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.

High-resolution spectroscopy of red giants and ‘yellow stragglers’ in the southern open cluster NGC 2539

2020 ◽  
Vol 494 (1) ◽  
pp. 1470-1489
Author(s):  
Cintia F Martinez ◽  
N Holanda ◽  
C B Pereira ◽  
N A Drake
Keyword(s):  
High Resolution ◽  
Open Cluster ◽  
Open Clusters ◽  
Solar Neighborhood ◽  
Spectroscopic Binaries ◽  
High Resolution Spectroscopy ◽  
Red Giants ◽  
Light Elements ◽  
Abundance Pattern ◽  
Solar Metallicity

ABSTRACT We present a detailed high-resolution spectroscopic analysis of 12 red giant stars, in single and binaries or multiples systems, classified as members of the intermediate-age (631 Myr) open cluster NGC 2539. We used FEROS echelle spectra and the standard LTE analysis to derive the atmospheric parameters for the stars and the abundance ratios of light elements (Li, C, N), light odd-Z elements (Na, Al), α-elements (Mg, Si, Ca, Ti), Fe-group elements (Cr, Fe, Ni), and n-capture elements (Y, Zr, Ce, Nd, Eu). Our results show that the sample star of NGC 2539 has low projected rotational velocities and an almost solar metallicity, with a mean of [Fe/H] = −0.03 ± 0.07 dex. The abundance pattern displays for the analyzed stars are, in general, similar to those presented by solar neighborhood stars, including giant members of others open clusters. In particular, light elements and Na abundance pattern shows anomalies resulting from the appearance of enriched material on the stellar surface, produced by mechanisms like the first dredge-up and/or thermohaline and rotation-induced mixing. We also identified two of the spectroscopic binaries of our sample as ‘yellow stragglers’ and we determined the nature of their companions.

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 Detailed chemical abundance analysis of the thick disk star cluster Gaia 1

2017 ◽  
Vol 609 ◽  
pp. A13 ◽  
Author(s):  
Andreas Koch ◽  
Terese T. Hansen ◽  
Andrea Kunder
Keyword(s):  
Globular Clusters ◽  
Open Cluster ◽  
Light Element ◽  
Thick Disk ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Low Mass ◽  
Red Giant ◽  
Significant Spread ◽  
Detailed Chemical

Star clusters, particularly those objects in the disk-bulge-halo interface are as yet poorly charted, despite the fact that they carry important information about the formation and the structure of the Milky Way. Here, we present a detailed chemical abundance study of the recently discovered object Gaia 1. Photometry has previously suggested it as an intermediate-age, moderately metal-rich system, although the exact values for its age and metallicity remained ambiguous in the literature. We measured detailed chemical abundances of 14 elements in four red giant members, from high-resolution (R = 25 000) spectra that firmly establish Gaia 1 as an object associated with the thick disk. The resulting mean Fe abundance is −0.62 ± 0.03(stat.)± 0.10(sys.) dex, which is more metal-poor than indicated by previous spectroscopy from the literature, but it is fully in line with values from isochrone fitting. We find that Gaia 1 is moderately enhanced in the α-elements, which allowed us to consolidate its membership with the thick disk via chemical tagging. The cluster’s Fe-peak and neutron-capture elements are similar to those found across the metal-rich disks, where the latter indicate some level of s-process activity. No significant spread in iron nor in other heavy elements was detected, whereas we find evidence of light-element variations in Na, Mg, and Al. Nonetheless, the traditional Na-O and Mg-Al (anti-)correlations, typically seen in old globular clusters, are not seen in our data. This confirms that Gaia 1 is rather a massive and luminous open cluster than a low-mass globular cluster. Finally, orbital computations of the target stars bolster our chemical findings of Gaia 1’s present-day membership with the thick disk, even though it remains unclear which mechanisms put it in that place.

scholarly journals Open clusters in APOGEE and GALAH

2019 ◽  
Vol 623 ◽  
pp. A80 ◽  
Author(s):  
R. Carrera ◽  
A. Bragaglia ◽  
T. Cantat-Gaudin ◽  
A. Vallenari ◽  
L. Balaguer-Núñez ◽  
...  
Keyword(s):  
High Resolution ◽  
Stellar Evolution ◽  
Open Cluster ◽  
Open Clusters ◽  
Radial Velocities ◽  
High Resolution Spectroscopy ◽  
Galactic Disc ◽  
Chemical Abundances ◽  
Cross Matching ◽  
Detailed Chemical

Context. Open clusters are ideal laboratories to investigate a variety of astrophysical topics, from the properties of the Galactic disc to stellar-evolution models. Knowing their metallicity and possibly detailed chemical abundances is therefore important. However, 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 using publicly available catalogues of surveys in combination with Gaia data. Methods. Open cluster stars have been identified in the APOGEE and GALAH spectroscopic surveys by cross-matching their latest data releases with stars for which high-probability astrometric membership has been derived in many clusters on the basis of the Gaia second data release. Results. Radial velocities were determined for 131 and 14 clusters from APOGEE and GALAH data, respectively. This is the first radial-velocity determination from high-resolution spectra for 16 systems. Iron abundances were obtained for 90 and 14 systems from APOGEE and GALAH samples, respectively. To our knowledge 66 of these clusters (57 in APOGEE and 9 in GALAH) do not have previous determinations in the literature. For 90 and 7 clusters in the APOGEE and GALAH samples, respectively, we also determined average abundances for Na, Mg, Al, Si, Ca, Cr, Mn, and Ni.

scholarly journals Formation rate of LB-1-like systems through dynamical interactions

2020 ◽  
Vol 72 (3) ◽  
Author(s):  
Ataru Tanikawa ◽  
Tomoya Kinugawa ◽  
Jun Kumamoto ◽  
Michiko S Fujii
Keyword(s):  
Open Cluster ◽  
Formation Rate ◽  
Open Clusters ◽  
Type Star ◽  
Dynamical Mechanism ◽  
Milky Way Galaxy ◽  
Triple Systems ◽  
Stellar Collisions ◽  
Solar Metallicity ◽  
Helium Star

Abstract We estimate formation rates of LB-1-like systems through dynamical interactions in the framework of the theory of stellar evolution before the discovery of the LB-1 system. The LB-1 system contains a ∼70 ${M_{\odot}}$ black hole (BH), a so-called pair instability (PI) gap BH, and a B-type star with solar metallicity, and has nearly zero eccentricity. The most efficient formation mechanism is as follows. In an open cluster, a naked helium star (with ∼20 ${M_{\odot}}$) collides with a heavy main sequence star (with ∼50 ${M_{\odot}}$) which has a B-type companion. The collision results in a binary consisting of the collision product and the B-type star with a high eccentricity. The binary can be circularized through the dynamical tide with radiative damping of the collision product envelope. Finally, the collision product collapses to a PI-gap BH, avoiding pulsational pair instability and pair instability supernovae because its He core is as massive as the pre-colliding naked He star. We find that the number of LB-1-like systems in the Milky Way galaxy is ∼0.01(ρoc/104 ${M_{\odot}}$ pc−3), where ρoc is the initial mass densities of open clusters. If we take into account LB-1-like systems with O-type companion stars, the number increases to ∼0.03(ρoc/104 ${M_{\odot}}$ pc−3). This mechanism can form LB-1-like systems at least ten times more efficiently than the other mechanisms: captures of B-type stars by PI-gap BHs, stellar collisions between other types of stars, and stellar mergers in hierarchical triple systems. We conclude that no dynamical mechanism can explain the presence of the LB-1 system.

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 Cepheid distances from the Baade–Wesselink method

2012 ◽  
Vol 8 (S289) ◽  
pp. 138-144 ◽  
Author(s):  
Wolfgang Gieren ◽  
Jesper Storm ◽  
Nicolas Nardetto ◽  
Alexandre Gallenne ◽  
Grzegorz Pietrzyński ◽  
...  
Keyword(s):  
Excellent Agreement ◽  
Surface Brightness ◽  
Recent Progress ◽  
Main Sequence ◽  
Near Infrared ◽  
Open Cluster ◽  
Open Clusters ◽  
Distance Scale ◽  
Systematic Uncertainties ◽  
Classical Cepheids

AbstractRecent progress on Baade–Wesselink (BW)-type techniques to determine the distances to classical Cepheids is reviewed. Particular emphasis is placed on the near-infrared surface-brightness (IRSB) version of the BW method. Its most recent calibration is described and shown to be capable of yielding individual Cepheid distances accurate to 6%, including systematic uncertainties. Cepheid distances from the IRSB method are compared to those determined from open cluster zero-age main-sequence fitting for Cepheids located in Galactic open clusters, yielding excellent agreement between the IRSB and cluster Cepheid distance scales. Results for the Cepheid period–luminosity (PL) relation in near-infrared and optical bands based on IRSB distances and the question of the universality of the Cepheid PL relation are discussed. Results from other implementations of the BW method are compared to the IRSB distance scale and possible reasons for discrepancies are identified.

scholarly journals The Gaia-ESO Survey: The inner disc, intermediate-age open cluster Pismis 18

2019 ◽  
Vol 626 ◽  
pp. A90 ◽  
Author(s):  
D. Hatzidimitriou ◽  
E. V. Held ◽  
E. Tognelli ◽  
A. Bragaglia ◽  
L. Magrini ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Proper Motion ◽  
Open Cluster ◽  
Open Clusters ◽  
High Resolution Spectroscopy ◽  
Distance Modulus ◽  
Chemical Abundance ◽  
High Confidence ◽  
Galactocentric Distance ◽  
Red Clump

Context. Pismis 18 is a moderately populated, intermediate-age open cluster located within the solar circle at a Galactocentric distance of about seven kpc. Few open clusters have been studied in detail in the inner disc region before the Gaia-ESO Survey. Aims. New data from the Gaia-ESO Survey allowed us to conduct an extended radial velocity membership study as well as spectroscopic metallicity and detailed chemical abundance measurements for this cluster. Methods. Gaia-ESO Survey data for 142 potential members, lying on the upper main sequence and on the red clump, yielded radial velocity measurements, which, together with proper motion measurements from the Gaia Second Data Release (Gaia DR2), were used to determine the systemic velocity of the cluster and membership of individual stars. Photometry from Gaia DR2 was used to re-determine cluster parameters based on high confidence member stars only. Cluster abundance measurements of six radial-velocity member stars with UVES high-resolution spectroscopy are presented for 23 elements. Results. The average radial velocity of 26 high confidence members is −27.5 ± 2.5 (std) km s−1 with an average proper motion of pmra = −5.65 ± 0.08 (std) mas yr−1 and pmdec = −2.29 ± 0.11 (std) mas yr−1. According to the new estimates, based on high confidence members, Pismis 18 has an age of τ = 700+40−50 Myr, interstellar reddening of E(B − V) = 0.562+0.012−0.026 mag and a de-reddened distance modulus of DM0 = 11.96+0.10−0.24 mag. The median metallicity of the cluster (using the six UVES stars) is [Fe/H] = +0.23 ± 0.05 dex, with [α/Fe] = 0.07 ± 0.13 and a slight enhancement of s- and r-neutron-capture elements. Conclusions. With the present work, we fully characterized the open cluster Pismis 18. We confirmed its present location in the inner disc. We estimated a younger age than the previous literature values and we gave, for the first time, its metallicity and its detailed abundances. Its [α/Fe] and [s-process/Fe], both slightly super-solar, are in agreement with other inner-disc open clusters observed by the Gaia-ESO survey.

scholarly journals The chemical composition of the oldest nearby open cluster Ruprecht 147

2018 ◽  
Vol 619 ◽  
pp. A176 ◽  
Author(s):  
Angela Bragaglia ◽  
Xiaoting Fu ◽  
Alessio Mucciarelli ◽  
Gloria Andreuzzi ◽  
Paolo Donati
Keyword(s):  
Chemical Composition ◽  
High Resolution ◽  
Motion Parallax ◽  
Open Cluster ◽  
Red Giants ◽  
Evolutionary Models ◽  
Chemical Abundance ◽  
Cluster Distance ◽  
Very High ◽  
Detailed Chemical

Context. Ruprecht 147 (NGC 6774) is the closest old open cluster, with a distance of less than 300 pc and an age of about 2.5 Gyr. It is therefore well suited for testing stellar evolution models and for obtaining precise and detailed chemical abundance information. Aims. We combined photometric and astrometric information coming from literature and the Gaia mission with very high-resolution optical spectra of stars in different evolutionary stages to derive the cluster distance, age, and detailed chemical composition. Methods. We obtained spectra of six red giants using HARPS-N at the Telescopio Nazionale Galileo (TNG). We also used European Southern Observatory (ESO) archive spectra of 22 main sequence (MS) stars, observed with HARPS at the 3.6 m telescope. The very high resolution (115 000) and the large wavelength coverage (about 380–680 nm) of the twin instruments permitted us to derive atmospheric parameters, metallicity, and detailed chemical abundances of 23 species from all nucleosynthetic channels. We employed both equivalent widths and spectrum synthesis. We also re-derived the cluster distance and age using Gaia parallaxes, proper motions, and photometry in conjunction with the PARSEC stellar evolutionary models. Results. We fully analysed those stars with radial velocity and proper motion/parallax in agreement with the cluster mean values. We also discarded one binary not previously recognised, and six stars near the MS turn-off because of their high rotation velocity. Our final sample consists of 21 stars (six giants and 15 MS stars). We measured metallicity (the cluster average [Fe/H] is +0.08, rms = 0.07) and abundances of light, α, Fe-peak, and neutron-capture elements. The Li abundance follows the expectations, showing a tight relation between temperature and abundance on the MS, at variance with M 67, and we did not detect any Li-rich giant. Conclusions. We confirm that Rup 147 is the oldest nearby open cluster. This makes it very valuable to test detailed features of stellar evolutionary models.

scholarly journals Long-term spectral variability of the O4If+ star HD 15570 in the open cluster IC 1805

2003 ◽  
Vol 212 ◽  
pp. 224-225
Author(s):  
V. Francesco Polcaro ◽  
Roberto F. Viotti ◽  
Laura Norci ◽  
Corinne Rossi ◽  
Philippe R.J. Eenens ◽  
...  
Keyword(s):  
High Resolution ◽  
Open Cluster ◽  
High Mass ◽  
Evolutionary Stage ◽  
Deep Blue ◽  
San Pedro ◽  
Young Open Cluster ◽  
Random Variability ◽  
Model C

We present preliminary results concerning the O4If+ star HD 15570. Of-type supergiants are believed to represent an evolved evolutionary stage of very high mass stars (Minit > 40 M⊙). Their low numbers and extreme peculiarity make each of these objects worth of continuous monitoring. HD 15570 dominates the very young open cluster IC 1805 and is thought to have had an initial mass ≥ 100 M⊙. Low-, intermediate- and high-resolution spectra were collected at the Loiano and San Pedro Mártir telescopes since 1992. The comparison of our high- and low-resolution spectra shows clear variability of a number of spectral features. It is worth noticing, that the variation of Hα seems to follow a repeated secular trend, increasing its equivalent width from ~ 3Å to more than 8 Å in a few years. At the same time, its profile is varying, from a shape quite similar to the theoretical one corresponding to the Klein & Castor (1978) model C, to a much more developed P-Cygni profile, with a deep blue absorption wing. The possibility of instrumental effects is ruled out by the remarkable constancy of the nearby diffuse interstellar band at 6613 Å and of the He ii 6683 Å absorption. The Hβ profile variability is evident from the comparison of the 1996 and 1998 high-resolution spectra. The emission component, which is clearly visible at all epochs, is absent in the 1996 spectrum when the line appears in pure absorption. No relevant line-profile variation seems to be present in the He ii and N iii lines contributing to the ‘feature f’, that looks remarkably constant, as well as Hγ, while their equivalent widths seem to show a modest amount of random variability.

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