Heavy Element Abundances in the Magellanic Clouds

1991 ◽  
Vol 9 (1) ◽  
pp. 82-83 ◽  
Author(s):  
Stephen C. Russell
Keyword(s):  
Neutron Capture ◽  
Heavy Element ◽  
Magellanic Clouds ◽  
Element Abundances ◽  
R Process

AbstractThis paper presents a brief discussion of the apparent underdepletion of the heavy neutron-capture elements (elements heavier than Ba), compared with Fe in the Magellanic Clouds. The s-process appears to have been only effective in forming elements in the light neutron-capture group (Sr, Y, Zr) in the Magellanic Clouds, but to have much reduced effectiveness in forming the heavy neutron-capture group. The abundances of the elements heavier than Ba have a distribution that indicates that they were produced by the r-process alone.

scholarly journals Chemical Evolution and Extremely Metal-Poor Stars

1998 ◽  
Vol 11 (1) ◽  
pp. 49-52
Author(s):  
Andrew McWilliam
Keyword(s):  
Neutron Capture ◽  
Heavy Element ◽  
Massive Stars ◽  
Small Sample ◽  
Heavy Elements ◽  
High Mass ◽  
Type Ii ◽  
Element Abundances ◽  
Halo Stars ◽  
R Process

Early abundance studies (e.g. Pagel 1968) showed that neutron-capture heavy elements (Z > 30) are present in halo stars, but deficient relative iron. Truran (1981) argued that at low [Fe/H] the chemical enrichment time scale was shorter than the lifetime of low-mass AGB progenitors, which are the main source of solar system heavy elements. He proposed that in the halo the heavy elements were produced by high mass stars, in type II supernova events (SNII), by rapid neutron capture nucleosynthesis (the r-process). Spite & Spite (1978) investigated the trend of heavy element abundances with metallicity, from a small sample of halo stars. They found that at [Fe/H]~ -1.5 the halo [heavy element/Fe] ratio is approximately solar; but at lower [Fe/H] there is a roughly linear decrease of [heavy element/Fe] with declining [Fe/H]. Subsequent observations confirmed the general trend of heavy elements in the halo: [M/Fe]~0 down to [Fe/H]~ -2, followed by a linear decline in [M/Fe] to lower [Fe/H] (e.g. Gilroy et al 1988, Lambert 1987). Additional evidence for the role of SNII in halo heavy element synthesis comes from the trend of [Eu/Fe] with [Fe/H]. Europium is an almost pure r-process element (Käppeler et al. 1989) and its abundance trend with metallicity is similar to the α element trend (e.g. O and Mg made in massive stars). The element ratios show an increase in [M/Fe] as [Fe/H] decreases from 0 to —1; below this point [Eu/Fe] and [α/Fe] remain constant at ~+0.3 dex. For α elements this behavior is thought to be due to the change in the relative contributions from type II SN and type la SN in the disk and halo (Tinsley 1979). The trend for Eu also indicates production by massive stars (e.g. SNII). Near [Fe/H]~ -2.5 Eu appears to decline relative to [Fe/H] (like other heavy elements, but unlike the α elements). This abundance trend has been used to constrain the numerous proposed astrophysical sites of the r-process (e.g. Mathews & Cowan 1990).

Distribution of R- and S-Process Elements in the Galactic Halo

1988 ◽  
Vol 132 ◽  
pp. 501-506
Author(s):  
C. Sneden ◽  
C. A. Pilachowski ◽  
K. K. Gilroy ◽  
J. J. Cowan
Keyword(s):  
Heavy Element ◽  
Galactic Halo ◽  
Low Noise ◽  
Heavy Elements ◽  
Process Synthesis ◽  
Element Abundances ◽  
Halo Stars ◽  
Abundance Patterns ◽  
R Process ◽  
Process Elements

Current observational results for the abundances of the very heavy elements (Z>30) in Population II halo stars are reviewed. New high resolution, low noise spectra of many of these extremely metal-poor stars reveal general consistency in their overall abundance patterns. Below Galactic metallicities of [Fe/H] Ã −2, all of the very heavy elements were manufactured almost exclusively in r-process synthesis events. However, there is considerable star-to-star scatter in the overall level of very heavy element abundances, indicating the influence of local supernovas on element production in the very early, unmixed Galactic halo. The s-process appears to contribute substantially to stellar abundances only in stars more metal-rich than [Fe/H] Ã −2.

scholarly journals Dust in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 57-62
Author(s):  
Paul Hodge
Keyword(s):  
Heavy Element ◽  
Magellanic Clouds ◽  
Dust Content ◽  
Optical Observations ◽  
Optical Data ◽  
Star Forming ◽  
Element Abundances ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Far Ultraviolet

The dust content of the Magellanic Clouds can be studied using optical, ultraviolet, infrared and, indirectly, radio wavelength data. All recent studies show that the dust content is lower than that of the Milky Way Galaxy for both Clouds and that the optical properties of the dust are different. At ultraviolet wavelengths, the 2165 Å “bump” in the extinction curve is significantly smaller than in the Galaxy (this now appears NOT to be a consequence of the lower heavy element abundances) and the far ultraviolet (shortward of ˜2000 Å) extinction is greater than in the Galaxy (this IS likely to be a consequence of the lower heavy element abundances). New optical data on background galaxies suggest that the total extinction in the central parts of both the LMC and the SMC is approximately 1.5 magnitudes. High local extinction values are derived from uv and optical observations of star-forming regions, where a spatial correlation with CO detections is sometimes, but not always, found.

scholarly journals Interstellar Phases in the Magellanic Clouds

1999 ◽  
Vol 190 ◽  
pp. 45-50 ◽  
Author(s):  
John M. Dickey ◽  
Monika Marx-Zimmer ◽  
Christian Düsterberg ◽  
Ulrich Mebold ◽  
Snezana Stanimirović ◽  
...  
Keyword(s):  
Heavy Element ◽  
Milky Way ◽  
Magellanic Clouds ◽  
Element Abundances ◽  
Lower Abundance ◽  
Cloud Temperature ◽  
Magellanic System

Surveys of λ21-cm absorption in the Magellanic System show that the cool phase of the HI is less abundant in the SMC than in the Milky Way, and may be so also in the LMC. The typical cool cloud temperature is colder than in the Milky Way, 30 to 40 K rather than 60 to 75 K. The lower abundance of cool phase HI can be traced to the lower heavy element abundances in the Magellanic environment. The cooler cloud temperatures are somewhat mysterious.

scholarly journals Element Abundances in Magellanic Cloud H II Regions from Carbon to Argon

1999 ◽  
Vol 190 ◽  
pp. 266-272 ◽  
Author(s):  
Donald R. Garnett
Keyword(s):  
Heavy Element ◽  
Hubble Space Telescope ◽  
Uv Spectroscopy ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
H Ii Regions ◽  
Ionized Gas ◽  
Mixing Processes ◽  
Element Abundances ◽  
C And N

I review measurements of heavy element abundances within H II regions in the Magellanic Clouds, highlighting in particular improved determinations of carbon abundances based on UV spectroscopy with Hubble Space Telescope. In general, the Magellanic Cloud H II regions show average underabundances in O, Ne, and S (relative to their Galactic counterparts) that are similar to those measured in Magellanic Cloud stars. However, comparison of stars and ionized gas shows discrepancies in C and N abundances that may be related to recently recognized mixing processes that may be operating in massive stars.

scholarly journals Neutron-Capture Element Abundances in Planetary Nebulae

Galaxies ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 50
Author(s):  
N. C. Sterling
Keyword(s):  
Neutron Capture ◽  
Observational Studies ◽  
Near Infrared ◽  
Dwarf Galaxy ◽  
Planetary Nebulae ◽  
Slow Neutron ◽  
Magellanic Clouds ◽  
Heavy Elements ◽  
Element Abundances ◽  
Open Questions

Nebular spectroscopy is a valuable tool for assessing the production of heavy elements by slow neutron(n)-capture nucleosynthesis (the s-process). Several transitions of n-capture elements have been identified in planetary nebulae (PNe) in the last few years, with the aid of sensitive, high-resolution, near-infrared spectrometers. Combined with optical spectroscopy, the newly discovered near-infrared lines enable more accurate abundance determinations than previously possible, and provide access to elements that had not previously been studied in PNe or their progenitors. Neutron-capture elements have also been detected in PNe in the Sagittarius Dwarf galaxy and in the Magellanic Clouds. In this brief review, I discuss developments in observational studies of s-process enrichments in PNe, with an emphasis on the last five years, and note some open questions and preliminary trends.

scholarly journals Chemical Abundances from Planetary Nebulae in the Magellanic Clouds

1995 ◽  
Vol 10 ◽  
pp. 476-479 ◽  
Author(s):  
M.J. Barlow
Keyword(s):  
Electron Temperature ◽  
Heavy Element ◽  
Planetary Nebulae ◽  
Density Fluctuations ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Chemical Abundances ◽  
Element Abundances

AbstractHeavy element abundances, in particular those of oxygen, obtained from recent spectroscopic surveys of Magellanic Cloud planetary nebulae (PN), are reviewed and compared with those derived for H regions and objects in our own galaxy. These abundances have been based on collisionally excited lines and are very sensitive to the adopted electron temperature. There is increasing evidence that temperature or density fluctuations within nebulae lead to the electron temperatures being overestimated, with the corollary that the heavy element abundances have been underestimated.

scholarly journals The lowest detected stellar Fe abundance: the halo star SMSS J160540.18−144323.1

2019 ◽  
Vol 488 (1) ◽  
pp. L109-L113 ◽  
Author(s):  
T Nordlander ◽  
M S Bessell ◽  
G S Da Costa ◽  
A D Mackey ◽  
M Asplund ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Neutron Capture ◽  
Halo Star ◽  
Abundance Pattern ◽  
Apparent Lack ◽  
Element Abundances ◽  
Metal Free ◽  
R Process ◽  
Population Iii Stars ◽  
Progenitor Stars

ABSTRACT We report the discovery of SMSS J160540.18−144323.1, a new ultra metal-poor halo star discovered with the SkyMapper telescope. We measure $\left[\rm {Fe}/\rm {H}\right]= -6.2 \pm 0.2$ (1D LTE), the lowest ever detected abundance of iron in a star. The star is strongly carbon-enhanced, $\left[\rm {C}/\rm {Fe}\right] = 3.9 \pm 0.2$, while other abundances are compatible with an α-enhanced solar-like pattern with $\left[\rm {Ca}/\rm {Fe}\right] = 0.4 \pm 0.2$, $\left[\rm {Mg}/\rm {Fe}\right] = 0.6 \pm 0.2$, $\left[\rm {Ti}/\rm {Fe}\right] = 0.8 \pm 0.2$, and no significant s- or r-process enrichment, $\left[\rm {Sr}/\rm {Fe}\right] \lt 0.2$ and $\left[\rm {Ba}/\rm {Fe}\right] \lt 1.0$ (3σ limits). Population III stars exploding as fallback supernovae may explain both the strong carbon enhancement and the apparent lack of enhancement of odd-Z and neutron-capture element abundances. Grids of supernova models computed for metal-free progenitor stars yield good matches for stars of about $10\, \rm M_\odot$ imparting a low kinetic energy on the supernova ejecta, while models for stars more massive than roughly $20\, \rm M_\odot$ are incompatible with the observed abundance pattern.

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