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Title: Fantastic Striations and Where to Find Them: The Origin of Magnetically Aligned Striations in Interstellar Clouds

Abstract

Thin, magnetically aligned striations of relatively moderate contrast with the background are commonly observed in both atomic and molecular clouds. They are also prominent in MHD simulations with turbulent converging shocks. The simulated striations develop within a dense, stagnated sheet in the midplane of the post-shock region where magnetically induced converging flows collide. We show analytically that the secondary flows are an inevitable consequence of the jump conditions of oblique MHD shocks. They produce the stagnated, sheet-like sub-layer through a secondary shock when, roughly speaking, the Alfvénic speed in the primary converging flows is supersonic, a condition that is relatively easy to satisfy in interstellar clouds. The dense sub-layer is naturally threaded by a strong magnetic field that lies close to the plane of the sub-layer. The substantial magnetic field makes the sheet highly anisotropic, which is the key to the striation formation. Specifically, perturbations of the primary inflow that vary spatially perpendicular to the magnetic field can easily roll up the sheet around the field lines without bending them, creating corrugations that appear as magnetically aligned striations in column density maps. On the other hand, perturbations that vary spatially along the field lines curve the sub-layer and alter itsmore » orientation relative to the magnetic field locally, seeding special locations that become slanted overdense filaments and prestellar cores through enhanced mass accumulation along field lines. In our scenario, the dense sub-layer, which is unique to magnetized oblique shocks, is the birthplace for both magnetically aligned diffuse striations and massive star-forming structures.« less

Authors:
; ;  [1];  [2]
  1. Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States)
  2. National Radio Astronomy Observatory, Charlottesville, VA 22904 (United States)
Publication Date:
OSTI Identifier:
22679788
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 847; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALFVEN WAVES; ANISOTROPY; BENDING; CLOUDS; COSMIC DUST; DENSITY; DISTURBANCES; INTERSTELLAR GRAINS; INTERSTELLAR SPACE; LAYERS; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; MASS; PERTURBATION THEORY; SIMULATION; STARS; TURBULENCE; VELOCITY

Citation Formats

Chen, Che-Yu, Li, Zhi-Yun, King, Patrick K., and Fissel, Laura M.. Fantastic Striations and Where to Find Them: The Origin of Magnetically Aligned Striations in Interstellar Clouds. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA898E.
Chen, Che-Yu, Li, Zhi-Yun, King, Patrick K., & Fissel, Laura M.. Fantastic Striations and Where to Find Them: The Origin of Magnetically Aligned Striations in Interstellar Clouds. United States. doi:10.3847/1538-4357/AA898E.
Chen, Che-Yu, Li, Zhi-Yun, King, Patrick K., and Fissel, Laura M.. Sun . "Fantastic Striations and Where to Find Them: The Origin of Magnetically Aligned Striations in Interstellar Clouds". United States. doi:10.3847/1538-4357/AA898E.
@article{osti_22679788,
title = {Fantastic Striations and Where to Find Them: The Origin of Magnetically Aligned Striations in Interstellar Clouds},
author = {Chen, Che-Yu and Li, Zhi-Yun and King, Patrick K. and Fissel, Laura M.},
abstractNote = {Thin, magnetically aligned striations of relatively moderate contrast with the background are commonly observed in both atomic and molecular clouds. They are also prominent in MHD simulations with turbulent converging shocks. The simulated striations develop within a dense, stagnated sheet in the midplane of the post-shock region where magnetically induced converging flows collide. We show analytically that the secondary flows are an inevitable consequence of the jump conditions of oblique MHD shocks. They produce the stagnated, sheet-like sub-layer through a secondary shock when, roughly speaking, the Alfvénic speed in the primary converging flows is supersonic, a condition that is relatively easy to satisfy in interstellar clouds. The dense sub-layer is naturally threaded by a strong magnetic field that lies close to the plane of the sub-layer. The substantial magnetic field makes the sheet highly anisotropic, which is the key to the striation formation. Specifically, perturbations of the primary inflow that vary spatially perpendicular to the magnetic field can easily roll up the sheet around the field lines without bending them, creating corrugations that appear as magnetically aligned striations in column density maps. On the other hand, perturbations that vary spatially along the field lines curve the sub-layer and alter its orientation relative to the magnetic field locally, seeding special locations that become slanted overdense filaments and prestellar cores through enhanced mass accumulation along field lines. In our scenario, the dense sub-layer, which is unique to magnetized oblique shocks, is the birthplace for both magnetically aligned diffuse striations and massive star-forming structures.},
doi = {10.3847/1538-4357/AA898E},
journal = {Astrophysical Journal},
number = 2,
volume = 847,
place = {United States},
year = {Sun Oct 01 00:00:00 EDT 2017},
month = {Sun Oct 01 00:00:00 EDT 2017}
}