Embedded binaries and their dense cores

Abstract

We explore the relationship between young, embedded binaries and their parent cores, using observations within the Perseus Molecular Cloud. We combine recently published VLA observations of young stars with core properties obtained from SCUBA-2 observations at 850 µm. Most embedded binary systems are found toward the centres of their parent cores, although several systems have components closer to the core edge. Wide binaries, defined as those systems with physical separations greater than 500 au, show a tendency to be aligned with the long axes of their parent cores, whereas tight binaries show no preferred orientation. We test a number of simple, evolutionary models to account for the observed populations of Class 0 and I sources, both single and binary. In the model that best explains the observations, all stars form initially as wide binaries. These binaries either break up into separate stars or else shrink into tighter orbits. Under the assumption that both stars remain embedded following binary breakup, we find a total star formation rate of 168 Myr −1 . Alternatively, one star may be ejected from the dense core due to binary breakup. This latter assumption results in a star formation rate of 247 Myr −1 . Both production rates are in satisfactory agreement with current estimates from other studies of Perseus. Future observations should be able to distinguish between these two possibilities. If our model continues to provide a good fit to other star-forming regions, then the mass fraction of dense cores that becomes stars is double what is currently believed.

Characterizing young protostellar disks with the CALYPSO IRAM-PdBI survey: large Class 0 disks are rare

“…Our multiplicity statistics in the CALYPSO sample (7 single and 8 multiples) at the Class 0 stage, although on an admittedly small sample, is not significantly different from the restricted sample of Connelley et al (2009). It has been suggested (Reipurth 2000;Sadavoy & Stahler 2017) that a large portion of Class 0 protostars form in non-hierarchical multiple systems that dynamically decay during the Class 0 phase, in which case the overall multiplicity fraction of Class 0 protostars should be higher than that of Class I protostars. Although our conclusions should be viewed as preliminary at this stage because of the small sample and inhomogeneous distances of our sources, our results do not seem to be consistent with this scenario, at least at the scales common in the CALYPSO sample and the Connelley sample since the overall multiplicity is found to be very similar in both samples.…”

Connecting the Scales: Large Area High-resolution Ammonia Mapping of NGC 1333

“…(Of these, IRAS 2A is not resolved in Spitzer data; we mark it as a single protostar although it has been confirmed to be a binary using radio data.) Simulations have also shown that fast compression is often associated with core fragmentation (Hennebelle et al 2003) which could explain the recent results reported by Sadavoy & Stahler (2017) that most stars form initially in wide binaries. In addition, based on the uncorrelated direction of the outflows from the binary system of IRAS 2A, Tobin et al (2015) concluded that it is evidence of core/envelope fragmentation by turbulence and not disk fragmentation due to gravitational instability.…”

Collisional N-body Dynamics Coupled to Self-gravitating Magnetohydrodynamics Reveals Dynamical Binary Formation

“…which is on the order of or below a single AU. (Recent work does suggest that perhaps only hundreds of AU need be resolved; Sadavoy & Stahler 2017. ) To resolve the Jeans length in pure Eulerian hydrodynamics λ J must be resolved by at least four grid cells (Truelove et al 1997), while in MHD at least six cells per Jeans length are needed to resolve Alfvén waves (Heitsch et al 2001), and as many as 32 cells per Jeans length would be needed to properly resolve self-consistent formation of magnetic fields through the microturbulent dynamo (Federrath et al 2011).…”