725 research outputs found
Lithium abundances in CEMP stars
Carbon-enhanced metal-poor (CEMP) stars are believed to show the chemical
imprints of more massive stars (M > 0.8 Msun) that are now extinct. In
particular, it is expected that the observed abundance of Li should deviate in
these stars from the standard Spite lithium plateau. We study here a sample of
11 metal-poor stars and a double-lined spectroscopic binary with -1.8 <[Fe/H]<
-3.3 observed with VLT/UVES spectrograph. Among these 12 metal-poor stars,
there are 8 CEMP stars for which we measure or constrain the Li abundance. In
contrast to previous arguments, we demonstrate that an appropriate regime of
dilution permits the existence of "Li-Spite plateau and C-rich" stars, whereas
some of the "Li-depleted and C-rich" stars call for an unidentified additional
depletion mechanism that cannot be explained by dilution alone. We find
evidence that rotation is related to the Li depletion in some CEMP stars.
Additionally, we report on a newly recognized double-lined spectroscopic binary
star in our sample. For this star, we develop a new technique from which
estimates of stellar parameters and luminosity ratios can be derived based on a
high-resolution spectrum alone, without the need for input from evolutionary
models.Comment: 62 pages, 16 figures, accepted for publication in Ap
Automated Determination of [Fe/H] and [C/Fe] from Low-Resolution Spectroscopy
We develop an automated spectral synthesis technique for the estimation of
metallicities ([Fe/H]) and carbon abundances ([C/Fe]) for metal-poor stars,
including carbon-enhanced metal-poor stars, for which other methods may prove
insufficient. This technique, autoMOOG, is designed to operate on relatively
strong features visible in even low- to medium-resolution spectra, yielding
results comparable to much more telescope-intensive high-resolution studies. We
validate this method by comparison with 913 stars which have existing
high-resolution and low- to medium-resolution to medium-resolution spectra, and
that cover a wide range of stellar parameters. We find that at low
metallicities ([Fe/H] < -2.0), we successfully recover both the metallicity and
carbon abundance, where possible, with an accuracy of ~ 0.20 dex. At higher
metallicities, due to issues of continuum placement in spectral normalization
done prior to the running of autoMOOG, a general underestimate of the overall
metallicity of a star is seen, although the carbon abundance is still
successfully recovered. As a result, this method is only recommended for use on
samples of stars of known sufficiently low metallicity. For these
low-metallicity stars, however, autoMOOG performs much more consistently and
quickly than similar, existing techniques, which should allow for analyses of
large samples of metal-poor stars in the near future. Steps to improve and
correct the continuum placement difficulties are being pursued.Comment: 8 pages, 7 figures; accepted for publication in A
A sequence of nitrogen-rich very red giants in the globular cluster NGC 1851
We present the abundances of N in a sample of 62 stars on the red giant
branch (RGB) in the peculiar globular cluster NGC 1851. The values of [N/Fe]
ratio were obtained by comparing the flux measured in the observed spectra with
that from synthetic spectra for up to about 15 features of CN. This is the
first time that N abundances are obtained for such a large sample of RGB stars
from medium-resolution spectroscopy in this cluster. With these abundances we
provide a chemical tagging of the split red giant branch found from several
studies in NGC 1851. The secondary, reddest sequence on the RGB is populated
almost exclusively by N-rich stars, confirming our previous suggestion based on
Stromgren magnitudes and colours. These giants are also, on average, enriched
in s-process elements such as Ba, and are likely the results of pollution from
low mass stars that experienced episodes of third dredge-up in the asymptotic
giant branch phase.Comment: Version to match the one in press on Astronomy and Astrophysic
An aluminium tool for multiple stellar generations in the globular clusters 47 Tuc and M 4
We present aluminium abundances for a sample of about 100 red giant stars in
each of the Galactic globular clusters 47 Tuc (NGC 104) and M 4 (NGC 6121). We
have derived homogeneous abundances from intermediate-resolution FLAMES/GIRAFFE
spectra. Aluminium abundances are from the strong doublet Al I at 8772-8773 A
as in previous works done for giants in NGC 6752 and NGC 1851, and nitrogen
abundances are extracted from a large number of features of the CN molecules,
by assuming a suitable carbon abundance. We added previous homogeneous
abundances of O and Na and newly derived abundances of Mg and Si for our
samples of 83 stars in M 4 and 116 stars in 47 Tuc to obtain the full set of
elements from proton-capture reactions produced by different stellar
generations in these clusters. By simultaneously studying the Ne-Na and Mg-Al
cycles of H-burning at high temperature our main aims are to understand the
nature of the polluters at work in the first generation and to ascertain
whether the second generation of cluster stars was formed in one or, rather,
several episodes of star formation. Our data confirm that in M 4 only two
stellar populations are visible. On the other hand, for 47 Tuc a cluster
analysis performed on our full dataset suggests that at least three distinct
groups of stars are present on the giant branch. The abundances of O, Na, Mg
and Al in the intermediate group can be produced within a pollution scenario;
results for N are ambiguous, depending on the C abundance we adopt for the
three groups.Comment: 11 pages, 9 figures, 2 on-line tables: accepted for publication on
Astronomy and Astrophysic
Infrared photometry of Young Massive Clusters in the starburst galaxy NGC 4214
We present the results of an infrared photometric survey performed with
NICS@TNG in the nearby starburst galaxy NGC 4214. We derived accurate
integrated JK magnitudes of 10 young massive clusters and compared them with
the already available Hubble Space Telescope ultraviolet colors. These clusters
are located in the combined ultraviolet-infrared colors planes on well defined
sequences, whose shapes allow a precise determination of their age. By means of
the comparison with suitable stellar evolution models we estimated ages,
metallicities, reddening and masses of these clusters. All the analyzed
clusters appear to be younger than log(t/yr)<8.4, moderately metal-rich and
slightly less massive than present-day Galactic globular clusters. The derived
ages for clusters belonging to the secondary HII star forming complex are
significantly larger than those previously estimated in the literature. We also
discuss the possibility of using the ultraviolet-infrared color-color diagram
to select candidate young massive clusters hosting multiple stellar
populations.Comment: 12 pages, 9 figures, accepted for publication by MNRA
Climate Change in North America: Risks, Impacts, and Adaptation. A Reflection Based on the IPCC Report AR6 – 2022
Cambio climático en América del Norte: riesgos, impactos y adaptación. Una reflexión basada en el Informe AR6 del IPCC – 2022Los efectos e impactos del cambio climático tienen un alcance mundial y una escala sin precedentes y la creciente frecuencia y severidad de los eventos extremos, desde el aumento de las temperaturas, las sequías, las precipitaciones extremas y el aumento del nivel del mar, han aumentado en toda América del Norte. Sin una acción inmediata, la adaptación al cambio climático será más difícil y costosa, particularmente para los grupos sociales y las actividades económicas y los ecosistemas más vulnerables de la zona. En este artículo reflexionamos sobre la evidencia recientemente producida por el Grupo de trabajo 2 del IPCC - el Panel Intergubernamental para el Cambio Climático de la ONU - en relación con la región de América del Norte (Canadá, EE. UU., México). Se emplean para el estudio, los métodos de evaluación de la información utilizada para el reporte sobre Impactos, adaptación y Vulnerabilidad y se analizan riesgos, impactos y medidas de adaptación, buscando resaltar su dimensión económica y financiera para la región de América del Norte. Es necesario en futuro, profundizar sobre los impactos del cambio climático a nivel subnacional en la región de América del Norte y en particular en México.The impacts of climate change are global in scope and unprecedented in scale, and the increasing frequency and severity of extreme events, from rising temperatures, droughts, extreme rainfall, and rising sea levels, have increased throughout North America. Without immediate action, adaptation to climate change will be more difficult and costly, particularly for the most vulnerable social groups and economic activities and ecosystems in the area. In this article we reflect on the evidence recently produced by the Working Group 2 of the IPCC - the UN Intergovernmental Panel on Climate Change - in relation to the North American region (Canada, USA, Mexico). The evaluation methods of the information used for the report on “Impacts, adaptation and Vulnerability” are based on impacts and adaptation assessments revised in the available literature on the topic. We also seek to highlight their economic and financial dimension for the North American region. In the future, it is necessary to delve into the impacts of climate change at the subnational level in the North American region and in Mexico
Reading the book: from "chemical anomalies" to "standard composition" of globular clusters
It is now commonly accepted that globular clusters (GCs) have undergone a
complex formation and that they host at least two stellar generations. This is
a recent paradigm and is founded on both photometric and spectroscopic
evidence. We concentrate on results based on high-resolution spectroscopy and
on how we moved from single to multiple stellar populations concept for GCs. We
underline that the peculiar chemical composition of GC stars is fundamental in
establishing the multiple populations scenario and briefly outline what can be
learned from observations. Finally, recent observational results on large
samples of stars in different evolutionary phases are discussed.Comment: 5 pages, 1 figure. To appear in the proceedings of "Reading the book
of globular clusters with the lens of stellar evolution", in the Memorie
della Societa Astronomica Italian
Na-O Anticorrelation And HB I. The Na-O anticorrelation in NGC 2808
We derived atmospheric parameters and elemental abundances of Fe, O and Na
for about 120 red giant stars in the Galactic globular cluster NGC 2808. Our
results are based on the analysis of medium-high resolution (R=22000-24000)
GIRAFFE spectra acquired with the FLAMES spectrograph at VLT-UT2 as a part of a
project aimed at studying the Na-O anticorrelation as a function of physical
parameters in globular clusters. We present here the anticorrelation of Na and
O abundances in NGC 2808, and we discuss the distribution function of stars
along this relation. Besides a bulk of O-normal stars, with composition typical
of field halo stars, NGC 2808 seems to host two other groups of O-poor and
super O-poor stars. In this regard, NGC 2808 is similar to M 13, the template
cluster for the Na-O anticorrelation. However, at variance with M 13, most
stars in NGC 2808 are O-rich. This might be related to the horizontal branch
morphologies which are very different in these two clusters. The average
metallicity we found for NGC 2808 is [Fe/H]=-1.10 (rms=0.065 dex, from 123
stars). We also found some evidence of a small intrinsic spread in metallicity,
but more definitive conclusions are hampered by the presence of a small
differential reddening.Comment: 12 pages, 6 tables, 7 figures. Accepted for publication on A&
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