scholarly journals NGC 3293 revisited by the Gaia-ESO Survey

2014 ◽  
Vol 9 (S307) ◽  
pp. 140-141
Author(s):  
Thierry Semaan ◽  
Thierry Morel ◽  
Eric Gosset ◽  
Juan Zorec ◽  
Yves Frémat ◽  
...  
Keyword(s):  
Massive Stars ◽  
Open Cluster ◽  
Second Step ◽  
Chemical Abundances ◽  
Hot Stars ◽  
Fundamental Parameters ◽  
Medium Resolution ◽  
Young Open Cluster ◽  
Extended View

AbstractIn the framework of the Gaia-ESO survey we have determined the fundamental parameters of a large number of B-type stars in the Galactic, young open cluster NGC 3293. The determination of the stellar parameters is based on medium-resolution spectra obtained with FLAMES/GIRAFFE at ESO-VLT. As a second step, we adopted the accurate parameters to determine the chemical abundances of these hot stars. We present a comparison of our results with those obtained by the 'VLT-FLAMES survey of massive stars' (Evans et al. 2005). Our study increases the number of objects analysed and provides an extended view of this cluster.

scholarly journals A new look at Sco OB1 association with Gaia DR2

2020 ◽  
Vol 495 (1) ◽  
pp. 1349-1359 ◽  
Author(s):  
L Yalyalieva ◽  
G Carraro ◽  
R Vazquez ◽  
L Rizzo ◽  
E Glushkova ◽  
...  
Keyword(s):  
Open Cluster ◽  
Three Dimensional ◽  
Star Formation History ◽  
Optical Data ◽  
Dimensional Structure ◽  
Fundamental Parameters ◽  
Time Estimates ◽  
Young Open Cluster ◽  
Pms Stars ◽  
Gaia Dr2

ABSTRACT We present and discuss photometric optical data in the area of the OB association Sco OB1 covering about 1 deg2. UBVI photometry is employed in tandem with Gaia DR2 data to investigate the three-dimensional structure and the star formation history of the region. By combining parallaxes and proper motions, we identify seven physical groups located between the young open cluster NGC 6231 and the bright nebula IC 4628. The most prominent group coincides with the sparse open cluster Trumpler 24. We confirm the presence of the intermediate-age star cluster VdB-Hagen 202, which is unexpected in this environment, and provide for the first time estimates of its fundamental parameters. After assessing individual groups membership, we derive mean proper motion components, distances, and ages. The seven groups belong to two different families. To the younger family (family I) belong several pre-main-sequence (PMS) stars as well. These are evenly spread across the field, and also in front of VdB-Hagen 202. VdB-Hagen 202, and two smaller, slightly detached, groups of similar properties form family II, which do not belong to the association, but are caught in the act of passing through it. As for the younger population, this forms an arc-like structure from the bright nebula IC 4628 down to NGC 6231, as previously found. Moreover, the PMS stars density seems to increase from NGC 6231 northward to Trumpler 24.

scholarly journals Star formation in the outer Galaxy: membership and fundamental parameters of the young open cluster NGC 1893

2011 ◽  
Vol 527 ◽  
pp. A77 ◽  
Author(s):  
L. Prisinzano ◽  
J. Sanz-Forcada ◽  
G. Micela ◽  
M. Caramazza ◽  
M. G. Guarcello ◽  
...  
Keyword(s):  
Star Formation ◽  
Open Cluster ◽  
Fundamental Parameters ◽  
Young Open Cluster

scholarly journals A comprehensive study of NGC 2345, a young open cluster with a low metallicity

2019 ◽  
Vol 631 ◽  
pp. A124 ◽  
Author(s):  
J. Alonso-Santiago ◽  
I. Negueruela ◽  
A. Marco ◽  
H. M. Tabernero ◽  
C. González-Fernández ◽  
...  
Keyword(s):  
Open Cluster ◽  
Complete Analysis ◽  
Be Stars ◽  
Test Bed ◽  
Chemical Abundances ◽  
Evolved Stars ◽  
Depth Analysis ◽  
Young Open Cluster ◽  
High Fraction ◽  
Low Metallicity

Context. NGC 2345 is a young open cluster that hosts seven blue and red supergiants, low metallicity, and a high fraction of Be stars, which makes it a privileged laboratory to study stellar evolution. Aims. We aim to improve the determination of the cluster parameters and study the Be phenomenon. Our objective is also to characterise the seven evolved stars found in NGC 2345 by deriving their atmospheric parameters and chemical abundances. Methods. We performed a complete analysis combining for the first time ubvy photometry with spectroscopy as well as the Gaia Data Release 2. We obtained spectra with classification purposes for 76 stars and high-resolution spectroscopy for an in-depth analysis of the blue and red evolved stars. Results. We identify a new red supergiant and 145 B-type likely members within a radius of 18.7 ± 1.2 arcmin, which implies an initial mass, Mcl ≈ 5200 M⊙. We find a distance of 2.5 ± 0.2 kpc for NGC 2345, placing it at RGC = 10.2 ± 0.2 kpc. Isochrone fitting supports an age of 56 ± 13 Ma, implying masses around 6.5 M⊙ for the supergiants. A high fraction of Be stars (≈10%) is found. From the spectral analysis we estimate an average vrad = +58.6 ± 0.5 km s−1 and a low metallicity, [Fe/H] = −0.28 ± 0.07, for the cluster. We also determine chemical abundances for Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the evolved stars. The chemical composition of the cluster is consistent with that of the Galactic thin disc. One of the K supergiants, S50, is a Li-rich star, presenting an A(Li) ≈ 2.1. An overabundance of Ba is found, supporting the enhanced s-process. Conclusions. NGC 2345 has a low metallicity for its Galactocentric distance, which is comparable to typical Large Magellanic Cloud stars. It is massive enough to serve as a test bed for theoretical evolutionary models for massive intermediate-mass stars.

scholarly journals An observational asteroseismic study of the pulsating B-type stars in the open cluster NGC 884

2013 ◽  
Vol 9 (S301) ◽  
pp. 479-480
Author(s):  
S. Saesen ◽  
M. Briquet ◽  
C. Aerts ◽  
A. Miglio ◽  
F. Carrier
Keyword(s):  
Chemical Composition ◽  
Recent Progress ◽  
Massive Stars ◽  
Open Cluster ◽  
Seismic Interpretation ◽  
Evolution Model ◽  
Stellar Structure ◽  
Current Status ◽  
Physical Description ◽  
Young Open Cluster

AbstractRecent progress in the seismic interpretation of field β Cep stars has resulted in improvements of the physical description in the stellar structure and evolution model computations of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. We present an observational asteroseismic study based on the discovery of numerous multi-periodic and mono-periodic B-type stars in the open cluster NGC 884 (χ Persei). Our study illustrates the current status of ensemble asteroseismology of this young open cluster.

scholarly journals Photometric Variability of OB-type stars as a New Window on Massive Stars

2014 ◽  
Vol 9 (S307) ◽  
pp. 171-175
Author(s):  
M. Kourniotis ◽  
A. Z. Bonanos ◽  
I. Soszyński ◽  
R. Poleski ◽  
G. Krikelis ◽  
...  
Keyword(s):  
Systematic Study ◽  
Massive Stars ◽  
Accurate Determination ◽  
Early Type ◽  
Stellar Rotation ◽  
Photometric Variability ◽  
Fundamental Parameters ◽  
Disk Formation

AbstractWe present the first systematic study of 4646 spectroscopically confirmed early-type massive stars in the Small Magellanic Cloud (SMC), using variability as a tool to confine the physics of OB-type massive stars. We report the discovery of ∼100 massive eclipsing systems which are useful for the accurate determination of the fundamental parameters of massive stars and we evaluate the frequency of multiplicity. In addition, we explore the occurrence of the Oe/Be phenomenon and provide a large number of candidate non-radial pulsators, which can be further studied via asteroseismology. The results of this work (Kourniotis et al. 2014) will contribute to a better understanding of the role of metallicity in triggering processes associated to matter ejections and/or disk formation, which in turn affect mass loss and stellar rotation.

scholarly journals Fundamental parameters of 4 massive eclipsing binaries in Westerlund 1

2010 ◽  
Vol 6 (S272) ◽  
pp. 515-516
Author(s):  
Eugenia Koumpia ◽  
Alceste Z. Bonanos
Keyword(s):  
Binary Systems ◽  
Local Group ◽  
Massive Stars ◽  
Eclipsing Binaries ◽  
Fundamental Parameters ◽  
Red Supergiants ◽  
The Masses ◽  
Rare Opportunity ◽  
Luminous Blue Variable

AbstractWesterlund 1 is one of the most massive young clusters known in the Local Group, with an age of 3-5 Myr. It contains an assortment of rare evolved massive stars, such as blue, yellow and red supergiants, Wolf-Rayet stars, a luminous blue variable, and a magnetar, as well as 4 massive eclipsing binary systems (Wddeb, Wd13, Wd36, WR77o, see Bonanos 2007). The eclipsing binaries present a rare opportunity to constrain evolutionary models of massive stars, the distance to the cluster and furthermore, to determine a dynamical lower limit for the mass of a magnetar progenitor. Wddeb, being a detached system, is of great interest as it allows determination of the masses of 2 of the most massive unevolved stars in the cluster. We have analyzed spectra of all 4 eclipsing binaries, taken in 2007-2008 with the 6.5 meter Magellan telescope at Las Campanas Observatory, Chile, and present fundamental parameters (masses, radii) for their component stars.

scholarly journals Non-LTE chemical abundances in Galactic open and globular clusters

2019 ◽  
Vol 628 ◽  
pp. A54 ◽  
Author(s):  
Mikhail Kovalev ◽  
Maria Bergemann ◽  
Yuan-Sen Ting ◽  
Hans-Walter Rix
Keyword(s):  
Globular Clusters ◽  
Chemical Abundances ◽  
Medium Resolution ◽  
Spectral Models ◽  
Galactic Clusters ◽  
Non Local ◽  
The Mean ◽  
Cluster Abundance ◽  
Good Agreement

Aims. We study the effects of non-local thermodynamic equilibrium (NLTE) on the determination of stellar parameters and abundances of Fe, Mg, and Ti from the medium-resolution spectra of FGK stars. Methods. We extended the Payne fitting approach to draw on NLTE and LTE spectral models. These were used to analyse the spectra of the Gaia-ESO benchmark stars and the spectra of 742 stars in 13 open and globular clusters in the Milky Way: NGC 3532, NGC 5927, NGC 2243, NGC 104, NGC 1851, NGC 2808, NGC 362, M 2, NGC 6752, NGC 1904, NGC 4833, NGC 4372, and M15. Results. Our approach accurately recovers effective temperatures, surface gravities, and abundances of the benchmark stars and clusters members. The differences between NLTE and LTE are significant in the metal-poor regime, [Fe/H] ≲ −1. The NLTE [Fe/H] values are systematically higher, whereas the average NLTE [Mg/Fe] abundance ratios are ∼0.15 dex lower, compared to LTE. Our LTE measurements of metallicities and abundances of stars in Galactic clusters are in a good agreement with the literature. Though, for most clusters, our study yields the first estimates of NLTE abundances of Fe, Mg, and Ti. Conclusion. All clusters investigated in this work are homogeneous in Fe and Ti, with the intra-cluster abundance variations of less then 0.04 dex. NGC 2808, NGC 4833, M 2, and M 15 show significant dispersions in [Mg/Fe]. Contrary to common assumptions, the NLTE analysis changes the mean abundance ratios in the clusters, but it does not influence the intra-cluster abundance dispersions.

scholarly journals Spectroscopy of Be stars in NGC 330

1994 ◽  
Vol 162 ◽  
pp. 269-270 ◽  
Author(s):  
Paolo A. Mazzali ◽  
F. Pasian ◽  
D.J. Lennon ◽  
P. Bonifacio ◽  
V. Castellani
Keyword(s):  
Open Cluster ◽  
Model Atmosphere ◽  
Evolutionary Status ◽  
Be Stars ◽  
Atmospheric Parameters ◽  
Medium Resolution ◽  
Young Open Cluster

Medium resolution (2Å/px) but high s/n spectra of approximately twenty of the brightest blue stars in the young open cluster NGC 330 in the SMC have been obtained with EFOSC1 on the ESO 3.6m telescope, and analyzed in order to determine the atmospheric parameters and the evolutionary status of the stars. LTE and NLTE model atmosphere calculations were used to determine the stellar parameters. The Teff values were derived from fits of the UV continua for all stars where these were available, using Robertson's (1974) B and V photometry to scale the Kurucz model fluxes for metallicity Z = 0.1Z⊙. Luminosities of the sample stars lie in the range 4.0 < log(L*/L⊙) < 5.0 and spectral types between B0 and late-B.

scholarly journals Line-blanketing in massive stars: new results

1999 ◽  
Vol 193 ◽  
pp. 129-137
Author(s):  
D. John Hillier
Keyword(s):  
Massive Stars ◽  
Emission Lines ◽  
Atomic Data ◽  
Iron Group ◽  
Numerical Techniques ◽  
Hot Stars ◽  
Charge Exchange Reaction ◽  
Present Generation ◽  
Individual Line

Until recently, a major deficiency of most spectroscopic modeling of hot stars was the neglect of line-blanketing. With the availability of new atomic data, faster computers, suitable approximations, and improved numerical techniques it is now feasible to include non-LTE line-blanketing due to CNO and iron group elements in atmospheric calculations. We highlight the capabilities of the present generation of models. New blanketing results are presented for WN and WC Wolf-Rayet stars, and for LBVs. Line-blanketing alters individual line strengths in unpredictable ways, and can significantly influence the determination of stellar parameters. We specifically highlight the UV spectral region in which the effects of Fe blanketing are directly manifested. The importance of the charge exchange reaction Fe2+ + H ⇌ Fe+ + H+ for modeling of the Fe emission lines in the extreme P-Cygni star HDE 316285 is illustrated.

scholarly journals Ultraviolet spectral libraries of massive stars at low metallicity

1999 ◽  
Vol 193 ◽  
pp. 616-617
Author(s):  
Carmelle Robert
Keyword(s):  
Stellar Population ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Solar Neighbourhood ◽  
Hot Stars ◽  
Star Forming ◽  
Distant Star ◽  
Medium Resolution ◽  
Low Metallicity ◽  
Spectral Libraries

Three new ultraviolet spectral libraries of massive, hot stars using high and medium resolution spectra of objects located in the solar neighbourhood and the Magellanic Clouds are presented. Massive stars display unique wind signatures which are relatively easy to study in the ultraviolet. These libraries are crucial tools when investigating the massive stellar population of distant star-forming galaxies.

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