J/A+A/618/A163 Stokes param. of Bok globules background stars (Jorquera+, 2018)
Magnetic fields in Bok globules:
multi-wavelength polarimetry as tracer across large spatial scales.
Jorquera S., Bertrang G. H.-M.
<Astron. Astrophys. 618, A163 (2018)>
=2018A&A...618A.163J 2018A&A...618A.163J (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Interstellar medium ; Magnetic fields
Keywords: magnetic fields - polarization - stars: formation - stars: low-mass -
ISM: clouds - instrumentation: polarimeters
Abstract:
The role of magnetic fields in the process of star formation is a
matter of continuous debate. Clear observational proof of the general
influence of magnetic fields on the early phase of cloud collapse is
still pending. In an earlier study on Bok globules with simple
structures, we find strong indications of dominant magnetic fields
across large spatial scales. The aim of this study is to test the
magnetic field influence across Bok globules with more complex density
structures. We apply near-infrared polarimetry to trace the magnetic
field structure on scales of 104-105au in selected Bok globules.
The combination of these measurements with archival data in the
optical and sub-mm wavelength range allows us to characterize the
magnetic field on scales of 103-106au. We present polarimetric
data in the near-infrared wavelength range for the three Bok globules
CB34, CB56, and [OMK2002] 18, combined with archival polarimetric data
in the optical wavelength range for CB34 and CB56, and in the sub
millimeter wavelength range for CB34 and [OMK2002] 18. We find a strong
polarization signal (P>2%) in the near-infrared for all three
globules. For CB34, we detect a connection between the structure on
scales of 104-105au to 105-106au. For CB56, we trace aligned
polarization segments in both the near-infrared and optical data,
suggesting a connection of the magnetic field structure across the
whole globule. In the case of [OMK2002]18, we find ordered
polarization structures on scales of 104-105au. We find strongly
aligned polarization segments on large scales which indicate dominant
magnetic fields across Bok globules with complex density structures.
To reconcile our findings in globules, the lowest mass clouds known,
and the results on intermediate (e.g. Taurus) and more massive (e.g.
Orion) clouds, we postulate a mass dependent role of magnetic fields,
whereby magnetic fields appear to be dominant on low and high mass but
rather sub dominant on intermediate mass clouds.
Description:
Observations of background stars of the Book globules CB34, CB56 and
[OMK2002] 18 were performed in the near-IR with the instrument Son OF
ISAAC (SOFI) at the 3.58m New Technology Telescope (NTT) from
November 11 to 15, 2015. Stokes parameters Q, U and I in the
near-infrared wavelength range for background stars of the globules
were derived using these observations. These parameters are later used
to calculate the polarization angle and polarization degree of the
background stars.
Objects:
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RA (ICRS) DE Designation(s)
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05 47 02.3 +21 00 10 CB 34 = [CB88] 34
07 14 36 -25 08.9 CB 56 = [CB88] 56
04 21 56.9 +15 29 47 [OMK2002] 18 = [OMK2002] 18a
04 22 01.1 +15 30 17 [OMK2002] 18 = [OMK2002] 18b
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
cb34.dat 52 37 Bok globule CB34
cb56.dat 51 6 Bok globule CB56
omk.dat 51 12 Bok globule [OMK2002] 18
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Byte-by-byte Description of file: cb34.dat cb56.dat omk.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right Ascension (J2000)
4- 5 I2 min RAm Right Ascension (J2000)
7- 11 F5.2 s RAs Right Ascension (J2000)
13 A1 --- DE- Declination sign (J2000)
14- 15 I2 deg DEd Declination (J2000)
17- 18 I2 arcmin DEm Declination (J2000)
20- 23 F4.1 arcsec DEs Declination (J2000)
25- 32 F8.1 --- Q Q value of the Stokes vector of the star
34- 41 F8.1 --- U U value of the Stokes vector of the star
44- 52 F9.2 --- I I value of the Stokes vector of the star
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Acknowledgements:
Sebastian Jorquera, sebastian.jorcq(at)gmail.com
(End) Sebastian Jorquera [Univ. de Chile], Patricia Vannier [CDS] 03-Sep-2018