Multicolour deep CCD photometric study of the moderately young
southern open star clusters NGC 3228, NGC 4103, NGC 5662 and 
NGC 6087

Sagar, Ram; Cannon, R. D.

doi:10.1051/aas:1997293

Cited by 10 publications

(3 citation statements)

References 33 publications

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“…All the authors provide NGC 4103 MS turn off age and are unanimous in its value. The age is 22-41 Myr according to Lyngå (1987), 24 ± 9 Myr according to LGM2.2, Sagar & Cannon (1997) find it to be about 30 Myr, Forbes (1996) estimated about 25 Myr and notes, that MS turn on age should not be much different, and according to Sanner et al (2001) the age is 20 ± 5 Myr. Again we give the lowest value of the cluster age of about 6 Myr and believe, that both cluster CMD and LF support this value.…”

Section: Ngc 4103mentioning

confidence: 96%

“…Young clusters are natural laboratories for the study of various issues related to star formation processes, e.g., the initial mass function (IMF), duration of star formation etc. In recent years, some remote young clusters have been studied using BV RI CCD observations (e.g., see Sagar & Griffiths 1991, Phelps & Janes 1993, Sagar & Cannon 1995, Sagar & Cannon 1997, Sagar & Griffiths 1998, Subramaniam & Sagar 1999, Sanner et al 2001, Pandey et al 2001, Piatti et al 2002. These observations were used for the construction of color-color diagrams, color-magnitude diagrams (CMDs) and luminosity functions (LFs).…”

Section: Introductionmentioning

confidence: 99%

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On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions

Пискунов

Belikov

Kharchenko

et al. 2004

Monthly Notices of the Royal Astronomical Society

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Based on the CCD observations of remote young open clusters NGC 2383, NGC 2384, NGC 4103, NGC 4755, NGC 7510 and Hogg 15, we construct their observed luminosity functions (LFs). The observed LFs are corrected for field star contamination determined with the help of galactic star count model. In the case of Hogg 15 and NGC 2383 we also considered the additional contamination from neighboring clusters NGC 4609 and NGC 2384 respectively. These corrections provided the realistic pattern of cluster LF in the vicinity of the MS turn on point and at fainter magnitudes, revealed the so called H-feature arising due to transition of the Pre-MS phase to MS, which is dependent on the cluster age. The theoretical LFs were constructed representing a cluster population model with continuous star formation for a short time scale and a power law Initial Mass Function (IMF) and these were fitted to the observed LF. As a result we are able to determine for each cluster a set of parameters, describing cluster population (the age, duration of star formation, IMF slope, and percentage of field star contamination). It was found that in spite of the non-monotonic behavior of observed LFs, cluster IMFs can be described as the power law functions with slopes similar to Salpeter's value. The present Main Sequence turn on cluster ages are several times lower than those derived from the fitting of theoretical isochrones to turn off region of the upper Main Sequences.

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Section: Ngc 4103mentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions

Пискунов

Belikov

Kharchenko

et al. 2004

Monthly Notices of the Royal Astronomical Society

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“…The cluster has been studied since the 1960s through optical data and more recently with near infrared 2MASS data. There is only one study based on CCD photometry with UBVRI data performed by Sagar & Cannon (1997). We refer the reader to the very recent study of Aidelman et al (2018) for a complete compilation of the parameters of the cluster determined by different authors, using different data and techniques.…”

Section: Ngc 6087mentioning

confidence: 99%

Astrometric and photometric study of Dias 4, Dias 6, and other five open clusters using ground-based and Gaia DR2 data

Dias

Monteiro

Lépine

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We present a study of 7 southern open clusters based on UBVRI CCD photomety (Johnsons-Cousins system) and Gaia DR2 data. Dias 4, Dias 6 and four other clusters had UBVRI photometric observations determined for the first time. From the observational UBVRI data we obtained photometric membership probability estimates and, using the proper motions from the UCAC5 catalog, we also determined the kinematic membership. From Gaia DR2 astrometric data we determine the stellar membership using proper motions and parallaxes, taking into account the full covariance matrix. For both independent sets of data and membership we apply our non subjective multidimensional global optimization tool to fit theoretical isochrones to determine the distance, age, reddening, metallicity and binary fraction of the clusters. The results of the mean proper motions, distances and ages are in agreement, but the ones obtained from Gaia DR2 data are more precise in both membership selection and estimated parameters. In the case of NGC 6087, the Cepheid S Nor, member of the open cluster, was used to obtain an independent distance estimate, confirming the one determined by our fitting method. We also report a serendipitous discovery of two new clusters in the extended field near what was originally Dias 4. 1 The latest version (3.5) can be accessed on line at https:// wilton.unifei.edu.br/ocdb/.has contributed in this topic through membership probability estimates from both photometric (Monteiro et al. 2017) and proper motion data (Dias et al. 2014(Dias et al. , 2018. In this study we show how the solution of this question evolved in the era of the Gaia mission (Gaia Collaboration et al. 2018a).The open clusters investigated in the present study were selected from DAML02 with the aim to provide a set of homogeneous UBVRI data and parameters determined from them in a non subjective isochrone-fitting approach. For all the clusters studied here, except for NGC 6087, these are the first results based on UBVRI data. The cluster NGC 6087 was observed in this run because the Cepheid S Nor, member of the cluster, allows us to obtain an independent check of the distance estimate by our isochrone fit method.Despite the fact that several of the clusters investigated in the present work had previous determinations of distances and ages, important corrections were needed given the discrepancies between results obtained by different works using different methods, as discussed by Netopil et al. (2015).

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Can massive Be/Oe stars be progenitors of long gamma ray bursts?

Martayan

Zorec²,

Frémat³

et al. 2010

A&A

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Context. The identification of long-gamma-ray-bursts (LGRBs) is still uncertain, although the collapsar engine of fast-rotating massive stars is gaining a strong consensus. Aims. We propose that low-metallicity Be and Oe stars, which are massive fast rotators, as potential LGRBs progenitors. Methods. We checked this hypothesis by 1) testing the global specific angular momentum of Oe/Be stars in the ZAMS with the SMC metallicity; 2) comparing the ZAMS (Ω/Ω c , M/M ) parameters of these stars with the area predicted theoretically for progenitors with metallicity Z = 0.002; and 3) calculating the expected rate of LGRBs/year/galaxy and comparing them with the observed ones. To this end, we determined the ZAMS linear and angular rotational velocities for SMC Be and Oe stars using the observed V sin i parameters, corrected from the underestimation induced by the gravitational darkening effect. Results. The angular velocities of SMC Oe/Be stars are on average Ω/Ω c = 0.95 in the ZAMS. These velocities are in the area theoretically predicted for the LGRBs progenitors. We estimated the yearly rate per galaxy of LGRBs and the number of LGRBs produced in the local Universe up to z = 0.2. We have considered that the mass range of LGRB progenitors corresponds to stars hotter than spectral types B0-B1 and used individual beaming angles from 5 to 15• . We thus obtain R predLGRB ∼ 10 −7 to ∼10 −6LGRBs/year/galaxy, which represents on average 2 to 14 LGRB predicted events in the local Universe during the past 11 years. The predicted rates could widely surpass the observed ones [(0.2−3) × 10 −7LGRBs/year/galaxy; 8LGRBs observed in the local Universe during the last 11 years] if the stellar counts were made from the spectral type B1-B2, in accordance with the expected apparent spectral types of the appropriate massive fast rotators. Conclusions. We conclude that the massive Be/Oe stars with SMC metallicity could be LGRBs progenitors. Nevertheless, other SMC O/B stars without emission lines, which have high enough specific angular momentum, can enhance the predicted R LGRB rate.

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Multicolour deep CCD photometric study of the moderately young southern open star clusters NGC 3228, NGC 4103, NGC 5662 and NGC 6087

Cited by 10 publications

References 33 publications

On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions

On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions

Astrometric and photometric study of Dias 4, Dias 6, and other five open clusters using ground-based and Gaia DR2 data

Can massive Be/Oe stars be progenitors of long gamma ray bursts?

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