Time-domain Study of the Young Massive Cluster Westerlund 2 with the Hubble Space Telescope. I

Sabbi, E.; Gennaro, Mario; Anderson, Jay; Bajaj, Varun; Bastian, N.; Gallagher, John S.; Gieles, M.; Lennon, D. J.; Nota, A.; Sahu, Kailash C.; Zeidler, Peter

doi:10.3847/1538-4357/ab7372

Cited by 6 publications

(9 citation statements)

References 68 publications

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“…In constructing our model we have extrapolated the period distribution of relatively low mass stars (mainly with m < 1.5 M ⊙ ) in young open clusters into the mass range 1.5 − 1.7 M ⊙ . Observations of resolved high mass clusters, like those of Sabbi et al (2020) for Westerlund 2, should be able to show whether more massive stars (up to ∼ 4 M ⊙ ) also display a bimodal period distribution. The origin of a bimodal period distribution amongst PMS stars in young clusters is still not entirely clear, but it could be due to a star-disc interaction during the PMS lifetime of the star.…”

Section: Discussionmentioning

confidence: 95%

On the origin of the bimodal rotational velocity distribution in stellar clusters: rotation on the pre-main sequence

Bastian

Kamann

Amard

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We address the origin of the observed bimodal rotational distribution of stars in massive young and intermediate age stellar clusters. This bimodality is seen as split main sequences at young ages and also has been recently directly observed in the Vsini distribution of stars within massive young and intermediate age clusters. Previous models have invoked binary interactions as the origin of this bimodality, although these models are unable to reproduce all of the observational constraints on the problem. Here, we suggest that such a bimodal rotational distribution is set-up early within a cluster’s life, i.e. within the first few Myr. Observations show that the period distribution of low-mass ($\lesssim\! 2 \, \mathrm{M}_\odot$) pre-main-sequence (PMS) stars is bimodal in many young open clusters, and we present a series of models to show that if such a bimodality exists for stars on the PMS that it is expected to manifest as a bimodal rotational velocity (at fixed mass/luminosity) on the main sequence for stars with masses in excess of ∼1.5 M⊙. Such a bimodal period distribution of PMS stars may be caused by whether stars have lost (rapid rotators) or been able to retain (slow rotators) their circumstellar discs throughout their PMS lifetimes. We conclude with a series of predictions for observables based on our model.

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Section: Discussionmentioning

confidence: 95%

On the origin of the bimodal rotational velocity distribution in stellar clusters: rotation on the pre-main sequence

Bastian

Kamann

Amard

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…From the isochrone fitting to CMDs (Zeidler et al 2015;Sabbi et al 2020) we know that the PMS turn- These groups divide the stars into different evolutionary stages and certain mass ranges. As the next step we create RV histograms of the three groups (see Fig.…”

Section: The Wd2 Velocity Profilementioning

confidence: 99%

“…We cross-correlate the HST and the Gaia catalogs. Of the 20,482 point sources in the HST catalog, 1239 are included in the Gaia DR2, of which 471 are cluster member stars based on the HST CMD selection (Zeidler et al 2015;Sabbi et al 2020). To select stars with a clean astrometric solution we use the following magnitude based limits as suggested by Lindegren et al (2018):…”

Section: The Gaia Dr2mentioning

confidence: 99%

“…Their analysis also revealed a possible protostellar outflow and let them identify both lobes as a blue and a red shifted counterpart. Time domain studies (e.g., Sabbi et al 2020) have the capability of detecting protoplanetary disks, stellar variability, and the binary fraction, which is important to the evolution of the whole cluster system (we refer to Portegies Zwart et al (2010) and Krumholz & McKee (2020) for a detailed overview).…”

Section: Introductionmentioning

confidence: 99%

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The Young Massive Star Cluster Westerlund 2 Observed with MUSE. III. A Cluster in Motion—The Complex Internal Dynamics

Zeidler

Sabbi

Nota

et al. 2021

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Analyzing the dynamical state of nearby young massive star clusters is essential for understanding star cluster formation and evolution during their earliest stages. In this work we analyze the stellar and gas kinematics of the young massive star cluster Westerlund 2 (Wd2) using data from the integral field unit Multi Unit Spectroscopic Explorer (MUSE) and complement them with proper motions from the Gaia DR2. The mean gas radial velocity of 15.9 km s−1 agrees with the assumption that Wd2 is the result of a cloud–cloud collision. The gas motions show the expansion of the H ii region, driven by the radiation from the many OB stars in the cluster center. The velocity profile of the cluster member stars reveals an increasing velocity dispersion with decreasing stellar mass and that the low-mass stars show five distinct velocity groups. Based on their spatial correlation with the cluster’s two clumps, we concluded that this is the imprint of the initial cloud collapse that formed Wd2. A thorough analysis of the dynamical state of Wd2, which determines a dynamical mass range of M dyn,Wd2 = (7.5 ± 1.9) × 104 − (4.4 ± 1.1) × 105 M ⊙ and exceeds the photometric mass by at least a factor of two, leads to the conclusion that Wd2 is not massive enough to remain gravitationally bound. Additionally we also identify 22 runaway candidates with peculiar velocities between 30 and 546 km s−1.

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“…for M 1.5 M ). The pre-main sequence origin of the bimodality can be tested through observations of the period distributions of stars in very young clusters, across a wide range of stellar masses, and ongoing surveys (e.g., of the Galactic cluster Westerlund 2 - Sabbi et al 2020) should be able to confirm or refute this hypothesis.…”

Section: Introductionmentioning

confidence: 99%

Exploring the role of binarity in the origin of the bimodal rotational velocity distribution in stellar clusters

Kamann

Bastian

Usher

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Many young and intermediate age massive stellar clusters host bimodal distributions in the rotation rates of their stellar populations, with a dominant peak of rapidly rotating stars and a secondary peak of slow rotators. The origin of this bimodal rotational distribution is currently debated and two main theories have been put forward in the literature. The first is that all/most stars are born as rapid rotators and that interacting binaries brake a fraction of the stars, resulting in two populations. The second is that the rotational distribution is a reflection of the early evolution of pre-main sequence stars, in particular, whether they are able to retain or lose their protoplanetary discs during the first few Myr. Here, we test the binary channel by exploiting multi-epoch VLT/MUSE observations of NGC 1850, a ∼100 Myr massive cluster in the LMC, to search for differences in the binary fractions of the slow and fast rotating populations. If binarity is the cause of the rotational bimodality, we would expect that the slowly rotating population should have a much larger binary fraction than the rapid rotators. However, in our data we detect similar fractions of binary stars in the slow and rapidly rotating populations (5.9 ± 1.1% and 4.5 ± 0.6%, respectively). Hence, we conclude that binarity is not a dominant mechanism in the formation of the observed bimodal rotational distributions.

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Time-domain Study of the Young Massive Cluster Westerlund 2 with the Hubble Space Telescope. I

Cited by 6 publications

References 68 publications

On the origin of the bimodal rotational velocity distribution in stellar clusters: rotation on the pre-main sequence

On the origin of the bimodal rotational velocity distribution in stellar clusters: rotation on the pre-main sequence

The Young Massive Star Cluster Westerlund 2 Observed with MUSE. III. A Cluster in Motion—The Complex Internal Dynamics

Exploring the role of binarity in the origin of the bimodal rotational velocity distribution in stellar clusters

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