title: Revealing the secrets of Westerlund 2 - A young massive star cluster observed with the Hubble Space Telescope
creator: Zeidler, Peter
subject: ddc-520
subject: 520 Astronomy and allied sciences
description: We present a detailed study of the Galactic young massive star cluster Westerlund 2 (Wd2) using an optical and near-infrared high resolution multi-band survey observed with the Hubble Space Telescope. Images obtained in Hα and Paβ filters allowed us to derive a high-resolution pixel-to-pixel E(B − V)_g gas extinction map. This map helped us to individually deredden the stellar photometry, to identify the cluster population, and to determine the properties of Wd2, such as distance (d = 4.16 kpc), total-to-selective extinction (RV = 3.95), and age (1.04 ± 0.72Myr). We identified 240 bona fide pre-main-sequence Hα excess emitters indicating active disk accretion. A careful analysis of the radial dependence of the Hα excess emission shows a 60% lower mass accretion rate in the cluster center, indicating a more rapid disk dispersal in close proximity to the massive OB-stars. We performed state-of-the-art artificial star tests to study the completeness-corrected spatial distribution of the stars. This revealed that Wd2 consists of two subclusters. Additionally, we determined the present-day mass function (PDMF) with a slope of G = −1.53 ± 0.05, which translates to a total  stellar cluster mass of (3.6±0.3)·10^4 M_sun. The spatial analysis of the PDMF and the young age of Wd2 indicates that the cluster is, most likely primordial, mass segregated. A spatially uniformly distributed low-mass (< 0.15 M_sun) population, extending into the gas and dust cloud, as well as a confined region of reddened stars, most likely caused by a foreground CO cloud, suggests that cloud-cloud collision might be the origin of the formation of Wd2.
date: 2017
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/22559/1/PhD_Thesis_final.pdf
identifier: DOI:10.11588/heidok.00022559
identifier: urn:nbn:de:bsz:16-heidok-225598
identifier:   Zeidler, Peter  (2017) Revealing the secrets of Westerlund 2 - A young massive star cluster observed with the Hubble Space Telescope.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/22559/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng