J/ApJ/741/21 Polarization of stars in Taurus (Chapman+, 2011)
The magnetic field in Taurus probed by infrared polarization.
Chapman N.L., Goldsmith P.F., Pineda J.L., Clemens D.P., Li D., Krco M.
<Astrophys. J., 741, 21 (2011)>
=2011ApJ...741...21C 2011ApJ...741...21C
ADC_Keywords: Polarization ; Extinction ; Molecular clouds ; Infrared sources
Keywords: magnetic fields - polarization
Abstract:
We present maps of the plane-of-sky magnetic field within two regions
of the Taurus molecular cloud: one in the dense core L1495/B213
filament and the other in a diffuse region to the west. The field is
measured from the polarization of background starlight seen through
the cloud. In total, we measured 287 high-quality near-infrared
polarization vectors in these regions. In L1495/B213, the percent
polarization increases with column density up to AV∼9mag, the limits
of our data. The radiative torques model for grain alignment can
explain this behavior, but models that invoke turbulence are
inconsistent with the data. We also combine our data with published
optical and near-infrared polarization measurements in Taurus. Using
this large sample, we estimate the strength of the plane-of-sky
component of the magnetic field in nine subregions. This estimation is
done with two different techniques that use the observed dispersion in
polarization angles. Our values range from 5 to 82uG and tend to be
higher in denser regions. In all subregions, the critical index of the
mass-to-magnetic flux ratio is sub-unity, implying that Taurus is
magnetically supported on large scales (∼2pc). Within the region
observed, the B213 filament takes a sharp turn to the north and the
direction of the magnetic field also takes a sharp turn, switching
from being perpendicular to the filament to becoming parallel. This
behavior can be understood if we are observing the rim of a bubble. We
argue that it has resulted from a supernova remnant associated with a
recently discovered nearby gamma-ray pulsar.
Description:
We used the Mimir instrument to observe H-band (1.6um) polarization of
background starlight seen through the Taurus molecular cloud. Mimir is
installed on the 1.8m Perkins telescope located near Flagstaff, AZ and
operated by Lowell Observatory. The observations spanned the nights of
2009 January 12-16 UT. We observed two regions within Taurus: one in a
low-density portion of the cloud (hereafter "Diffuse") and the other
toward a high-density region, B213/L1495 (hereafter "Filament"). The
Diffuse region is rectangular covering roughly 4:51m-4:53m in RA and
25:26'-27:05' in DEC. The Filament region is not quite rectangular,
but spans approximately 4:16m-4:19m in RA and 27:11'-28:31' in DEC.
Coordinates are J2000. Each region consisted of an overlapping mosaic
of 10'x10' Mimir fields of view (FOVs).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 52 125 H-band polarization for stars in the diffuse region
table2.dat 52 162 H-band polarization for stars in the filament region
--------------------------------------------------------------------------------
See also:
J/ApJ/703/1964 : Spectra of three nearby star-forming regions (Furlan+, 2009)
J/ApJ/647/1180 : Infrared photometry of Taurus SFR (Luhman+, 2006)
Byte-by-byte Description of file: table1.dat table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/162] Star number
5- 6 I2 h RAh [4] Hour of right ascension (J2000)
8- 9 I2 min RAm Minute of right ascension (J2000)
11- 14 F4.1 s RAs Second of right ascension (J2000)
16 A1 --- DE- [+] Sign of declination (J2000)
17- 18 I2 deg DEd [25/28] Degree of declination (J2000)
20- 21 I2 arcmin DEm Arcminute of declination (J2000)
23- 24 I2 arcsec DEs Arcsecond of declination (J2000)
26- 29 F4.2 % Pol [0.28/6.12] Degree of polarization
31- 34 F4.2 % e_Pol Pol uncertainty
36- 38 I3 deg theta [-74/89] Polarization angle θ (1)
40- 41 I2 deg e_theta Theta uncertainty
43- 47 F5.2 mag Av [0.3/13.04] Extinction (2)
49- 52 F4.2 mag e_Av Av uncertainty
--------------------------------------------------------------------------------
Note (1): Angles are equatorial, measured east from north.
Note (2): Extinction map from Pineda et al. (2010ApJ...721..686P 2010ApJ...721..686P).
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 13-Feb-2013