The Young Open Cluster Berkeley 55

Negueruela, I.; Marco, A.

doi:10.1088/0004-6256/143/2/46

Cited by 13 publications

(15 citation statements)

References 56 publications

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“…We find NGC 6520 to be quite a bit younger than most previous estimates, i.e. about 60 ± 10 Myr, consistent with stars of spectral type B4 and B5 in the cluster (Negueruela & Marco 2012). Its distance of about 2 ± 0.2 kpc (putting it on the outer edge of the Scutum-Centaurus spiral arm (Churchwell et al 2009)) has been reasonably estimated, but the distance to Barnard 86 has never been measured.…”

Section: Discussionsupporting

confidence: 76%

A New Look at Open Cluster NGC 6520

Odell

2013

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We use CCD and photoelectric photometry with Strömgren filters along with medium resolution spectra to investigate NGC 6520, an open cluster very nearly in the direction of the galactic center. We find an age of 60 Myr, a distance of 2 kpc, and an average reddening E(b-y) = 0.295, but which increases toward the south. The average heliocentric radial velocity of the B stars is −29 km s −1 , while the velocity of the nearby Barnard 86 is about 0 (heliocentric, −11 km s −1 compared to the LSR). This velocity difference amounts to about 1.8 kpc since the cluster formed, implying that it is extremely doubtful NGC 6520 is related to Barnard 86.

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Section: Discussionsupporting

confidence: 76%

A New Look at Open Cluster NGC 6520

Odell

2013

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“…We selected likely blue members from Th62 and confirmed evolved members from Mermilliod et al (2008). To make sure that we were not leaving out member stars of comparable brightness, we applied the criteria described in Negueruela & Marco (2012) over the 2MASS data to select more targets. We chose early-type stars using their QIR index (Negueruela & Schurch 2007).…”

Section: Spectral Classificationmentioning

confidence: 99%

“…Santos & Bica (1993) measuring the EW s of the Balmer lines and, more recently, Majaess et al (2013) using new BV JH and Padova isochrones obtained a similar value (log τ = 7.89 ± 0.15), even if the age of the Pleiades is now believed to be ≈ 120 Ma old. With an age just short of 100 Ma, NGC 6067 is the oldest cluster containing K0 -K2 Ib-II supergiants (see the discussion in Negueruela & Marco 2012).…”

Section: Fitting Isochronesmentioning

confidence: 99%

NGC 6067: a young and massive open cluster with high metallicity

Alonso-Santiago

Negueruela

Marco

et al. 2017

Monthly Notices of the Royal Astronomical Society

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NGC 6067 is a young open cluster hosting the largest population of evolved stars among known Milky Way clusters in the 50 -150 Ma age range. It thus represents the best laboratory in our Galaxy to constrain the evolutionary tracks of 5 -7 M stars.We have used high-resolution spectra of a large sample of bright cluster members (45), combined with archival photometry, to obtain accurate parameters for the cluster as well as stellar atmospheric parameters. We derive a distance of 1.78 ± 0.12 kpc, an age of 90 ± 20 Ma and a tidal radius of 14.8 +6.8 −3.2 arcmin. We estimate an initial mass above 5 700 M , for a present-day evolved population of two Cepheids, two A supergiants and 12 red giants with masses ≈ 6 M .We also determine chemical abundances of Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the red clump stars. We find a supersolar metallicity, [Fe/H]=+0.19±0.05, and a homogeneous chemical composition, consistent with the Galactic metallicity gradient. The presence of a Li-rich red giant, star 276 with A(Li)=2.41, is also detected. An over-abundance of Ba is found, supporting the enhanced s-process.The ratio of yellow to red giants is much smaller than one, in agreement with models with moderate overshooting, but the properties of the cluster Cepheids do not seem consistent with current Padova models for supersolar metallicity.

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“…The Galactic sample in Levesque & Massey (2012) shows a more clear secondary maximum at mid K, but in the MW most of the K supergiants are low-luminosity objects, and many are found in clusters too old to host real RSGs. Therefore, a significant fraction of K Ib stars should not be real supergiants but A16, page 18 of 24 high-luminosity red giants (Negueruela & Marco 2012). Thus, the apparent bimodality in the MW arises from the inclusion of a number of objects that are physically red giants in spite of their morphological classification.…”

Section: Spectral Type Distributionmentioning

confidence: 99%

Spectral type, temperature, and evolutionary stage in cool supergiants

Dorda

Negueruela

González-Fernández

et al. 2016

A&A

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Context. In recent years, our understanding of red supergiants has been questioned by strong disagreements between stellar atmospheric parameters derived with different techniques. Temperature scales have been disputed, and the possibility that spectral types do not depend primarily on temperature has been raised. Aims. We explore the relations between different observed parameters, and we explore the ability to derive accurate intrinsic stellar parameters from these relations through the analysis of the largest spectroscopic sample of red supergiants to date. Methods. We obtained intermediate-resolution spectra of a sample of about 500 red supergiants in the Large and the Small Magellanic Cloud. From these spectra, we derive spectral types and measure a large set of photospheric atomic lines. We explore possible correlations between different observational parameters, also making use of near-and mid-infrared colours and literature on photometric variability.Results. Direct comparison between the behaviour of atomic lines (Fe i, Ti i, and Ca ii) in the observed spectra and a comprehensive set of synthetic atmospheric models provides compelling evidence that effective temperature is the prime underlying variable driving the spectral-type sequence between early G and M2 for supergiants. In spite of this, there is a clear correlation between spectral type and luminosity, with later spectral types tending to correspond to more luminous stars with heavier mass loss. This trend is much more marked in the LMC than in the SMC. The population of red supergiants in the SMC is characterised by a higher degree of spectral variability, early spectral types (centred on type K1) and low mass-loss rates (as measured by dust-sensitive mid-infrared colours). The population in the LMC displays less spectroscopic variability and later spectral types. The distribution of spectral types is not single-peaked. Instead, the brightest supergiants have a significantly different distribution from less luminous objects, presenting mostly M subtypes (centred on M2), and increasing mass-loss rates for later types. In this regard, the behaviour of red supergiants in the LMC is not very different from that of Milky Way objects. Conclusions. The observed properties of red supergiants in the SMC and the LMC cannot be described correctly by standard evolutionary models. The very strong correlation between spectral type and bolometric luminosity, supported by all data from the Milky Way, cannot be reproduced at all by current evolutionary tracks.

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The Young Open Cluster Berkeley 55

Cited by 13 publications

References 56 publications

A New Look at Open Cluster NGC 6520

A New Look at Open Cluster NGC 6520

NGC 6067: a young and massive open cluster with high metallicity

Spectral type, temperature, and evolutionary stage in cool supergiants

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