scholarly journals Chemical Abundance Analysis of Tucana III, the Second r-process Enhanced Ultra-faint Dwarf Galaxy

2019 ◽  
Vol 882 (2) ◽  
pp. 177 ◽  
Author(s):  
J. L. Marshall ◽  
T. Hansen ◽  
J. D. Simon ◽  
T. S. Li ◽  
R. A. Bernstein ◽  
...  
Keyword(s):  
Dwarf Galaxy ◽  
Chemical Abundance ◽  
R Process

scholarly journals The Faintest Dwarf Galaxies

2019 ◽  
Vol 57 (1) ◽  
pp. 375-415 ◽  
Author(s):  
Joshua D. Simon
Keyword(s):  
Dark Matter ◽  
Binary Stars ◽  
Luminosity Function ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Sloan Digital Sky Survey ◽  
Stellar Kinematics ◽  
Chemical Abundance ◽  
Abundance Patterns ◽  
R Process

The lowest luminosity ([Formula: see text] L[Formula: see text]) Milky Way satellite galaxies represent the extreme lower limit of the galaxy luminosity function. These ultra-faint dwarfs are the oldest, most dark matter–dominated, most metal-poor, and least chemically evolved stellar systems known. They therefore provide unique windows into the formation of the first galaxies and the behavior of dark matter on small scales. In this review, we summarize the discovery of ultra-faint dwarfs in the Sloan Digital Sky Survey in 2005 and the subsequent observational and theoretical progress in understanding their nature and origin. We describe their stellar kinematics, chemical abundance patterns, structural properties, stellar populations, orbits, and luminosity function, as well as what can be learned from each type of measurement. We conclude the following: ▪ In most cases, the stellar velocity dispersions of ultra-faint dwarfs are robust against systematic uncertainties such as binary stars and foreground contamination. ▪ The chemical abundance patterns of stars in ultra-faint dwarfs require two sources of r-process elements, one of which can likely be attributed to neutron star mergers. ▪ Even under conservative assumptions, only a small fraction of ultra-faint dwarfs may have suffered significant tidal stripping of their stellar components. ▪ Determining the properties of the faintest dwarfs out to the virial radius of the Milky Way will require very large investments of observing time with future telescopes. Finally, we offer a look forward at the observations that will be possible with future facilities as the push toward a complete census of the Local Group dwarf galaxy population continues.

scholarly journals R-process enrichment from a single event in an ancient dwarf galaxy

Nature ◽  
2016 ◽  
Vol 531 (7596) ◽  
pp. 610-613 ◽  
Author(s):  
Alexander P. Ji ◽  
Anna Frebel ◽  
Anirudh Chiti ◽  
Joshua D. Simon
Keyword(s):  
Dwarf Galaxy ◽  
Single Event ◽  
R Process

scholarly journals The age–chemical abundance structure of the Galaxy I: evidence for a late-accretion event in the outer disc at z ∼ 0.6

2020 ◽  
Vol 494 (2) ◽  
pp. 2561-2575 ◽  
Author(s):  
Jianhui Lian ◽  
Daniel Thomas ◽  
Claudia Maraston ◽  
Olga Zamora ◽  
Jamie Tayar ◽  
...  
Keyword(s):  
Dwarf Galaxy ◽  
Dimensional Space ◽  
Large Fraction ◽  
Three Dimensional ◽  
Element Abundance ◽  
Late Time ◽  
Chemical Abundance ◽  
Galactocentric Distance ◽  
Gas Accretion ◽  
A Minor

ABSTRACT We investigate the age–chemical abundance structure of the outer Galactic disc at a galactocentric distance of r > 10 kpc as recently revealed by the SDSS/APOGEE survey. Two sequences are present in the [α/Fe]–[Fe/H] plane with systematically different stellar ages. Surprisingly, the young sequence is less metal rich, suggesting a recent dilution process by additional gas accretion. As the stars with the lowest iron abundance in the younger sequence also show an enhancement in α-element abundance, the gas accretion event must have involved a burst of star formation. In order to explain these observations, we construct a chemical evolution model. In this model, we include a relatively short episode of gas accretion at late times on top of an underlying secular accretion over long time-scales. Our model is successful at reproducing the observed distribution of stars in the three-dimensional space of [α/Fe]–[Fe/H]–age in the outer disc. We find that a late-time accretion with a delay of $8.2\,$Gyr and a time-scale of 0.7 Gyr best fits the observed data, in particular the presence of the young, metal-poor sequence. Our best-fitting model further implies that the amount of accreted gas in the late-time accretion event needs to be about three times the local gas reservoir in the outer disc at the time of accretion in order to sufficiently dilute the metal abundance. Given this large fraction, we interpret the late-time accretion event as a minor merger presumably with a gas-rich dwarf galaxy with a mass $M_*\lt 10^{9}\, \mathrm{ M}_{\odot }$ and a gas fraction of ∼75 per cent.

scholarly journals The R-process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5−455510

2020 ◽  
Vol 897 (1) ◽  
pp. 78 ◽  
Author(s):  
Vinicius M. Placco ◽  
Rafael M. Santucci ◽  
Zhen Yuan ◽  
Mohammad K. Mardini ◽  
Erika M. Holmbeck ◽  
...  
Keyword(s):  
Chemical Abundance ◽  
Abundance Pattern ◽  
R Process

scholarly journals The Pristine survey – IX. CFHT ESPaDOnS spectroscopic analysis of 115 bright metal-poor candidate stars

2019 ◽  
Vol 492 (3) ◽  
pp. 3241-3262 ◽  
Author(s):  
Kim A Venn ◽  
Collin L Kielty ◽  
Federico Sestito ◽  
Else Starkenburg ◽  
Nicolas Martin ◽  
...  
Keyword(s):  
Galactic Halo ◽  
Model Atmosphere ◽  
Dynamical Analysis ◽  
Success Rates ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Detailed Model ◽  
Bayesian Inference Method ◽  
R Process ◽  
Gaia Dr2

ABSTRACT A chemo-dynamical analysis of 115 metal-poor candidate stars selected from the narrow-band Pristine photometric survey is presented based on CFHT high-resolution ESPaDOnS spectroscopy. We have discovered 28 new bright (V < 15) stars with [Fe/H] < −2.5 and 5 with [Fe/H] < −3.0 for success rates of 40 (28/70) and 19 per cent (5/27), respectively. A detailed model atmosphere analysis is carried out for the 28 new metal-poor stars. Stellar parameters were determined from SDSS photometric colours, Gaia DR2 parallaxes, MESA/MIST stellar isochrones, and the initial Pristine survey metallicities, following a Bayesian inference method. Chemical abundances are determined for 10 elements (Na, Mg, Ca, Sc, Ti, Cr, Fe, Ni, Y, and Ba). Most stars show chemical abundance patterns that are similar to the normal metal-poor stars in the Galactic halo; however, we also report the discoveries of a new r-process-rich star, a new CEMP-s candidate with [Y/Ba] > 0, and a metal-poor star with very low [Mg/Fe]. The kinematics and orbits for all of the highly probable metal-poor candidates are determined by combining our precision radial velocities with Gaia DR2 proper motions. Some stars show unusual kinematics for their chemistries, including planar orbits, unbound orbits, and highly elliptical orbits that plunge deeply into the Galactic bulge (Rperi < 0.5 kpc); also, eight stars have orbital energies and actions consistent with the Gaia-Enceladus accretion event. This paper contributes to our understanding of the complex chemo-dynamics of the metal-poor Galaxy, and increases the number of known bright metal-poor stars available for detailed nucleosynthetic studies.

scholarly journals The chemical signature of jet-driven hypernovae

2020 ◽  
Author(s):  
J J Grimmett ◽  
Bernhard Müller ◽  
Alexander Heger ◽  
Projjwal Banerjee ◽  
Martin Obergaulinger
Keyword(s):  
Large Mass ◽  
High Electron ◽  
Metal Enrichment ◽  
Chemical Abundance ◽  
Stellar Envelope ◽  
Chemical Signature ◽  
R Process ◽  
Process Component ◽  
Process Material ◽  
Good Agreement

Abstract Hypernovae powered by magnetic jets launched from the surface of rapidly rotating millisecond magnetars are one of the leading models to explain broad-lined Type Ic supernovae (SNe Ic-BL), and have been implicated as an important source of metal enrichment in the early Universe. We investigate the nucleosynthesis in such jet-driven hypernovae using a parameterised, but physically motivated, approach that analytically relates an artificially injected jet energy flux to the power available from the energy in differential rotation in the proto-neutron star. We find ejected 56Ni masses of $0.05\, \mathrm{M}_\odot \tt {- }0.45\, \mathrm{M}_\odot$ in our most energetic models with explosion energy >1052 erg. This is in good agreement with the range of observationally inferred values for SNe Ic-BL. The 56Ni is mostly synthesised in the shocked stellar envelope, and is therefore only moderately sensitive to the jet composition. Jets with a high electron fraction Ye = 0.5 eject more 56Ni by a factor of 2 than neutron-rich jets. We can obtain chemical abundance profiles in good agreement with the average chemical signature observed in extremely metal-poor (EMP) stars presumably polluted by hypernova ejecta. Notably, [Zn/Fe] ≳ 0.5 is consistently produced in our models. For neutron-rich jets, there is a significant r-process component, and agreement with EMP star abundances in fact requires either a limited contribution from neutron-rich jets or a stronger dilution of r-process material in the interstellar medium than for the slow SN ejecta outside the jet. The high [C/Fe] ≳ 0.7 observed in many EMP stars cannot be consistently achieved due to the large mass of iron in the ejecta, however, and remains a challenge for jet-driven hypernovae based on the magneto-rotational mechanism.

scholarly journals Chemical Abundance Analysis of Threeα-poor, Metal-poor Stars in the Ultrafaint Dwarf Galaxy Horologium I

2018 ◽  
Vol 852 (2) ◽  
pp. 99 ◽  
Author(s):  
D. Q. Nagasawa ◽  
J. L. Marshall ◽  
T. S. Li ◽  
T. T. Hansen ◽  
J. D. Simon ◽  
...  
Keyword(s):  
Dwarf Galaxy ◽  
Chemical Abundance

scholarly journals The formation of the Milky Way halo and its dwarf satellites; a NLTE-1D abundance analysis

2017 ◽  
Vol 608 ◽  
pp. A89 ◽  
Author(s):  
L. Mashonkina ◽  
P. Jablonka ◽  
T. Sitnova ◽  
Yu. Pakhomov ◽  
P. North
Keyword(s):  
Milky Way ◽  
Dwarf Galaxy ◽  
Chemical Species ◽  
Dwarf Spheroidal Galaxies ◽  
Massive Galaxies ◽  
Type Ia ◽  
Ursa Minor ◽  
R Process ◽  
Ia Supernovae ◽  
Process Elements

We present the non-local thermodynamic equilibrium (NLTE) abundances of up to 10 chemical species in a sample of 59 very metal-poor (VMP, −4 ≤ [Fe/H] ≾−2) stars in seven dwarf spheroidal galaxies (dSphs) and in the Milky Way (MW) halo. Our results are based on high-resolution spectroscopic datasets and homogeneous and accurate atmospheric parameters determined in Paper I. We show that once the NLTE effects are properly taken into account, all massive galaxies in our sample, that is, the MW halo and the classical dSphs Sculptor, Ursa Minor, Sextans, and Fornax, reveal a similar plateau at [α/Fe] ≃ 0.3 for each of the α-process elements: Mg, Ca, and Ti. We put on a firm ground the evidence for a decline in α/Fe with increasing metallicity in the Boötes I ultra-faint dwarf galaxy (UFD), that is most probably due to the ejecta of type Ia supernovae. For Na/Fe, Na/Mg, and Al/Mg, the MW halo and all dSphs reveal indistinguishable trends with metallicity, suggesting that the processes of Na and Al synthesis are identical in all systems, independent of their mass. The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical dSphs, similarly to the MW halo, calling for two different nucleosynthesis channels for Sr. We show that Sr in the massive galaxies is well correlated with Mg suggesting a strong link to massive stars and that its origin is essentially independent of Ba, for most of the [Ba/H] range. Our three UFDs, that is Boötes I, UMa II, and Leo IV, are depleted in Sr and Ba relative to Fe and Mg, with very similar ratios of [Sr/Mg] ≃−1.3 and [Ba/Mg] ≃−1 on the entire range of their Mg abundances. The subsolar Sr/Ba ratios of Boötes I and UMa II indicate a common r-process origin of their neutron-capture elements. Sculptor remains the classical dSph, in which the evidence for inhomogeneous mixing in the early evolution stage, at [Fe/H] <−2, is the strongest.

scholarly journals APOGEE Chemical Abundance Patterns of the Massive Milky Way Satellites

2021 ◽  
Vol 923 (2) ◽  
pp. 172
Author(s):  
Sten Hasselquist ◽  
Christian R. Hayes ◽  
Jianhui Lian ◽  
David H. Weinberg ◽  
Gail Zasowski ◽  
...  
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Magellanic Clouds ◽  
Chemical Abundance ◽  
Element Abundances ◽  
Abundance Patterns ◽  
Galaxy Environment ◽  
Red Giant

Abstract The SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey has obtained high-resolution spectra for thousands of red giant stars distributed among the massive satellite galaxies of the Milky Way (MW): the Large and Small Magellanic Clouds (LMC/SMC), the Sagittarius Dwarf Galaxy (Sgr), Fornax (Fnx), and the now fully disrupted Gaia Sausage/Enceladus (GSE) system. We present and analyze the APOGEE chemical abundance patterns of each galaxy to draw robust conclusions about their star formation histories, by quantifying the relative abundance trends of multiple elements (C, N, O, Mg, Al, Si, Ca, Fe, Ni, and Ce), as well as by fitting chemical evolution models to the [α/Fe]–[Fe/H] abundance plane for each galaxy. Results show that the chemical signatures of the starburst in the Magellanic Clouds (MCs) observed by Nidever et al. in the α-element abundances extend to C+N, Al, and Ni, with the major burst in the SMC occurring some 3–4 Gyr before the burst in the LMC. We find that Sgr and Fnx also exhibit chemical abundance patterns suggestive of secondary star formation epochs, but these events were weaker and earlier (∼5–7 Gyr ago) than those observed in the MCs. There is no chemical evidence of a second starburst in GSE, but this galaxy shows the strongest initial star formation as compared to the other four galaxies. All dwarf galaxies had greater relative contributions of AGB stars to their enrichment than the MW. Comparing and contrasting these chemical patterns highlight the importance of galaxy environment on its chemical evolution.

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