Volume 635, March 2020
|Number of page(s)||10|
|Section||Interstellar and circumstellar matter|
|Published online||06 March 2020|
High-precision polarimetry of nearby stars (d < 50 pc)
Mapping the interstellar dust and magnetic field inside the Local Bubble★
Department of Physics and Astronomy, University of Turku,
2 FINCA, University of Turku, 20014 Turku, Finland
3 Department of Astronomy and Astrophysics, University of Chicago, Chicago IL 60637, USA
4 Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
5 Leibniz-Institut für Sonnenphysik, 79104 Freiburg, Germany
6 Greenhill observatory, School of Natural Sciences, University of Tasmania, Private Bag 37, Hobart, TAS 7001, Australia
Accepted: 27 January 2020
Context. We investigate the linear polarization produced by interstellar dust aligned by the magnetic field in the solar neighborhood (d < 50 pc). We also look for intrinsic effects from circumstellar processes, specifically in terms of polarization variability and wavelength dependence.
Aims. 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.
Methods. High-precision broad-band (BV R) polarization observations are made of 361 stars in spectral classes F to G, with detection sensitivity at the level of or better than 10−5 (0.001%). The sample consists of 125 stars in the magnitude range 6–9 observed at the 2.2 m 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 1.27 m H127 telescope of the Greenhill Observatory, Tasmania. Identical copies of the Dipol-2 polarimeter are used on these three sites.
Results. Statistically significant (>3σ) polarization is found in 115 stars, and >2σ 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 ribbon magnetic field. From long-term multiple observations, a number (~20) of stars show evidence of intrinsic variability at the 10−5 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 signal-to-noise measurements of nearby stars with very low polarization also provide a useful dataset for calibration purposes.
Key words: techniques: polarimetric / dust, extinction / ISM: magnetic fields / ISM: structure / circumstellar matter / stars: activity
Tables 6 and 7 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/635/A46.
© ESO 2020
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