Intermediate to low-mass stellar content of Westerlund 1

Brandner, W.; Clark, J. S.; Stolte, A.; Waters, Rens; Negueruela, I.; Goodwin, S. P.

doi:10.1051/0004-6361:20077579

Cited by 115 publications

(182 citation statements)

References 62 publications

(108 reference statements)

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“…Recent deep-IR imaging identifies the MS and pre-MS populations of Wd 1, leading to a photometric distance of 4.0±0.3 kpc (Brandner et al 2008), consistent with both 4.7 ± 1.1 kpc from an analysis of near-IR photometry of the WR stars in Wd 1 (Crowther et al 2006), and on an atomic hydrogen absorption distance of 3.9±0.7 kpc (Kothes & Dougherty 2007). …”

Section: The Stellar Sourcessupporting

confidence: 71%

Radio emission from the massive stars in the galactic super star cluster Westerlund 1

Dougherty

Clark

Negueruela

et al. 2010

A&A

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Aims. Current mass-loss rate estimates imply that main sequence line-driven winds are not sufficient to strip away the H-rich envelope to yield Wolf-Rayet (WR) stars. The rich transitional population of the young massive cluster Westerlund 1 (Wd 1) provides an ideal laboratory to observe and constrain mass-loss processes throughout the transitional phase of stellar evolution. Methods. We present an analysis of deep radio continuum observations of Wd 1 obtained with the Australia Telescope Compact Array at four frequency bands that permit investigation of the intrinsic characteristics of the radio emission. Results. We detect 18 cluster members, a sample dominated by the cool hypergiants, with additional detections amongst the hotter OB supergiants and WR stars. The radio properties of the sample are diverse, with thermal, non-thermal and composite thermal/nonthermal sources present. Mass-loss rates determined for stars with partially optically thick stellar winds are ∼10 −5 M yr −1 across all spectral types, insufficient to enable the formation of WRs during a massive star lifetime, and the stars must undergo a period of greatly enhanced mass loss. The sgB[e] star W9, the brightest radio source in Wd 1, may provide an example, with a current mass-loss rate an order of magnitude higher than the other cluster members, and an extended nebula interpreted as a wind from an earlier epoch with a density ∼3× the current wind. Such an envelope structure in W9 is reminiscent of luminous blue variables, and one that shows evidence of two eras of high, possibly eruptive mass loss. Surprisingly, three of the OB supergiants are detected, implying unusually dense winds, though they are embedded in more extended emission regions that may influence the derived parameters. They also may have composite spectra, suggesting binarity, which can lead to a higher flux than expected from a stellar wind. Spatially resolved nebulae are associated with three of the four RSGs and three of the six YHGs in the cluster, which are due to quiescent mass loss rather than outbursts. The extended nebulae of W20 and W26 have a cometary morphology, implying significant interaction with either the intracluster medium or cluster wind. For some of the cool star winds, the ionizing source may be a companion star though the cluster radiation density is sufficiently high to provide the necessary ionizing radiation. Five WR stars are detected with composite spectra, interpreted as arising in colliding-wind binaries.

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Section: The Stellar Sourcessupporting

confidence: 71%

Radio emission from the massive stars in the galactic super star cluster Westerlund 1

Dougherty

Clark

Negueruela

et al. 2010

A&A

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“…The data set used in the present analysis has been extensively described in Brandner et al (2008) -hereafter B08-and used also in Gennaro et al (2011) -hereafter G11. We refer the reader to these two papers for a full description of the data reduction and analysis process.…”

Section: The Datamentioning

confidence: 99%

“…Wd 1 is a ∼ 5 Myr old, ∼ 2 pc across (half-mass radius of ∼ 1 pc, see Brandner et al 2008), and ∼ 5×10 4 M cluster making it the most massive young cluster in the Galaxy (Clark et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Hierarchical formation of Westerlund 1: a collapsing cluster with no primordial mass segregation?

Gennaro

Goodwin

Parker

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We examine the level of substructure and mass segregation in the massive, young cluster Westerlund 1. We find that it is relatively smooth, with little or no mass segregation, but with the massive stars in regions of significantly higher than average surface density. While an expanding or bouncing-back scenario for the evolution of Westerlund 1 cannot be ruled out, we argue that the most natural model to explain these observations is one in which Westerlund 1 formed with no primordial mass segregation and at a similar or larger size than we now observe.

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“…Thus, the availability of a large database with a fine grid of chemical compositions, masses, and ages will allow us to improve our understanding of the star formation process taking full advantage of the growing amount of data of very young clusters and associations in the Milky Way (e.g. Stolte et al 2005;Delgado et al 2007;Brandner et al 2008), the Small Magellanic Cloud (e.g. Gouliermis et al 2006b;Nota et al 2006;Carlson et al 2007;Gouliermis et al 2007b;Sabbi et al 2007;Gouliermis et al 2008;Cignoni et al 2009Cignoni et al , 2010, and the Large Magellanic Cloud (e.g.…”

Section: Introductionmentioning

confidence: 99%

The Pisa pre-main sequence tracks and isochrones

Tognelli

Moroni

Degl’Innocenti

2011

A&A

268

419

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Context. In recent years new observations of pre-main sequence stars (pre-MS) with Z ≤ Z have been made available. To take full advantage of the continuously growing amount of data of pre-MS stars in different environments, we need to develop updated pre-MS models for a wide range of metallicity to assign reliable ages and masses to the observed stars. Aims. We present updated evolutionary pre-MS models and isochrones for a fine grid of mass, age, metallicity, and helium values. Methods. We use a standard and well-tested stellar evolutionary code (i.e. FRANEC), that adopts outer boundary conditions from detailed and realistic atmosphere models. In this code, we incorporate additional improvements to the physical inputs related to the equation of state and the low temperature radiative opacities essential to computing low-mass stellar models. Results. We make available via internet a large database of pre-MS tracks and isochrones for a wide range of chemical compositions (Z = 0.0002−0.03), masses (M = 0.2−7.0 M ), and ages (1−100 Myr) for a solar-calibrated mixing length parameter α (i.e. 1.68). For each chemical composition, additional models were computed with two different mixing length values, namely α = 1.2 and 1.9. Moreover, for Z ≥ 0.008, we also provided models with two different initial deuterium abundances. The characteristics of the models have been discussed in detail and compared with other work in the literature. The main uncertainties affecting theoretical predictions have been critically discussed. Comparisons with selected data indicate that there is close agreement between theory and observation.

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Intermediate to low-mass stellar content of Westerlund 1

Cited by 115 publications

References 62 publications

Radio emission from the massive stars in the galactic super star cluster Westerlund 1

Radio emission from the massive stars in the galactic super star cluster Westerlund 1

Hierarchical formation of Westerlund 1: a collapsing cluster with no primordial mass segregation?

The Pisa pre-main sequence tracks and isochrones

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