On the massive stellar population of the super star cluster Westerlund 1

Clark, J. S.; Negueruela, I.; Crowther, P. A.; Goodwin, S. P.

doi:10.1051/0004-6361:20042413

Cited by 282 publications

(577 citation statements)

References 75 publications

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“…Neither Danks 1 or 2 are visible in the MSX data -at the distance of the complex (see Sect. 4), it is likely that we could have only detected red supergiants or hot stars associated with a significant IR excess (similar to the case of Westerlund 1, Clark et al 2004). WR 48a is present and visible as the bright blue-ish object in the centre of the field; the emission is due to its dusty circumstellar environment (=MSX6C G305.3614+00.0561; Clark & Porter 2004, in prep.).…”

Section: Msx Mid-ir Datamentioning

confidence: 60%

Triggered massive star formation in the vicinity of WR 48a

Clark

Porter

2004

A&A

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114

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Abstract. We utilise Midcourse Space Experiment mid-IR imaging and published data to discuss the (massive) star formation region at galactic longitude ∼305 • , apparently associated with the Wolf Rayet WR 48a and the attendant clusters Danks 1 and 2. A spectacular three lobed wind blown bubble surrounds the aforementioned sources, for which we may infer a minimum age of ∼3 Myr from the presence of the WCL star. Near IR data reveals the presence of numerous embedded sources on the periphery of the wind blown bubble. The presence of coincindent H 2 O, OH and methanol maser emission is suggestive of ongoing massive star formation, which is suppported by the fluxes of the associated IR sources, and the requisite LyC flux required to support the emission from the subset that have associated ucH  regions. Consideration of the integrated radio flux of the complex implies that a minimum of 31 O7V stars must be present, under the assumption of no photon leakage. Given the age and morphology of the complex and in particular the observation that the central exciting clusters have entirely cleared their natal material, we expect this assumption will be violated, and hence that the true population of massive stars is likely to be significantly larger. If confirmed, the G305 complex represents one of the most massive regions of ongoing triggered star formation currently identified in the galaxy.

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Section: Msx Mid-ir Datamentioning

confidence: 60%

Triggered massive star formation in the vicinity of WR 48a

Clark

Porter

2004

A&A

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114

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“…Another distinctive feature of WR stars -the near-IR excess caused by free-free emission in their winds -has been exploited to yield further discoveries (Homeier et al 2003;Hadfield et al 2007;Mauerhan, Van Dyk & Morris 2011). These efforts, alongside several serendipitous discoveries (e.g., Clark et al 2005, Mauerhan et al 2010a, have brought the recognised Galactic WR star population to ∼635 as of March 2014 1 .…”

Section: Introductionmentioning

confidence: 99%

Spatial distribution of Galactic Wolf–Rayet stars and implications for the global population

Rosslowe

Crowther

2015

Monthly Notices of the Royal Astronomical Society

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We construct revised near-infrared absolute magnitude calibrations for 126 Galactic Wolf-Rayet (WR) stars at known distances, based in part upon recent large scale spectroscopic surveys. Application to 246 WR stars located in the field, permits us to map their Galactic distribution. As anticipated, WR stars generally lie in the thin disk (∼40 pc half width at half maximum) between Galactocentric radii 3.5-10 kpc, in accordance with other star formation tracers. We highlight 12 WR stars located at vertical distances of 300 pc from the midplane. Analysis of the radial variation in WR subtypes exposes a ubiquitously higher N W C /N W N ratio than predicted by stellar evolutionary models accounting for stellar rotation. Models for non-rotating stars or accounting for close binary evolution are more consistent with observations. We consolidate information acquired about the known WR content of the Milky Way to build a simple model of the complete population. We derive observable quantities over a range of wavelengths, allowing us to estimate a total number of 1200 +300 −100 Galactic WR stars, implying an average duration of ∼ 0.25 Myr for the WR phase at the current Milky Way star formation rate. Of relevance to future spectroscopic surveys, we use this model WR population to predict follow-up spectroscopy to K S ≃ 13 mag will be necessary to identify 95% of Galactic WR stars. We anticipate that ESA's Gaia mission will make few additional WR star discoveries via low-resolution spectroscopy, though will significantly refine existing distance determinations. Appendix A provides a complete inventory of 322 Galactic WR stars discovered since the VIIth catalogue (313 including Annex), including a revised nomenclature scheme.

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“…These objects are significantly more luminous than OCs (M V < ∼ −8 up to M V ∼ −15), making them promising candidate young GCs. Once thought to be absent in the Milky Way, recent observations suggest that their census may be quite incomplete, as some prominent cases have been found recently in the Galaxy as well (Clark et al 2005;Figer 2008;Messineo et al 2009). …”

Section: Introductionmentioning

confidence: 99%

An HST/WFPC2 survey of bright young clusters in M 31

Perina

Cohen²,

Barmby

et al. 2010

A&A

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Aims. We present the main results of an imaging survey of possible young massive clusters (YMC) in M 31 performed with the Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST), with the aim of estimating their age and their mass. We obtained shallow (to B ∼ 25) photometry of individual stars in 19 clusters (of the 20 targets of the survey). We present the images and color magnitude diagrams (CMDs) of all of our targets. Methods. Point spread function fitting photometry of individual stars was obtained for all the WFPC2 images of the target clusters, and the completeness of the final samples was estimated using extensive sets of artificial stars experiments. The reddening, age, and metallicity of the clusters were estimated by comparing the observed CMDs and luminosity functions (LFs) with theoretical models. Stellar masses were estimated by comparison with theoretical models in the log(Age) vs. absolute integrated magnitude plane, using ages estimated from our CMDs and integrated J, H, K magnitudes from 2MASS-6X. Results. Nineteen of the twenty surveyed candidates were confirmed to be real star clusters, while one turned out to be a bright star. Three of the clusters were found not to be good YMC candidates from newly available integrated spectroscopy and were in fact found to be old from their CMD. Of the remaining sixteen clusters, fourteen have ages between 25 Myr and 280 Myr, two have older ages than 500 Myr (lower limits). By including ten other YMC with HST photometry from the literature, we assembled a sample of 25 clusters younger than 1 Gyr, with mass ranging from 0.6 × 10 4 M to 6 × 10 4 M , with an average of ∼3 × 10 4 M . Our estimates of ages and masses well agree with recent independent studies based on integrated spectra. Conclusions. The clusters considered here are confirmed to have masses significantly higher than Galactic open clusters (OC) in the same age range. Our analysis indicates that YMCs are relatively common in all the largest star-forming galaxies of the Local Group, while the lack of known YMC older than 20 Myr in the Milky Way may stem from selection effects.

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On the massive stellar population of the super star cluster Westerlund 1

Cited by 282 publications

References 75 publications

Triggered massive star formation in the vicinity of WR 48a

Triggered massive star formation in the vicinity of WR 48a

Spatial distribution of Galactic Wolf–Rayet stars and implications for the global population

An HST/WFPC2 survey of bright young clusters in M 31

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