The mechanisms which could lead to chemo-thermal instabilities and fragmentation during the formation of primordial protostars are investigated analytically. We introduce new analytic approximations for H2 cooling rates bridging the optically thin and thick regimes. These allow us to discuss chemo–thermal instabilities up to densities when protostars become optically thick to continuum radiatio...

We simulate the early stages of the evolution of turbulent, virialized, high-mass protostellar cores, with primary attention to how cores fragment, and whether they form a small or large number of protostars. Our simulations use the Orion adaptive mesh refinement code to follow the collapse from ∼ 0.1 pc scales to ∼ 10 AU scales, for durations that cover the main fragmentation phase, using thre...

We present high resolution (R ∼ 34,000) optical (6330 8750 Å) spectra obtained with the HIRES spectrograph on the W. M. Keck I telescope of stars in Taurus-Auriga whose circumstellar environment suggests that they are less evolved than optically revealed T Tauri stars. Many of the stars are seen only via scattered light. The sample includes 15 Class I stars and all Class II stars that power Her...

The Trifid nebula is a young HII region undergoing a burst of star formation. In this article, we report on far-infrared and millimeter continuum and line observations of several massive and bright protostellar sources in the vicinity of the exciting star of the nebula, just behind the ionization front. These objects are probably young protostars (Class 0) and are associated with very massive c...

We test the hypothesis that the starless cores may be gravitationally bound clouds supported largely by thermal pressure by comparing observed molecular line spectra to theoretical spectra produced by a simulation that includes hydrodynamics, radiative cooling, variable molecular abundance, and radiative transfer in a simple one-dimensional model. The results suggest that the starless cores can...

We present the results of a survey of a small sample (14) of low-mass protostars (LIR < 103 L⊙) for 6.7 GHz methanol maser emission performed using the ATNF Parkes radio telescope. No new masers were discovered. We find that the lower luminosity limit for maser emission is near 103 L⊙, by comparison of the sources in our sample with previously detected methanol maser sources. We examine the IRA...

A method for following fragmentation simulations further in time using smoothed particle hydrodynamics (SPH) is presented. In a normal SPH simulation of the collapse and fragmentation of a molecular cloud, high-density regions of gas that form proto-stars are represented by many particles with small separations. These high-density regions require small time steps, limiting the time for which th...

In this chapter we describe how elements have been and are still being formed in the galaxy and how they are transformed into the reservoir of materials present in protostellar environments. We discuss the global cycle of matter from stars, where nucleosynthesis produces heavy elements that are ejected through explosions and winds into the interstellar medium (ISM), through the formation and ev...

Abstract Outflows and winds launched from young stars play a crucial role in the evolution of protostars early stages planet formation. However, specific details mechanism behind these phenomena, including how they affect protoplanetary disk structure, are still debated. We present JWST NIRSpec integral field unit observations atomic H 2 lines 1 to 5.1 μ m toward low-mass protostar TMC1A. For f...

The collapse and fragmentation of initially prolate and oblate, magnetic molecular clouds is calculated in three dimensions with a gravitational, radiative hydrodynamics code. The code includes magnetic field effects in an approximate manner: magnetic pressure, tension, braking, and ambipolar diffusion are all modelled. The parameters varied for both the initially prolate and oblate clouds are ...