Abundance analyses of helium-rich subluminous B stars

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Naslim N., Jeffery C. S., Ahmad A., Behara N. T., ŞAHİN T.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, cilt.409, sa.2, ss.582-590, 2010 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 409 Sayı: 2
  • Basım Tarihi: 2010
  • Doi Numarası: 10.1111/j.1365-2966.2010.17324.x
  • Dergi Adı: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Sayfa Sayıları: ss.582-590
  • Anahtar Kelimeler: stars: abundances, stars: chemically peculiar, stars: early-type, stars: evolution, subdwarfs, IA PROGENITOR SURVEY, DWARF COOLING CURVE, SUBDWARF-O-STARS, SPECTRAL-ANALYSIS, EXTREME HELIUM, WHITE-DWARF, SDB STARS, MASS-LOSS, CHEMICAL-COMPOSITION, HOT SUBDWARFS
  • Akdeniz Üniversitesi Adresli: Hayır

Özet

The connection between helium-rich hot subdwarfs of spectral types O and B ( He-sdB) has been relatively unexplored since the latter were found in significant numbers in the 1980s. In order to explore this connection further, we have analysed the surface composition of six He-sdB stars, including LB 1766, LB 3229, SB 21 (= Ton-S 137 = BPS 29503-0009), BPS 22940-0009, BPS 29496-0010 and BPS 22956-0094. Opacity-sampled line-blanketed model atmospheres have been used to derive atmospheric properties and elemental abundances. All the stars are moderately metal poor compared with the Sun ([ Fe/H] approximate to -0.5). Four stars are nitrogen rich, two of these are carbon rich and at least four appear to be neon rich. The data are insufficient to rule out binarity in any of the sample. The surface composition and locus of the N-rich He-sdBs are currently best explained by the merger of two helium white dwarfs, or possibly by the merger of a helium white dwarf with a post-sdB white dwarf. C-rich He-sdBs require further investigation.

The connection between helium-rich hot subdwarfs of spectral types O and B (He-sdB) has been relatively unexplored since the latter were found in significant numbers in the 1980s. In order to explore this connection further, we have analysed the surface composition of six He-sdB stars, including LB 1766, LB 3229, SB 21 (= Ton-S 137 = BPS 29503−0009), BPS 22940−0009, BPS 29496−0010 and BPS 22956−0094. Opacity-sampled line-blanketed model atmospheres have been used to derive atmospheric properties and elemental abundances. All the stars are moderately metal poor compared with the Sun ([Fe/H]≈−0.5). Four stars are nitrogen rich, two of these are carbon rich and at least four appear to be neon rich. The data are insufficient to rule out binarity in any of the sample. The surface composition and locus of the N-rich He-sdBs are currently best explained by the merger of two helium white dwarfs, or possibly by the merger of a helium white dwarf with a post-sdB white dwarf. C-rich He-sdBs require further investigation.