Integrated spectral properties of 22 small angular diameter  galactic open clusters

Ahumada, A. V.; Clariá, J. J.; Bica, E.

doi:10.1051/0004-6361:20077608

Cited by 14 publications

(27 citation statements)

References 47 publications

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“…(1) Lifetime calculated relative to the known age of the stars in the young cluster Pismis 24 (cf. Massey et al 2001 andAhumada et al 2007) using the census given in line 1. (2) Free-fall time measured from the mean values of the volume-averaged density given line 5: t free−fall = 3π 32G ρ (3) The numbers of OB3 stars in Cygnus X and thus the statistical lifetimes of high-mass young stellar objects have been corrected from the values given in Motte et al (2007). 3.…”

Section: Discussionmentioning

confidence: 99%

The earliest phases of high-mass star formation: the NGC 6334-NGC 6357 complex

Russeil¹,

Zavagno²,

Motte

et al. 2010

A&A

135

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Context. Our knowledge of high-mass star formation has been mainly based on follow-up studies of bright sources found by IRAS, and has thus been incomplete for its earliest phases, which are inconspicuous at infrared wavelengths. With a new generation of powerful bolometer arrays, unbiased large-scale surveys of nearby high-mass star-forming complexes now search for the high-mass analog of low-mass cores and class 0 protostars. Aims. Following the pioneering study of Cygnus X, we investigate the star-forming region NGC 6334-NGC 6357 (∼1.7 kpc). Methods. We study the complex NGC 6334-NGC 6357 in an homogeneous way following the previous work of Motte and collaborators. We used the same method to extract the densest cores which are the most likely sites for high-mass star formation. We analyzed the SIMBA/SEST 1.2 mm data presented in Munoz and coworkers, which covers all high-column density areas (A v ≥ 15 mag) of the NGC 6334-NGC 6357 complex and extracted dense cores following the method used for Cygnus X. We constrain the properties of the most massive dense cores (M > 100 M ) using new molecular line observations (as SiO, N 2 H + ,H 13 CO + , HCO + (1-0) and CH 3 CN) with Mopra and a complete cross-correlation with infrared databases (MSX, GLIMPSE, MIPSGAL) and literature. Results. We extracted 163 massive dense cores of which 16 are more massive than 200 M . These high-mass dense cores have a typical FWHM size of 0.37 pc, an average mass of M ∼ 600 M , and a volume-averaged density of ∼1.5 × 10 5 cm −3 . Among these massive dense cores, 6 are good candidates for hosting high-mass infrared-quiet protostars, 9 cores are classified as high-luminosity infrared protostars, and we find only one high-mass starless clump (∼0.3 pc, ∼4 × 10 4 cm −3 ) that is gravitationally bound. Conclusions. Since our sample is derived from a single molecular complex and covers every embedded phase of high-mass star formation, it provides a statistical estimate of the lifetime of massive stars. In contrast to what is found for low-mass class 0 and class I phases, the infrared-quiet protostellar phase of high-mass stars may last as long as their more well known high-luminosity infrared phase. As in Cygnus X, the statistical lifetime of high-mass protostars is shorter than found for nearby, low-mass star-forming regions which implies that high-mass pre-stellar and protostellar cores are in a dynamic state, as expected in a molecular cloud where turbulent and/or dynamical processes dominate.

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Section: Discussionmentioning

confidence: 99%

The earliest phases of high-mass star formation: the NGC 6334-NGC 6357 complex

Russeil¹,

Zavagno²,

Motte

et al. 2010

A&A

135

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“…The unit of time was estimated from the number and age of OB stars. The adopted age of OB stars in NGC 6334-NGC 6357 comes from the age of the cluster Pismis 24, which is between 1.73 Myr (Massey et al 2001) and 5 ± 3 Myr (Ahumada et al 2007). This means that from our number of ∼230 OB stars, one high-mass young object corresponds to a statistical lifetime of between ∼7.5 × 10 3 yr and ∼2.2 × 10 4 yr. We can then, in NGC 6334-NGC 6357, estimate that the starless and the protostellar phases have a statistical lifetime of 7.5 × 10 3 −2.2 × 10 4 yr and 1.1 × 10 5 −3.3 × 10 5 yr, respectively.…”

Section: The Ob Stars Censusmentioning

confidence: 99%

Statistical study of OB stars in NGC 6334 and NGC 6357

Russeil

Zavagno

Adami

et al. 2012

A&A

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Context. Star-forming complexes are large structures exhibiting massive star-formation at different stages of evolution, from dense cores to well-developed H ii regions. They are very interesting for the study of the formation and evolution of stars. NGC 6334 and NGC 6357 are two active and relatively nearby star-forming complexes. From the extinction map and the sub-mm cold dust emission, and because they have similar velocities, these regions are most likely connected. However, located in the direction of the Galactic center their radial velocity is not representative of their distance. An alternative is then to determine the distance of NGC 6334 and NGC 6357 from their stellar content. Aims. Our aim is to perform a census of O-B3 ionising stars in NGC 6334 and NGC 6357, to determine the extinction coefficient, and the distance of both regions. A census of O-B3 stars is an essential basis for estimating the statistical lifetime of the earliest massive star-forming phases. Methods. We performed a U, B, V, and R photometric survey of a large area covering NGC 6334 and NGC 6357 with the VIMOS (ESO-VLT) and the MOSAIC (CTIO) instruments. This allows us to have a complete census of O to B3 stars up to V = 22.6 mag. The OB stars are selected based on their U − B and B − V colors. The most robust extinction coefficient is determined from color−color plots before computing the distance of the OB stars. Results. We find a higher value than typical of the diffuse interstellar medium for R V of 3.53 ± 0.08 and 3.56 ± 0.15 for NGC 6357 and NGC 6334, respectively. Adopting these R V values, the distances of NGC 6357 and NGC 6334 are 1.9 ± 0.4 kpc and 1.7 ± 0.3 kpc. We conclude that, within the error bars, both regions are thus at the same distance of 1.75 kpc (weighted mean). We confirm that the value of R V is linked to the large dust grain content. In particular, we found that there are more very small grains in NGC 6357 than in NGC 6334, suggesting that NGC 6357 could be more evolved than NGC 6334. Placed in the Galactic context, the NGC 6334-NGC 6357 complex appears to be located at the inner edge of the Sagittarius-Carina arm. Our census of O to B3 stars leads to a count of ∼230, which allows us to determine the statistical lifetime of the earliest phases of the massive stars. The starless and the protostellar phases have a mean statistical lifetime of ∼1.5 × 10 4 yr and ∼2.2 × 10 5 yr, respectively.

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“…This procedure consists of achieving the best possible match between the analysed cluster spectrum and a template spectrum of known age and metallicity. This method presents the advantage of permitting a simultaneous determination of both foreground reddening and age (e.g., Ahumada et al 2007;Benítez-Llambay et al 2012). Although there exists a template library covering λ < 4600 Å that represents the integrated spectral evolution of SCs in the Magellanic Clouds (Santos et al 1995), the age range of this database corresponds to clusters younger than ∼170 Myr, namely, those much younger than those analysed in this work.…”

Section: Reddening and Age Determinationmentioning

confidence: 99%

“…However, it is important to highlight that even a small error in the E(B − V) may have noticeable effects on the other quantities. Template spectra are very useful in deriving individual cluster parameters not only in our Galaxy (e.g., Schiavon et al 2005;Ahumada et al 2007) but also in distant galaxies (e.g., Jablonka et al 1998;Trancho et al 2007). They are also useful for testing stellar population models (Lyubenova et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Reddening and age of six poorly studied star clusters of the Large Magellanic Cloud derived from integrated spectra

Minniti

Ahumada

Clariá

et al. 2014

A&A

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Aims. To increase the number of studied star clusters (SCs) of the Large Magellanic Cloud (LMC), we present flux-calibrated integrated spectra in the optical range (λ = 3700-6800 Å) for six poorly studied LMC SCs of IVA type. This type corresponds to the age range between 200 and 400 Myr. We also aim at creating a new template spectrum representative of this age range at the metallicity level of the LMC. Methods. Foreground reddening E(B − V) values and ages are derived by applying the template matching method that consists of comparing the line strengths and continuum distribution of the cluster spectra with those of template cluster spectra with known properties. The equivalent width (EW) of the Balmer lines and the diagnostic diagrams involving the sum of EWs of selected spectral lines were also employed as age indicators. Results. For the first time, we provide estimates of the clusters' reddenings and ages. As expected, all the clusters appear to be of nearly the same age, their mean value being (400 ± 100) Myr, while the resulting mean E(B − V) values range between 0.00 and 0.10 mag.Conclusions. The present cluster sample complements previous ones in an effort to gather a spectral library with several clusters per age bin. By averaging the reddening-corrected integrated spectra, weighted by their signal-to-noise ratios (S/N), a new high S/N template spectrum of 400 Myr has been created.

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Integrated spectral properties of 22 small angular diameter galactic open clusters

Cited by 14 publications

References 47 publications

The earliest phases of high-mass star formation: the NGC 6334-NGC 6357 complex

The earliest phases of high-mass star formation: the NGC 6334-NGC 6357 complex

Statistical study of OB stars in NGC 6334 and NGC 6357

Reddening and age of six poorly studied star clusters of the Large Magellanic Cloud derived from integrated spectra

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