J/MNRAS/451/74 Excited-state hydroxyl maser polarimetry (Green+, 2015)
Excited-state hydroxyl maser polarimetry: who ate all the πs?
Green J.A., Caswell J.L., McClure-Griffiths N.M.
<Mon. Not. R. Astron. Soc., 451, 74-92 (2015)>
=2015MNRAS.451...74G 2015MNRAS.451...74G (SIMBAD/NED BibCode)
ADC_Keywords: Masers ; Polarization ; Magnetic fields
Keywords: magnetic fields - masers - polarization
Abstract:
We present polarimetric maser observations with the Australia Telescope
Compact Array of excited-state hydroxyl (OH) masers. We observed 30 fields
of OH masers in full Stokes polarization with the Compact Array Broadband
Backend at both the 6030 and 6035 MHz excited-state OH transitions, and
the 6668 MHz methanol maser transition, detecting 70 sites of maser
emission. Amongst the OH we found 112 Zeeman pairs, of which 18 exhibited
candidate π components. This is the largest single full polarimetric
study of multiple sites of star formation for these frequencies, and
the rate of 16 percent π components clearly indicates that the π
component exists, and is comparable to the percentage recently found for
ground-state transitions. This significant percentage of π components,
with consistent proportions at both ground- and excited-state transitions,
argues against Faraday rotation suppressing the π component emission.
Our simultaneous observations of methanol found the expected low level
of polarization, with no circular detected, and linear only found at
the =<10 percent level for the brightest sources.
Description:
We targeted 30 fields of known exOH masers associated with high-mass
star formation (Caswell 2003MNRAS.341..551C 2003MNRAS.341..551C) with the Australia Telescope
Compact Array (ATCA). Using the Compact Array Broadband Backend (CABB;
Wilson et al. 2011MNRAS.416..832W 2011MNRAS.416..832W), we simultaneously observed both exOH
transitions at 6030.7485 and 6035.0932 MHz, and the 6668.518 MHz methanol
maser transition. CABB was configured to the CFB 1M-0.5 mode (Wilson et al.
2011MNRAS.416..832W 2011MNRAS.416..832W), with six concatenated 1 MHz "zoom" bands centred at
each of the exOH transitions (providing ∼170 km/s velocity coverage), and
eight concatenated 1 MHz "zoom" bands at the methanol frequency (providing
∼200 km/s velocity coverage). The velocity channel separations were 0.024
and 0.022 km/s for the exOH and methanol transitions, respectively.
The observations were obtained from 2011 August 29 to 2011 September 02
using the extended 6 km array configuration (6B; Frater, Brooks & Whiteoak
1992JEEEA..12..103F 1992JEEEA..12..103F). Observations of each of the 30 target fields were
made with an average of 50 min total integration time, split across five
cuts, interspersed with calibrators and spread across a 12 h period of
local sidereal time to enable good coverage of the UV plane.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 91 149 Maser detections (≥5σ in two or more
adjacent channels) as measured with the ATCA
table2.dat 72 271 Polarized excited-state OH features associated
with Zeeman splitting
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See also:
J/A+A/325/255 : 5cm OH masers survey (Baudry+ 1997)
J/A+A/366/481 : ATCA/VLA OH 1612 MHz survey. III. (Sevenster+, 2001)
J/A+A/414/235 : OH maser emission from star forming regions
(Szymczak+, 2004)
J/ApJS/160/220 : Full-polarization observations of OH masers (Fish+, 2005)
J/other/PASA/26.454 : Precise positions of methanol masers (Caswell, 2009)
J/ApJS/227/26 : ATCA obs. of ground-state OH masers (Qiao+, 2016)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Name Source name
16- 17 I2 h RAh Hour of Right Ascension (J2000)
19- 20 I2 min RAm Minute of Right Ascension (J2000)
22- 26 F5.2 s RAs Second of Right Ascension (J2000)
28 A1 --- DE- Sign of the Declination (J2000)
29- 30 I2 deg DEd Degree of Declination (J2000)
32- 33 I2 arcmin DEm Arcminute of Declination (J2000)
35- 38 F4.1 arcsec DEs Arcsecond of Declination (J2000)
40- 43 I4 MHz Freq [6030/6668] Maser transition frequency
45- 50 F6.1 Jy Fpeak [0.2/2350.1] Peak flux density
51- 52 A2 --- n_Fpeak Note on Fpeak, denoting the polarization
percentage of at least one emission feature (1)
54- 58 F5.2 --- PBC [1/16.67] Primary beam correction to be applied
to listed flux density to account for offset
position of source from primary beam centre
60- 65 F6.1 km/s Vpeak [-108/73.4] Peak velocity
67- 72 F6.1 km/s b_Vel [-111.5/70] Velocity range, lower value
74- 79 F6.1 km/s B_Vel [-105/77] Velocity range, upper value
81- 91 A11 --- Ref Previous reference(s) (2)
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Note (1): Note as folllows:
c = >0 per cent, <50 per cent circularly polarized;
C = >50 per cent circularly polarized;
l = >0 per cent, <50 per cent linearly polarized;
L = >50 per cent linearly polarized.
If no letter is present, it is considered unpolarized.
Note (2): Reference as follows:
HW95 = Houghton & Whiteoak (1995MNRAS.273.1033H 1995MNRAS.273.1033H);
C95 = Caswell & Vaile (1995MNRAS.273..328C 1995MNRAS.273..328C);
C97 = Caswell (1997MNRAS.289..203C 1997MNRAS.289..203C);
C03 = Caswell (2003MNRAS.341..551C 2003MNRAS.341..551C);
C09 = Caswell (2009, J/other/PASA/26.454);
C11 = Caswell, Kramer & Reynolds (2011MNRAS.414.1914C 2011MNRAS.414.1914C).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Name Source name
16- 19 I4 MHz Freq [6030/6035] Frequency
21- 27 F7.2 km/s VLSR [-106.44/72.49] Local standard of rest velocity
29- 31 A3 --- Pol Type of polarized components (1)
33- 38 F6.2 Jy Sp [0.08/153] Peak flux density
40- 42 A3 --- Type Zeeman splitting type (2)
44- 47 A4 --- Num Zeeman splitting number
49- 60 A12 --- Comp First component of the pair/triplet
62- 66 F5.1 mG Strength [-10.4/11.4]? Field strength
68- 70 F3.1 mG e_Strength [0.1/4.6]? Uncertainty in Strength
72 A1 --- Rel [AB] Reliability indicator (3)
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Note (1): Type of polarized components as follows:
LHC = Left-hand circular polarization;
LIN = Linear polarization;
RHC = Right-hand circular polarization.
Note (2): Type as follows:
P = Denotes Zeeman pair;
T = Denotes possible Zeeman triplet;
X = Denotes a linearly polarized component which could not readily be
attributed to a Zeeman pair/triplet.
Note (3): All Zeeman associations are spatially coincident within the
observational errors, but a reliability indicator is given to identify:
A = those which we believe to be the most reliable;
B = those that may be spatially offset opposite polarized single features
blended within the ATCA position accuracy or are spectrally blended.
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 03-Dec-2019