scholarly journals Abundances of Be Stars in Very Young Open Clusters

2000 ◽  
Vol 175 ◽  
pp. 59-62 ◽  
Author(s):  
A. Marco ◽  
G. Bernabeu ◽  
J.M. Torrejón ◽  
J.J. Rodes ◽  
J. Fabregat
Keyword(s):  
Open Clusters ◽  
Be Stars ◽  
Ccd Photometry ◽  
The Galaxy

AbstractWe present here standard uvbyβ CCD photometry for five open clusters of the Galaxy in order to determine abundances of Be stars, as a function of age.

scholarly journals Massive Oe/Be stars at low metallicity: candidate progenitors of long GRBs?

2010 ◽  
Vol 6 (S272) ◽  
pp. 300-301
Author(s):  
Christophe Martayan ◽  
Dietrich Baade ◽  
Juan Zorec ◽  
Yves Frémat ◽  
Juan Fabregat ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Gamma Ray ◽  
Massive Stars ◽  
Rotational Velocity ◽  
Open Clusters ◽  
Be Stars ◽  
Gamma Ray Burst ◽  
Specific Behaviour ◽  
The Galaxy ◽  
Low Metallicity

AbstractAt low metallicity B-type stars rotate faster than at higher metallicity, typically in the SMC. As a consequence, a larger number of fast rotators is expected in the SMC than in the Galaxy, in particular more Be/Oe stars. With the ESO-WFI in its slitless mode, we examined the SMC open clusters and found an occurence of Be stars 3 to 5 times larger than in the Galaxy. The evolution of the angular rotational velocity seems to be the main key on the understanding of the specific behaviour and stellar evolution of such stars at different metallicities. With the results of this WFI study and using observational clues on the SMC WR stars and massive stars, as well as the theoretical indications of long gamma-ray burst progenitors, we identify the low metallicity massive Be and Oe stars as potential LGRB progenitors. Therefore the expected rates and numbers of LGRB are calculated and compared to the observed ones, leading to a good probability that low metallicity Be/Oe stars are actually LGRB progenitors.

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 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 Star clusters as tracers of galactic subsystems

1993 ◽  
Vol 153 ◽  
pp. 323-324
Author(s):  
B. Barbuy ◽  
E. Bica ◽  
S. Ortolani
Keyword(s):  
Spatial Distribution ◽  
Galaxy Formation ◽  
Formation Process ◽  
Globular Clusters ◽  
Star Clusters ◽  
Open Clusters ◽  
Horizontal Branch ◽  
The Galaxy ◽  
Magnitude Difference

We have obtained CCD BVRI colour-magnitude diagrams for a series of disk globular clusters, improving parameters and detecting a new one: Lyngå 7. Using the magnitude difference between turn-off and horizontal branch Δ(TO-HB) as an age discriminator, and their spatial distribution we compare old disk open clusters, young halo globular clusters, and metal-rich disk globular clusters, obtaining clues to the Galaxy formation process.

scholarly journals Pulsations of Ob-Stars: New Observations

1998 ◽  
Vol 185 ◽  
pp. 347-354 ◽  
Author(s):  
Dietrich Baade
Keyword(s):  
Main Sequence ◽  
Physical Parameters ◽  
Be Stars ◽  
Instability Strip ◽  
Ob Stars ◽  
Analysis Strategies ◽  
The Galaxy ◽  
Order Line ◽  
Nonradial Pulsation ◽  
Radial Pulsations

Improved observing and data analysis strategies have initiated a considerable expansion of the empirical knowledge about the pulsations of OB stars. Possible correlations between physical parameters and associated pulsation characteristics are becoming more clearly perceivable. This starts to include the asteroseismologically fundamental areas of g-modes and rapid rotation. The β Cephei instability strip continues to be the only locus where radial pulsations occur (but apparently not in all stars located in that strip). Except for spectral types B8/B9 near the main sequence, where pulsations are hardly detected even at low amplitudes, any major group of stars in the Galaxy that are obviously not candidate pulsators still remains to be identified. However, the incidence and amplitudes of OB star pulsations decrease steeply with metallicity. The behaviour of high-luminosity stars is less often dominated by very few modes. In broad-lined stars the moving-bump phenomenon is more common than low-order line-profile variability. But its relation to nonradial pulsation is not clear. The beating of low-ℓ nonradial pulsation modes that have identical angular mode indices may be the clockwork of the outbursts of at least some Be stars. The physics of this episodic mass loss process remains to be identified.

scholarly journals The Evolutionary Evidence for Be/Black Hole Binaries

2000 ◽  
Vol 175 ◽  
pp. 689-692
Author(s):  
Natalya V. Raguzova ◽  
Vladimir M. Lipunov
Keyword(s):  
Black Holes ◽  
Binary Systems ◽  
Be Stars ◽  
Evolutionary Track ◽  
Binary Black Holes ◽  
Black Hole Binaries ◽  
Eccentric Orbits ◽  
Evolutionary Scenario ◽  
The Galaxy ◽  
Near Future

AbstractUsing a Monte Carlo simulation of the modern scenario of the evolution of binary systems (the “Scenario Machine”), we calculate the number of binary black holes with Be stars and their expected observational properties. So far, only two possible candidates for Be/BH binaries have been proposed among the observable sources, the superluminal source GRS 1915+105 in the Galaxy and RX J0117.6–7330 in the SMC. We obtained an evolutionary track that can lead to the formation of such systems. The modern evolutionary scenario predicts the existence of binary black holes on eccentric orbits around Be stars and such systems may be discovered in the near future.

scholarly journals An Overview of the Globular Cluster System of the Galaxy

1988 ◽  
Vol 126 ◽  
pp. 37-48
Author(s):  
Robert Zinn
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
Cluster System ◽  
Open Clusters ◽  
The Galaxy ◽  
Globular Cluster System ◽  
Harlow Shapley

Harlow Shapley (1918) used the positions of globular clusters in space to determine the dimensions of our Galaxy. His conclusion that the Sun does not lie near the center of the Galaxy is widely recognized as one of the most important astronomical discoveries of this century. Nearly as important, but much less publicized, was his realization that, unlike stars, open clusters, HII regions and planetary nebulae, globular clusters are not concentrated near the plane of the Milky Way. His data showed that the globular clusters are distributed over very large distances from the galactic plane and the galactic center. Ever since this discovery that the Galaxy has a vast halo containing globular clusters, it has been clear that these clusters are key objects for probing the evolution of the Galaxy. Later work, which showed that globular clusters are very old and, on average, very metal poor, underscored their importance. In the spirit of this research, which started with Shapley's, this review discusses the characteristics of the globular cluster system that have the most bearing on the evolution of the Galaxy.

scholarly journals Search for Pulsational Instability among h Persei Stars

1995 ◽  
Vol 155 ◽  
pp. 299-300
Author(s):  
J. Krzesinski
Keyword(s):  
Northern Hemisphere ◽  
Open Clusters ◽  
Age Group ◽  
Be Stars ◽  
Double Cluster

AbstractThe northern-hemisphere double cluster h and χ Persei is one of the richest young open clusters. At least half of the brightest stars in the cluster appear to be variables and most of them axe Be stars. Till now there was no evidence for the presence of β Cephei stars in the cluster. It is remarkable that the similar age southern cluster NGC 3293 and other clusters belonging to the same age group are documented as clusters in which β Cephei stars have been observed. In this work we report finding one suspected β Cephei-like object, basing on our own observations.

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