Efficiencies of Low-Mass Star and Star Cluster Formation

By C. Matzner, C. McKee. 2000

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Using a quantitative model for bipolar outflows driven by hydromagnetic protostellar winds, we calculate the efficiency of star formation assuming that available gas is either converted into stars or ejected in outflows. We estimate the efficiency of a single star formation event in a protostellar core, finding 25%-70% for cores with various possible degrees of flattening. The core mass function and the stellar initial mass function have similar slopes because the efficiency is not sensitive to its parameters. We then consider the disruption of gas from a dense molecular clump in which a cluster of young stars is being born. In both cases, we present analytical formulae for the efficiencies that compare favorably against observations and, for clusters, against numerical simulations. We predict efficiencies in the range of 30%-50% for the regions that form clusters of low-mass stars. In our model, star formation and gas dispersal happen concurrently. We neglect the destructive effects of massive stars: our results are therefore upper limits to the efficiency in regions more massive than about 3000 M☉ .

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/d83b59251783e99f9fa4dd9dc597147f296cd540

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Citations in the corpus

Stellar, brown dwarf and multiple star properties from a radiation hydrodynamical simulation of star cluster formation (2011, background): “…in globally unbound molecular clouds (Clark & Bonnell 2004; Clark et al. 2005), or that magnetic support (Price & Bate 2008, 2009), kinetic feedback (Matzner & McKee 2000; Krumholz, Matzner & McKee 2006; Nakamura & Li 2007) or a combination (e.g. Wang et al. 2010) reduces the star formation rate.”
The Progenitors of Dwarf Spheroidal Galaxies (2002, background): “Even though upper limits for the efficiency of low-mass star formation may reach 30% to 50% when the effects of massive stars are neglected (Matzner & McKee 2000), one expects to find that much of the gas remains after stars form.”
Flows, Fragmentation, and Star Formation. I. Low-Mass Stars in Taurus (2002, background): “Taurus would seem to be a good candidate for minimal effects of local turbulence because it lacks highmass stars, though low-mass stars may inject substantial amounts of energy through their bipolar outflows (Matzner & McKee 1999, 2000).”
THE DISRUPTION OF GIANT MOLECULAR CLOUDS BY RADIATION PRESSURE & THE EFFICIENCY OF STAR FORMATION IN GALAXIES (2009, methodology): “The jets deposit momentum into the surrounding gas at a rate Fjet = ǫjetṀaccvjet exp−t/tjet (A21) The jets expel mass at a fractionǫjet ≈ 0.1−0.3 of the mass accretion rate (Matzner & McKee 2000), at a velocity vjet that depends on the mass of the star.”
Global Models for the Evolution of Embedded, Accreting Protostellar Disks (2007, background): “We again follow McKee & Tan (2003) in adopting ε = 0.5, a value typical of low-mass star formation (Matzner & McKee 2000).”
The Stellar IMF, Core Mass Function, & The Last-Crossing Distribution (2012, background): “However, the calculation here suggests that such corrections should be order unity, and arguments from observations and models of outflows similarly suggest a modest core ∼ 0.5 (Matzner & McKee 2000; Stanke et al. 2006; Alves et al. 2007; Enoch et al. c© 0000 RAS, MNRAS 000, 000–000 2008).”
LIMITING ACCRETION ONTO MASSIVE STARS BY FRAGMENTATION-INDUCED STARVATION (2010, background): “Each molecular cloud core collapses to form a single star or at most a close binary system, with protostellar feedback processes determining the efficiency of the process (Matzner & McKee 2000).”
The evolution of the spectral energy distribution in massive young stellar objects (2008, background): “The fraction of accreting material that is expelled in the outflow is of the order of fout ∼ 0.5 (Matzner & McKee 2000; McKee & Tan 2003), although even higher fractions have been proposed (Churchwell 1997) to justify the large ratio between the masses of the flow and of the driving protostar…”
On the mass function of star clusters (2002, background): “Sparse embedded clusters remove their gas on a time-scale comparable to the cluster-formation time-scale because the primary mechanism is the accumulation of the increasing number of outflows as the stellar population builds up (Matzner & McKee 2000).”
The Global Evolution of Giant Molecular Clouds. I. Model Formulation and Quasi-Equilibrium Behavior (2006, unknown): “First, the momentum injected into a cloud by an outflow is of order Ṁ∗vw, where Ṁ∗ is the star formation rate and vw ∼ 40 km s−1 is the rough momentum input per unit mass of stars formed for hydromagnetic winds (Matzner & McKee 2000; Richer et al. 2000).”
ANALYTICAL THEORY FOR THE INITIAL MASS FUNCTION. II. PROPERTIES OF THE FLOW (2009, background): “Such a nearly constant star formation efficiency of cores is predicted theoretically if magnetically-driven outflows are the primary mediating factor from cores to stars (Matzner & McKee 2000).”
Supernova hosts for gamma-ray burst jets: dynamical constraints (2002, background): “This proposal was recently revived by Matzner & McKee (2000) and Tan, Matzner & McKee (2001).”
On the fraction of star formation occurring in bound stellar clusters (2012, methodology): “As such, their influence may not reach very far, contrary to earlier theoretical expectations (e.g. Matzner & McKee 2000).”
NON-IDEAL MHD EFFECTS AND MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION (2011, background): “…(see, e.g., Machida et al. 2010) but, if the efficiency of star formation in individual low-mass cores is of order 1/3 (Alves et al. 2007; André et al. 2010), the majority of the envelope mass must be removed by some other process, most likely a (fast) protostellar wind (Matzner & McKee 2000).”
Physical Processes in the Interstellar Medium (2014, background): “The factor of ∼3 decrease in mass between cores and stars is thought to be the result of feedback processes, mostly protostellar outflows, that eject a fixed fraction of the mass in a core rather than letting it accrete onto the star (Matzner & McKee, 2000).”
Theory of Star Formation (2007, background): “Both Nakano, Hasegawa, & Norman (1995) and Matzner & McKee (2000) found that ǫcore is only weakly dependent on the core mass, so that the CMF and the IMF should be similar in shape, as observed (§3.3).”
ON THE ROLE OF DISKS IN THE FORMATION OF STELLAR SYSTEMS: A NUMERICAL PARAMETER STUDY OF RAPID ACCRETION (2009, methodology): “Using simple models of core collapse in which angular momentum is conserved in the collapse process and part of the matter is cast away by protostellar outflows (Matzner & McKee 2000), we find that both ξ and Γ are higher in massive star formation than in low-mass star formation.”