Which young clusters and associations are we missing today?

Kirk

Sills

et al. 2016

A&A

Context. Stars form predominantly in groups usually denoted as clusters or associations. The observed stellar groups display a broad spectrum of masses, sizes, and other properties, so it is often assumed that there is no underlying structure in this diversity. Aims. Here we show that the assumption of an unstructured multitude of cluster or association types might be misleading. Current data compilations of clusters in the solar neighbourhood show correlations among cluster mass, size, age, maximum stellar mass, etc. In this first paper we take a closer look at the correlation of cluster mass and radius. Methods. We use literature data to explore relations in cluster and molecular core properties in the solar neighbourhood. Results. We show that for embedded clusters in the solar neighbourhood a clear correlation exists between cluster mass and half-mass radius of the form M c = CR γ c with γ = 1.7 ± 0.2. This correlation holds for infrared K-band data, as well as for X-ray sources and clusters containing a hundred stars up to those consisting of a few tens of thousands of stars. The correlation is difficult to verify for clusters containing fewer than 30 stars owing to low-number statistics. Dense clumps of gas are the progenitors of the embedded clusters. We find almost the same slope for the mass-size relation of dense, massive clumps as for the embedded star clusters. This might point to a direct translation from gas to stellar mass: however, it is difficult to relate size measurements for clusters (stars) to those for gas profiles. Taking multiple paths for clump mass into cluster mass into account, we obtain an average star-formation efficiency of 18% +9.3 −5.7 for the embedded clusters in the solar neighbourhood. Conclusions. The derived mass-radius relation gives constraints for the theory of clustered star formation. Analytical models and simulations of clustered star formation have to reproduce this relation in order to be realistic.

Section: Systematic Effectsmentioning

confidence: 81%

Observational constraints on star cluster formation theory

Kirk

Sills

et al. 2016

A&A

“…The cluster dynamics after gas expulsion hasbeeninvestigated thoroughly in the past (e.g., Lada et al 1984;Goodwin 1997;Adams 2000;Geyer & Burkert 2001;Kroupa et al 2001;Boily & Kroupa 2003a, 2003bFellhauer & Kroupa 2005;Goodwin & Bastian 2006;Baumgardt & Kroupa 2007;Lüghausen et al 2012;Pfalzner et al , 2015b.…”

Section: Introductionmentioning

confidence: 99%

Cluster Dynamics Largely Shapes Protoplanetary Disk sizes

Vincke

2016

ApJ

Self Cite

103

To what degree the cluster environment influences the sizes of protoplanetary disks surrounding young stars is still an open question. This is particularly true for the short-lived clusters typical for the solar neighborhood, in which the stellar density and therefore the influence of the cluster environment change considerably over the first 10 Myr. In previous studies,the effect of the gas on the cluster dynamics has oftenbeen neglected;this is remedied here. Using the code NBody6++,we study the stellar dynamics in different developmental phases-embedded, expulsion, and expansion-including the gas, and quantify the effect of fly-bys on the disksize. We concentrate on massive clusters (M cl 10 3 -6 * 10 4 M Sun ), which are representative for clusters like the Orion Nebula Cluster (ONC) or NGC 6611. We find that not only the stellar density but also the duration of the embedded phase matters. The densest clusters react fastest to the gas expulsion and drop quickly in density, here 98% of relevant encounters happen before gas expulsion. By contrast, disks in sparser clusters are initially less affected, but because these clusters expand moreslowly,13% of disks are truncated after gas expulsion. For ONC-like clusters, we find that disks larger than 500 au are usuallyaffected by the environment, which corresponds to the observation that 200 ausized disks are common. For NGC 6611-like clusters, disksizes are cut-down on average to roughly 100 au. A testable hypothesis would be that the disks in the center of NGC 6611 should be on average ≈20 au and therefore considerably smaller than those in the ONC.

“…Observations meets theory in clustered star formation Figure 2. Evelutionary tracks of young clusters according to Pfalzner et al (2015), assuming a star fromation efficiency that depends on the local gas density .…”

Section: Two Types Of Clustermentioning

confidence: 99%

Observations meets theory in clustered star formation

2019

Proc. IAU

Self Cite

Stars form predominantly in groups which display a broad spectrum of masses, sizes, and other properties. Despite this diversity there exist an underlying structure that can constrain cluster formation theories. We show how combining observations with simulations allows to disclose this underlying structure. One example is the mass-radius relation for young embedded associations which follows Mc = CR γ c with γ = 1.7 ± 0.2.0.2, which is directly related to the mass-radius relation of clumps. Results based on GAIA 2D have demonstrated that young stellar groups (1-5 Myr) expand and that this expansion process is largely over by an age of 10-20 Myr. Such a behaviour is expected within the gas expulsion scenario. However, the effect of gas expulsion depends strongly on a the SFE, the gas expulsion time scale, etc.Here it is demonstrated how existing and upcoming data are able to constrain these parameters and correspondingly the underlying models.