THE MAGNETIC FIELD OF CLOUD 3 IN L204

The L204 dark cloud complex is a nearby filamentary structure in Ophiuchus North that has no signs of active star formation. Past studies show that L204 is interacting with the nearby runaway O star, [zeta] Oph, and hosts a magnetic field that is coherent across parsec-length scales. Near-infrared H...

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Bibliographic Details
Published in:The Astrophysical journal 2014-10, Vol.793 (2), p.1-10
Main Authors: Cashman, Lauren R, Clemens, D P
Format: Article
Language:English
Subjects:
Astronomical instruments
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Clouds
DUSTS
EFFICIENCY
ILLUMINANCE
Illumination
Linear polarization
MAGNETIC FIELDS
POLARIMETRY
POLARIZATION
STARS
TELESCOPES
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Summary:The L204 dark cloud complex is a nearby filamentary structure in Ophiuchus North that has no signs of active star formation. Past studies show that L204 is interacting with the nearby runaway O star, [zeta] Oph, and hosts a magnetic field that is coherent across parsec-length scales. Near-infrared H-band (1.6 mu m) linear polarization measurements were obtained for 3896 background stars across a 1[degrees] x 1[degrees].5 region centered on the dense Cloud 3 in L204, using the Mimir near-infrared instrument on the 1.8 m Perkins Telescope. Analysis of these observations reveals both large-scale properties and small-scale changes in the magnetic field direction in Cloud 3. In the northern and western [zeta] Oph facing regions of the cloud, the magnetic field appears to be pushed up against the face of the cloud. This may indicate that the UV flux from [zeta] Oph has compressed the magnetic field on the western edge of L204. The plane-of-sky magnetic field strength is estimated to be ~ll-26 mu G using the Chandrasekhar-Fermi method. The polarimetry data also reveal that the polarization efficiency (PE = P sub(H)/A sub(V)) steadily decreases with distance from [zeta] Oph (-0.09% + or - 0.03% mag super(-1) pc super(-1)). Additionally, power-law fits of PE versus A sub(V) for localized samples of probe stars show steeper negative indices with distance from [zeta] Oph. Both findings highlight the importance of external illumination, here from [zeta] Oph, in aligning dust grains to embedded magnetic fields.
ISSN:1538-4357
0004-637X
1538-4357
DOI:10.1088/0004-637X/793/2/126