Volume 615, July 2018
|Number of page(s)||21|
|Section||Interstellar and circumstellar matter|
|Published online||10 July 2018|
Spectropolarimetry of Galactic stars with anomalous extinction sightlines★
European Southern Observatory,
Garching b. München,
2 Korea Astronomy and Space Science Institute, Daejeon 34055, Korea
3 Korea University of Science and Technology, 217 Gajungro, Yuseong-gu, Daejeon 34113, Korea
4 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching b. München, Germany
5 INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
6 Anton Pannekoek Institute for Astronomy, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
7 MAS—Millennium Institute of Astrophysics, Casilla 36-D, 7591245 Santiago, Chile
8 Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
9 University of Zagreb, Faculty of Electrical Engineering and Computing, Department of Applied Physics, Unska 3, 10000 Zagreb, Croatia
10 Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
11 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
Accepted: 20 March 2018
Highly reddened type Ia supernovae (SNe Ia) with low total-to-selective visual extinction ratio values, RV, also show peculiar linear polarization wavelength dependencies with peak polarizations at short wavelengths (λmax ≲ 0.4 μm). It is not clear why sightlines to SNe Ia display such different continuum polarization profiles from interstellar sightlines in the Milky Way with similar RV values. We investigate polarization profiles of a sample of Galactic stars with low RV values, along anomalous extinction sightlines, with the aim to find similarities to the polarization profiles that we observe in SN Ia sightlines. We undertook spectropolarimetry of 14 stars, used archival data for 3 additional stars, and ran dust extinction and polarization simulations (by adopting the picket-fence alignment model) to infer a simple dust model (size distribution, alignment) that can reproduce the observed extinction and polarization curves. Our sample of Galactic stars with low RV values and anomalous extinction sightlines displays normal polarization profiles with an average λmax ~ 0.53 μm, and is consistent within 3σ to a larger coherent sample of Galactic stars from the literature. Despite the low RV values of dust toward the stars in our sample, the polarization curves do not show any similarity to the continuum polarization curves observed toward SNe Ia with low RV values. There is a correlation between the best-fit Serkowski parameters K and λmax, but we did not find any significant correlation between RV and λmax. Our simulations show that the K–λmax relationship is an intrinsic property of polarization. Furthermore, we have shown that in order to reproduce polarization curves with normal λmax and low RV values, a population of large (a ≥ 0.1μm) interstellar silicate grains must be contained in the dust composition.
Key words: polarization / ISM: general / dust, extinction / supernovae: general / galaxies: ISM
The reduced spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/615/A42
© ESO 2018
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.