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J/A+A/614/A100     Molecular clouds los magnetic field structure (Tahani+, 2018)

Helical magnetic fields in molecular clouds? A new method to determine the line-of-sight magnetic field structure in molecular clouds. Tahani M., Plume R., Brown J.C., Kainulainen J. <Astron. Astrophys. 614, A100 (2018)> =2018A&A...614A.100T (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Magnetic fields Keywords: methods: observational - ISM: magnetic fields - stars: formation - magnetic fields Abstract: Magnetic fields pervade in the interstellar medium (ISM) and are believed to be important in the process of star formation, yet probing magnetic fields in star formation regions is challenging. Aims. We propose a new method to use Faraday rotation measurements in small-scale star forming regions to find the direction and magnitude of the component of magnetic field along the line of sight. We test the proposed method in four relatively nearby regions of Orion A, Orion B, Perseus, and California. We use rotation measure data from the literature. We adopt a simple approach based on relative measurements to estimate the rotation measure due to the molecular clouds over the Galactic contribution. We then use a chemical evolution code along with extinction maps of each cloud to find the electron column density of the molecular cloud at the position of each rotation measure data point. Combining the rotation measures produced by the molecular clouds and the electron column density, we calculate the line-of-sight magnetic field strength and direction. In California and Orion A, we find clear evidence that the magnetic fields at one side of these filamentary structures are pointing towards us and are pointing away from us at the other side. Even though the magnetic fields in Perseus might seem to suggest the same behavior, not enough data points are available to draw such conclusions. In Orion B, as well, there are not enough data points available to detect such behavior. This magnetic field reversal is consistent with a helical magnetic field morphology. In the vicinity of available Zeeman measurements in OMC-1, OMC-B, and the dark cloud Barnard 1, we find magnetic field values of -23±38uG, -129±28uG, and 32±101uG, respectively, which are in agreement with the Zeeman measurements. Description: We propose a new method to use Faraday rotation measurements in small scale star forming regions to find the direction and magnitude of the component of magnetic field along the line-of-sight. We test the proposed method in four relatively nearby regions of Orion A, Orion B, California, and Perseus. Tables 1, 3, 4, and 6 show the result magnetic fields for these regions. Tables 2, 5, and 7 show the result magnetic fields that do not change direction within their uncertainty range for Orion A, California, and Perseus respectively. Negative values indicate magnetic fields pointed away from the observer and positive values are towards the observer. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 65 34 Line-of-sight magnetic field in Orion A table2.dat 65 14 Line-of-sight magnetic field in Orion A (Table 1), but only points with fixed direction table3.dat 65 8 Line-of-sight magnetic field in Orion B table4.dat 65 35 Line-of-sight magnetic field in California table5.dat 65 15 Line-of-sight magnetic field in California (Table 4), but only points with fixed direction table6.dat 65 24 Line-of-sight magnetic field in Perseus table7.dat 65 11 Line-of-sight magnetic field in Perseus (Table 6), but only points with fixed direction
See also: J/ApJ/702/1230 : Rotation measure image of the sky (Taylor+, 2009) Byte-by-byte Description of file: table?.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Point Point Numbers in the figures 6, 7, 8, 9 5- 9 F5.2 deg RAdeg Right ascension (J2000) 13- 18 F6.2 deg DEdeg Declination (J2000) 21- 25 F5.2 mag AV Extinction in V band 29- 34 F6.1 rad/m2 RMon Rotation measure (1) 37- 42 F6.1 rad/m2 RMmc Rotation measure of Molecular Cloud (2) 46- 50 I5 uG Blos Line of sight magnetic field of the Cloud 54- 57 I4 uG E_Blos Upper uncertainty of magnetic Field 62- 65 I4 uG e_Blos Lower uncertainty of magnetic Field
Note (1): RMon is the rotation measure obtained from Taylor et al. (2009, Cat. J/ApJ/702/1230) catalog. Note (2): RMmc is the rotation measure of the molecular cloud alone, as explained in the paper.
Acknowledgements: Mehrnoosh Tahani, mtahani(at)ucalgary.ca
(End) Mehrnoosh Tahani [Univ. Calgary], Patricia Vannier [CDS] 06-Mar-2018
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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