scholarly journals Flare Stars in Star Clusters and Associations

1975 ◽  
Vol 67 ◽  
pp. 1-14 ◽  
Author(s):  
V. A. Ambartsumian ◽  
L. V. Mirzoyan
Keyword(s):  
Stellar Evolution ◽  
Star Clusters ◽  
Open Clusters ◽  
Point Of View ◽  
Flare Activity ◽  
Theoretical Point ◽  
Star Clusters And Associations ◽  
Stellar Flare ◽  
Dwarf Stars ◽  
Flare Stars

The study of stellar evolution can be undertaken either from a purely theoretical point of view or from a more observational approach. The present standpoint is the second one. It starts from the concepts of stellar evolution in associations and open clusters and from stellar flare activity. Statistical considerations show that flare activity is a regular stage in the evolution of stars through which all the dwarf stars go.

scholarly journals Optical Flares: Observations and Interpretations

1995 ◽  
Vol 151 ◽  
pp. 47-54 ◽  
Author(s):  
L.V. Mirzoyan
Keyword(s):  
Stellar Evolution ◽  
Star Clusters ◽  
Flare Activity ◽  
Star Clusters And Associations ◽  
Stellar Flare ◽  
Evolutionary Path ◽  
Early Stages ◽  
Stellar Flares ◽  
The Galaxy ◽  
Flare Stars

AbstractObservational results on flare stars in the Galaxy and their interpretation, based on the observational approach to early stages of stellar evolution at Byurakan, are considered. The evolutionary path of red flare stars is determined. Stellar flare activity is explained as an internal phenomenon of stars. The significance of photographic observations of stellar flares in star clusters and associations is emphasized.

scholarly journals Flare stars in star clusters, associations and solar vicinity

1990 ◽  
Vol 137 ◽  
pp. 1-13
Author(s):  
L.V. Mirzoyan
Keyword(s):  
Star Clusters ◽  
Evolutionary Stage ◽  
Flare Activity ◽  
Star Clusters And Associations ◽  
Dwarf Stars ◽  
Stellar Flares ◽  
Ceti Type ◽  
Flare Stars ◽  
Red Dwarf Stars ◽  
T Tau

The observational data on flare stars observed in star clusters and associations as well as in the solar vicinity (the UV Ceti type stars) are discussed. The analysis of these data show that they constitute one common class of objects possessing flare activity and the differences between them are conditioned by the age differences. The stage of flare activity is an evolutionary stage, one of the earliest stages of evolution passed by all red dwarf stars. It comes before the end of their T Tau stage of evolution. The UV Ceti type flare stars in the solar vicinity seem to be the population of the general galactic field, which were formed in the systems, already desintegrated. Most probably the stellar flares are the result of the release of the the surplus energy having intra-stellar origin.

scholarly journals The Red Dwarf Star Population in the Galaxy

1995 ◽  
Vol 151 ◽  
pp. 55-56 ◽  
Author(s):  
L.V. Mirzoyan
Keyword(s):  
Star Clusters ◽  
Space Distribution ◽  
Dwarf Star ◽  
Star Clusters And Associations ◽  
Dwarf Stars ◽  
The Galaxy ◽  
Flare Stars ◽  
Red Dwarf Stars ◽  
T Tau ◽  
Stellar Associations

Red dwarf stars in the Galaxy occur in three forms: as flare stars, T Tau stars and red dwarf stars of constant brightness. Haro (1957) suggested that all these stars present regular evolutionary stages of red dwarf stars.The space distribution of UV Cet flare stars in the solar vicinity indicates that these low luminosity stars belong to the disk population of the Galaxy. Therefore one can suppose that all red dwarf stars have a space distribution which is similar to that of the flare stars (Mirzoyan et al. 1988a). Only a small part of them is found in star clusters and associations. The T Tau stars are an exception: because of their very short lifetime, all of them are found in stellar associations.The space distribution of red dwarf stars is determined by the fact that all of them are formed in star clusters and associations and are finally lost from their stellar systems and merge into the general galactic field (Mirzoyan 1995).

scholarly journals Prospects for studies of UV Cet-type flare stars

1990 ◽  
Vol 137 ◽  
pp. 371-391
Author(s):  
M. Rodono'
Keyword(s):  
General Trend ◽  
Activity Level ◽  
Flare Activity ◽  
Stellar Flare ◽  
Dwarf Stars ◽  
Relevant Role ◽  
Average Activity ◽  
Flare Stars ◽  
Red Dwarf Stars ◽  
Activity Behaviour

The present review addresses selected questions on UV Cet-type red-dwarf stars primarily concerning the physics involved in the various aspects and phases of the flare phenomenon, rather than the average activity behaviour of the flare stars. In fact, while flare activity level and general trend are reasonably well established, a fully consistent physical picture of both solar and stellar flare events is still missing. Some recent results are presented with the aim of showing which observations are needed and the relevant role that coordinated multiband studies can play.

scholarly journals Star Clusters in Irregular Galaxies in the Local Group

2002 ◽  
Vol 207 ◽  
pp. 94-104
Author(s):  
Eva K. Grebel
Keyword(s):  
Globular Clusters ◽  
Local Group ◽  
Cluster Formation ◽  
Star Clusters ◽  
Open Clusters ◽  
High Angular Resolution ◽  
Star Clusters And Associations ◽  
Star Forming ◽  
Star Forming Regions ◽  
Irregular Galaxies

I summarize our knowledge of star clusters and associations in irregular galaxies other than the Magellanic Clouds in the Local Group. Surveys affording complete area coverage at high angular resolution are still lacking. Confirmed globular clusters are known only in NGC 6822 and WLM. Very few dIrrs contain populous or sparse open clusters. There is a pronounced deficiency of intermediate-age and young clusters. Apart from parent galaxy mass, the lack of interactions may be a key reason for the lack of cluster formation in the dIrrs. All dIrrs have one or several short-lived OB associations in the star-forming regions in their centers.

scholarly journals I. Clusters and Associations

1959 ◽  
Vol 7 ◽  
pp. 3-12
Keyword(s):  
Stellar Evolution ◽  
Past History ◽  
Star Clusters ◽  
Galactic Structure ◽  
Empirical Approach ◽  
Star Clusters And Associations ◽  
Different Ages ◽  
The Face ◽  
History Of ◽  
Evolutionary Interpretation

Renewed interest in the study of star clusters and associations has been aroused by at least three developments.(a) Interpretation of the color-magnitude (C-M) diagrams of clusters and associations with a theory of stellar evolution promises to give data on galactic structure problems. Information of kinematic relations, origins, and past history of stars over the face of the H-R diagram will be available when proper evolutionary interpretation is achieved. Only by assembling C-M diagrams of many clusters of different ages and richness can the empirical approach to evolution be fully exploited.

scholarly journals The Gaia-ESO survey: Calibrating a relationship between age and the [C/N] abundance ratio with open clusters

2019 ◽  
Vol 629 ◽  
pp. A62 ◽  
Author(s):  
G. Casali ◽  
L. Magrini ◽  
E. Tognelli ◽  
R. Jackson ◽  
R. D. Jeffries ◽  
...  
Keyword(s):  
Open Cluster ◽  
Empirical Relationship ◽  
Star Clusters ◽  
Open Clusters ◽  
Open Star Clusters ◽  
Mixing Processes ◽  
Dwarf Stars ◽  
Additional Tool ◽  
Giant Stars ◽  
Stellar Ages

Context. In the era of large high-resolution spectroscopic surveys such as Gaia-ESO and APOGEE, high-quality spectra can contribute to our understanding of the Galactic chemical evolution by providing abundances of elements that belong to the different nucleosynthesis channels, and also by providing constraints to one of the most elusive astrophysical quantities: stellar age. Aims. Some abundance ratios, such as [C/N], have been proven to be excellent indicators of stellar ages. We aim at providing an empirical relationship between stellar ages and [C/N] using open star clusters, observed by the Gaia-ESO and APOGEE surveys, as calibrators. Methods. We used stellar parameters and abundances from the Gaia-ESO Survey and APOGEE Survey of the Galactic field and open cluster stars. Ages of star clusters were retrieved from the literature sources and validated using a common set of isochrones. We used the same isochrones to determine for each age and metallicity the surface gravity at which the first dredge-up and red giant branch bump occur. We studied the effect of extra-mixing processes in our sample of giant stars, and we derived the mean [C/N] in evolved stars, including only stars without evidence of extra mixing. By combining the Gaia-ESO and APOGEE samples of open clusters, we derived a linear relationship between [C/N] and (logarithmic) cluster ages. Results. We apply our relationship to selected giant field stars in the Gaia-ESO and APOGEE surveys. We find an age separation between thin- and thick-disc stars and age trends within their populations, with an increasing age towards lower metallicity populations. Conclusions. With this empirical relationship, we are able to provide an age estimate for giant stars in which C and N abundances are measured. For giant stars, the isochrone fitting method is indeed less sensitive than for dwarf stars at the turn-off. Our method can therefore be considered as an additional tool to give an independent estimate of the age of giant stars. The uncertainties in their ages is similar to those obtained using isochrone fitting for dwarf stars.

Commission 37: Star Clusters and Associations (Amas Stellaires Et Associations)

1988 ◽  
Vol 20 (01) ◽  
pp. 509-535
Author(s):  
D.C. Heggie ◽  
G.L.H. Harris ◽  
K.C. Freeman ◽  
J.E. Hesser ◽  
P.E. Nissen ◽  
...  
Keyword(s):  
Observational Data ◽  
Rapid Growth ◽  
Globular Clusters ◽  
Star Clusters ◽  
Dynamical Theory ◽  
Open Clusters ◽  
Star Clusters And Associations ◽  
Cluster Systems ◽  
The Individual ◽  
Astronomy And Astrophysics

The last three years have been very productive for cluster research, especially now that observations with CCDs have become so routine. After a section on recent meetings, and one on data catalogues (by J.-C. Mermilliod), subsequent sections of this report go into details on individual topics: associations (P.E. Nissen), open clusters (G.L.H. Harris), globular clusters and cluster systems (R.E. White) and dynamical theory (D.C. Heggie).The rapid growth in the volume of observational data has meant regrettably that the information has had to be tabulated in an even more compressed form than in earlier Reports. As in previous Reports, three-figure references are to Astronomy and Astrophysics Abstracts, and two-figure references to Physics Abstracts. Most entries cover publications from 1 July 1984 to 30 June 1987, but some exceptions are noted under the individual sections. For abbreviations see §6.

scholarly journals COMMISSION 37: STAR CLUSTERS AND ASSOCIATIONS

2008 ◽  
Vol 4 (T27A) ◽  
pp. 277-279
Author(s):  
Despina Hatzidimitriou ◽  
Charles J. Lada ◽  
Ata Sarajedini ◽  
Russell D. Cannon ◽  
Kyle McC. Cudworth ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Globular Clusters ◽  
Galactic Disk ◽  
Star Clusters ◽  
Open Clusters ◽  
Stellar Rotation ◽  
Star Clusters And Associations ◽  
Stellar Spectroscopy ◽  
Wide Range ◽  
Massive Star Evolution

Star clusters are valuable tools for theoretical and observational astronomy across a wide range of disciplines from cosmology to stellar spectroscopy. For example, properties of globular clusters are used to constrain stellar evolutionary models, nucleosynthesis and chemical evolution, as well as the star formation and assembly histories of galaxies and the distribution of dark matter in present-day galaxies. Open clusters are widely used as stellar laboratories for the study of specific stellar phenomena (e.g., various emission-line stars, pulsating pre-MS stars, magnetic massive stars, binarity, stellar rotation, etc.). They also provide observational constraints on models of massive star evolution and of Galactic disk formation and chemical evolution.

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