J/A+A/588/A45 R-band polarisation of stars in Gal 110-13 direction (Neha+, 2016)
Magnetic field geometry of an unusual cometary cloud Gal 110-13.
Neha S., Maheswar G., Soam A., Lee C.W., Tej A.
<Astron. Astrophys., 588, A45-45 (2016)>
=2016A&A...588A..45N 2016A&A...588A..45N (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Polarization
Keywords: ISM: clouds - polarization - ISM: magnetic fields -
ISM: individual: Gal 110-13
Abstract:
We carried out optical polarimetry of an isolated cloud, Gal 110-13,
to map the plane-of-the-sky magnetic field geometry. The main aim of
the study is to understand the most plausible mechanism responsible
for the unusual cometary shape of the cloud in the context of its
magnetic field geometry.
When unpolarized starlight passes through the intervening interstellar
dust grains that are aligned with their short axes parallel to the
local magnetic field, it gets linearly polarized. The plane-of-the-sky
magnetic field component can therefore be traced by doing polarization
measurements of background stars projected on clouds. Because the
light in the optical wavelength range is most efficiently polarized by
the dust grains typically found in the outer layers of the molecular
clouds, optical polarimetry enables us to trace the magnetic field
geometry of the outer layers of the clouds.
We made R-band polarization measurements of 207 stars in the direction
of Gal 110-13. The distance of Gal 110-13 was determined as
∼450±80pc using our polarization and 2MASS near-infrared data. The
foreground interstellar contribution was removed from the observed
polarization values by observing a number of stars located in the
vicinity of Gal 110-13 which has Hipparcos parallax measurements. The
plane-of-the-sky magnetic field lines are found to be well ordered and
aligned with the elongated structure of Gal 110-13. Using structure
function analysis, we estimated the strength of the plane-of-the-sky
component of the magnetic field as ∼25µG.
Based on our results and comparing them with those from simulations,
we conclude that compression by the ionization fronts from 10 Lac is
the most plausible cause of the comet-like morphology of Gal 110-13
and of the initiation of subsequent star formation.
Description:
The optical linear polarization observations of the region associated
with Gal 110-13 were carried out with the ARIES IMaging POLarimeter
(AIMPOL), mounted at the f/13 Cassegrain focus of the 104-cm
Sampurnanand telescope of ARIES, Nainital, India. It consists of a
field lens in combination with the camera lens (85mm, f/1.8); in
between them, an achromatic, rotatable half-wave plate (HWP) are used
as modulator and a Wollaston prism beam-splitter as analyzer.
We used a standard Johnson RKC filter (λeff=0.760um)
photometric band for the polarimetric observations.
Objects:
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RA (2000) DE Designation(s)
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23 37 39 +48 29.8 GAL 110-13 = GAL 110-13
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 40 207 Polarization results of 207 stars
(with P/σP≥2) observed in the direction
of Gal 110-13
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/207] Star sequential number
4 A1 --- n_Seq [a-e] Note on Seq (1)
6- 15 F10.6 deg RAdeg Right ascension (J2000)
17- 25 F9.6 deg DEdeg Declination (J2000)
27- 29 F3.1 % Pol R-band polarisation
31- 33 F3.1 % e_Pol rms uncertainty on Pol
35- 37 I3 deg theta R-band polarisation position angle
39- 40 I2 deg e_theta rms uncertainty on theta
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Note (1): Spectral type as follows:
a = B9V
b = B9
c = K0
d = K5Ve
e = B8V
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 13-Jun-2016