The Puzzling Frequencies of CEMP and NEMP Stars

Pols, O. R.; Izzard, Robert G.; Glebbeek, Evert; Stancliffe, Richard J.

doi:10.1071/as08076

Cited by 7 publications

(8 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…From the difference between C and N, it is possible to distinguish the contribution from low‐ and intermediate‐mass AGB stars as the enrichment source of the observed metal‐poor stars. Pols et al (2009) showed that the IMF with the Gaussian distribution peaked at ∼10 M ⊙ (Komiya et al 2007) is rejected when trying to match the fraction between C‐rich and N‐rich stars, based on binary population synthesis models (see also Izzard et al 2009). Fluorine: F is one of the most interesting elements, although F abundances are estimated from only one infrared line from stellar spectra.…”

Section: Resultsmentioning

confidence: 99%

The evolution of isotope ratios in the Milky Way Galaxy

Kobayashi¹,

Karakas²,

Umeda³

2011

Monthly Notices of the Royal Astronomical Society

383

472

View full text Add to dashboard Cite

Isotope ratios have opened a new window into the study of the details of stellar evolution, supernovae and galactic chemical evolution. We present the evolution of the isotope ratios of elemental abundances (from C to Zn) in the solar neighbourhood, bulge, halo and thick disc, using chemical evolution models with updated yields of asymptotic giant branch (AGB) stars and core-collapse supernovae. The evolutionary history of each element is different owing to the effects of the initial progenitor mass and metallicity on element production. In the bulge and thick disc the star formation time-scale is shorter than in the solar neighbourhood, leading to higher [alpha/Fe] ratios. Likewise, the smaller contribution from Type Ia supernovae in these regions leads to lower [Mn/Fe] ratios. Also in the bulge, the abundances of [(Na, Al, P, Cl, K, Sc, Cu, Zn)/Fe] are higher because of the effect of metallicity on element production from core-collapse supernovae. According to our predictions, it is possible to find metal-rich stars ([Fe/H] greater than or similar to -1) that formed in the early Universe as a result of rapid star formation. The chemical enrichment time-scale of the halo is longer than in the solar neighbourhood, and consequently the ratios of [(C, F)/Fe] and C-12/C-13 are higher owing to a significant contribution from low-mass AGB stars. While the [alpha/Fe] and [Mn/Fe] ratios are the same as in the solar neighbourhood, the [(Na, Al, P, Cl, K, Sc, Cu, Zn)/Fe] ratios are predicted to be lower. Furthermore, we predict that isotope ratios such as Mg-24/Mg-25,Mg-26 are larger because of the contribution from low-metallicity supernovae. Using isotopic ratios, it is possible to select stars that formed in a system with a low chemical enrichment efficiency such as the satellite galaxies that were accreted on to our own Milky Way Galaxy

show abstract

Section: Resultsmentioning

confidence: 99%

The evolution of isotope ratios in the Milky Way Galaxy

Kobayashi¹,

Karakas²,

Umeda³

2011

Monthly Notices of the Royal Astronomical Society

383

472

View full text Add to dashboard Cite

show abstract

“…Others argued that the observed paucity of very N-rich stars puts strong constraints on the IMF at low metallicity (e.g. Komiya et al 2007) or may require a much more efficient dredge-up of carbon in low-mass, low-metallicity AGB stars than shown by detailed evolution models available to date (see Pols et al 2009;Izzard et al 2009 for a discussion). We argue that dQNe model is a promising explanation for both the ubiquity of CEMP-s stars and the near-absence of NEMP stars without the need for a revision of dredge-up models of AGB stars.…”

Section: Trends In Nitrogenmentioning

confidence: 99%

A new model for the origin of very metal poor stars and their chemical composition

Ouyed

2012

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

The genesis and chemical patterns of the metal poor stars in the galactic halo remains an open question. Current models do not seem to give a satisfactory explanation for the observed abundances of Lithium in the galactic metal-poor stars and the existence of carbon-enhanced metal-poor (CEMP) and Nitrogen-enhanced metal-poor (NEMP) stars. In order to deal with some of these theoretical issues, we suggest an alternative explanation, where some of the Pop. III SNe are followed by the detonation of their neutron stars (Quark-Novae; QNe). In QNe occurring a few days to a few weeks following the preceding SN explosion, the neutronrich relativistic QN ejecta leads to spallation of 56 Ni processed in the ejecta of the preceding SN explosion and thus to "iron/metal impoverishment" of the primordial gas swept by the combined SN+QN ejecta. We show that the generation of stars formed from fragmentation of pristine clouds swept-up by the combined SN+QN ejecta acquire a metallicity with −7.5 < [Fe/H] < −1.5 for dual explosions with 2 < t delay (days) < 30. Spallation leads to the depletion of 56 Ni and formation of sub-Ni elements such as Ti, V, Cr, and Mn providing a reasonable account of the trends observed in galactic halo metal-poor stars. CEMP stars form in dual explosions with short delays (t delay < 5 days). These lead to important destruction of 56 Ni (and thus to a drastic reduction of the amount of Fe in the swept up cloud) while preserving the carbon processed in the outer layers of the SN ejecta. Lithium is produced from the interaction of the neutron-rich QN ejecta with the outer (oxygen-rich) layers of the SN ejecta. A Lithium plateau with 2 < A(Li) < 2.4 can be produced in our model as well as a corresponding 6 Li plateau with 6 Li/ 7 Li < 0.3.

show abstract

“…In addition to carbon enhancement, rare CEMP stars exhibit nitrogen overabundances, typically with [N/Fe] > 1.0 and [N/C] > 0.5, although this phenomenon depends on metallicity, it appears to be more frequent at [Fe/H] < 2.8 (∼ factor of 10) (Bessell & Norris 1982;Johnson et al 2007;Pols et al 2009Pols et al , 2012Roederer et al 2014a). The existence of a population of nitrogenenhanced metal-poor (NEMP) stars was predicted from the same evolution scenario, since AGB stars efficiently cycle carbon into nitrogen in their envelopes.…”

Section: Introductionmentioning

confidence: 99%

Metal-poor Stars Observed with the Automated Planet Finder Telescope. I. Discovery of Five Carbon-enhanced Metal-poor Stars from LAMOST

Mardini¹,

Li²,

Placco³

et al. 2019

ApJ

View full text Add to dashboard Cite

We report on the discovery of five carbon-enhanced metal-poor (CEMP) stars in the metallicity range of −3.3 < [Fe/H] < −2.4. These stars were selected from the LAMOST DR3 low-resolution (R∼ 2,000) spectroscopic database as metal-poor candidates and followed-up with high-resolution spectroscopy (R∼110,000) with the LICK/APF. Stellar parameters and individual abundances for 25 chemical elements (from Li to Eu) are presented for the first time. These stars exhibit chemical abundance patterns that are similar to those reported in other literature studies of very and extremely metal-poor stars. One of our targets, J2114−0616, shows high enhancement in carbon ([C/Fe]=1.37), nitrogen ([N/Fe]= 1.88), barium ([Ba/Fe]=1.00), and europium ([Eu/Fe]=0.84). Such chemical abundance pattern suggests that J2114−0616 can be classified as CEMP-r/s star. In addition, the star J1054+0528 can be classified as a CEMP-rI star, with [Eu/Fe]=0.44 and [Ba/Fe]=−0.52. The other stars in our sample show no enhancements in neutron-capture elements and can be classified as CEMP-no stars. We also performed a kinematic and dynamical analysis of the sample stars based on Gaia DR2 data. The kinematic parameters, orbits, and binding energy of these stars, show that J2114−0616 is member of the outer halo population, while the remaining stars belong to the inner halo population but with an accreted origin. Collectively, these results add important constraints on the origin and evolution of CEMP stars as well as on their possible formation scenarios.

show abstract

The Puzzling Frequencies of CEMP and NEMP Stars

Abstract: Abstract:We present the results of binary population simulations of carbon-and nitrogen-enhanced metalpoor (CEMP and NEMP) stars. We show that the observed paucity of very nitrogen-rich stars puts strong constraints on possible modifications of the initial mass function at low metallicity.

Cited by 7 publications

References 16 publications

The evolution of isotope ratios in the Milky Way Galaxy

The evolution of isotope ratios in the Milky Way Galaxy

A new model for the origin of very metal poor stars and their chemical composition

Metal-poor Stars Observed with the Automated Planet Finder Telescope. I. Discovery of Five Carbon-enhanced Metal-poor Stars from LAMOST

Contact Info

Product

Resources

About