J/ApJ/860/82 ALMA obs. of polarization in the IM Lup disk (Hull+, 2018)
ALMA observations of polarization from dust scattering in the IM Lup
protoplanetary disk.
Hull C.L.H., Yang H., Li Z.-Y., Kataoka A., Stephens I.W., Andrews S.,
Bai X., Cleeves L.I., Hughes A.M., Looney L., Perez L.M., Wilner D.
<Astrophys. J., 860, 82 (2018)>
=2018ApJ...860...82H 2018ApJ...860...82H
ADC_Keywords: Polarization; YSOs; Millimetric/submm sources
Keywords: polarization ; protoplanetary disks ; scattering ; stars: formation ;
stars: protostars
Abstract:
We present 870µm ALMA observations of polarized dust emission
toward the Class II protoplanetary disk IM Lup. We find that the
orientation of the polarized emission is along the minor axis of the
disk, and that the value of the polarization fraction increases
steadily toward the center of the disk, reaching a peak value of
∼1.1%. All of these characteristics are consistent with models of
self-scattering of submillimeter-wave emission from an optically thin
inclined disk. The distribution of the polarization position angles
across the disk reveals that, while the average orientation is along
the minor axis, the polarization orientations show a significant
spread in angles; this can also be explained by models of pure
scattering. We compare the polarization with that of the Class I/II
source HL Tau. A comparison of cuts of the polarization fraction
across the major and minor axes of both sources reveals that IM Lup
has a substantially higher polarization fraction than HL Tau toward
the center of the disk. This enhanced polarization fraction could be
due a number of factors, including higher optical depth in HL Tau, or
scattering by larger dust grains in the more evolved IM Lup disk.
However, models yield similar maximum grain sizes for both HL Tau
(72µm) and IM Lup (61µm, this work). This reveals continued
tension between grain-size estimates from scattering models and from
models of the dust emission spectrum, which find that the bulk of the
(unpolarized) emission in disks is most likely due to millimeter-sized
(or even centimeter-sized) grains.
Description:
We used ALMA to observe dust polarization at 870um toward IM Lup on
2017 April 24 and 26. The pointing center was RAJ2000=15:56:09.172,
DEJ2000=-37:56:06.483. The observations have a synthesized beam
(resolution element) of 0.50"x0.40" at a position angle of 76.9°,
corresponding to a linear resolution of ∼72au at a distance of
161±10pc.
Objects:
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RA (ICRS) DE Designation(s)
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15 56 09.176 -37 56 06.11 IM Lup = V* IM Lup
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 57 52 ALMA polarization data
image/* . 10 FITS images behind the Figure 1
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See also:
J/ApJS/213/13 : 1.3mm polarization maps of star-forming cores (Hull+, 2014)
J/A+A/592/A49 : TW Hya CO (2-1), CN (2-1) & CS (5-4) data cubes (Teague+, 2016)
J/A+A/600/A20 : Lupus YSOs X-shooter spectroscopy (Alcala+, 2017)
J/ApJ/847/92 : Polarization data toward Serpens SMM1 (Hull+, 2017)
J/ApJ/842/L9 : ALMA obs. of Ser-emb 8 polarized dust emission (Hull+, 2017)
J/ApJ/845/44 : 340GHz SMA obs. of 50 protoplanetary disks (Tripathi+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 F10.5 deg RAdeg [239.038/239.039] Right Ascension (J2000)
12- 20 F9.5 deg DEdeg [-37.94/-37.93] Declination (J2000)
22- 28 F7.3 mJy/beam I [11.7/118.8] Stokes I total intensity
30- 34 F5.3 mJy/beam Pol [0.06/1.4] Polarized intensity
36- 39 F4.1 deg chi [23.8/66.4] Polarization position angle
41- 43 F3.1 deg e_chi [0.4/7.7] Uncertainty in chi
45- 50 F6.4 --- Pfrac [0.003/0.02] Fractional polarization
52- 57 F6.4 --- e_Pfrac [0.0002/0.002] Uncertainty in Pfrac
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 03-Jul-2019