J/A+A/635/A46 High-precision polarimetry of nearby stars (Piirola+, 2020)
High-precision polarimetry of nearby stars (d<50 pc).
Mapping the interstellar dust and magnetic field inside the Local Bubble.
Piirola V., Berdyugin A., Frisch P.C., Kagitani M., Sakanoi T.,
Berdyugina S., Cole A.A., Harlingten C., Hill K.
<Astron. Astrophys. 635, A46 (2020)>
=2020A&A...635A..46P 2020A&A...635A..46P (SIMBAD/NED BibCode)
ADC_Keywords: Stars, nearby ; Polarization
Keywords: techniques: polarimetric - dust, extinction - ISM: magnetic fields -
ISM: structure - circumstellar matter - stars: activity
Abstract:
We investigate the linear polarization produced by interstellar dust
aligned by the magnetic field in the solar neighborhood (d<50pc). We
also look for intrinsic effects from circumstellar processes,
specifically in terms of polarization variability and wavelength
dependence. We aim to detect and map dust clouds which give rise to
statistically significant amounts of polarization of the starlight
passing through the cloud, and to determine the interstellar magnetic
field direction from the position angle of the observed polarization.
High-precision broad-band (BVR) polarization observations are made of
361 stars in spectral classes F to G, with detection sensitivity at
the level of or better than 10E-5 (0.001%). The sample consists of
125 stars in the magnitude range 6-9 observed at the 2.2m UH88
telescope on Mauna Kea, 205 stars in the magnitude range 3-6 observed
at the Japanese (Tohoku) T60 telescope on Haleakala, and 31 stars in
the magnitude range 4-7 observed at the 1.27m H127 telescope of the
Greenhill Observatory, Tasmania. Identical copies of the Dipol-2
polarimeter are used on these three sites. Statistically significant
(>3sigma) polarization is found in 115 stars, and >2sigma detection
in 178 stars, out of the total sample of 361 stars. Polarization maps
based on these data show filament-like patterns of polarization
position angles which are related to both the heliosphere geometry,
the kinematics of nearby clouds, and the Interstellar Boundary
EXplorer (IBEX) ribbon magnetic field. From long-term multiple
observations, a number (18) of stars show evidence of intrinsic
variability at the 10E-5 level. This can be attributed to
circumstellar effects (e.g., debris disks and chromospheric activity).
The star HD 101805 shows a peculiar wavelength dependence, indicating
size distribution of scattering particles different from that of a
typical interstellar medium. Our high-S/N measurements of nearby stars
with very low polarization also provide a useful dataset for
calibration purposes.
Description:
We carried out observations in 2014-2019 at three telescopes, the
2.2 m UH88 telescope on Mauna Kea, the Tohoku60 cm telescope (T60) on
Haleakala, and the University of Tasmania (UTAS) 1.27m (H127)
telescope at Greenhill Observatory, Tasmania. Observations were made
with the simultaneous three-color (BV R) polarimeter Dipol-2.
Identical copies of the instrument are used at each of the three
sites. At UH88 and T60 the observations were carried out in remote
operation mode. Some additional data on the stars in our sample were
obtained at the Nordic Optical Telescope (NOT) and William Herschel
Telescope (WHT) at ORM, La Palma.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table6.dat 88 125 Polarization data from the UH88 telescope
table7.dat 88 205 Polarization data from the T60 telescope
table8.dat 88 31 Broad-band (400-800nm) polarimetric data of
nearby stars observed at the H127 telescope
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Byte-by-byte Description of file: table6.dat table7.dat table8.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- HD HD number
8- 9 I2 h RAh Right ascension (J2000.0)
11- 12 I2 min RAm Right ascension (J2000.0)
14- 17 F4.1 s RAs Right ascension (J2000.0)
19 A1 --- DE- Declination sign (J2000.0)
20- 21 I2 deg DEd Declination (J2000.0)
23- 24 I2 arcmin DEm Declination (J2000.0)
26- 27 I2 arcsec DEs Declination (J2000.0)
29- 34 F6.2 deg GLON Galactic longitude
36- 41 F6.2 deg GLAT Galactic latitude
43- 46 F4.2 mag Vmag V magnitude
47 A1 --- l_plx [~] limit flag on plx
48- 53 F6.2 mas plx Parallax
55- 60 A6 --- SpType Spectral type
62- 65 I4 ppm q Normalized Stokes parameter q
67- 70 I4 ppm u Normalized Stokes parameter u
72- 74 I3 ppm p Normalized Polarization degree p
76- 77 I2 ppm e_p Standard error of p
79- 83 F5.1 deg theta Position angle (equatorial frame of reference)
85- 88 F4.1 deg e_theta Error of theta
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Acknowledgements:
Vilppu Piirola, piirola(at)utu.fi
(End) Patricia Vannier [CDS] 07-Feb-2020