find elongated stellar substructures. We detected the previously known substructure in Sextans, and al…
We present carbon abundances of red giants in Milky Way globular clusters and dwarf spheroidal galaxies (dSphs). Our sample includes measurements of carbon abundances for 154 giants in the clusters NGC 2419, M68, and M15 and 398 giants in the dSphs Sculptor, Fornax, Ursa Minor, and Draco. This sample doubles the number of dSph stars with measurements of [C/Fe]. The [C/Fe] ratio in the clusters decreases with increasing luminosity above log(L/L_sun) ~= 1.6, which can be explained by deep mixing in evolved giants. The same decrease is observed in dSphs, but the initial [C/Fe] of the dSph giants …
The study of the chemical abundances of metal-poor stars in dwarf galaxies provides a venue to constrain paradigms of chemical enrichment and galaxy formation. Here we present metallicity and carbon abundance measurements of 100 stars in Sculptor from medium-resolution (R ~ 2000) spectra taken with the Magellan/Michigan Fiber System mounted on the Magellan-Clay 6.5m telescope at Las Campanas Observatory. We identify 24 extremely metal-poor star candidates ([Fe/H] < -3.0) and 21 carbon-enhanced metal-poor (CEMP) star candidates. Eight carbon-enhanced stars are classified with at least 2$σ$ conf…
