9,836 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
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
Optical Surface Photometry of a Sample of Disk Galaxies. II Structural Components
This work presents the structural decomposition of a sample of 11 disk
galaxies, which span a range of different morphological types. The U, B, V, R,
and I photometric information given in Paper I (color and color-index images
and luminosity, ellipticity, and position-angle profiles) has been used to
decide what types of components form the galaxies before carrying out the
decomposition. We find and model such components as bulges, disks, bars, lenses
and rings.Comment: 14 figures. Accepted for publication in A&
The Infrared Massive Stellar Content of M83
We present an analysis of archival Spitzer images and new ground-based and
Hubble Space Telescope (HST) near-infrared (IR) and optical images of the field
of M83 with the goal of identifying rare, dusty, evolved massive stars. We
present point source catalogs consisting of 3778 objects from
Infrared Array Camera (IRAC) Band 1 (3.6 m) and Band 2 (4.5 m), and
975 objects identified in Magellan 6.5m FourStar near-IR and
images. A combined catalog of coordinate matched near- and mid-IR point sources
yields 221 objects in the field of M83. Using this photometry we identify 185
massive evolved stellar candidates based on their location in color-magnitude
and color-color diagrams. We estimate the background contamination to our
stellar candidate lists and further classify candidates based on their
appearance in Wide Field Camera 3 (WFC3) observations of M83. We find 49
strong candidates for massive stars which are very promising objects for
spectroscopic follow-up. Based on their location in a versus
diagram, we expect at least 24, or roughly 50%, to be confirmed as red
supergiants.Comment: 32 pages, 23 figures, accepted for publication in A&
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