CEMP star

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CEMP stars ( English carbon-enhanced metal-poor stars , carbon-enriched metal-poor stars ) are peculiar stars with a different chemical composition of the photosphere . While carbon is 10 times more common in their atmospheres, the metal content is at least 100 times lower than that of the sun. CEMP stars occur quite frequently in the halo population of the Milky Way and their frequency increases with decreasing metal content up to 50% for the extremely metal-poor stars of Population II with a metal content of one ten thousandth of the Sun's value .

Classification

CEMP stars are divided into the following classes:

  • CEMP-S stars are enriched with elements that arise from the s-process . They are the result of a previous mass transfer of the carbon-enriched atmosphere of a AGB star to the CEMP star in a close binary star system .
  • CEMP-no stars do not contain a disproportionate abundance of elements from a neutron capture process . They are likely formed from extremely metal-poor stars and are a result of late-stage carbon burning, internal mixing, and severe mass loss from stellar winds
  • In addition to elements from the s-process , CEMP-R / S stars also contain an abundance of elements from rapid neutron capture, the r-process .

Emergence

Various hypotheses have been presented for the formation of the CEMP star:

  • The high proportion of carbon is the result of previous generations of stars, from whose material the CEMP star was created.
  • Low mass, low metallicity stars undergo an unknown mixing event, which transports the carbon into the atmosphere .
  • In a double star scenario, carbon is transferred from a thermally pulsating AGB star to the current CEMP star by means of Roche-Lobe Overflow. This mechanism is also used to explain the formation of barium stars and CH giants.

meaning

Based on the distribution of the CEMP stars, the halo population of the Milky Way can be divided into two groups. In the inner halo at a distance of less than 5 kiloparsecs from the galactic plane, CEMP stars are rather rare, while their frequency in the outer halo increases significantly with decreasing metal content. From the distribution it is concluded that the outer halo is the result of an accretion of smaller subsystems. The stars of the inner halo, on the other hand, were mainly formed during the collapse during the formation of the Milky Way.

Examples

Individual evidence

  1. ↑ Catherine R. Kennedy et al: [O / Fe] ESTIMATES FOR CARBON-ENHANCED METAL-POOR STARS FROM NEAR-IR SPECTROSCOPY . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1101.2260v1 .
  2. ↑ Vinicius M. Placco et al .: A SEARCH FOR UNRECOGNIZED CARBON-ENHANCED METAL-POOR STARS IN THE GALAXY . In: Astrophysics. Solar and Stellar Astrophysics . 2010, arxiv : 1001.2512v1 .
  3. ↑ Maria Lugaro, Amanda I. Karakas, Richard J. Stancliffe, Carlos Rijs: The s process in asymptotic giant branch stars of low metallicity and the composition of carbon-enhanced metal-poor stars . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1112.2757v1 .
  4. ↑ Thomas Masseron and others: Lithium Abundances in CEMP stars . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1203.3295v2 .
  5. ^ C. Abate, OR Pols, RG Izzart, SS Mohamed and SE de Mink: Wind Roche-lobe overflow: Application to carbon-enhanced metal-poor stars . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1302.4441v1 .
  6. ↑ Daniela Carollo and others: CARBON-ENHANCED METAL-POOR STARS IN THE INNER AND OUTER HALO COMPONENTS OF THE MILKY WAY . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1103.3067v1 .
  7. ↑ Timothy C. Beers, Daniela Carollo: The Assembly of the Halo System of the Milky Way as Revealed by SDSS / SEGUE - The CEMP Star Connection Implications for Galaxy Formation . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1111.2764v1 .