J/A+AS/141/175 Dark clouds imaging polarimetry (Sen+, 2000)
Imaging polarimetry of some selected dark clouds
Sen A.K., Gupta Ranjan, Ramaprakash A.N., Tandon S.N.
<Astron. Astrophys. Suppl. Ser. 141, 175 (2000)>
=2000A&AS..141..175S 2000A&AS..141..175S
ADC_Keywords: Bok globules ; Polarization
Keywords: dark clouds - ISM: dust -
ISM: magnetic field, polarization, polarimeter -
techniques: polarimetric
Abstract:
A set of eight Bok Globules CB3, CB25, CB39, CB52, CB54, CB58, CB62
and CB246 were observed polarimetrically in white light, using our
Imaging Polarimater (IMPOL), from the 1.2m IR telescope at Mount Abu,
India. The observations were carried out on different nights during
the period December 1997 and April 1998. The CCD images obtained from
the instrument (IMPOL) were analyzed, to produce polarization map of
the Bok Globules. The stars in the field, which are mostly background
to the cloud show typically 2% linear polarization. Clouds which are
less dynamic (having 12CO line widths ΔV<2.5km/s) in general
show slightly better alignment of polarization vectors with the
projected direction of galactic plane. On the other hand, the more
dynamic group of clouds has polarization vectors more scattered and
poorly aligned with the projected direction of the galactic plane.
However one of the clouds observed, CB58, does not follow this trend
very well.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tables.dat 53 244 Observed linear polarization values for various
field stars in clouds CB25, CB246, CB25N, CB3,
CB39, CB3N, CB52, CB54A, CB54B, CB58 and CB62
(tables 4 to 14 of the paper)
tables.tex 76 420 LaTeX version of the tables
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Byte-by-byte Description of file: tables.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Cloud Cloud name
7- 8 I2 --- Seq Star sequential number in the cloud
10- 11 I2 h RAh Right ascension (J2000)
13- 14 I2 min RAm Right ascension (J2000)
16- 19 F4.1 s RAs Right ascension (J2000)
21 A1 --- DE- Declination sign (J2000)
22- 23 I2 deg DEd Declination (J2000)
25- 26 I2 arcmin DEm Declination (J2000)
28- 29 I2 arcsec DEs Declination (J2000)
31- 35 F5.3 % Pol Observed linear polarisation
37- 41 F5.3 % e_Pol rms uncertainty on Pol
43- 47 F5.1 deg Theta Position angle
49- 53 F5.2 mag mag Relative magnitude (1)
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Note (1): The magnitudes are just a conversion from the CCD counts and therefore
it is merely an indication of the relative intensity of the stars.
One should also note that the magnitude scale is not necessarily
same for all the clouds.
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Table 15: The average direction of polarization vectors (θaverage)
and the dispersions in the direction of polarization
(σθ) for the observed clouds.
(stars with p<0.5% and/or Ep/p>0.5 have been excluded)
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Cloud θaverage σθ
(in degree) (in degree)
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CB3 65.6 15.6
CB3N 63.5 6.0
CB25 151.4 5.8
CB25N 153.6 8.8
CB39 158.9 10.7
CB52 147.2 50.4
CB54A 106.1 37.5
CB54B 135.5 23.8
CB58 108.5 39.6
CB62 poor data poor data
CB246 67.4 20.2
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Acknowledgements: Ranjan Gupta
History: Before 12-Oct-2000, CB256 was misprinted for CB246 in tables.dat
(End) Patricia Bauer [CDS] 02-Aug-1999