OVRO N2H+ Observations of Class 0 Protostars: Constraints on the Formation of Binary Stars

TL;DR

This study uses OVRO interferometry to analyze N2H+ emission in nine low-mass protostellar cores, revealing insights into their kinematics, support mechanisms, and implications for binary star formation.

Contribution

It provides the first detailed kinematic analysis of Class 0 protostellar cores, linking core angular momentum to binary star formation.

Findings

N2H+ cores are compact and coincide with dust emission.

Thermal and turbulent support are significant; rotation is negligible.

Core angular momentum is intermediate and conserved from prestellar to binary stages.

Abstract

We present the results of an interferometric study of the N2H+(1--0) emission from nine nearby, isolated, low-mass protostellar cores, using the OVRO millimeter array. The main goal of this study is the kinematic characterization of the cores in terms of rotation, turbulence, and fragmentation. Eight of the nine objects have compact N2H+ cores with FWHM radii of 1200 -- 3500 AU, spatially coinciding with the thermal dust continuum emission. The only more evolved (Class I) object in the sample (CB 188) shows only faint and extended N2H+ emission. The mean N2H+ line width was found to be 0.37 km/s. Estimated virial masses range from 0.3 to 1.2 M_sun. We find that thermal and turbulent energy support are about equally important in these cores, while rotational support is negligible. The measured velocity gradients across the cores range from 6 to 24 km/s/pc. Assuming these gradients are produced by bulk rotation, we find that the specific angular momenta of the observed Class 0 protostellar cores are intermediate between those of dense (prestellar) molecular cloud cores and the orbital angular momenta of wide PMS binary systems. There appears to be no evolution (decrease) of angular momentum from the smallest prestellar cores via protostellar cores to wide PMS binary systems. In the context that most protostellar cores are assumed to fragment and form binary stars, this means that most of the angular momentum contained in the collapse region is transformed into orbital angular momentum of the resulting stellar binary systems.