J/A+A/538/A136 VLBA SiO maser maps of the star OH 44.8-2.3 (Amiri+, 2012)
VLBA SiO maser observations of the OH/IR star OH 44.8-2.3:
magnetic field and morphology.
Amiri N., Vlemmings W.H.T., Kemball A.J., van Langevelde H.J.
<Astron. Astrophys. 538, A136 (2012)>
=2012A&A...538A.136A 2012A&A...538A.136A
ADC_Keywords: Masers ; Magnetic fields ; Polarization
Keywords: Stars - magnetic fields - polarization - masers
Abstract:
SiO maser emission occurs in the extended atmosphere of evolved stars
and can be studied at high angular resolution. As compact,
high-brightness components they can be used as important tracers of
the dynamics at distances close to the central star. The masers also
serve as probes of the evolutionary path from spherically symmetric
AGB stars to aspherical PNe. Very long baseline interferometry (VLBI)
observations of Mira variables indicate that SiO masers are
significantly linearly polarized with linear polarization fractions up
to 100%. However, no information is available at high angular
resolution for SiO masers in higher mass loss OH/IR stars. Theory
indicates a different SiO pumping mechanism in higher mass loss
evolved stars.
We extend the VLBI SiO maser studies to OH/IR stars. The observations
enable us to understand the SiO pumping mechanisms in higher mass-loss
evolved objects and to compare them with Mira variables. Additionally,
polarimetric observations of SiO masers help us to understand the
magnetic field strength and morphology and to distinguish between
conflicting polarization theories.
Description:
The 43GHz SiO maser observations of the OH/IR star OH 44.8-2.3 were
performed with the VLBA in full polarization spectral line mode.
Auxiliary EVLA observations were performed to allow for the absolute
calibration of the polarization angle. The Zeeman splitting was
measured by cross correlating the right and left circular polarization
spectra, as well as the S-curve fitting. Additionally, we analyzed the
1612MHz OH maser observations of OH 44.8-2.3 from the VLA archive.
Objects:
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RA (2000) DE Designation(s)
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19 21 36.5 +09 27 56 OH 44.8-2.3 = IRAS 19192+0922
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 63 15 Results of the magnetic field determination of
the SiO maser features of OH 44.8-2.3 obtained
from the VLBA observations
maps.dat 65 3 *List of FITS maps
maps/* . 3 Individual FITS maps (Dim=512x512)
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Note on maps.dat: Scale=5e-05"/pix. Dim =512x512.
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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- 2 I2 --- Seq Sequential number of feature
4- 5 I2 h RAh Right ascension (J2000.0)
7- 8 I2 min RAm Right ascension (J2000.0)
10- 20 F11.8 s RAs Right ascension (J2000.0)
22 A1 --- DE- Declination sign (J2000.0)
23- 24 I2 deg DEd Declination (J2000.0)
26- 27 I2 arcmin DEm Declination (J2000.0)
29- 38 F10.7 arcsec DEs Declination (J2000.0)
40- 44 F5.1 km/s Vel Velocity (LSR)
46- 49 F4.2 Jy I Intensity of SiO maser feature (43GHz)
51- 53 I3 % ml ?=- Linear polarization fraction
55 A1 --- l_B Limit flag on B
56- 59 F4.1 10-4T B Magnetic field (Gauss)
61- 63 F3.1 10-4T e_B ? rms uncertainty on B (Gauss)
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Byte-by-byte Description of file: maps.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Source Source name (OH 44.8-2.3)
13- 21 F9.5 deg RAdeg Right ascension in decimal degrees (J2000)
22- 30 F9.5 deg DEdeg Declination in decimal degrees (J2000)
32- 48 A17 --- FileName Name of the FITS map im subdirectory maps
51- 65 A15 --- Title Title of the map (1)
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Note (1): The background contours represent the total intensity image.
The fractional linear polarization for the individual maser features
is shown in table1.
Scale=5e-05"/pix. Dim =512x512. V(lsr)=-60.812km/s
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Acknowledgements:
Nikta Amiri, amiri(at)strw.leidenuniv.nl
(End) Patricia Vannier [CDS] 13-Feb-2012