J/ApJ/650/945 Polarisation around filamentary dark cloud GF 9 (Poidevin+, 2006)
Comparison of magnetic field structures on different scales in and around the
filamentary dark cloud GF 9.
Poidevin F., Bastien P.
<Astrophys. J., 650, 945-955 (2006)>
=2006ApJ...650..945P 2006ApJ...650..945P
ADC_Keywords: Molecular clouds ; Polarization
Keywords: dust, extinction - ISM: clouds - ISM: individual (GF 9, LDN 1082) -
magnetic fields - polarization
Abstract:
New visible polarization data combined with existing IR and FIR
polarization data are used to study how the magnetic field threading
the filamentary molecular cloud GF 9 connects to larger structures in
its general environment. When visible and NIR polarization data are
combined, no evidence is found for a plateau in the polarization above
extinction AV∼1.3, as seen in dark clouds in Taurus. This lack of
saturation effect suggests that even in the denser parts of GF 9
magnetic fields can be probed. The visible polarization is smooth and
has a well-defined orientation. In the core region, the IR and FIR
data are also well defined, but each with a different direction. A
multiscale analysis of the magnetic field shows that on the scale of a
few times the mean radial dimension of the molecular cloud, it is as
if the magnetic field were blind to the spatial distribution of the
filaments, while on smaller scales in the core region, multiwavelength
polarimetry shows a rotation of the magnetic field lines in these
denser phases. Finally, the Chandrasekhar and Fermi method is used to
evaluate the magnetic field strength, indicating that the core region
is approximately magnetically critical. A global interpretation
suggests that in the core region an original poloidal field could have
been twisted by a rotating elongated (core+envelope) structure. There
is no evidence for turbulence, and ambipolar diffusion does not seem
to be effective at the present time.
Description:
The observations were carried out on the 1.6m telescope at the
Observatoire du Mont Megantic (OMM), Quebec, Canada, between 2000
September and 2003 July, using an 8.2" aperture hole and a broadband
red filter (RG645: 7660Å central wavelength, 2410Å FWHM).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 70 78 Visible Polarization Data
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- GSC ? GSC number (Cat. I/220)
12- 14 I3 --- GF9 GF9 number, [PB2006] GF 9-NNN in Simbad
15- 17 A3 --- m_GF9 [bis ] Multiplicity index on GF9,
[PB2006] GF 9-69bis in Simbad
19- 20 I2 h RAh Right ascension (J2000)
22- 23 I2 min RAm Right ascension (J2000)
25- 28 F4.1 s RAs Right ascension (J2000)
30 A1 --- DE- Declination sign (J2000)
31- 32 I2 deg DEd Declination (J2000)
34- 35 I2 arcmin DEm Declination (J2000)
37- 40 F4.1 arcsec DEs Declination (J2000)
42- 45 F4.2 % Pol ?=- Degree of polarization
47- 50 F4.2 % e_Pol ?=- rms uncertainty on Pol
51 A1 --- n_Pol [a] a: Suspected variable polarisation (1)
53- 57 F5.1 deg polPA ?=- Equatorial position angle
59- 62 F4.1 deg e_polPA ?=- rms uncertainty on PA
63 A1 --- n_polPA [a] a: Suspected variable polarisation (1)
65- 68 F4.2 mag AV Visible extinction coefficient from
Dobashi et al. (2005, Cat. VII/244)
70 I1 --- P/e_P>3 [0/1]? 1 when P>3e_P, else 0
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Note (1): Stars with Suspected Variable Polarization:
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GF9 Pol e_Pol PA e_PA JD
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35 2.75 0.12 135.8 1.3 2452054.64583
35 0.43 0.13 163.2 8.7 2452141.72222
86 10.70 0.41 131.3 1.1 2452830.75347
86 12.41 0.37 15.4 0.8 2452835.78125
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 21-Jul-2008