1,226 research outputs found
On the Sodium versus Iron Correlation in Late B-Type Stars
With an aim to study whether the close correlation between [Na/H] and [Fe/H]
recently found in A-type stars further persists in the regime of B-type stars,
the abundances of Na were determined for 30 selected sharp-lined late B-type
stars (10000K < T_eff < 14000K) from the Na I 5890/5896 doublet. These Na
abundances were then compared with the O and Fe abundances (derived from the O
I 6156-8 and Fe II 6147/6149 lines) showing anti-correlated peculiarities. It
turned out that, unlike the case of A-type stars, [Na/H] is roughly constant at
a slightly subsolar level ([Na/H] ~ -0.2 (+/-0.2)) without any significant
correlation with [Fe/H] which shows considerable dispersion ranging from ~ -0.6
to ~ +1.0. This may serve as an important observational constraint for
understanding the abundance peculiarities along with the physical mechanism of
atomic diffusion in upper main-sequence stars of late A through late B-type
including Am and HgMn stars.Comment: 20 pages, 8 figures, accepted for publication in Publ. Astron. Soc.
Japan (Vol. 66, No. 1, 2014
Beryllium Abundances of Solar-Analog Stars
An extensive beryllium abundance analysis was conducted for 118 solar analogs
(along with 87 FGK standard stars) by applying the spectrum synthesis technique
to the near-UV region comprising the Be II line at 3131.066 A, in an attempt to
investigate whether Be suffers any depletion such as the case of Li showing a
large diversity. We found that, while most of these Sun-like stars are
superficially similar in terms of their A(Be) (Be abundances) around the solar
value within ~ +/- 0.2dex, 4 out of 118 samples turned out strikingly
Be-deficient (by more than ~2 dex) and these 4 stars belong to the group of
lowest v_e sin i (projected rotation velocity). Moreover, even for the other
majority showing an apparent similarity in Be, we can recognize a tendency that
A(Be) gradually increases with an increase in v_e sin i. These observational
facts suggest that any solar analog star (including the Sun) generally suffers
some kind of Be depletion during their lives, where the rotational velocity (or
the angular momentum) plays an important role in the sense that depletion tends
to be enhanced by slower rotation. Hence, our findings require that the
occasionally stated view "G-type dwarfs with T_eff ~< 6000 K are essentially
homogeneous in Be with their original composition retained" should be revised.
Also, our analysis indicates that the difference of ~0.2 dex in A(Be) between
the solar photosphere and the meteorite really exists, implying that "UV
missing opacity" is irrelevant at least for this Be II line.Comment: 18 pages, 12 figures, 3 tables and 3 electronic tables (included as
ancillary files), accepted for publication in Publ. Astron. Soc. Japan (2011,
Vol. 63, No. 4
Non-LTE Line-Formation and Abundances of Sulfur and Zinc in F, G, and K Stars
Extensive statistical-equilibrium calculations on neutral sulfur and zinc
were carried out, in order to investigate how the non-LTE effect plays a role
in the determination of S and Zn abundances in F, G, and K stars. Having
checked on the spectra of representative F-type stars (Polaris, Procyon, and
alpha Per) and the Sun that our non-LTE corrections yield a reasonable
consistency between the abundances derived from different lines, we tried an
extensive non-LTE reanalysis of published equivalent-width data of S I and Zn I
lines for metal-poor halo/disk stars. According to our calculations, S I
9212/9228/9237 lines suffer significant negative non-LTE corrections amounting
to <~ 0.2--0.3 dex, while LTE is practically valid for S I 8683/8694 lines.
Embarrassingly, as far as the very metal-poor regime is concerned, a marked
discordance is observed between the [S/Fe] values from these two abundance
indicators, in the sense that the former attains a nearly flat plateau (or even
a slight downward bending) while the latter shows an ever-increasing trend with
a further lowering of metallicity. The reason for this discrepancy is yet to be
clarified. Regarding Zn, we almost confirmed the characteristic tendencies of
[Zn/Fe] reported from recent LTE studies (i.e., an evident/slight increase of
[Zn/Fe] with a decrease of [Fe/H] for very metal-poor/disk stars), since the
non-LTE corrections for the Zn I 4722/4810 and 6362 lines (tending to be
positive and gradually increasing towards lower [Fe/H]) are quantitatively of
less significance (<~ 0.1 dex).Comment: 33 pages, 7 figures, PASJ, Vol. 57, No. 5 (2005) in pres
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