Invited review abstract
Origin of high-mass stars in Cygnus-X
Abstract
I will present IRAM PdBI continuum and molecular line observations towards the 5 most massive dense cores of Cygnus X (Bontemps et al. 2009, arXiv: 0909.2315). Located at 1.7 kpc, Cygnus X offers the opportunity of reaching small scales (less than 2000 AU) to identify individual collapsing objects. A few, but massive fragments are found within these cores, a total of 9 are found to be precursor of OB stars. Comparing the fragmentation properties with theoretical predictions, it seems that the level of fragmentation in these cores is higher than in the turbulence regulated collapse scenario, but is not as high as expected in a pure gravo-turbulent scenario where the distribution of mass is dominated by low-mass protostars.
To go one step further in understanding the origin of these massive protostars, we analysed the PdBI H13CO+ and H13CN line emission (Csengeri et al., submitted). In the turbulence regulation scenario, a strong micro-turbulence is expected which should be observed down to the smallest scales. On the other hand a significant effect of competitive accretion could be observed by means of a detailed kinematical study. In these dense gas tracers all the cores indeed exhibit very rich and complex kinematics such as several line components and interacting flows of dense gas are found just around protostars. The level of turbulent support at the scale of protostars is found to be smaller than pointed by previous single-dish observations, which suggest a dynamical origin and fast evolution for the fragmentation of dense cores.
To put in context the origin of massive cores, the link between small (~0.01 pc) and large (~pc) scale kinematics must be investigated. I will briefly present our recent studies of the most massive structure within Cygnus X, the DR21 filament (Schneider et al. 2010, arXiv:1003.4198), that point to its dynamic origin.
To go one step further in understanding the origin of these massive protostars, we analysed the PdBI H13CO+ and H13CN line emission (Csengeri et al., submitted). In the turbulence regulation scenario, a strong micro-turbulence is expected which should be observed down to the smallest scales. On the other hand a significant effect of competitive accretion could be observed by means of a detailed kinematical study. In these dense gas tracers all the cores indeed exhibit very rich and complex kinematics such as several line components and interacting flows of dense gas are found just around protostars. The level of turbulent support at the scale of protostars is found to be smaller than pointed by previous single-dish observations, which suggest a dynamical origin and fast evolution for the fragmentation of dense cores.
To put in context the origin of massive cores, the link between small (~0.01 pc) and large (~pc) scale kinematics must be investigated. I will briefly present our recent studies of the most massive structure within Cygnus X, the DR21 filament (Schneider et al. 2010, arXiv:1003.4198), that point to its dynamic origin.