1,007 research outputs found
Chemical Abundances from the Continuum
The calculation of solar absolute fluxes in the near-UV is revisited,
discussing in some detail recent updates in theoretical calculations of
bound-free opacity from metals. Modest changes in the abundances of elements
such as Mg and the iron-peak elements have a significant impact on the
atmospheric structure, and therefore self-consistent calculations are
necessary. With small adjustments to the solar photospheric composition, we are
able to reproduce fairly well the observed solar fluxes between 200 and 270 nm,
and between 300 and 420 nm, but find too much absorption in the 270-290 nm
window. A comparison between our reference 1D model and a 3D time-dependent
hydrodynamical simulation indicates that the continuum flux is only weakly
sensitive to 3D effects, with corrections reaching <10% in the near-UV, and <2%
in the optical.Comment: 10 pages, 5 figures, to appear in the proceedings of the conference A
Stellar Journey, a symposium in celebration of Bengt Gustafsson's 65th
birthday, June 23-27, 2008, Uppsal
Fe I line shifts in the optical spectrum of the Sun
New improvements in the measurement of both the optical solar spectrum and
laboratory wavelengths for lines of neutral iron are combined to extract
central wavelength shifts for 1446 lines observed in the Sun. This provides the
largest available database of accurate solar wavelengths useful as a reference
for comparison with other solar-type stars. It is shown how the velocity shifts
correlate with line strength, approaching a constant value, close to zero, for
lines with equivalent widths larger than 200 mA.Comment: Latex file (5 pages), uses l-aa.sty and epsfig.sty (included); 3
Postscript figures, 1 ASCII table, accepted for publication in Astronomy and
Astrophysics Supplement Serie
Bridging Model and Observed Stellar Spectra
Accurate model stellar fluxes are key for the analysis of observations of
individual stars or stellar populations. Model spectra differ from real stellar
spectra due to limitations of the input physical data and adopted
simplifications, but can be empirically calibrated to maximise their
resemblance to actual stellar spectra. I describe a least-squares procedure of
general use and test it on the MILES library.Comment: 7 pages, 6 figures, accepted for publication in MNRA
Oxygen Abundances in Nearby FGK Stars and the Galactic Chemical Evolution of the Local Disk and Halo
Atmospheric parameters and oxygen abundances of 825 nearby FGK stars are
derived using high-quality spectra and a non-LTE analysis of the 777 nm O I
triplet lines. We assign a kinematic probability for the stars to be thin-disk
(P1), thick-disk (P2), and halo (P3) members. We confirm previous findings of
enhanced [O/Fe] in thick-disk (P2>0.5) relative to thin-disk (P1>0.5) stars
with [Fe/H]<-0.2, as well as a "knee" that connects the mean [O/Fe]-[Fe/H]
trend of thick-disk stars with that of thin-disk members at [Fe/H]>-0.2.
Nevertheless, we find that the kinematic membership criterion fails at
separating perfectly the stars in the [O/Fe]-[Fe/H] plane, even when a very
restrictive kinematic separation is employed. Stars with "intermediate"
kinematics (P1<0.7, P2<0.7) do not all populate the region of the [O/Fe]-[Fe/H]
plane intermediate between the mean thin-disk and thick-disk trends, but their
distribution is not necessarily bimodal. Halo stars (P3>0.5) show a large
star-to-star scatter in [O/Fe]-[Fe/H], but most of it is due to stars with
Galactocentric rotational velocity V-200 km/s
follow an [O/Fe]-[Fe/H] relation with almost no star-to-star scatter. Early
mergers with satellite galaxies explain most of our observations, but the
significant fraction of disk stars with "ambiguous" kinematics and abundances
suggests that scattering by molecular clouds and radial migration have both
played an important role in determining the kinematic and chemical properties
of solar neighborhood stars.Comment: ApJ, in press. Complete tables 2-6 are available in the source
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