A High-resolution Multiband Survey of Westerlund 2 with the Hubble Space Telescope. III. The Present-day Stellar Mass Function

Zeidler, Peter; Nota, A.; Grebel, Eva K.; Sabbi, E.; Pasquali, A.; Tosi, M.; Christian, C. A.

doi:10.3847/1538-3881/153/3/122

Cited by 28 publications

(34 citation statements)

References 90 publications

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“…This could indicate mass segregation in the complex. Similar trends are also observed in other clusters like NGC 346 (Sabbi et al 2008), NGC 3603 (Harayama et al 2008), and Westerlund 2 (Zeidler et al 2017).…”

Section: Present Day Mass Functionsupporting

confidence: 86%

Stellar population of the superbubble N 206 in the LMC

Ramachandran

Hamann

Hainich

et al. 2018

A&A

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Context. Clusters or associations of early-type stars are often associated with a “superbubble” of hot gas. The formation of such superbubbles is caused by the feedback from massive stars. The complex N 206 in the Large Magellanic Cloud (LMC) exhibits a superbubble and a rich massive star population. Aims. Our goal is to perform quantitative spectral analyses of all massive stars associated with the N 206 superbubble in order to determine their stellar and wind parameters. We compare the superbubble energy budget to the stellar energy input and discuss the star formation history of the region. Methods. We observed the massive stars in the N 206 complex using the multi-object spectrograph FLAMES at ESO’s Very Large Telescope (VLT). Available ultra-violet (UV) spectra from archives are also used. The spectral analysis is performed with Potsdam Wolf–Rayet (PoWR) model atmospheres by reproducing the observations with the synthetic spectra. Results. We present the stellar and wind parameters of the OB stars and the two Wolf–Rayet (WR) binaries in the N 206 complex. Twelve percent of the sample show Oe/Be type emission lines, although most of them appear to rotate far below critical. We found eight runaway stars based on their radial velocity. The wind-momentum luminosity relation of our OB sample is consistent with the expectations. The Hertzsprung–Russell diagram (HRD) of the OB stars reveals a large age spread (1–30 Myr), suggesting different episodes of star formation in the complex. The youngest stars are concentrated in the inner part of the complex, while the older OB stars are scattered over outer regions. We derived the present day mass function for the entire N 206 complex as well as for the cluster NGC 2018. The total ionizing photon flux produced by all massive stars in the N 206 complex is Q0 ≈ 5 × 1050 s−1, and the mechanical luminosity of their stellar winds amounts to Lmec = 1.7 × 1038 erg s−1. Three very massive Of stars are found to dominate the feedback among 164 OB stars in the sample. The two WR winds alone release about as much mechanical luminosity as the whole OB star sample. The cumulative mechanical feedback from all massive stellar winds is comparable to the combined mechanical energy of the supernova explosions that likely occurred in the complex. Accounting also for the WR wind and supernovae, the mechanical input over the last five Myr is ≈ 2.3 × 1052 erg. Conclusions. The N206 complex in the LMC has undergone star formation episodes since more than 30 Myr ago. From the spectral analyses of its massive star population, we derive a current star formation rate of 2.2 × 10−3 M⊙ yr−1. From the combined input of mechanical energy from all stellar winds, only a minor fraction is emitted in the form of X-rays. The corresponding input accumulated over a long time also exceeds the current energy content of the complex by more than a factor of five. The morphology of the complex suggests a leakage of hot gas from the superbubble.

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Section: Present Day Mass Functionsupporting

confidence: 86%

Stellar population of the superbubble N 206 in the LMC

Ramachandran

Hamann

Hainich

et al. 2018

A&A

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“…A separate clue to what might be going on here comes from the structure of Wd2 itself: Zeidler et al (2017) have commented on the presence of the 'northern clump' offset from the main cluster by almost an arcminute: they argue that this would be consistent with late merging behaviour if Wd2 has built up from sub-clusters. These authors, along with Furukawa et al (2009) and others studying the molecular gas, have also raised the possibility that a larger scale molecular cloud collision was the ultimate trigger for Wd2's formation.…”

Section: Discussionmentioning

confidence: 98%

“…For these, we clarify their basic stellar parameters and ask whether they are potentially recent ejections. Westerlund 2 is one of a limited number of dense clusters in the Milky Way estimated to be more massive than 10 4 M -recently, Zeidler et al (2017) have obtained (3.6 ± 0.3) × 10 4 M . About the oldest age estimated for it is 2.5 Myrs (Rauw et al 2007): this cluster is young enough that the first supernova explosion is probably yet to happen.…”

Section: Introductionmentioning

confidence: 99%

Massive stars in the hinterland of the young cluster, Westerlund 2

Drew

Herrero

Mohr-Smith

et al. 2018

Monthly Notices of the Royal Astronomical Society

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An unsettled question concerning the formation and distribution of massive stars is whether they must be born in massive clusters and, if found in less dense environments, whether they must have migrated there. With the advent of wide-area digital photometric surveys, it is now possible to identify massive stars away from prominent Galactic clusters without bias. In this study we consider 40 candidate OB stars found in the field around the young massive cluster, Westerlund 2, by Mohr-Smith et al (2017): these are located inside a box of 1.5×1.5 square degrees and are selected on the basis of their extinctions and K magnitudes. We present VLT/X-shooter spectra of two of the hottest O stars, respectively 11 and 22 arcmin from the centre of Westerlund 2. They are confirmed as O4V stars, with stellar masses likely to be in excess of 40 M . Their radial velocities relative to the non-binary reference object, MSP 182, in Westerlund 2 are −29.4±1.7 and −14.4±2.2 km s −1 , respectively. Using Gaia DR2 proper motions we find that between 8 and 11 early O/WR stars in the studied region (including the two VLT targets, plus WR 20c and WR 20aa) could have been ejected from Westerlund 2 in the last one million years. This represents an efficiency of massive-star ejection of up to ∼ 25%. On sky, the positions of these stars and their proper motions show a near N-S alignment. We discuss the possibility that these results are a consequence of prior sub-cluster merging combining with dynamical ejection.

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“…The mass segregation is the phenomenon in which massive stars are more centrally concentrated than low mass stars in clusters and has been reported in many clusters (e.g., Joshi et al 2014;Piatti 2016;Zeidler et al 2017;Dib et al 2018;Joshi et al 2020). The mass segregation effect can be triggered due to the dynamical evolution of the cluster or may be imprint of star formation process itself (Sagar et al 1988).…”

Section: Mass Segregationmentioning

confidence: 99%

Photometric and kinematic study of the three intermediate age open clusters NGC 381, NGC 2360, and Berkeley 68

Maurya

Joshi

2020

Monthly Notices of the Royal Astronomical Society

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We present UBVR c I c photometric study of three intermediate age open star clusters NGC 381, NGC 2360, and Berkeley 68 (Be 68). We examine the cluster membership of stars using recently released Gaia DR2 proper motions and obtain a total of 116, 332, and 264 member stars in these three clusters. The mean reddening of E(B − V) = 0.36±0.04, 0.08±0.03, and 0.52±0.04 mag are found in the direction of these clusters where we observe an anomalous reddening towards NGC 381. We fitted the solar metallicity isochrones to determine age and distance of the clusters which are found to be log(Age) = 8.65±0.05, 8.95±0.05, and 9.25±0.05 yr with the respective distance of 957±152, 982±132, and 2554±387 pc for the clusters NGC 381, NGC 2360, and Be 68. A two-stage power law in the mass function (MF) slope is observed in the cluster NGC 381, however, we observe only a single MF slope in the clusters NGC 2360 and Be68. To study a possible spatial variation in the slope of MF we estimate slopes separately in the inner and the outer regions of these clusters and notice a steeper slope in outer region. The dynamic study of these clusters reveals deficiency of lowmass stars in their inner regions suggesting the mass segregation process in all these clusters. The relaxation times of 48.5, 78.9, and 87.6 Myr are obtained for the clusters NGC 381, NGC 2360, and Be 68, respectively which are well below to their respective ages. This suggests that all the clusters are dynamically relaxed.

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A High-resolution Multiband Survey of Westerlund 2 with the Hubble Space Telescope. III. The Present-day Stellar Mass Function

Cited by 28 publications

References 90 publications

Stellar population of the superbubble N 206 in the LMC

Stellar population of the superbubble N 206 in the LMC

Massive stars in the hinterland of the young cluster, Westerlund 2

Photometric and kinematic study of the three intermediate age open clusters NGC 381, NGC 2360, and Berkeley 68

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