Flare activity and cluster membership probability of flare stars

2008 ◽  
pp. 65-66
Author(s):  
L. V. Mirzoyan ◽  
V. V. Hambarian ◽  
A. L. Mirzoyan
Keyword(s):  
Flare Activity ◽  
Membership Probability ◽  
Cluster Membership ◽  
Flare Stars

scholarly journals Flare Activity and Cluster Membership Probability of Flare Stars

1995 ◽  
Vol 151 ◽  
pp. 65-66 ◽  
Author(s):  
L.V. Mirzoyan ◽  
V.V. Hambarian ◽  
A.L. Mirzoyan
Keyword(s):  
Flare Activity ◽  
Stellar Clusters ◽  
Proper Motions ◽  
Membership Probability ◽  
Cluster Membership ◽  
Galactic Field ◽  
Stellar Flares ◽  
Membership Criterion ◽  
Flare Stars ◽  
Stellar Clusters And Associations

Mirzoyan (1976) showed that the concentration of flare stars around the center of the Pleiades cluster (Alcyone) was the same, irrespective of their proper motions. At that time, however, proper motions of only a few flare stars were known. The result was confirmed on the basis of more extensive observational material (Chavushian 1979, Mirzoyan 1983). Photographic observations of stellar flares in the general galactic field during 181 hours yielded the detection of only a single flare, i.e. the percentage of flare stars in the general galactic field is about 10% of the total number of flare stars detected in the regions of stellar clusters and associations (Chavushian 1979, Mirzoyan et al. 1988).This result shows that flare activity can be considered as a definitive cluster membership criterion, which appears to be a better one than the cluster membership probability, which is based on proper motions. To prove this, cluster membership probabilities (Stauffer et al. 1991) for 408 Pleiades cluster flare stars from the catalogue by Haro et al. (1982), are used (Table 1).

How could Precise Stellar Radial Velocities Help to Understand Field and Cluster Member Flare Stars?

1999 ◽  
Vol 170 ◽  
pp. 218-222
Author(s):  
G. Szécsényi-Nagy
Keyword(s):  
Radial Velocity ◽  
Proper Motion ◽  
Variable Stars ◽  
Radial Velocities ◽  
Solar Neighborhood ◽  
Final Decision ◽  
Data Set ◽  
Membership Probability ◽  
Cluster Membership ◽  
Flare Stars

AbstractUntil recently the problem of collecting high resolution spectra of flare stars has been intractable since the techniques available have not been sensitive enough to reach these extremely faint objects. Although many of the nearest stars (and practically all of the nearby variable stars) belong to this class, even the ones nearest to our sun are fainter than magnitude 8 or 10. In determining the radial velocity of nearby flare stars astronomers accepted the available accuracy of ~ 1 km/s. This may be adequate for the classification of the objects into age classes (according their kinematic properties).The other considerable group of flare stars is taken traditionally as a natural by-product of star formation processes which go on in clusters and associations. Until recently there has not been any serious attack against the widely popular hypothesis that all but a few of the flare stars discovered in the fields of stellar aggregates (their number exceeds that of the solar neighborhood flare stars) are physical members of the systems. The discovery (Szécsényi-Nagy et al. 1997, 1998) that hundreds of flare stars found in the field of M45 may not be cluster members may change the situation. Most flare stars observed there are very faint and consequently they were missing from previously published lists of Pleiades members. For one third of the objects only reliable membership probabilities have been determined, and many of them are listed as probable non-members (Haro, Chavira, & Gonzalez 1982). However, a recently published photographic proper motion survey of the Pleiades’ field (Souchay & Schilbach 1995) provided reliable membership probability values for many stars of extremely low luminosity too. Based on that about 85% of the well-documented flare stars can be – and have been – identified. Our results (Szécsényi-Nagy et al. 1997) undoubtedly prove that a substantial fraction (~ 40%) of the so called Pleiades flare stars are (more or less) definitely non-members. Since all of these new cluster membership probability calculations have been based on stellar proper motion values, in order to be able to reach a final decision, we badly need some other independent data set for the very same stars. It is to be shown that precise stellar radial velocities, an unexploited – because almost unknown – parameter for flare stars, could solve the problem by supporting or disproving these faint objects’ cluster membership. Consequently the flare stars of these two kinds (which are accidentally mixed on the photographic plates) could be classified into different age groups and their evolutionary stages and tracks could be investigated more deeply.Our intention is to persuade astronomers involved in stellar radial velocity business that developing and using a method of high precision stellar radial-velocity measurement for late dK/dM stars is not a waste of time but a really feasible job and that we can and will contribute to the success of it by identifying the best tartgets, taking part in the necessary observations and evaluating the data.

scholarly journals Young and Old Subsystems of Flare Stars

1995 ◽  
Vol 151 ◽  
pp. 63-64
Author(s):  
L.V. Mirzoyan ◽  
V.V. Hambarian
Keyword(s):  
Evolutionary Status ◽  
Wide Field ◽  
Flare Activity ◽  
Multiple Systems ◽  
Star Evolution ◽  
Orion Association ◽  
Evolutionary Connection ◽  
Long Time ◽  
Flare Stars ◽  
T Tau

Photographic observations with wide-field telescopes of flare stars in the Orion association and the Pleiades cluster have been carried out since 40 years. About 500 flare stars were found in each of these systems. The ages of these stellar systems differ by one or two orders of magnitude (Mirzoyan 1991). This fact allows us to compare them, in order to show that they fit into the concept, suggested first by Haro (1957), that the evolutionary status of flare stars is a stage of red dwarf star evolution which follows that of the T Tau stars (Haro 1976, Ambartsumian & Mirzoyan 1970).The basic difference between the Orion and Pleiades subsystems of flare stars has been known for a long time: the coexistence of flare stars and T Tau stars in the Orion association, and the absence of the latter group in the Pleiades. Some of the T Tau stars show flare activity (Haro 1964). This fact and the existence of multiple systems of trapezium type, which are dynamically unstable, in the Orion association, are arguments in favour of an evolutionary connection between these two types of stars.

scholarly journals Flare Stars Database

1994 ◽  
Vol 161 ◽  
pp. 380-382
Author(s):  
M. Tsvetkov ◽  
M. Chukova ◽  
K. Tsvetkova
Keyword(s):  
Wide Field ◽  
Flare Activity ◽  
The Galaxy ◽  
Statistical Regularities ◽  
Ceti Type ◽  
Formation And Evolution ◽  
Flare Stars ◽  
Machine Readable

The important role of flare stars (UV Ceti type variables) in astrophysics is due to the fact that the flare activity is not only typical for red stars with small masses but is a necessary stage during their evolution. The flare star search in stellar aggregates has led to the accumulation of rich observational material allowing us to look for statistical regularities in star formation and evolution. At present, there are more than 1500 known flare stars in the Galaxy; these were discovered mainly during the last 30 years. Most results of the long term monitoring with wide-field telescopes are listed in existing catalogues of flare stars in stellar aggregates and in the solar neighbourhood. These catalogues and their machine-readable versions were the basis for the present database of flare stars in the Galaxy.

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 Reliable photometric membership (RPM) of galaxies in clusters – I. A machine learning method and its performance in the local universe

2020 ◽  
Vol 493 (3) ◽  
pp. 3429-3441
Author(s):  
Paulo A A Lopes ◽  
André L B Ribeiro
Keyword(s):  
Machine Learning ◽  
Galaxy Evolution ◽  
Large Scale ◽  
Machine Learning Techniques ◽  
Gradient Boosting ◽  
Support Vector ◽  
Validation Data ◽  
Membership Probability ◽  
Cluster Membership ◽  
Stochastic Gradient Boosting

ABSTRACT We introduce a new method to determine galaxy cluster membership based solely on photometric properties. We adopt a machine learning approach to recover a cluster membership probability from galaxy photometric parameters and finally derive a membership classification. After testing several machine learning techniques (such as stochastic gradient boosting, model averaged neural network and k-nearest neighbours), we found the support vector machine algorithm to perform better when applied to our data. Our training and validation data are from the Sloan Digital Sky Survey main sample. Hence, to be complete to $M_r^* + 3$, we limit our work to 30 clusters with $z$phot-cl ≤ 0.045. Masses (M200) are larger than $\sim 0.6\times 10^{14} \, \mathrm{M}_{\odot }$ (most above $3\times 10^{14} \, \mathrm{M}_{\odot }$). Our results are derived taking in account all galaxies in the line of sight of each cluster, with no photometric redshift cuts or background corrections. Our method is non-parametric, making no assumptions on the number density or luminosity profiles of galaxies in clusters. Our approach delivers extremely accurate results (completeness, C $\sim 92{\rm{ per\ cent}}$ and purity, P $\sim 87{\rm{ per\ cent}}$) within R200, so that we named our code reliable photometric membership. We discuss possible dependencies on magnitude, colour, and cluster mass. Finally, we present some applications of our method, stressing its impact to galaxy evolution and cosmological studies based on future large-scale surveys, such as eROSITA, EUCLID, and LSST.

Open cluster membership probability based on K-means clustering algorithm

2016 ◽  
Vol 42 (1) ◽  
pp. 49-59 ◽  
Author(s):  
Mohamed Abd El Aziz ◽  
I. M. Selim ◽  
A. Essam
Keyword(s):  
Clustering Algorithm ◽  
Open Cluster ◽  
Membership Probability ◽  
Cluster Membership

scholarly journals Flare Star Observations in the Praesepe Region

1977 ◽  
Vol 42 ◽  
pp. 120-125
Author(s):  
I. Jankovics
Keyword(s):  
Observational Data ◽  
Flare Star ◽  
Flare Activity ◽  
List Type ◽  
The Sun ◽  
Type Number ◽  
Orion Association ◽  
Order Of Magnitude ◽  
Photographic Survey ◽  
Flare Stars

In a program of systematic search for flare stars in clusters and associations we have carried out a photographic survey in the region of Praesepe. The previously obtained interesting results in the Pleiades cluster and the Orion association stimulated us to continue the work of Haro (1968) and Rosino (1966) in Praesepe. The importance of observations in this cluster is obvious if we consider the following circumstances: 1. Praesepe and Pleiades have nearly the same distance from the Sun, 160 and 125 pc, respectively.2. There exists a difference in age between the 2 clusters of at least one order of magnitude.3. The use of Schmidt telescopes allows observations in large cluster regions.A great number of observational data are desirable for comparison of flare activity in the regions of Pleiades and Praesepe.

scholarly journals A prediction of the flare activity of stellar aggregates

1990 ◽  
Vol 137 ◽  
pp. 113-116
Author(s):  
M.A. Mnatsakanian ◽  
A.L. Mirzoyan
Keyword(s):  
Statistical Prediction ◽  
Flare Activity ◽  
Flare Stars

The problem of the statistical prediction of flare activity of a group of flare stars in stellar aggregates is considered.

scholarly journals New Triggering Mechanism for Red Dwarf Flares

1983 ◽  
Vol 71 ◽  
pp. 609-611
Author(s):  
M.K. Das ◽  
J.N. Tandon
Keyword(s):  
Solar Flares ◽  
Galactic Cosmic Rays ◽  
Flare Activity ◽  
Radio Bursts ◽  
Triggering Mechanism ◽  
X Ray ◽  
Flare Stars ◽  
M Stars ◽  
Radio Band ◽  
Radio Flare

The flare phenomenon associated with dMe stars has received much attention in recent years (Gershberg 1975). Most of the flares have been detected in both optical and radio band (Lovell 1969; Kunkel 197U; Karpen et al, 1977). But as expected (Tandon 1976) only a few display weak soft X-ray emission (Karpen et al, 1977; Haisch and Linsky 1978)- Simultaneous X-ray, optical and radio observations of YZ CMi by Karpen et al (1977) shows no X-ray emission above 3σ level accompanying minor flares. Even coincident X-ray coverage with seven radio bursts shows no enhanced X-ray emission. Recently Haisch et al (1981) detected one well resolved X-ray flare on dM5e flare star Proxima Centauri and one coincident optical and radio flare out of five optical and twelve radio flare events. However, the X-ray flare on Proxima Centauri is not accompanied by any ultraviolet, optical or radio emission. Observations on flare stars show that they are more energetic, 102 - 103 times, than the corresponding solar flares. Considering the flare activity in dwarf M-stars to be similar but more energetic to that of a large solar flare, Tandon (1961) proposed red dwarf flares to be the source of low energy galactic cosmic rays. This hypothesis has been reexplored recently by Lovell (1974).

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