270 research outputs found
Radial velocities and metallicities from infrared Ca II triplet spectroscopy of open clusters II. Berkeley 23, King 1, NGC 559, NGC 6603 and NGC 7245
Context: Open clusters are key to studying the formation and evolution of the
Galactic disc. However, there is a deficiency of radial velocity and chemical
abundance determinations for open clusters in the literature. Aims: We intend
to increase the number of determinations of radial velocities and metallicities
from spectroscopy for open clusters. Methods: We acquired medium-resolution
spectra (R~8000) in the infrared region Ca II triplet lines (~8500 AA) for
several stars in five open clusters with the long-slit IDS spectrograph on the
2.5~m Isaac Newton Telescope (Roque de los Muchachos Observatory, Spain).
Radial velocities were obtained by cross-correlation fitting techniques. The
relationships available in the literature between the strength of infrared Ca
II lines and metallicity were also used to derive the metallicity for each
cluster. Results: We obtain = 48.6+/-3.4, -58.4+/-6.8, 26.0+/-4.3 and
-65.3+/-3.2 km s-1 for Berkeley 23, NGC 559, NGC 6603 and NGC 7245,
respectively. We found [Fe/H] =-0.25+/-0.14 and -0.15+/-0.18 for NGC 559 and
NGC 7245, respectively. Berkeley 23 has a low metallicity, [Fe/H]
=-0.42+/-0.13, similar to other open clusters in the outskirts of the Galactic
disc. In contrast, we derived a high metallicity ([Fe/H] =+0.43+/-0.15) for NGC
6603, which places this system among the most metal rich known open clusters.
To our knowledge, this is the first determination of radial velocities and
metallicities from spectroscopy for these clusters, except NGC 6603, for which
radial velocities had been previously determined. We have also analysed ten
stars in the line of sight to King 1. Because of the large dispersion obtained
in both radial velocity and metallicity, we cannot be sure that we have sampled
true cluster members.Comment: 10 pages, 5 figures, accepted for publication in A&A (minor
modifications
NGC 6705 a young -enhanced Open Cluster from OCCASO data
The stellar [/Fe] abundance is sometimes used as a proxy for stellar
age, following standard chemical evolution models for the Galaxy, as seen by
different observational results. In this work we show that the Open Cluster
NGC6705/M11 has a significant -enhancement [/Fe] dex,
despite its young age (300 Myr), challenging the current paradigm. We use
high resolution (R) high signal-to-noise (70) spectra of 8 Red
Clump stars, acquired within the OCCASO survey. We determine very accurate
chemical abundances of several elements, using an equivalent width
methodology (Si, Ca and Ti), and spectral synthesis fits (Mg and O). We obtain
[Si/Fe]=, [Mg/Fe]=, [O/Fe]=,
[Ca/Fe]= and [Ti/Fe]=. Our results place these
cluster within the group of young [/Fe]-enhanced field stars recently
found by several authors in the literature. The ages of our stars have an
uncertainty of around 50 Myr, much more precise than for field stars. By
integrating the cluster's orbit in several non-axisymmetric Galactic
potentials, we establish the M11's most likely birth radius to lie between
6.8-7.5 kpc from the Galactic center, not far from its current position. With
the robust Open Cluster age scale, our results prove that a moderate
[/Fe]-enhancement is no guarantee for a star to be old, and that not
all -enhanced stars can be explained with an evolved blue straggler
scenario. Based on our orbit calculations, we further argue against a Galactic
bar origin of M11.Comment: 10 pages, 6 figures, accepted in A&
A machine learning-based tool for open cluster membership determination in Gaia DR3
Membership studies characterising open clusters with Gaia data, most using
DR2, are so far limited at magnitude G = 18 due to astrometric uncertainties at
the faint end. Our goal is to extend current open cluster membership lists with
faint members and to characterise the low-mass end, which members are important
for many applications, in particular for ground-based spectroscopic surveys. We
use a deep neural network architecture to learn the distribution of highly
reliable open cluster member stars around known clusters. After that, we use
the trained network to estimate new open cluster members based on their
similarities in a high-dimensional space, five-dimensional astrometry plus the
three photometric bands. Due to the improved astrometric precisions of Gaia DR3
with respect to DR2, we are able to homogeneously detect new faint member stars
(G > 18) for the known open cluster population. Our methodology can provide
extended membership lists for open clusters down to the limiting magnitude of
Gaia, which will enable further studies to characterise the open cluster
population, e.g. estimation of their masses, or their dynamics. These extended
membership lists are also ideal target lists for forthcoming ground-based
spectroscopic surveys.Comment: 10 pages, 6 figures. Submitted to Astronomy & Astrophysic
The (im)possibility of strong chemical tagging
Interstellar matter and star formatio
The multiplicity fraction in 202 open clusters from Gaia
In this study, we estimate the fraction of binaries with high mass ratios for
202 open clusters in the extended solar neighbourhood (closer than 1.5 kpc from
the Sun). This is one of the largest homogeneous catalogues of multiplicity
fractions in open clusters to date, including the unresolved and total
(close-binary) multiplicity fractions of main-sequence systems with mass ratio
larger than . The unresolved multiplicity fractions are
estimated applying a flexible mixture model to the observed Gaia
colour-magnitude diagrams of the open clusters. Then we use custom Gaia
simulations to account for the resolved systems and derive the total
multiplicity fractions. The studied open clusters have ages between 6.6 Myr and
3.0 Gyr and total high-mass-ratio multiplicity fractions between 6% and 80%,
with a median of 18%. The multiplicity fractions increase with the mass of the
primary star, as expected. The average multiplicity fraction per cluster
displays an overall decreasing trend with the open cluster age up to ages about
100 Myr, above which the trend increases. Our simulations show that most of
this trend is caused by complex selection effects (introduced by the mass
dependence of the multiplicity fraction and the magnitude limit of our sample).
Furthermore, the multiplicity fraction is not significantly correlated with the
clusters' position in the Galaxy. The spread in multiplicity fraction decreases
significantly with the number of cluster members (used as a proxy for cluster
mass). We also find that the multiplicity fraction decreases with metallicity,
in line with recent studies using field stars.Comment: 17 pages, 13 figures, resubmitted to A&A following referee comment
Age determination for 269 DR2 Open Clusters
. Gaia Second Data Release provides precise astrometry and
photometry for more than 1.3 billion sources. This catalog opens a new era
concerning the characterization of open clusters and test stellar models,
paving the way for a better understanding of the disc properties. . The
aim of the paper is to improve the knowledge of cluster parameters, using only
the unprecedented quality of the Gaia photometry and astrometry. . We
make use of the membership determination based on the precise Gaia astrometry
and photometry. We apply anautomated Bayesian tool, BASE-9, to fit stellar
isochrones on the observed G, GBP, GRP magnitudes of the high probability
member stars. . We derive parameters such as age, distance modulus and
extinction for a sample of 269 open clusters, selecting only low reddening
objects and discarding very young clusters, for which techniques other than
isochrone-fitting are more suitable for estimating ages.Comment: 14 pages, 11 figures. Submitte
One Star to Tag Them All (OSTTA): I. Radial velocities and chemical abundances for 20 poorly studied open clusters
Context: Open clusters are ideal laboratories to investigate a variety of
astrophysical topics, from the properties of the Galactic disc to stellar
evolution models. For this purpose, we need to know their chemical composition
in detail. Unfortunately, the number of systems with chemical abundances
determined from high resolution spectroscopy remains small. Aims: Our aim is to
increase the number of open clusters with radial velocities and chemical
abundances determined from high resolution spectroscopy by sampling a few stars
in clusters not studied previously. Methods: We obtained high resolution
spectra with the FIES spectrograph at NOT for 41 stars belonging to 20 open
clusters. These stars have high astrometric membership probabilities,
determined from the Gaia second data release. Results: We derived radial
velocities for all the observed stars, which were used to confirm their
membership to the corresponding clusters. For Gulliver\,37 we cannot be sure
the observed star is a real member. We derived atmospheric parameters for the
32 stars considered real cluster members. We discarded five stars because they
have very low gravity or atmospheric parameters were not properly constrained
due to low signal-to-noise ratio spectra. Therefore, detailed chemical
abundances were determined for 28 stars belonging to 17 clusters. For most of
them, this is the first chemical analysis available in the literature. Finally,
we compared the clusters in our sample to a large population of well studied
clusters. The studied systems follow the trends, both chemical and kinematical,
described by the majority of open clusters. Worth noticing that the three most
metal-poor studied clusters (NGC\,1027, NGC\,1750 and Trumpler 2) are enhanced
in Si but not in the other alpha-elements studied (Mg, Ca and Ti).Comment: 19 pages Accepted for publication on A&
Unraveling UBC 274: a morphological, kinematical and chemical analysis of a disrupting open cluster
We do a morphological, kinematic and chemical analysis of the disrupting
cluster UBC 274 (2.5 Gyr, pc) to study its global properties. We use
HDBSCAN to obtain a new membership list up to 50 pc from its centre and up to
magnitude using Gaia EDR3 data. We use high resolution and high
signal-to-noise spectra to obtain atmospheric parameters of 6 giants and
subgiants, and individual abundances of 18 chemical species. The cluster has a
highly eccentric (0.93) component, tilted 10 deg with respect to the
plane of the Galaxy, which is morphologically compatible with the result of a
test-particle simulation of a disrupting cluster. Our abundance analysis shows
that the cluster has a subsolar metallicity of [Fe/H]. Its
chemical pattern is compatible with that of Ruprecht 147, of similar age but
located closer to the Sun, with the remarkable exception of neutron-capture
elements, which present an overabundance of . The
cluster's elongated morphology is associated with the internal part of its
tidal tail, following the expected dynamical process of disruption. We find a
significant sign of mass segregation where the most massive stars appear 1.5
times more concentrated than other stars. The cluster's overabundance of
neutron-capture elements can be related to the metallicity dependence of the
neutron-capture yields due to the secondary nature of these elements, predicted
by some models. UBC 274 presents a high chemical homogeneity at the level of
dex in the sampled region of its tidal tails.Comment: Accepted by A&
The Open Cluster Chemical Abundances from Spanish Observatories survey (OCCASO)
We present the motivation, design and current status of the Open Cluster
Chemical Abundances from Spanish Observatories survey (OCCASO). Using the high
resolution spectroscopic facilities available at Spanish observatories, OCCASO
will derive chemical abundances in a sample of 20 to 25 open clusters older
than 0.5 Gyr. This sample will be used to study in detail the formation and
evolution of the Galactic disc using open clusters as tracers.Comment: 6 pages, 1 figure, Highlights of Spanish Astrophysics VIII,
Proceedings of the XI Scientific Meeting of the Spanish Astronomical Society
held on September 8 - 12, 2014, in Teruel, Spain. A. J. Cenarro, F. Figueras,
C. Hern\'andez-Monteagudo, J. Trujillo, and L. Valdivielso (eds.
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