The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Perseus Protostars. VI. Characterizing the Formation Mechanism for Close Multiple Systems

Abstract

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of multiple protostar systems in the Perseus molecular cloud previously detected by the Karl G. Jansky Very Large Array (VLA). We observed 17 close (<600 AU separation) multiple systems at 1.3 mm in continuum and five molecular lines (i.e., 12 CO, C 18 O, 13 CO, H 2 CO, SO) to characterize the circum-multiple environments in which these systems are forming. We detect at least one component in the continuum for the 17 multiple systems. In three systems, one companion is not detected, and for two systems the companions are unresolved at our observed resolution. We also detect circum-multiple dust emission toward 8 out of 9 Class 0 multiples. Circum-multiple dust emission is not detected toward any of the 8 Class I multiples. Twelve systems are detected in the dense gas tracers toward their disks/inner envelopes. For these 12 systems, we use the dense gas observations to characterize their formation mechanism. The velocity gradients in the circum-multiple gas are clearly orthogonal to the outflow directions in 8 out of the 12 systems, consistent with disk fragmentation. Moreover, only two systems with separations <200 AU are inconsistent with disk fragmentation, in addition to the two widest systems (>500 AU). Our results suggest that disk fragmentation via gravitational instability is an important formation mechanism for close multiple systems, but further statistics are needed to better determine the relative fraction formed via this method.

The Perseus ALMA Chemistry Survey (PEACHES). I. The Complex Organic Molecules in Perseus Embedded Protostars

“…Per-emb 17 is a close binary system with a separation of 0 278 ± 0 014 (83.3 ± 4.0 au with a distance of 300 pc; Tobin et al 2018). Our observations show clear double-peaked features for most of the emission (Figure 9).…”

“…B5 has a dominant embedded protostar, IRS1, along with three gravitationally bound gas condensation at a separation greater than 1000 au (Pineda et al 2015). Furthermore, the protostellar multiplicity in Perseus has been extensively studied by the VLA Nascent Disk and Multiplicity Survey (VANDAM) of Perseus protostars, showing a multiplicity fraction of 0.57 ± 0.09 and 0.23 ± 0.08 for Class 0 and I protostars, respectively (Tobin et al 2016(Tobin et al , 2018Segura-Cox et al 2018;Tychoniec et al 2018). Murillo et al (2016) further characterized the spectral energy distributions of all sources identified in the VANDAM survey to derive protostellar properties, such as bolometric luminosities (L bol ), bolometric temperatures (T bol ), and evolutionary stage classification.…”

Interferometric Observations of Magnetic Fields in Forming Stars

“…The VLA Nascent Disk and Multiplicity Survey of Perseus Protostars (VANDAM) by Tobin et al (2016b) found a bimodality in the multiplicity of systems; they argued that the wide multiples are the result of turbulent fragmentation, whereas the tight multiples are the result of disk fragmentation. This latter conclusion was strengthened in a follow-up study by Tobin et al (2018), who observed a sample of tight binaries from the VANDAM survey with ALMA in both continuum and spectral lines.…”

Highly Ordered and Pinched Magnetic Fields in the Class 0 Protobinary System L1448 IRS 2

“…The contours in the right panel of Figure 1 also show the binary companion (L1448 IRS 2B), which is separated from the primary by about 0 6 (corresponding to ∼180 au at the target distance) toward the west. This companion is less bright in the 1 mm continuum and has been detected at 9 mm (Ka-band; Tobin et al 2016) and at 1 mm (Tobin et al 2018). The blue and red contours overlaid in the figure are CO 2-1 molecular line data taken by ALMA (2013.1.00031.S; Tobin et al 2018).…”