J/ApJS/151/271 Millennium Arecibo 21-cm Survey. III. (Heiles+, 2004)
The Millennium Arecibo 21 centimeter Absorption-Line Survey.
III. Techniques for spectral polarization and results for Stokes V.
Heiles C., Troland T.H.
<Astrophys. J. Suppl. Ser., 151, 271-297 (2004)>
=2004ApJS..151..271H 2004ApJS..151..271H
ADC_Keywords: Radio sources ; Polarization
Keywords: polarization - radio lines: ISM - surveys
Abstract:
We outline the theory and practice of measuring the four Stokes
parameters of spectral lines in emission/absorption observations. We
apply these concepts to our Arecibo H I absorption line data and
present the results. We include a detailed discussion of instrumental
effects arising from polarized beam structure and its interaction with
the spatially extended emission line structure. At Arecibo, linear
polarization [Stokes (Q,U)] has much larger instrumental effects than
circular (Stokes V). We show how to reduce the instrumental
contributions to V and to evaluate upper limits to its remaining
instrumental errors by using the (Q,U) results. These efforts work
well for opacity spectra but not for emission spectra. Arecibo's large
central blockage exacerbates these effects, particularly for emission
profiles, and other telescopes with weaker sidelobes are not as
susceptible. We present graphical results for 41 sources; we analyze
these absorption spectra in terms of Gaussian components, which number
136, and present physical parameters including magnetic field for
each.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 100 135 Table of Gaussian Fit Parameters Having
ΔB{||}<100µG
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See also:
J/ApJS/145/329 : Millennium Arecibo 21-cm Survey (Heiles+, 2003)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 F5.2 K TB Component intrinsic peak brightness
7- 11 F5.3 --- tau Component central opacity
13- 17 F5.3 --- e_tau Error in tau
19- 23 F5.1 km/s VLSR Central Local Standard of Rest velocity
25- 27 F3.1 km/s e_VLSR Error in VLSR
29- 33 F5.2 km/s DelV Gaussian Full-Width of Half-Maximum
35- 38 F4.2 km/s e_DelV Error in DelV
40- 45 F6.2 K Tspin Spin Temperature
47- 52 F6.2 K e_Tspin Error in Tspin
54- 58 I5 K Tkmax Component kinetic temperature
60- 64 F5.2 10+20/cm2 NHI H I column density
66- 70 F5.1 0.1nT B Magnetic field in microGauss
72- 75 F4.1 0.1nT e_B Error in B
77 A1 --- f_B [s] Indicates a statistically usable component
79- 83 F5.1 deg GLON Galactic longitude
85- 89 F5.1 deg GLAT Galactic latitude
91- 98 A8 --- Name Source name
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History:
From electronic version of the journal
References:
Heiles & Troland, Paper I 2003ApJS..145..329H 2003ApJS..145..329H, Cat. J/ApJS/145/329
Heiles & Troland, Paper II 2003ApJ...586.1067H 2003ApJ...586.1067H
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 07-May-2004