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 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 High-resolution spectroscopy of giant stars in the open clusters IC 4651 and IC 4725

2017 ◽  
Vol 95 (9) ◽  
pp. 862-868 ◽  
Author(s):  
Orlando J. Katime Santrich ◽  
Silvia Rossi
Keyword(s):  
High Resolution ◽  
Solar Spectrum ◽  
Open Clusters ◽  
High Resolution Spectroscopy ◽  
Local Thermal Equilibrium ◽  
Atmospheric Parameters ◽  
Chemical Abundances ◽  
Abundance Pattern ◽  
Giant Stars ◽  
Disk Structure

Open clusters are important astrophysical laboratories to study the stellar formation and evolution and to verify the disk structure of the Milky Way. We present calculations of stellar atmospheric parameters and s-process abundances for nine giant stars in the galactic open clusters IC 4651 and IC 4725. These objects have their memberships confirmed from dynamic studies and chemical analysis. The high-resolution spectra are available in the FEROS ESO archive. We have applied a line by line analysis relative to Juno solar spectrum to determine the stellar atmospheric parameters and chemical abundances of Y II, Zr I, La II, Ce II, and Nd II under the local thermal equilibrium hypothesis. The obtained results were compared to the literature values. The derived s-process abundance pattern agrees with the most recent behaviors reported for giant stars in galactic open clusters.

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 Masses and ages for metal-poor stars

2019 ◽  
Vol 627 ◽  
pp. A173 ◽  
Author(s):  
M. Valentini ◽  
C. Chiappini ◽  
D. Bossini ◽  
A. Miglio ◽  
G. R. Davies ◽  
...  
Keyword(s):  
High Resolution ◽  
Seismic Data ◽  
Age Determination ◽  
High Resolution Spectroscopy ◽  
Chemical Abundances ◽  
Abundance Pattern ◽  
Halo Stars ◽  
Stellar Ages ◽  
First Results ◽  
Detailed Chemical

Context. Very metal-poor halo stars are the best candidates for being among the oldest objects in our Galaxy. Samples of halo stars with age determination and detailed chemical composition measurements provide key information for constraining the nature of the first stellar generations and the nucleosynthesis in the metal-poor regime. Aims. Age estimates are very uncertain and are available for only a small number of metal-poor stars. We present the first results of a pilot programme aimed at deriving precise masses, ages, and chemical abundances for metal-poor halo giants using asteroseismology and high-resolution spectroscopy. Methods. We obtained high-resolution UVES spectra for four metal-poor RAVE stars observed by the K2 satellite. Seismic data obtained from K2 light curves helped improve spectroscopic temperatures, metallicities, and individual chemical abundances. Mass and ages were derived using the code PARAM, investigating the effects of different assumptions (e.g. mass loss and [α/Fe]-enhancement). Orbits were computed using Gaia DR2 data. Results. The stars are found to be normal metal-poor halo stars (i.e. non C-enhanced), and an abundance pattern typical of old stars (i.e. α and Eu-enhanced), and have masses in the 0.80−1.0 M⊙ range. The inferred model-dependent stellar ages are found to range from 7.4 Gyr to 13.0 Gyr with uncertainties of ∼30%−35%. We also provide revised masses and ages for metal-poor stars with Kepler seismic data from the APOGEE survey and a set of M4 stars. Conclusions. The present work shows that the combination of asteroseismology and high-resolution spectroscopy provides precise ages in the metal-poor regime. Most of the stars analysed in the present work (covering the metallicity range of [Fe/H] ∼ −0.8 to −2 dex) are very old >9 Gyr (14 out of 19 stars), and all of the stars are older than >5 Gyr (within the 68 percentile confidence level).

scholarly journals High-resolution spectroscopy of the old open cluster Collinder 261: abundances of iron and other elements

2005 ◽  
Vol 441 (1) ◽  
pp. 131-140 ◽  
Author(s):  
E. Carretta ◽  
A. Bragaglia ◽  
R. G. Gratton ◽  
M. Tosi
Keyword(s):  
High Resolution ◽  
Open Cluster ◽  
High Resolution Spectroscopy

scholarly journals The nature of the NGC 2546: Not one but two open clusters

2020 ◽  
Vol 633 ◽  
pp. A146 ◽  
Author(s):  
A. D. Alejo ◽  
J. F. González ◽  
M. E. Veramendi
Keyword(s):  
Radial Velocity ◽  
Binary Stars ◽  
Open Cluster ◽  
Open Clusters ◽  
Spectroscopic Binaries ◽  
Physical Parameters ◽  
Distance Modulus ◽  
Cluster Membership ◽  
Spectroscopic Observations ◽  
Astrometric Data

Context. As part of a broader project on the role of binary stars in clusters, we present a spectroscopic study of the open cluster NGC 2546, which is a large cluster lacking previous spectroscopic analysis. Aims. We report the finding of two open clusters in the region of NGC 2546. For the two star groups, we determine radial velocity, parallax, proper motion, reddening, distance modulus, and age, using our spectroscopic observations and available photometric and astrometric data, mainly from the second Gaia data release (Gaia-DR2). We also determine the orbit of four spectroscopic binaries in these open clusters. Methods. From mid-resolution spectroscopic observations for 28 stars in the NGC 2546 region, we determined radial velocities and evaluate velocity variability. To analyze double-lined spectroscopic binaries, we used a spectral separation technique and fit the spectroscopic orbits using a least-squares code. The presence of two stellar groups is suggested by the radial velocity distribution and confirmed by available photometric and astrometric data. We applied a multi-criteria analysis to determine cluster membership, and obtained kinematic and physical parameters of the clusters. Results. NGC 2546 is actually two clusters, NGC 2546A and NGC 2546B, which are not physically related to each other. NGC 2546A has an age of about 180 Myr and a distance of 950 pc. It has a half-number radius of 8 pc and contains about 480 members brighter than G = 18 mag. NGC 2546B is a very young cluster (<10 Myr) located at a distance of 1450 pc. It is a small cluster with 80 members and a half-number radius of 1.6 pc. Stars less massive than 2.5 M⊙ in this cluster would be pre-main-sequence objects. We detected four spectroscopic binaries and determined their orbits. The two binaries of NGC 2546A contain chemically peculiar components: HD 68693 is composed of two mercury-manganese stars and HD 68624 has a Bp silicon secondary. Among the most massive objects of NGC 2546B, there are two binary stars: HD 68572, with P = 124.2 d, and CD -37 4344 with P = 10.4 d.

scholarly journals Metallicities for 13 nearby open clusters from high-resolution spectroscopy of dwarf and giant stars

2008 ◽  
Vol 493 (1) ◽  
pp. 309-316 ◽  
Author(s):  
N. C. Santos ◽  
C. Lovis ◽  
G. Pace ◽  
J. Melendez ◽  
D. Naef
Keyword(s):  
High Resolution ◽  
Open Clusters ◽  
High Resolution Spectroscopy ◽  
Giant Stars
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