scholarly journals A phylogenetic approach to chemical tagging

2018 ◽  
Vol 618 ◽  
pp. A65 ◽  
Author(s):  
Sergi Blanco-Cuaresma ◽  
Didier Fraix-Burnet
Keyword(s):  
Chemical Elements ◽  
Phylogenetic Analyses ◽  
Open Cluster ◽  
Open Clusters ◽  
Evolutionary Stage ◽  
The Sun ◽  
Chemical Abundances ◽  
Chemical Tagging ◽  
The Galaxy ◽  
History Of

Context. The chemical tagging technique is a promising approach to reconstructing the history of the Galaxy by only using stellar chemical abundances. Multiple studies have undertaken this analysis and they have raised several challenges. Aims. Using a sample of open cluster stars, we wish to address two issues: minimize chemical abundance differences whose origin is linked to the evolutionary stage of the stars and not their original composition and evaluate a phylogenetic approach to group stars based on their chemical composition. Methods. We derived differential chemical abundances for 207 stars, belonging to 34 open clusters, using the Sun as reference star (classical approach) and a dwarf plus a giant star from the open cluster M 67 as reference (new approach). These abundances were then used to perform two phylogenetic analyses: cladistics (maximum parsimony) and neighbor joining, together with a partitioning unsupervised classification analysis with k-means. The resulting groupings were finally confronted to the true open cluster memberships of the stars. Results. We successfully reconstruct most of the original open clusters when carefully selecting a subset of the abundances derived differentially with respect to M 67. We find a set of eight chemical elements that yield the best result and discuss the possible reasons for these elements to be good tracers of the history of the Galaxy. Conclusions. Our study shows that unraveling the history of the Galaxy by only using stellar chemical abundances is greatly improved provided that i) we perform a differential spectroscopic analysis with respect to an open cluster instead of the Sun, ii) select the chemical elements that are good tracers of the history of the Galaxy, and iii) use tools that are adapted to detect evolutionary tracks such as phylogenetic approaches.

scholarly journals Chemical abundances of open clusters from high-resolution infrared spectra – II. NGC 752

2019 ◽  
Vol 491 (1) ◽  
pp. 544-559
Author(s):  
G Böcek Topcu ◽  
M Afşar ◽  
C Sneden ◽  
C A Pilachowski ◽  
P A Denissenkov ◽  
...  
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Open Cluster ◽  
Light Element ◽  
Open Clusters ◽  
Evolutionary Stage ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Element Abundances ◽  
Solar Metallicity

ABSTRACT We present a detailed near-infrared chemical abundance analysis of 10 red giant members of the Galactic open cluster NGC 752. High-resolution (R ≃ 45000) near-infrared spectral data were gathered with the Immersion Grating Infrared Spectrograph, providing simultaneous coverage of the complete H and K bands. We derived the abundances of H-burning (C, N, O), α (Mg, Si, S, Ca), light odd-Z (Na, Al, P, K), Fe-group (Sc, Ti, Cr, Fe, Co, Ni), and neutron-capture (Ce, Nd, Yb) elements. We report the abundances of S, P, K, Ce, and Yb in NGC 752 for the first time. Our analysis yields solar-metallicity and solar abundance ratios for almost all of the elements heavier than the CNO group in NGC 752. O and N abundances were measured from a number of OH and CN features in the H band, and C abundances were determined mainly from CO molecular lines in the K band. High-excitation $\rm{C\,\small {I}}$ lines present in both near-infrared and optical spectra were also included in the C abundance determinations. Carbon isotopic ratios were derived from the R-branch band heads of first overtone (2−0) and (3−1) 12CO and (2−0) 13CO lines near 23 440 Å and (3−1) 13CO lines at about 23 730 Å. The CNO abundances and 12C/13C ratios are all consistent with our giants having completed ‘first dredge-up’ envelope mixing of CN-cyle products. We independently assessed NGC 752 stellar membership from Gaia astrometry, leading to a new colour–magnitude diagram for this cluster. Applications of Victoria isochrones and MESA models to these data yield an updated NGC 752 cluster age (1.52 Gyr) and evolutionary stage indications for the programme stars. The photometric evidence and spectroscopic light element abundances all suggest that the most, perhaps all of the programme stars are members of the helium-burning red clump in this cluster.

scholarly journals Reanalysis of nearby open clusters using Gaia DR1/TGAS and HSOY

2018 ◽  
Vol 615 ◽  
pp. A12 ◽  
Author(s):  
Steffi X. Yen ◽  
Sabine Reffert ◽  
Elena Schilbach ◽  
Siegfried Röser ◽  
Nina V. Kharchenko ◽  
...  
Keyword(s):  
Milky Way ◽  
Open Cluster ◽  
Star Clusters ◽  
Open Clusters ◽  
Parameter Estimates ◽  
Cluster Membership ◽  
Fitting Procedure ◽  
Cluster Data ◽  
The Galaxy ◽  
Automatic Tool

Context. Open clusters have long been used to gain insights into the structure, composition, and evolution of the Galaxy. With the large amount of stellar data available for many clusters in the Gaia era, new techniques must be developed for analyzing open clusters, as visual inspection of cluster color-magnitude diagrams is no longer feasible. An automatic tool will be required to analyze large samples of open clusters. Aims. We seek to develop an automatic isochrone-fitting procedure to consistently determine cluster membership and the fundamental cluster parameters. Methods. Our cluster characterization pipeline first determined cluster membership with precise astrometry, primarily from TGAS and HSOY. With initial cluster members established, isochrones were fitted, using a χ2 minimization, to the cluster photometry in order to determine cluster mean distances, ages, and reddening. Cluster membership was also refined based on the stellar photometry. We used multiband photometry, which includes ASCC-2.5 BV, 2MASS JHKs, and Gaia G band. Results. We present parameter estimates for all 24 clusters closer than 333 pc as determined by the Catalogue of Open Cluster Data and the Milky Way Star Clusters catalog. We find that our parameters are consistent to those in the Milky Way Star Clusters catalog. Conclusions. We demonstrate that it is feasible to develop an automated pipeline that determines cluster parameters and membership reliably. After additional modifications, our pipeline will be able to use Gaia DR2 as input, leading to better cluster memberships and more accurate cluster parameters for a much larger number of clusters.

scholarly journals A Gaia DR2 view of the open cluster population in the Milky Way

2018 ◽  
Vol 618 ◽  
pp. A93 ◽  
Author(s):  
T. Cantat-Gaudin ◽  
C. Jordi ◽  
A. Vallenari ◽  
A. Bragaglia ◽  
L. Balaguer-Núñez ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Milky Way ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Open Cluster ◽  
Open Clusters ◽  
Number Of Clusters ◽  
History Of ◽  
Gaia Dr2

Context. Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise astrometry at the submilliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. Aims. In this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. Methods. We compiled a list of thousands of known or putative clusters from the literature. We then applied an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. Results. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of Gaia DR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study.

scholarly journals Hidden infrared star clusters in our Galaxy: follow-up observations

2009 ◽  
Vol 5 (S266) ◽  
pp. 366-366
Author(s):  
Jura Borissova ◽  
Radostin Kurtev ◽  
Margaret M. Hanson ◽  
Leonid Georgiev ◽  
Valentin Ivanov ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Star Cluster ◽  
Open Clusters ◽  
Star Formation History ◽  
Stellar Disk ◽  
Physical Parameters ◽  
Formation History ◽  
The Galaxy ◽  
History Of ◽  
Infrared Star

AbstractWe are reporting some recent results from our long-term program aimed at characterizing the obscured present-day star cluster population in the Galaxy. Our goal is to expand the current census of the Milky Way's inner stellar disk to guide models seeking to understand the structure and recent star-formation history of our Galaxy. The immediate goal is to derive accurate cluster physical parameters using precise infrared photometry and spectroscopy. So far, we observed approximately 60 star cluster candidates selected from different infrared catalogs. Their nature, reddening, distance, age and mass are analyzed. Two of them, Mercer 3 and Mercer 5, are new obscured Milky Way globular clusters. Among the newly identified open clusters, the objects [DBS2003] 179, Mercer 23, Mercer 30, Mercer 70, and [DBS2003] 106 are particularly interesting because they contain massive young OB and Wolf–Rayet stars with strong emission lines.

scholarly journals OCCASO – III. Iron peak and α elements of 18 open clusters. Comparison with chemical evolution models and field stars

2019 ◽  
Vol 490 (2) ◽  
pp. 1821-1842 ◽  
Author(s):  
L Casamiquela ◽  
S Blanco-Cuaresma ◽  
R Carrera ◽  
L Balaguer-Núñez ◽  
C Jordi ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Open Cluster ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Chemical Abundances ◽  
Homogeneous Sample ◽  
Giant Stars ◽  
Stellar Nucleosynthesis ◽  
Solar Abundances ◽  
Red Giant

ABSTRACT The study of open-cluster chemical abundances provides insights on stellar nucleosynthesis processes and on Galactic chemo-dynamical evolution. In this paper we present an extended abundance analysis of 10 species (Fe, Ni, Cr, V, Sc, Si, Ca, Ti, Mg, O) for red giant stars in 18 OCCASO clusters. This represents a homogeneous sample regarding the instrument features, method, line list and solar abundances from confirmed member stars. We perform an extensive comparison with previous results in the literature, and in particular with the Gaia FGK Benchmark stars Arcturus and $\mu$-Leo. We investigate the dependence of [X/Fe] with metallicity, Galactocentric radius (6.5 kpc < RGC < 11 kpc), age (0.3 Gyr < Age < 10 Gyr), and height above the plane (|z| < 1000 pc). We discuss the observational results in the chemo-dynamical framework, and the radial migration impact when comparing with chemical evolution models. We also use APOGEE DR14 data to investigate the differences between the abundance trends in RGC and |z| obtained for clusters and for field stars.

scholarly journals The Hertzsprung-Russell Diagram of Metal-Poor Disk Stars

1978 ◽  
Vol 80 ◽  
pp. 273-276
Author(s):  
Sidney van den Bergh
Keyword(s):  
Velocity Field ◽  
Globular Cluster ◽  
High Velocity ◽  
Population Model ◽  
Open Cluster ◽  
Ultraviolet Excess ◽  
Red Giants ◽  
The Sun ◽  
The Galaxy ◽  
Red Giant

A quarter of a century ago Keenan and Keller (1953) showed that the majority of high-velocity stars near the Sun outline a Hertzsprung-Russell diagram similar to that of old Population I. This result, which did not appear to fit into Baade's (1944) two-population model of the Galaxy was ignored (except by Roman 1965) for the next two decades. Striking confirmation of the results of Keenan and Keller was, however, obtained by Hartwick and Hesser (1972). Their work appears to show that high-velocity field stars with an ultraviolet excess (which measures Fe/H) of δ(U-B) ≃ +0m.11 lie on a red giant branch that is more than a magnitude fainter than the giant branch of the strong-lined globular cluster 47 Tuc for which δ(U-B) ≃ +0m.10. Furthermore Demarque and McClure (1977) show that the red giants in the old metal poor [δ(U-B) ≃ +0m.11] open cluster NGC 2420 are significantly fainter than are those in 47 Tuc. Calculations by these authors show that the observed differences between the giants in 47 Tuc and in NGC 2420 can be explained if either (1) 47 Tuc is richer in helium than NGC 2420 by ΔY ≃ 0.1 or (2) if 47 Tuc has a ten times lower value of Z(CNO) than does NGC 2420.

scholarly journals Small-scale star formation as revealed by VVVX galactic cluster candidates

2020 ◽  
Vol 499 (3) ◽  
pp. 3522-3533
Author(s):  
J Borissova ◽  
R Kurtev ◽  
N Amarinho ◽  
J Alonso-García ◽  
S Ramírez Alegría ◽  
...  
Keyword(s):  
Star Formation ◽  
Open Cluster ◽  
Open Clusters ◽  
Small Scale ◽  
Filamentary Structure ◽  
Public Survey ◽  
The Galaxy ◽  
Low Mass ◽  
Young Clusters ◽  
Dust Complex

ABSTRACT We report a search and analysis of obscured cluster candidates in the ‘VISTA Variables in the Via Lactea eXtended (VVVX)’ ESO Public Survey area encompassing the region between 229${_{.}^{\circ}}$4 < l < 295${_{.}^{\circ}}$2 and −4${_{.}^{\circ}}$3 < b < 4${_{.}^{\circ}}$4 of the southern Galactic disc. We discover and propose 88 new clusters. We improve the completeness of the embedded cluster population in this region, adding small size (linear diameters of 0.2–1.4 pc) and relatively far objects (heliocentric distance between 2 and 4 kpc) to existing catalogues. Nine candidates are proposed to be older open cluster candidates. Three of them (VVVX CL 204,  CL 207, CL  208) have sufficient numbers of well-resolved stellar members to allow us to determine some basic cluster parameters. We confirm their nature as older, low-mass open clusters. Photometric analysis of 15 known clusters shows that they have ages above 20 Myr, and masses below 2000 M⊙: in general, their proper motions follow the motion of the disc. We outline some groups of clusters, most probably formed within the same dust complex. Broadly, our candidates follow the network of filamentary structure in the remaining dust. Thus, in this part of the southern disc of the Galaxy, we have found recent star formation, producing small size and young clusters, in addition to the well-known, massive young clusters, including NGC 3603, Westerlund 2, and the Carina Nebula Complex.

scholarly journals Open Cluster System: Kinematics, Orbits

1995 ◽  
Vol 164 ◽  
pp. 374-375 ◽  
Author(s):  
E. M. Nezhinskij ◽  
L. P. Ossipkov ◽  
S.A. Kutuzov
Keyword(s):  
Open Cluster ◽  
Cluster System ◽  
Open Clusters ◽  
Distance Scale ◽  
The Sun ◽  
Cylindrical Coordinates ◽  
Galactocentric Distance

This study is based on the catalogue of 69 open clusters by Barkhatova et al. (1987) and cluster distances taken from Hagen (1970). Most of the dimensionless characteristics discussed here are insensitive to the distance scale. Galactocentric cylindrical coordinates of clusters and the corresponding velocities have been calculated with the accepted galactocentric distance of the Sun R⊙ = 8.2 kpc and the galactocentric velocity of the Sun sR = −9 km/s, sθ = 228 km/s, sz = 7 km/s.

scholarly journals NGC 6705 a young α-enhanced open cluster from OCCASO data

2018 ◽  
Vol 610 ◽  
pp. A66 ◽  
Author(s):  
L. Casamiquela ◽  
R. Carrera ◽  
L. Balaguer-Núñez ◽  
C. Jordi ◽  
C. Chiappini ◽  
...  
Keyword(s):  
Spectral Synthesis ◽  
Open Cluster ◽  
High Signal ◽  
Galactic Centre ◽  
Chemical Abundances ◽  
Blue Straggler ◽  
The Galaxy ◽  
Galactic Potentials ◽  
Red Clump ◽  
Current Paradigm

Context. The stellar [α/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. Aim. In this work, we aim to show that the open cluster NGC 6705/M 11 has a significant α-enhancement [α/Fe] > 0.1 dex, despite its young age (~300 Myr), challenging the current paradigm. Methods. We used high resolution (R > 65 000) high signal-to-noise (~70) spectra of eight red clump stars, acquired within the OCCASO survey. We determined very accurate chemical abundances of several α elements, using an equivalent width methodology (Si, Ca and Ti), and spectral synthesis fits (Mg and O). Results. We obtain [Si/Fe] = 0.13 ± 0.05, [Mg/Fe] = 0.14 ± 0.07, [O/Fe] = 0.17 ± 0.07, [Ca/Fe] = 0.06 ± 0.05, and [Ti/Fe] = 0.03 ± 0.03. Our results place these clusters within the group of young [α/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 M 11’s most likely birth radius as lying between 6.8–7.5 kpc from the Galactic centre, not far from its current position. Conclusions. With the robust open cluster age scale, our results prove that a moderate [α/Fe]-enhancement is no guarantee for a star to be old, and that not all α-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 M 11.

scholarly journals The AMBRE project: searching for the closest solar siblings

2018 ◽  
Vol 619 ◽  
pp. A130 ◽  
Author(s):  
V. Adibekyan ◽  
P. de Laverny ◽  
A. Recio-Blanco ◽  
S. G. Sousa ◽  
E. Delgado-Mena ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Chemical Characterization ◽  
Isotopic Ratios ◽  
The Sun ◽  
Chemical Abundances ◽  
Carbon Isotopic ◽  
Yield Information ◽  
Stellar Ages ◽  
The Galaxy ◽  
Astrometric Data

Context. Finding solar siblings, that is, stars that formed in the same cluster as the Sun, will yield information about the conditions at the Sun’s birthplace. Finding possible solar siblings is difficult since they are spread widely throughout the Galaxy. Aims. We search for solar sibling candidates in AMBRE, the very large spectra database of solar vicinity stars. Methods. Since the ages and chemical abundances of solar siblings are very similar to those of the Sun, we carried out a chemistry- and age-based search for solar sibling candidates. We used high-resolution spectra to derive precise stellar parameters and chemical abundances of the stars. We used these spectroscopic parameters together with Gaia DR2 astrometric data to derive stellar isochronal ages. Gaia data were also used to study the kinematics of the sibling candidates. Results. From about 17 000 stars that are characterized within the AMBRE project, we first selected 55 stars whose metallicities are closest to the solar value (−0.1 ≤ [Fe/H] ≤ 0.1 dex). For these stars we derived precise chemical abundances of several iron-peak, α- and neutron-capture elements, based on which we selected 12 solar sibling candidates with average abundances and metallicities between −0.03 and 0.03 dex. Our further selection left us with four candidates with stellar ages that are compatible with the solar age within observational uncertainties. For the two of the hottest candidates, we derived the carbon isotopic ratios, which are compatible with the solar value. HD 186302 is the most precisely characterized and probably the most probable candidate of our four best candidates. Conclusions. Very precise chemical characterization and age estimation is necessary to identify solar siblings. We propose that in addition to typical chemical tagging, the study of isotopic ratios can give further important information about the relation of sibling candidates with the Sun. Ideally, asteroseismic age determinations of the candidates could solve the problem of imprecise isochronal ages.

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