scholarly journals Comparative Study of Young Open Clusters: Age Determination and Stellar Content

1980 ◽  
Vol 85 ◽  
pp. 245-245
Author(s):  
J. C. Mermilliod
Keyword(s):  
Comparative Study ◽  
Age Groups ◽  
Age Determination ◽  
Open Clusters ◽  
Red Giants ◽  
Be Stars ◽  
Stellar Content ◽  
Blue Stragglers ◽  
The Mean ◽  
Hr Diagram

75 young open clusters have been divided into 14 age groups on the basis of their MV/U-B diagrams. Composite HR diagrams have been constructed and empirical isochronous curves estimated (Figure 1). The left envelope defines a ZAMS. The mean position of the red giants in the HR diagram has been investigated, as well as the occurrence and location of Ap, Am and Be stars and of blue stragglers. Red giants appear mainly in clumps (shaded area).

scholarly journals Composite Colour-Magnitude and Colour-Colour Diagrams for Be Stars in Open Clusters

1982 ◽  
Vol 98 ◽  
pp. 23-26
Author(s):  
J.-C. Mermilliod
Keyword(s):  
Age Groups ◽  
Open Clusters ◽  
Be Stars ◽  
Photoelectric Photometry ◽  
Absolute Magnitudes ◽  
Colour Indices

By the end of 1980, the total number of Be stars discovered in the field of open clusters amounted to 180 stars distributed in 60 clusters. Among these, 110 Be stars belong to 32 clusters included in the sample I studied, which contains 75 open clusters younger than the Hyades. But only 88 stars with complete UBV photoelectric photometry have been taken into consideration here. The concept of age groups, defined elsewhere (Mermilliod 1981a), is used throughout the present analysis, as well as the new estimate of the colour excesses and distance moduli I obtained for these 32 clusters. Under the assumption of uniform reddening across the clusters, absolute magnitudes and dereddened colour indices have been calculated for the 88 Be stars.

scholarly journals UOCS*. III. UVIT catalogue of open clusters with machine learning based membership using Gaia EDR3 astrometry

2021 ◽  
Author(s):  
Vikrant V Jadhav ◽  
Clara M Pennock ◽  
Annapurni Subramaniam ◽  
Ram Sagar ◽  
Prasanta Kumar Nayak
Keyword(s):  
Machine Learning ◽  
Main Sequence ◽  
Learning Algorithm ◽  
Ultra Violet ◽  
Gaussian Mixture ◽  
Open Clusters ◽  
Red Giants ◽  
Cluster Membership ◽  
Blue Stragglers ◽  
Red Clump

Abstract We present a study of six open clusters (Berkeley 67, King 2, NGC 2420, NGC 2477, NGC 2682 and NGC 6940) using the Ultra Violet Imaging Telescope (UVIT) aboard ASTROSAT and Gaia EDR3. We used combinations of astrometric, photometric and systematic parameters to train and supervise a machine learning algorithm along with a Gaussian mixture model for the determination of cluster membership. This technique is robust, reproducible and versatile in various cluster environments. In this study, the Gaia EDR3 membership catalogues are provided along with classification of the stars as members, candidates and field in the six clusters. We could detect 200–2500 additional members using our method with respect to previous studies, which helped estimate mean space velocities, distances, number of members and core radii. UVIT photometric catalogues, which include blue stragglers, main-sequence and red giants are also provided. From UV–Optical colour-magnitude diagrams, we found that majority of the sources in NGC 2682 and a few in NGC 2420, NGC 2477 and NGC 6940 showed excess UV flux. NGC 2682 images have ten white dwarf detection in far-UV. The far-UV and near-UV images of the massive cluster NGC 2477 have 92 and 576 members respectively, which will be useful to study the UV properties of stars in the extended turn-off and in various evolutionary stages from main-sequence to red clump. Future studies will carry out panchromatic and spectroscopic analysis of noteworthy members detected in this study.

scholarly journals Estimation of Age Using Dimensions of Apical Foramina of Teeth

2021 ◽  
Vol 10 (10) ◽  
pp. 705-710
Author(s):  
Aklesha Behera ◽  
Archana Santhanam ◽  
Herald J. Sherlin ◽  
Gifrina Jayaraj ◽  
Don K.R.
Keyword(s):  
Age Estimation ◽  
Age Groups ◽  
Age Determination ◽  
Forensic Odontology ◽  
Estimation Methods ◽  
P Value ◽  
Age Group ◽  
Human Beings ◽  
Mean Diameter ◽  
The Mean

BACKGROUND Forensic odontology is an ever growing and a flourishing science. The science deals in criminal laws by using dental knowledge. People who practice forensic odontology are called as forensic dentists. They are asked to determine the age, sex, race, occupation, previous dental history and various other determinants like DNA verification in unidentified human beings. Teeth are a very special tissue in the human body. Teeth are the only tissue which can survive through extreme climatic and environmental conditions like heat, cold etc. hence many a times retains its morphology. Age estimation has been studied by many researchers but age estimation methods have been incapable of providing the age estimation in older age groups. The study aims to determine the age using the dimensions of the apical foramen from middle age to old age groups. METHODS A descriptive ex vivo study, was done from December 2019 to March 2020. Freshly extracted teeth were collected and cleaned using hydrogen peroxide. The teeth selected were single rooted teeth like incisors, canine and premolars in the age group of 30 to 40 years, 41 - 50 years, 51 - 60 years and 61 - 70 years. Apical one third of the teeth was sectioned, mounted over a slide and placed perpendicular to the lens of the stereomicroscope. Using Mag Vision and Image J software, photomicrographs and measurements were taken. Data procured was tabulated and statistical analysis was done using Statistical Package for the Social Sciences (SPSS) version 20. RESULTS In 30 - 40 years age group, the mean diameter of all single rooted teeth was 0.35 mm. Among the 41 - 50 years age group, the mean diameter was 0.43mm. In 51 - 60 years age group it was 0.41mm and in the 61 - 70 years age group, the mean diameter was 0.36 mm. Pearson chi square P value for incisor is 0.280, canine is 0.223 and premolar is 0.326. CONCLUSIONS Age estimation can be done using physiological dimensions of apical foramen. From the present study, dimensions of apical foramen decreases with increasing age due to cementum deposition. KEY WORDS Age Determination, Apical Foramen Diameter, Single Rooted Teeth

Growth and Habits of the Sea Mullet, Mugil dobula Gnnther, in Western Australia

1951 ◽  
Vol 2 (2) ◽  
pp. 193 ◽  
Author(s):  
JM Thomson
Keyword(s):  
Fresh Water ◽  
Western Australia ◽  
Age Groups ◽  
Age Determination ◽  
River System ◽  
The Mean ◽  
Pass Through ◽  
Considerable Individual Variation ◽  
Incomplete Sampling ◽  
Western Australian

Morphologically and physiologically, the sea mullet of Western Australia seems to be identical with that of the eastern Australian coast. No raciation can be detected either within Western Australian waters or between the stocks of eastern and Western Australia. However, the mean growth rate varies from one estuary to another and from year to year within any particular river system. Growth is isometric and shows considerable individual variation though tending to a mean rate. Increase in length is seasonal, practically stopping in midwinter and reaching a peak in midsummer. The seasons of fish and scale growth are contemporaneons. The annuli form at the end of September or the beginning of October, when growth recommences after the winter cessation. Mullet mature at a size of 31–35 cm. (12 1/2-13 3/4 in. length to caudal fin) at the end of their third year. The movement of mullet from the fishing grounds as they increase in size leads to an incomplete sampling of the population so that Petersen's method of age determination is inappIicable owing to the apparent nonprogression of the modes. Of 7110 mullet tagged, only 97 or 1.35 per cent. were returned. The return for separate tagging operations varied from nil to 25 per cent. and according to localities from nil to 16 per cent. Only three fish were retaken outside the rivers in which they were tagged. These showed a northerly movement. Inside the rivers the young fish spread out over the estuary and into the fresh water; but the older age-groups remain in the slightly brackish or fresh water except during the migration season, when they pass through the saline estuaries on the way to the sea.

scholarly journals Variable Be Stars in h and χ Persei

1987 ◽  
Vol 92 ◽  
pp. 505-508
Author(s):  
C.L. Waelkens ◽  
P. Lampens ◽  
J. Cuypers ◽  
J. Denoyelle ◽  
D. Heynderickx ◽  
...  
Keyword(s):  
Age Groups ◽  
Variable Stars ◽  
Age Group ◽  
Be Stars ◽  
Stellar Content ◽  
Photometric Variability ◽  
Double Cluster

The double cluster h and χ Persei has since long been known to be rich in Be stars (Trumpler, 1926). It belongs to an age group in which various types of variable stars occur (Mermilliod, 1981). Other clusters of this age group are NGC 3293, the cluster that is richest in β Cephei variables (Balona and Engelbrecht, 1983), IC 2581, NGC 4755, and NGC 6871. The comparison of the characteristics of variable stars in all these clusters and in clusters of other age groups could reveal to which extent the cluster stellar content is determined by age and by other parameters, such as galactic location, and so metallicity. Since h and χ Persei are very rich clusters that have not yet been studied intensively as far as stellar variability is concerned (Percy, 1972), we have undertaken a study of the photometric variability of the brightest stars in the double cluster. Our first interest was to detect β Cephei variables, but it rapidly turned out that the double cluster contains a considerable amount of highly variable Be stars.

scholarly journals The log L/log Te diagram for intermediate mass pop I red giants

1984 ◽  
Vol 105 ◽  
pp. 105-107
Author(s):  
M. Grenon ◽  
J.C. Mermilliod
Keyword(s):  
Open Cluster ◽  
Age Groups ◽  
Open Clusters ◽  
Red Giants ◽  
Intermediate Mass ◽  
Double Stars ◽  
Young Clusters ◽  
Red Giant

The best empirical evolutionary tracks are provided by open cluster HR diagrams. The scarcity of giants in young clusters implies that diagrams of clusters having similar ages and metallicities have to be summed. Using UBV data, Mermilliod (1981a) has divided the nearby open clusters into 14 age groups, and has described the properties of the composite diagrams MV/(B-V) and Mbol/log T. Several features complicate the structure of composite HRD, namely the presence of double stars which often mimic extended blue loops and the contamination by non-member stars difficult to identify as such in distant clusters. In order to refine the red giant observed evolutionary properties, cluster giants have been remeasured in the Geneva photometry and with the spectrovelocimeter CORAVEL.

scholarly journals Extremely precise age and metallicity of the open cluster NGC 2506 using detached eclipsing binaries

2020 ◽  
Vol 499 (1) ◽  
pp. 1312-1339
Author(s):  
E Knudstrup ◽  
F Grundahl ◽  
K Brogaard ◽  
D Slumstrup ◽  
J A Orosz ◽  
...  
Keyword(s):  
Open Cluster ◽  
Age Determination ◽  
Open Clusters ◽  
Eclipsing Binaries ◽  
Stellar Structure ◽  
Red Giants ◽  
Effective Temperatures ◽  
Red Giant ◽  
The Masses ◽  
Giant Branch Stars

ABSTRACT Accurate stellar parameters of stars in open clusters can help constrain models of stellar structure and evolution. Here, we wish to determine the age and metallicity content of the open cluster NGC 2506. To this end, we investigated three detached eclipsing binaries (DEBs; V2032, V4, and V5) for which we determined their masses and radii, as well as four red giant branch stars for which we determined their effective temperatures, surface gravities, and metallicities. Three of the stars in the DEBs have masses close to the cluster turn-off mass, allowing for extremely precise age determination. Comparing the values for the masses and radii of the binaries to BaSTI (a Bag of Stellar Tracks and Isochrones) isochrones, we estimated a cluster age of 2.01 ± 0.10 Gyr. This does depend on the models used in the comparison, where we have found that the inclusion of convective core-overshooting is necessary to properly model the cluster. From red giant branch stars, we determined values for the effective temperatures, the surface gravities, and the metallicities. From these we find a cluster metallicity of −0.36 ± 0.10 dex. Using this value and the values for the effective temperatures, we determine the reddening to be E(b − y) = 0.057 ± 0.004 mag. Furthermore, we derived the distance to the cluster from Gaia parallaxes and found 3.101 ± 0.017 kpc, and we have performed a radial velocity membership determination for stars in the field of the cluster. Finally, we report on the detection of oscillation signals in γ Dor and δ Scuti members in data from the Transiting Exoplanet Survey Satellite (TESS) mission, including the possible detection of solar-like oscillations in two of the red giants.

scholarly journals Asteroseismology of Red-Giant Stars as a Novel Approach in the Search for Gravitational Waves

2015 ◽  
Vol 11 (A29B) ◽  
pp. 363-364
Author(s):  
Tiago L. Campante ◽  
Ilídio Lopes ◽  
D. Bossini ◽  
A. Miglio ◽  
W. J. Chaplin
Keyword(s):  
Gravitational Waves ◽  
Open Clusters ◽  
Red Giants ◽  
Natural Oscillations ◽  
Giant Stars ◽  
Novel Approach ◽  
Oscillation Modes ◽  
The Mean ◽  
Red Giant Stars ◽  
Red Giant

AbstractStars are massive resonators that may be used as gravitational-wave (GW) detectors with isotropic sensitivity. New insights on stellar physics are being made possible by asteroseismology, the study of stars by the observation of their natural oscillations. The continuous monitoring of oscillation modes in stars of different masses and sizes (e.g., as carried out by NASA's Kepler mission) opens the possibility of surveying the local Universe for GW radiation. Red-giant stars are of particular interest in this regard. Since the mean separation between red giants in open clusters is small (a few light years), this can in principle be used to look for the same GW imprint on the oscillation modes of different stars as a GW propagates across the cluster. Furthermore, the frequency range probed by oscillations in red giants complements the capabilities of the planned eLISA space interferometer. We propose asteroseismology of red giants as a novel approach in the search for gravitational waves.

scholarly journals On the self-consistent physical parameters of LMC intermediate-age clusters

2008 ◽  
Vol 4 (S256) ◽  
pp. 391-396
Author(s):  
Leandro O. Kerber ◽  
Basílio X. Santiago
Keyword(s):  
Stellar Population ◽  
Evolutionary Model ◽  
Open Clusters ◽  
Physical Parameters ◽  
Distance Modulus ◽  
Red Giants ◽  
Stellar Content ◽  
Self Consistent ◽  
Red Clump ◽  
Good Agreement

AbstractThe LMC clusters with similar ages to the Milky Way open clusters are in general more metal-poor and more populous than the latter, being located close enough to allow their stellar content to be well resolved. Therefore, they are unique templates of simple stellar population (SSP), being crucial to calibrate models describing the integral light as well as to test the stellar evolution theory. With this in mind we analyzed HST/WFPC2 (V, B − V) colour-magnitude diagrams (CMDs) of 15 populous LMC clusters with ages between ~0.3 Gyr and ~4 Gyr using different stellar evolutionary models. Following the approach described by Kerber, Santiago & Brocato (2007), we determined accurate and self-consistent physical parameters (age, metallicity, distance modulus and reddening) for each cluster by comparing the observed CMDs with synthetic ones generated using isochrones from the PEL and BaSTI libraries. These determinations were made by means of simultaneous statistical comparison of the main-sequence fiducial line and the red clump position, offering objective and robust criteria to select the best models. We compared these results with the ones obtained by Kerber, Santiago & Brocato (2007) using the Padova isochrones. This revealed that there are significant trends in the physical parameters due to the choice of stellar evolutionary model and treatment of convective core overshooting. In general, models that incorporate overshooting presented more reliable results than those that do not. Furthermore, the Padova models fitted better the data than the PEL and BaSTI models. Comparisons with the results found in the literature demonstrated that our derived metallicities are in good agreement with the ones from the spectroscopy of red giants. We also confirmed that, independent of the adopted stellar evolutionary library, the recovered 3D distribution for these clusters is consistent with a thick disk roughly aligned with the LMC disk as defined by field stars. Finally, we also provide new estimates of distance modulus to the LMC center, that are marginally consistent with the canonical value of 18.50 mag.

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