Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III

Ji, Alexander P.; Li, T. S.; Simon, Joshua D.; Marshall, J. L.; Vivas, A. Katherina; Pace, Andrew B.; Bechtol, K.; Drlica-Wagner, A.; Koposov, S. E.; Hansen, Terese T.; Allam, S.; Gruendl, R. A.; Johnson, Michael D.; McNanna, M.; Noël, N. E. D.; Tucker, D. L.; Walker, A. R.

doi:10.3847/1538-4357/ab6213

Cited by 54 publications

(56 citation statements)

References 157 publications

(195 reference statements)

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“…Minor et al (2019) used a similar method to investigate Ret II with a smaller spectroscopic sample, concluding that f b > 0.5 at 90% confidence. This result is strongly inconsistent with our measurements, which will require further investigation, but we note that the Minor et al analysis relies on the very small quoted velocity uncertainties from , which subsequent work suggests may have been underestimated (Ji et al 2020). The first photometric determination of the binary fraction in UFDs was by Geha et al (2013), who modeled HST color-magnitude diagrams of Hercules and Leo IV to measure f b = 0.47 +0.16 −0.14 and f b = 0.47 +0.37 −0.17 , respectively.…”

Section: Discussioncontrasting

confidence: 94%

A Statistical Detection of Wide Binary Systems in the Ultra-Faint Dwarf Galaxy Reticulum II

Safarzadeh,

Simon,

Loeb

2021

Preprint

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Binary stars can inflate the observed velocity dispersion of stars in dark matter dominated systems such as ultra-faint dwarf galaxies (UFDs). However, the population of binaries in UFDs is poorly constrained by observations, with preferred binary fractions for individual galaxies ranging from a few percent to nearly unity. Searching for wide binaries through nearest neighbor (NN) statistics (or the two-point correlation function) has been suggested in the literature, and we apply this method for the first time to detect wide binaries in a UFD. By analyzing the positions of stars in Reticulum II (Ret II) from Hubble Space Telescope images, we search for angularly resolved wide binaries in Ret II. We find that the distribution of their NN distances shows an enhancement at projected separations of 8 relative to a model containing no binaries. We show that such an enhancement can be explained by a binary fraction of f b ≈ 0.07 +0.04 −0.03 , with modest evidence for a smaller mean separation than is seen in the solar neighborhood. We also use the observed magnitude distribution of stars in Ret II to constrain the initial mass function over the mass range 0.34 − 0.78 M , finding that a shallow power-law slope of α = 1.10 +0.30 −0.09 matches the data.

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Section: Discussioncontrasting

confidence: 94%

A Statistical Detection of Wide Binary Systems in the Ultra-Faint Dwarf Galaxy Reticulum II

Safarzadeh,

Simon,

Loeb

2021

Preprint

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“…Our values are different from the velocities determined for the stars by Simon et al (2020), who find V hel =−108.6±1.0 kms −1 , −108.1±1.0kms −1 , and −109.3±1.0kms −1 for J220423, J220409, and J220352, respectively. However, J220423 and J220409 were both observed at high airmass, 1.8 and 1.6 respectively, which can cause offsets in the radial velocities (Ji et al 2020), and J220352 is likely in a binary system (Simon et al 2020).…”

Section: Observationsmentioning

confidence: 97%

Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis*

Hansen¹,

Marshall²,

Simon³

et al. 2020

ApJ

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We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy GrusII. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metalpoor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass ( 20 M e) corecollapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of GrusII could have occurred through substantial high-mass stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of the r-process elements in this star matches the scaled r-process pattern of the solar system and r-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of r-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of GrusII would increase the likelihood of any of these events occurring. The time delay between the α and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in GrusII. Unified Astronomy Thesaurus concepts: Chemical abundances (224); Dwarf galaxies (416); Chemically peculiar stars (226); Stellar abundances (1577)

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“…The abundances of s-process elements show large variation even among our simulated UFDs, which are uncontaminated by r-process enrichment. Ba and Sr abundances are higher in the L-UFD than in M- (Suda et al 2008(Suda et al , 2017, together with the latest data added manually, based on the following studies (Martin et al 2007;Koch et al 2008;Adén et al 2009;Feltzing et al 2009;Koch et al 2009;Frebel et al 2010;Norris et al 2010c, a, b;Adén et al 2011;Lai et al 2011;Simon et al 2011;Gilmore et al 2013;Koch et al 2013;Vargas et al 2013;Frebel et al 2014;Ishigaki et al 2014;Koch & Rich 2014;François et al 2016;Ji et al 2016b, d, c;Martin et al 2016;Roederer et al 2016;Hansen et al 2017;Kirby et al 2017;Venn et al 2017;Chiti et al 2018;Nagasawa et al 2018;Ji et al 2019b;Hansen et al 2020;Ji et al 2020). and S-UFDs, even if we compare stars with similar Fe abundances.…”

Section: Agb S-process Enrichment Modelmentioning

confidence: 99%

“…Indeed, for some stars, the possibility of pure r-process has already been eliminated (e.g. Car II, Ji et al 2020). We thus make a working assumption and place an empirical detection limit for [Eu/H] ∼ −3.5.…”

Section: No R-process Contribution To Ba and Srmentioning

confidence: 99%

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s-process enrichment of ultrafaint dwarf galaxies

Tarumi

Suda

Voort

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We study the production of barium (Ba) and strontium (Sr) in ultrafaint dwarf galaxies (UFDs). Both r- and s- processes produce these elements, and one can infer the contribution of the r-process from the characteristic r-process abundance pattern, whereas the s-process contribution remains largely unknown. We show that the current s-process yield from asymptotic giant branch (AGB) stars is not sufficient to explain the Ba and Sr abundances observed in UFDs. Production of these elements would need to be efficient from the beginning of star formation in the galaxies. The discrepancy of nearly or more than 1 dex is not reconciled even if we consider s-process in super-AGB stars. We consider a possible resolution by assuming rotating massive stars (RMSs) and electron-capture supernovae (ECSNe) as additional contributors. We find that the RMSs could be the origin of Ba in UFDs if ∼10 per cent of massive stars are rotating at 300 km s−1. As for ECSNe, we argue that their fraction is less than 2 per cent of core-collapse supernova. It narrows the progenitor mass-range to ≲ 0.1 M⊙ at −3 ≲ [Fe/H] ≲ −2. We also explore another resolution by modifying the stellar initial mass function (IMF) in UFDs and find a top-light IMF model that reproduces the observed level of Ba-enrichment. Future observations that determine or tightly constrain the europium and nitrogen abundances are crucial to identify the origin of Ba and Sr in UFDs.

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Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III

Cited by 54 publications

References 157 publications

A Statistical Detection of Wide Binary Systems in the Ultra-Faint Dwarf Galaxy Reticulum II

A Statistical Detection of Wide Binary Systems in the Ultra-Faint Dwarf Galaxy Reticulum II

Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis*

s-process enrichment of ultrafaint dwarf galaxies

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