J/A+A/569/L1 Polarization hole in a starless core (Alves+, 2014)
On the radiation driven alignment of dust grains:
Detection of the polarization hole in a starless core.
Alves F.O., Frau P., Girart J.M., Franco G.A.P., Santos F.P., Wiesemeyer H.
<Astron. Astrophys. 569, L1 (2014)>
=2014A&A...569L...1A 2014A&A...569L...1A
ADC_Keywords: YSOs ; Polarization ; Interstellar medium ; Infrared sources ;
Millimetric/submm sources
Keywords: stars: formation - ISM: magnetic fields - techniques: polarimetric -
ISM: individual objects: Core 109
Abstract:
We aim to investigate the polarization properties of a starless core
in a very early evolutionary stage. Linear polarization data reveal
the properties of the dust grains in the distinct phases of the
interstellar medium. Our goal is to investigate how the polarization
degree and angle correlate with the cloud and core gas. We use
optical, near infrared and submillimeter polarization observations
toward the starless object Pipe-109 in the Pipe nebula. Our data cover
a physical scale range of 0.08 to 0.4pc, comprising the dense gas,
envelope and the surrounding cloud. The cloud polarization is well
traced by the optical data. The near infrared polarization is produced
by a mixed population of grains from the core border and the cloud
gas. The optical and near infrared polarization toward the cloud reach
the maximum possible value and saturate with respect to the visual
extinction. The core polarization is predominantly traced by the
submillimeter data and have a steep decrease with respect to the
visual extinction. Modeling of the submillimeter polarization
indicates a magnetic field main direction projected onto the
plane-of-sky and loss of grain alignment for densities higher than
6x104cm-3 (or AV>30mag). Pipe-109 is immersed in a magnetized
medium, with a very ordered magnetic field. The absence of internal
source of radiation significantly affects the polarization
efficiencies in the core, creating a polarization hole at the center
of the starless core. This result supports the theory of dust grain
alignment via radiative torques.
Description:
Polarization information for the optical, near infrared and submm
data. The observations were performed with the 1.6m telescope of the
Observatorio do Pico dos Dias (LNA/MCTI) and the Atacama Pathfinder
Experiment (APEX). The observed fields cover the envelope and the
dense gas associated to the starless core Pipe-109 in the Pipe nebula.
Since the optical and near infrared polarization are produced by
absorption of background starlight radiation, the equatorial
coordinates refer to background stars. Stokes parameters Q and U, the
polarization degree, position angle and uncertainties are provided. On
the other hand, the submm polarization data are produced by continuum
thermal emission from dust grains, therefore the coordinates refer to
the polarization that arises from the several pixels within the
telescope primary beam. Stokes I, polarization degree, position angle
and uncertainties are provided.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
opt.dat 81 80 Optical polarization data of the starless core Pipe-109
nir.dat 81 700 Near-IR polarization data of the starless core Pipe-109
submm.dat 64 87 Submm polarization data of the starless core Pipe-109
list.dat 86 6 List of FITS maps
fits/* . 6 Individual FITS files
--------------------------------------------------------------------------------
See also:
J/ApJ/725/2232 : Deep NIR survey of the Pipe Nebula. II. (Roman-Zuniga+, 2010)
J/ApJ/699/742 : Properties of cores in the Pipe Nebula (Rathborne+, 2009)
Byte-by-byte Description of file: opt.dat nir.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 11 F5.2 s RAs Right ascension (J2000)
13 A1 --- DE- Declination sign (J2000)
14- 15 I2 deg DEd Declination (J2000)
17- 18 I2 arcmin DEm Declination (J2000)
20- 24 F5.2 arcsec DEs Declination (J2000)
29- 36 F8.5 --- Q Stokes parameter Q
38- 45 F8.5 --- U Stokes parameter U
48- 54 F7.5 --- e_POL Measured error (fit)
57- 63 F7.5 --- POL Polarization degree (G1)
66- 70 F5.1 deg PA Polarization position angle
75- 81 F7.5 --- s_POL Theoretical error in polarisation (photon noise)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: submm.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
3- 8 F6.2 arcsec oRA Offset in Right ascension (J2000) (1)
11- 16 F6.2 arcsec oDE Offset in Declination (J2000)
20- 24 F5.3 Jy Int Flux density (in Jy/beam)
28- 32 F5.3 Jy e_Int Error in flux density (in Jy/beam)
36- 40 F5.3 --- POL Polarization degree (G1)
44- 48 F5.3 --- e_POL Measured error in polarization degree
51- 56 F6.3 deg PA Polarization position angle
59- 64 F6.3 deg e_PA Error in position angle
--------------------------------------------------------------------------------
Note (1): The offsets in right ascension and declination are given with respect
to RA=17:35:47.700 and DE=-25:32:52.90 (the peak of emission).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 F3.1 arcsec/pix Scale Scale of the image
24- 25 I2 --- Nx [32] Number of pixels along X-axis
26 A1 --- --- [x]
27- 28 I2 --- Ny [32] Number of pixels along Y-axis
30- 31 I2 Kibyte size [11] Size of FITS file
33- 53 A21 --- FileName Name of FITS file in subdirectory fits
55- 86 A32 --- Title Title of the file
--------------------------------------------------------------------------------
Global notes:
Note (G1): The polarization degree is dimensionless because it is defined as
the polarized intensity divided by the total intensity (the same is valid for
Stokes parameters Q and U). By multiplying this column by 100, one has this
quantity in '%' unity.
--------------------------------------------------------------------------------
Acknowledgements:
Felipe Alves, falves(at)astro.uni-bonn.de
(End) Felipe Alves [AIfA, Germany], Emmanuelle Perret [CDS] 20-Aug-2014