A Keplerian disk around a Class 0 source: ALMA observations of VLA1623A

Abstract: Context: Rotationally supported disks are critical in the star formation process. The questions of when do they form and what factors influence or hinder their formation have been studied but are largely unanswered. Observations of early stage YSOs are needed to probe disk formation. Aims: VLA1623 is a triple non-coeval protostellar system, with a weak magnetic field perpendicular to the outflow, whose Class 0 component, VLA1623A, shows a disk-like structure in continuum with signatures of rotation in line emission. We aim to determine whether this structure is in part or in whole a rotationally supported disk, i.e. a Keplerian disk, and what are its characteristics. Methods: ALMA Cycle 0 Early Science 1.3 mm continuum and C$^{18}$O (2-1) observations in the extended configuration are presented here and used to perform an analysis of the disk-like structure using PV diagrams and thin disk modelling with the addition of foreground absorption. Results: The PV diagrams of the C$^{18}$O line emission suggest the presence of a rotationally supported component with a radius of at least 50 AU. Kinematical modelling of the line emission shows that the disk out to 180 AU is actually rotationally supported, with the rotation being well described by Keplerian rotation out to at least 150 AU, and the central source mass to be $\sim$0.2 M${sun}$ for an inclination of 55$^{\circ}$. Pure infall and conserved angular momentum rotation models are excluded. Conclusions: VLA1623A, a very young Class 0 source, presents a disk with an outer radius $R{\rm out}$ = 180 AU with a Keplerian velocity structure out to at least 150 AU. The weak magnetic fields and recent fragmentation in this region of rho Ophiuchus may have played a lead role in the formation of the disk.

Analysis of ALMA Observations: A Keplerian Disk Around VLA1623A

In the study titled "A Keplerian disk around a Class 0 source: ALMA observations of VLA1623A," the researchers present compelling evidence for the presence of a Keplerian disk in a very young Class 0 protostellar system. The observations carried out using the Atacama Large Millimeter/submillimeter Array (ALMA) provide significant insights into the kinematic structure of VLA1623A, a component within the triple protostellar system located in the ρ Ophiuchus cloud complex.

Key Findings

The ALMA observations reveal a disk-like structure around VLA1623A, characterized by a rotationally supported or Keplerian velocity profile extending up to at least 150 AU. The presence of a weak magnetic field perpendicular to the disk's rotational axis and recent fragmentation are posited to have played crucial roles in the formation of this disk. The mass of the central protostar was estimated to be approximately 0.2 M⊙ with an inclination of 55°, supported by kinematic modeling.

The study employed PV diagram analysis and modeling approaches to distinguish between various potential kinematical structures. The investigations ruled out pure infall and conserved angular momentum models, instead firmly supporting a Keplerian rotational structure.

Implications and Discussions

The detection of an early-stage Keplerian disk poses significant implications for the understanding of star formation processes. Traditionally, Keplerian disks have been observed in later stages of protostellar evolution, such as Class II sources. The discovery in the Class 0 stage suggests that disk formation can occur much earlier than previously recognized, raising questions about the mechanisms underlying disk formation at these stages.

Key factors influencing Keplerian disk formation may include weak magnetic fields, fragmentation, and possibly turbulence. The misalignment between the magnetic field and the rotational axis likely reduces magnetic braking efficiency, facilitating disk growth. This aligns with theoretical predictions by Krumholz et al., which propose early disk formation in systems with similar characteristics.

The observational capabilities of ALMA, with enhanced sensitivity and resolution, have afforded a more detailed interrogation of the disk's structure and extended the understanding of rotational dynamics at nascent stages of star formation. However, the study notes complexity in disentangling disk features from foreground absorption, highlighting a need for continued investigation into environmental factors.

Future Directions

The findings point towards several avenues for future research. Detailed magnetic field studies could elaborate on their role in disk formation, considering varied configurations and strengths. Furthermore, examining additional Class 0 sources using high-resolution instruments like ALMA may reveal common patterns and diversities in disk formation processes.

Understanding the fragmentation process and its impact on the stability and evolution of young protostellar systems will also be crucial. The dynamics of three-body interactions, especially in multiple protostar systems like VLA1623, remain an intriguing area for exploration.

Finally, modeling efforts refining the interplay between rotation, magnetic fields, and accretion processes in the earliest stages of star formation will continue to enhance theoretical frameworks. As observation techniques and technology advance, providing an increasingly detailed view of these universal processes, more nuanced insights into protostellar development will emerge, further bridging observational and theoretical astronomy.