J/ApJ/872/56 R-band linear polarization of Gaia stars (Panopoulou+, 2019)
Demonstration of magnetic field tomography with starlight polarization toward
a diffuse sightline of the ISM.
Panopoulou G.V., Tassis K., Skalidis R., Blinov D., Liodakis I.,
Pavlidou V., Potter S.B., Ramaprakash A.N., Readhead A.C.S., Wehus I.K.
<Astrophys. J., 872, 56 (2019)>
=2019ApJ...872...56P 2019ApJ...872...56P
ADC_Keywords: Polarization; Interstellar medium; Stars, distances; Optical
Keywords: ISM: clouds ; ISM: magnetic fields ; techniques: polarimetric
Abstract:
The availability of large data sets with stellar distance and
polarization information will enable a tomographic reconstruction of
the (plane-of-the-sky-projected) interstellar magnetic field in the
near future. We demonstrate the feasibility of such a decomposition
within a small region of the diffuse interstellar medium (ISM). We
combine measurements of starlight (R-band) linear polarization
obtained using the RoboPol polarimeter with stellar distances from the
second Gaia data release. The stellar sample is brighter than 17mag in
the R-band and reaches out to several kiloparsecs from the Sun. HI
emission spectra reveal the existence of two distinct clouds along the
line of sight. We decompose the line-of-sight-integrated stellar
polarizations to obtain the mean polarization properties of the two
clouds. The two clouds exhibit significant differences in terms of
column density and polarization properties. Their mean
plane-of-the-sky magnetic field orientation differs by 60°. We
show how our tomographic decomposition can be used to constrain our
estimates of the polarizing efficiency of the clouds as well as the
frequency dependence of the polarization angle of polarized dust
emission. We also demonstrate a new method to constrain cloud
distances based on this decomposition. Our results represent a preview
of the wealth of information that can be obtained from a tomographic
map of the ISM magnetic field.
Description:
We performed polarimetric observations of our sample during 2016,
2017, and 2018 with the RoboPol polarimeter, which is mounted on the
1.3m Ritchey-Chretien telescope at the Skinakas Observatory in Crete,
Greece. The instrument is an imaging polarimeter, which uses two
half-wave plates and two Wollaston prisms to simultaneously measure
the relative Stokes parameters q=Q/I and u=U/I (I is the total
intensity and Q, U are the absolute Stokes parameters). Observations
were conducted during 13 nights from 2016 May to July, during five
nights in 2017 July, and during six nights in 2018 August.
The observing time for science targets was about 66hr in total.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 139 196 Catalog of stellar polarization measurements
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See also:
II/226 : Stellar polarization catalogs agglomeration (Heiles, 2000)
I/284 : The USNO-B1.0 Catalog (Monet+ 2003)
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+, 2018)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/ApJS/2/389 : Observations of O and B stars (Hiltner, 1956)
J/ApJS/136/463 : Distances and metallicities of HVCs and IVCs (Wakker, 2001)
J/A+A/384/1050 : Interstellar polarization. VI. (Berdyugin+, 2002)
J/ApJ/603/584 : Polarimetry toward Musca dark cloud (Pereyra+, 2004)
J/A+A/462/621 : UBVRI polarisation in NGC 5749 (Vergne+, 2007)
J/ApJ/728/104 : Optical polarization for 878 Hipparcos stars (Santos+ 2011)
J/A+A/561/A24 : Polarization at high galactic latitude (Berdyugin+, 2014)
J/ApJ/807/5 : R-band polarimetry data in Lupus I region (Franco+, 2015)
J/MNRAS/452/715 : Optical polarization of the Polaris Flare (Panopoulou+, 2015)
J/A+A/594/A116 : HI4PI spectra and column density maps (HI4PI team+, 2016)
J/ApJ/838/80 : JHK polarimetry of stars behind bubble N4 (Chen+, 2017)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- Gaia Gaia DR2 (I/345) catalog identifier
21- 32 A12 --- USNO USNO-B1 (I/284) catalog identifier
34- 42 F9.5 deg RAdeg [293.9/295.9] Right Ascension (J2000)
44- 51 F8.5 deg DEdeg [71.8/72.5] Declination (J2000)
53- 60 F8.5 --- q [-0.007/0.04] Stokes q value (Q/I)
62- 68 F7.5 --- e_q [0.0009/0.02] The 1σ uncertainty in q
70- 77 F8.5 --- u [-0.04/0.03] Stokes u value (U/I)
79- 85 F7.5 --- e_u [0.0009/0.02] The 1σ uncertainty in u
87- 93 F7.5 --- Pl [0.0002/0.04] Fractional linear polarization
95-101 F7.5 --- e_Pl [0.0009/0.02] The 1σ uncertainty in Pl
103-109 F7.5 --- dPl [0.0001/0.04] Debiased fractional linear
polarization
111-115 F5.1 --- theta [-58/72.4] Polarization angle
117-120 F4.1 --- e_theta [1.4/59.5] The 1σ uncertainty in theta
122-126 I5 pc rest [21/10806]? Estimated distance (r_est)
from Bailer-Jones+ (2018, I/347) (1)
128-131 I4 pc b_rest [21/9536]? Lower bound of 68% confidence interval
in rest
133-137 I5 pc B_rest [21/12338]? Upper bound of 68% confidence interval
in rest
139 I1 --- Flag [0/2]? Source flag (2)
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Note (1): Blanks indicate "NaN" values.
Note (2): Source flag as follows:
0 = intrinsically polarized candidate;
1 = source is in the 1-Cloud region (mainly Low Velocity Cloud (LVC)
emission region);
2 = source is in the 2-Cloud region (significant contribution from
the Intermediate Velocity Cloud (IVC) and LVC region);
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 03-Jun-2019