244 research outputs found
Lithium-rich stars in the Sloan Digital Sky Survey
We report the discovery of 23 lithium-rich post-main-sequence stars,
identified from moderate-resolution SDSS spectroscopy and confirmed with
high-resolution spectra taken at the Hobby-Eberly Telescope. These new Li-rich
stars cover a broad range in mass and evolutionary phase, including bright
giants and post-AGB stars. The process responsible for preserving or producing
excess lithium in a small fraction of evolved stars remains unclear.Comment: 5 pages, XII International Symposium on Nuclei in the Cosmos, August
5-12, 2012, Cairns, Australia. To appear in Proceedings of Scienc
Comparing the Ca II H and K Emission Lines in Red Giant Stars
Measurements of the asymmetry of the emission peaks in the core of the Ca II
H line for 105 giant stars are reported. The asymmetry is quantified with the
parameter V/R, defined as the ratio between the maximum number of counts in the
blueward peak and the redward peak of the emission profile. The Ca II H and K
emission lines probe the differential motion of certain chromospheric layers in
the stellar atmosphere. Data on V/R for the Ca II K line are drawn from
previous papers and compared to the analogous H line ratio, the H and K spectra
being from the same sets of observations. It is found that the H line V/R value
is +0.04 larger, on average, than the equivalent K line ratio, however, the
difference varies with B-V color. Red giants cooler than B-V = 1.2 are more
likely to have the H line V/R larger than the K line V/R, whereas the opposite
is true for giants hotter than B-V = 1.2. The differences between the Ca II H
and K line asymmetries could be caused by the layers of chromospheric material
from which these emission features arise moving with different velocities in an
expanding outflow.Comment: 36 pages, 12 figures, 2 tables. Accepted to PASP. Corrected a typo in
Table
Optimal Integrated Abundances for Chemical Tagging of Extragalactic Globular Clusters
High resolution integrated light (IL) spectroscopy provides detailed
abundances of distant globular clusters whose stars cannot be resolved.
Abundance comparisons with other systems (e.g. for chemical tagging) require
understanding the systematic offsets that can occur between clusters, such as
those due to uncertainties in the underlying stellar population. This paper
analyses high resolution IL spectra of the Galactic globular clusters 47 Tuc,
M3, M13, NGC 7006, and M15 to (1) quantify potential systematic uncertainties
in Fe, Ca, Ti, Ni, Ba, and Eu and (2) identify the most stable abundance ratios
that will be useful in future analyses of unresolved targets. When stellar
populations are well-modelled, uncertainties are ~0.1-0.2 dex based on
sensitivities to the atmospheric parameters alone; in the worst case scenarios,
uncertainties can rise to 0.2-0.4 dex. The [Ca I/Fe I] ratio is identified as
the optimal integrated [alpha/Fe] indicator (with offsets <0.1 dex), while [Ni
I/Fe I] is also extremely stable to within <0.1 dex. The [Ba II/Eu II] ratios
are also stable when the underlying populations are well modelled and may also
be useful for chemical tagging.Comment: 28 pages, 4 figures, accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
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