2,150 research outputs found
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
A catalogue of accurate wavelengths in the optical spectrum of the Sun
We present accurate measurements of the central wavelengths of 4947 atomic
absorption lines in the solar optical spectrum. The wavelengths, precise to a
level ~ 50-150 m/s, are given for both flux and disc-centre spectra, as
measured in relatively recent FTS solar atlases. This catalogue modernizes
existing sources based on photographic measurements and provides a benchmark to
test and perform wavelength calibrations of astronomical spectra. It will also
permit observers to improve the absolute wavelength calibration of solar
optical spectra when lamps are not available at the telescope.Comment: 3 pages, 1 ASCII table (4947 records, download the source to view);
uses aa.cls (included); accepted for publication in A&A
Magnetostatic interactions between magnetic nanotubes
The investigation of interactions between magnetic nanotubes is complex and
often involves substantial simplifications. In this letter an analytical
expression for the magnetostatic interaction, taking into account the geometry
of the tubes, has been obtained. This expression allows for the definition of a
critical vertical separation for relative magnetization between nanotubes and
can be used for tailoring barcode-type nanostructures with prospective
applications such as biological separation and transport.Comment: 4 pages, 5 figure
Lithium abundances in nearby FGK dwarf and subgiant stars: internal destruction, Galactic chemical evolution, and exoplanets
We derive atmospheric parameters and lithium abundances for 671 stars and
include our measurements in a literature compilation of 1381 dwarf and subgiant
stars. First, a "lithium desert" in the effective temperature (Teff) versus
lithium abundance (A_Li) plane is observed such that no stars with Teff~6075 K
and A_Li~1.8 are found. We speculate that most of the stars on the low A_Li
side of the desert have experienced a short-lived period of severe surface
lithium destruction as main-sequence or subgiant stars. Next, we search for
differences in the lithium content of thin-disk and thick-disk stars, but we
find that internal processes have erased from the stellar photospheres their
possibly different histories of lithium enrichment. Nevertheless, we note that
the maximum lithium abundance of thick-disk stars is nearly constant from
[Fe/H]=-1.0 to -0.1, at a value that is similar to that measured in very
metal-poor halo stars (A_Li~2.2). Finally, differences in the lithium abundance
distribution of known planet-host stars relative to otherwise ordinary stars
appear when restricting the samples to narrow ranges of Teff or mass, but they
are fully explained by age and metallicity biases. We confirm the lack of a
connection between low lithium abundance and planets. However, we find that no
low A_Li planet-hosts are found in the desert Teff window. Provided that subtle
sample biases are not responsible for this observation, this suggests that the
presence of gas giant planets inhibit the mechanism responsible for the lithium
desert.Comment: ApJ, in press. Complete Tables 1 and 3 are available upon reques
Line formation in solar granulation VI. [C I], C I, CH and C2 lines and the photospheric C abundance
The solar photospheric carbon abundance has been determined from [C I], C I,
CH vibration-rotation, CH A-X electronic and C2 Swan electronic lines by means
of a time-dependent, 3D, hydrodynamical model of the solar atmosphere.
Departures from LTE have been considered for the C I lines. These turned out to
be of increasing importance for stronger lines and are crucial to remove a
trend in LTE abundances with the strengths of the lines. Very gratifying
agreement is found among all the atomic and molecular abundance diagnostics in
spite of their widely different line formation sensitivities. The mean of the
solar carbon abundance based on the four primary abundance indicators ([C I], C
I, CH vibration-rotation, C_2 Swan) is log C = 8.39 +/- 0.05, including our
best estimate of possible systematic errors. Consistent results also come from
the CH electronic lines, which we have relegated to a supporting role due to
their sensitivity to the line broadening. The new 3D based solar C abundance is
significantly lower than previously estimated in studies using 1D model
atmospheres.Comment: Accepted for A&A, 13 page
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