Striations in the Taurus molecular cloud: Kelvin-Helmholtz instability or MHD waves?

TL;DR

This study investigates the origin of striations in the Taurus molecular cloud, suggesting they result from velocity modulations caused by Kelvin-Helmholtz instability or MHD waves, supported by new CO emission observations.

Contribution

It provides new observational evidence linking striations to MHD processes like Kelvin-Helmholtz instability or magnetosonic waves in molecular clouds.

Findings

Identified a periodic pattern of blue and redshifted emission associated with striations.

Line ratio variations are small and not correlated with striation locations.

A model of unresolved CO-emitting substructures explains the observed line ratios.

Abstract

The origin of striations aligned along the local magnetic field direction in the translucent envelope of the Taurus molecular cloud is examined with new observations of 12CO and 13CO J=2-1 emission obtained with the 10~m submillimeter telescope of the Arizona Radio Observatory. These data identify a periodic pattern of excess blue and redshifted emission that is responsible for the striations. For both 12CO and 13CO, spatial variations of the J=2-1 to J=1-0 line ratio are small and are not spatially correlated with the striation locations. A medium comprised of unresolved CO emitting substructures (cells) with a beam area filling factor less than unity at any velocity is required to explain the average line ratios and brightness temperatures. We propose that the striations result from the modulation of velocities and the beam filling factor of the cells as a result of either the Kelvin-Helmholtz instability or magnetosonic waves propagating through the envelope of the Taurus molecular cloud. Both processes are likely common features in molecular clouds that are sub-Alfvenic and may explain low column density, cirrus-like features similarly aligned with the magnetic field observed throughout the interstellar medium in far-infrared surveys of dust emission.