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Shuo Kong
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We present high resolution (0.2, 1000 AU) 1.3 mm ALMA observations of massive infrared dark cloud clump, G028.37+00.07-C1, thought to harbor the early stages of massive star formation. Using $rm N_2D^+$(3-2) we resolve the previously identified C1-S core, separating the bulk of its emission from two nearby protostellar sources. C1-S is thus identified as a massive ($sim50:M_odot$), compact ($sim0.1:$pc diameter) starless core, e.g., with no signs of outflow activity. Being highly deuterated, this is a promising candidate for a pre-stellar core on the verge of collapse. An analysis of its dynamical state indicates a sub-virial velocity dispersion compared to a trans-Alfvenic turbulent core model. However, virial equilibrium could be achieved with sub-Alfvenic conditions involving $sim2:$mG magnetic field strengths.
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We study the formation of massive Population III binary stars using a newly developed radiation hydrodynamics code with the adaptive mesh refinement and adaptive ray-tracing methods. We follow the evolution of a typical primordial star-forming cloud obtained from a cosmological hydrodynamics simulation. Several protostars form as a result of disk fragmentation and grow in mass by the gas accretion, which is finally quenched by the radiation feedback from the protostars. Our code enables us, for the first time, to consider the feedback by both the ionizing and dissociating radiation from the multiple protostars, which is essential for self-consistently determining their final masses. At the final step of the simulation, we observe a very wide ($gtrsim 10^4,mathrm{au}$) binary stellar system consisting of $60$ and $70,M_odot$ stars. One of the member stars also has two smaller mass ($10,M_odot$) companion stars orbiting at $200$ and $800,mathrm{au}$, making up a mini-triplet system. Our results suggest that massive binary or multiple systems are common among Population III stars.
The Next Generation Very Large Array (ngVLA) has excellent capabilities to unveil various dynamical and chemical processes in massive star formation at the unexplored innermost regions. Based on the recent observations of ALMA/VLA as well as theoretical predictions, we propose several intriguing topics in massive star formation from the perspective of the ngVLA. In the disk scale of $lesssim$ 100 au around massive protostars, dust grains are expected to be destructed/sublimated because the physical conditions of temperature, shocks, and radiation are much more intense than those in the envelopes, which are typically observed as hot cores. The high sensitivity and resolution of the ngVLA will enable us to detect the gaseous refractories released by dust destruction, e.g., SiO, NaCl, and AlO, which trace disk kinematics and give new insights into the metallic elements in star-forming regions, i.e., astromineralogy. The multi-epoch survey by the ngVLA will provide demographics of forming massive multiples with separations of $lesssim$ 10 au with their proper motion. Combining with observations of refractory molecular lines and hydrogen recombination lines, we can reproduce the three-dimensional orbital motions of massive proto-binaries. Moreover, the 1-mas resolution of the ngVLA could possibly take the first-ever picture of the photospheric surface of an accreting protostar, if it is bloated to the au scale by the high accretion rates of mass and thermal energy.
I review massive star formation in our Galaxy, focusing on initial conditions in Infrared Dark Clouds (IRDCs), including the search for massive pre-stellar cores (PSCs), and modeling of later stages of massive protostars, i.e., hot molecular cores (HMCs). I highlight how developments in astrochemistry, coupled with rapidly improving theoretical/computational and observational capabilities are helping to improve our understanding of the complex process of massive star formation.
The current census of, and stellar population in, massive Galactic star clusters is reviewed. In particular, we concentrate on a recent survey of obscured Galactic Giant H II (GHII) regions and the associated stellar clusters embedded in them. The regions have been selected as the most luminous radio continuum sources, and as such the stellar clusters appear to be among the youngest massive clusters in the Galaxy. The emergent stellar populations are further studied through near infrared spectroscopy of the brighter members. We also discuss the massive stellar clusters within 50 pc of the Galactic center (GC), comparing their known properties to those found in the GHII region survey. It is suggested that the somewhat younger clusters associated with the GHII regions are more suited to measuring the initial mass function in massive star clusters. Narrow band images in the central pc of the GC are presented which identify the young stellar sequence associated with the evolved He I emission line stars.
Interferometric observations of the W33A massive star-formation region, performed with the Submillimeter Array (SMA) and the Very Large Array (VLA) at resolutions from 5 arcsec (0.1 pc) to 0.5 arcsec (0.01 pc) are presented. Our three main findings are: (1) parsec-scale, filamentary structures of cold molecular gas are detected. Two filaments at different velocities intersect in the zone where the star formation is occurring. This is consistent with triggering of the star-formation activity by the convergence of such filaments, as predicted by numerical simulations of star formation initiated by converging flows. (2) The two dusty cores (MM1 and MM2) at the intersection of the filaments are found to be at different evolutionary stages, and each of them is resolved into multiple condensations. MM1 and MM2 have markedly different temperatures, continuum spectral indices, molecular-line spectra, and masses of both stars and gas. (3) The dynamics of the hot-core MM1 indicates the presence of a rotating disk in its center (MM1-Main) around a faint free-free source. The stellar mass is estimated to be approximately 10 Msun. A massive molecular outflow is observed along the rotation axis of the disk.
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