Initial Conditions for Star Clusters

Kroupa, Pavel

doi:10.1007/978-1-4020-8431-7_8

Cited by 107 publications

(124 citation statements)

References 162 publications

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“…But the Spitzer instability could be a very fast ( < ∼ 0.5 Myr) process if the birth cluster is very dense (e.g. Kroupa 2008). Highprecision proper motion measurements for the massive field stars are therefore required to determine the timing of their ejections, thereby distinguishing between the primordial and the dynamical origins of mass segregation in young clusters (Gvaramadze & Bomans 2008b).…”

Section: Discussionmentioning

confidence: 99%

Massive runaway stars in the Large Magellanic Cloud

Gvaramadze

Kroupa

Pflamm-Altenburg

2010

A&A

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The origin of massive field stars in the Large Magellanic Cloud (LMC) has long been an enigma. The recent measurements of large offsets (∼100 km s −1 ) between the heliocentric radial velocities of some very massive (O2-type) field stars and the systemic LMC velocity provides a possible explanation of this enigma and suggests that the field stars are runaway stars ejected from their birthplaces at the very beginning of their parent cluster's dynamical evolution. A straightforward way to prove this explanation is to measure the proper motions of the field stars and to show that they are moving away from one of the nearby star clusters or OB associations. This approach is, however, complicated by the long distance to the LMC, which makes accurate proper motion measurements difficult. We used an alternative approach for solving the problem (first applied for Galactic field stars), based on the search for bow shocks produced by runaway stars. The geometry of detected bow shocks would allow us to infer the direction of stellar motion, thereby determining their possible parent clusters. In this paper we present the results of a search for bow shocks around six massive field stars that have been proposed as candidate runaway stars. Using archival Spitzer Space Telescope data, we found a bow shock associated with one of our programme stars, the O2 V((f*)) star BI 237, which is the first-ever detection of bow shocks in the LMC. Orientation of the bow shock suggests that BI 237 was ejected from the OB association LH 82 (located at 120 pc in projection from the star). A by-product of our search is the detection of bow shocks generated by four OB stars in the field of the LMC and an arc-like structure attached to the candidate luminous blue variable R81 (HD 269128). The geometry of two of these bow shocks is consistent with the possibility that their associated stars were ejected from the 30 Doradus star-forming complex. We discuss implications of our findings for the problem of the origin of runaway stars and the early dynamical evolution of star clusters.

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Section: Discussionmentioning

confidence: 99%

Massive runaway stars in the Large Magellanic Cloud

Gvaramadze

Kroupa

Pflamm-Altenburg

2010

A&A

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“…also . Kroupa (2002) and formalized the mathematical concept of Ω M ecl ,r h dyn , which is here used for the first time to derive the initial conditions of observed star clusters.…”

Section: Inverse Dynamical Population Synthesismentioning

confidence: 99%

Inverse dynamical population synthesis

Marks

Kroupa

2012

A&A

246

302

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Binary populations in young star clusters show multiplicity fractions both lower and up to twice as high as those observed in the Galactic field. We follow the evolution of a population of binary stars in dense and loose star clusters starting with an invariant initial binary population and a formal multiplicity fraction of unity, and demonstrate that these models can explain the observed binary properties in Taurus, ρ Ophiuchus, Chamaeleon, Orion, IC 348, Upper Scorpius A, Praesepe, and the Pleiades. The model needs to consider solely different birth densities for these regions. The evolved theoretical orbital-parameter distributions are highly probable parent distributions for the observed ones. We constrain the birth conditions (stellar mass, M ecl , and half-mass radius, r h ) for the derived progenitors of the star clusters and the overall present-day binary fractions allowed by the present model. The results compare very well with properties of molecular cloud clumps on the verge of star formation. Combining these with previously and independently obtained constraints on the birth densities of globular clusters, we identify a weak stellar mass -half-mass radius correlation for cluster-forming cloud clumps, r h /pc ∝ (M ecl /M ) 0.13 ± 0.04 . The ability of the model to reproduce the binary properties in all the investigated young objects, covering present-day densities from 1−10 stars pc −3 (Taurus) to 2 × 10 4 stars pc −3 (Orion), suggests that environment-dependent dynamical evolution plays an important role in shaping the present-day properties of binary populations in star clusters, and that the initial binary properties may not vary dramatically between different environments.

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“…The dynamical status of each stellar complex can be assessed by the crossing and the two-body relaxation time-scales (e.g., Spitzer 1987, see also Binney & Tremaine 2008;Kroupa 2008), which are given as:…”

Section: Structural (Second Generation) Parametersmentioning

confidence: 99%

Hierarchical star formation across the grand-design spiral NGC 1566

Gouliermis

Elmegreen²,

Elmegreen

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We investigate how star formation is spatially organized in the grand-design spiral NGC 1566 from deep HST photometry with the Legacy ExtraGalactic UV Survey (LEGUS). Our contour-based clustering analysis reveals 890 distinct stellar conglomerations at various levels of significance. These star-forming complexes are organized in a hierarchical fashion with the larger congregations consisting of smaller structures, which themselves fragment into even smaller and more compact stellar groupings. Their size distribution, covering a wide range in length-scales, shows a power-law as expected from scale-free processes. We explain this shape with a simple "fragmentation and enrichment" model. The hierarchical morphology of the complexes is confirmed by their mass-size relation which can be represented by a powerlaw with a fractional exponent, analogous to that determined for fractal molecular clouds. The surface stellar density distribution of the complexes shows a log-normal shape similar to that for supersonic non-gravitating turbulent gas. Between 50 and 65 per cent of the recentlyformed stars, as well as about 90 per cent of the young star clusters, are found inside the stellar complexes, located along the spiral arms. We find an age-difference between young stars inside the complexes and those in their direct vicinity in the arms of at least 10 Myr. This timescale may relate to the minimum time for stellar evaporation, although we cannot exclude the in situ formation of stars. As expected, star formation preferentially occurs in spiral arms. Our findings reveal turbulent-driven hierarchical star formation along the arms of a grand-design galaxy.

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Initial Conditions for Star Clusters

Cited by 107 publications

References 162 publications

Massive runaway stars in the Large Magellanic Cloud

Massive runaway stars in the Large Magellanic Cloud

Inverse dynamical population synthesis

Hierarchical star formation across the grand-design spiral NGC 1566

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