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A grid of MARCS mod...
A grid of MARCS model atmospheres for late-type stars II. S stars and their properties
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- Van Eck, Sophie (författare)
- Univ Libre Bruxelles, Inst Astron & Astrophys, CP 226,Blvd Triomphe, B-1050 Brussels, Belgium.
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- Neyskens, Pieter (författare)
- Univ Libre Bruxelles, Inst Astron & Astrophys, CP 226,Blvd Triomphe, B-1050 Brussels, Belgium.
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- Jorissen, Alain (författare)
- Univ Libre Bruxelles, Inst Astron & Astrophys, CP 226,Blvd Triomphe, B-1050 Brussels, Belgium.
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- Plez, Bertrand (författare)
- Univ Montpellier, CNRS, Lab Univers & Particules Montpellier, F-34095 Montpellier, France.
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- Edvardsson, Bengt (författare)
- Uppsala universitet,Institutionen för fysik och astronomi
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- Eriksson, Kjell (författare)
- Uppsala universitet,Institutionen för fysik och astronomi
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- Gustafsson, Bengt (författare)
- Uppsala universitet,Institutionen för fysik och astronomi
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- Jorgensen, Uffe Gråe (författare)
- Niels Bohr Inst, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark.;Geol Museum, Ctr Star & Planet Format, Oster Voldgade 5, DK-1350 Copenhagen, Denmark.
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- Nordlund, Åke (författare)
- Niels Bohr Inst, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark.;Geol Museum, Ctr Star & Planet Format, Oster Voldgade 5, DK-1350 Copenhagen, Denmark.
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Univ Libre Bruxelles, Inst Astron & Astrophys, CP 226,Blvd Triomphe, B-1050 Brussels, Belgium Univ Montpellier, CNRS, Lab Univers & Particules Montpellier, F-34095 Montpellier, France. (creator_code:org_t)
- 2017-04-19
- 2017
- Engelska.
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 601
- Relaterad länk:
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https://www.aanda.or...
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https://urn.kb.se/re...
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https://doi.org/10.1...
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Abstract
Ämnesord
Stäng
- S-type stars are late-type giants whose atmospheres are enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing asymptotic giant branch. A grid of MARCS model atmospheres has been computed for S stars, covering the range 2700 <= T-eff (K) <= 4000, 0.50 <= C/O less than or similar to 0.99, 0 <= log g <= 5, [Fe/H] = 0., -0.5 dex, and [s/Fe] = 0, 1, and 2 dex (where the latter quantity refers to the global overabundance of s-process elements). The MARCS models make use of a new ZrO line list. Synthetic spectra computed from these models are used to derive photometric indices in the Johnson and Geneva systems, as well as TiO and ZrO band strengths. A method is proposed to select the model best matching any given S star, a non-trivial operation since the grid contains more than 3500 models covering a five-dimensional parameter space. The method is based on the comparison between observed and synthetic photometric indices and spectral band strengths, and has been applied on a vast subsample of the Henize sample of S stars. Our results confirm the old claim by Piccirillo (1980, MNRAS, 190, 441) that ZrO bands in warm S stars (T-eff > 3200 K) are not caused by the C /O ratio being close to unity, as traditionally believed, but rather by some Zr overabundance. The TiO and ZrO band strengths, combined with V - K and J - K photometric indices, are used to select T-eff, C/O, [Fe/H] and [s/Fe]. The Geneva U - B1 and B2 - V1 indices (or any equivalent) are good at selecting the gravity. The defining spectral features of dwarf S stars are outlined, but none is found among the Henize S stars. More generally, it is found that, at T-eff = 3200 K, a change of C/O from 0.5 to 0.99 has a strong impact on V - K (2 mag). Conversely, a range of 2 mag in V - K corresponds to a 200 K shift along the (T-eff, V - K) relationship (for a fixed C/O value). Hence, the use of a (T-eff, V - K) calibration established forMstars will yield large errors for S stars, so that a specific calibration must be used, as provided in the present paper. Using the atmospheric parameters derived by our method for the sample of Henize S stars, we show that the extrinsic-intrinsic dichotomy among S stars reveals itself very clearly as a bimodal distribution in the e ff ective temperatures. Moreover, the increase of s-process element abundances with increasing C/O ratios and decreasing temperatures is apparent among intrinsic stars, confirming theoretical expectations.
Ämnesord
- NATURVETENSKAP -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)
Nyckelord
- stars: atmospheres
- stars: fundamental parameters
- stars: late-type
- stars: AGB and post-AGB
- stars: abundances
- stars: general
Publikations- och innehållstyp
- ref (ämneskategori)
- art (ämneskategori)
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