The VLA Nascent Disk and Multiplicity Survey of Perseus Protostars (VANDAM). II. Multiplicity of Protostars in the Perseus Molecular Cloud

TL;DR

This study uses high-resolution VLA observations to analyze the multiplicity of 94 protostars in the Perseus cloud, revealing a bimodal distribution of companion separations and insights into fragmentation mechanisms.

Contribution

It provides the first comprehensive multiplicity statistics for Perseus protostars at high resolution, highlighting the roles of turbulent and disk fragmentation.

Findings

Multiplicity fraction (MF) is 0.40±0.06.

Companion star fraction (CSF) is 0.71±0.06.

Bimodal separation distribution with peaks at 75 AU and 3000 AU.

Abstract

We present a multiplicity study of all known protostars (94) in the Perseus molecular cloud from a Karl G. Jansky Very Large Array (VLA) survey at Ka-band (8 mm and 1 cm) and C-band (4 cm and 6.6 cm). The observed sample has a bolometric luminosity range between 0.1 L$_{\odot}$ and $\sim$33 L$_{\odot}$, with a median of 0.7 L$_{\odot}$. This multiplicity study is based on the Ka-band data, having a best resolution of $\sim$0.065" (15 AU) and separations out to $\sim$43" (10000 AU) can be probed. The overall multiplicity fraction (MF) is found to be of 0.40$\pm$0.06 and the companion star fraction (CSF) is 0.71$\pm$0.06. The MF and CSF of the Class 0 protostars are 0.57$\pm$0.09 and 1.2$\pm$0.2, and the MF and CSF of Class I protostars are both 0.23$\pm$0.08. The distribution of companion separations appears bi-modal, with a peak at $\sim$75 AU and another peak at $\sim$3000 AU. Turbulent fragmentation is likely the dominant mechanism on $>$1000 AU scales and disk fragmentation is likely to be the dominant mechanism on $<$200 AU scales. Toward three Class 0 sources we find companions separated by $<$30 AU. These systems have the smallest separations of currently known Class 0 protostellar binary systems. Moreover, these close systems are embedded within larger (50 AU to 400 AU) structures and may be candidates for ongoing disk fragmentation.