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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
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:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 70 78 Visible Polarization Data
Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
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
Note (1): Stars with Suspected Variable Polarization: ---------------------------------------------- GF9 Pol e_Pol PA e_PA JD ---------------------------------------------- 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 ----------------------------------------------
History: From electronic version of the journal
(End) Patricia Vannier [CDS] 21-Jul-2008
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