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J/A+A/615/A42 Anomalous extinction sightlines stars polarisation (Cikota+, 2018)

Spectropolarimetry of Galactic stars with anomalous extinction sightlines. Cikota A., Hoang T., Taubenberger S., Patat F., Mazzei P., Cox N.L.J., Zelaya P., Cikota S., Tomasella L., Benetti S., Rodeghiero G. <Astron. Astrophys. 615, A42 (2018)> =2018A&A...615A..42C (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, nearby ; Polarization ; Extinction Keywords: polarization - ISM: general - dust, extinction - supernovae: general - galaxies: ISM Abstract: 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≲0.4um). 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∼0.53um, 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 ≥0.1um) interstellar silicate grains must be contained in the dust composition. Description: Given are final polarization curves of stars with anomalous extinction sightlines, observed with FORS2, AFOSC, and CAFOS, and shown in Fig. 1. The filename consists of the instrument name with which the star was observed (FORS2, AFOSC, or CAFOS), and the star name, in the following form: instrument_star.dat File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file sources.dat 92 14 List of studied stars files/* 126 20 Individual files with final polarization curves
Byte-by-byte Description of file: sources.dat
Bytes Format Units Label Explanations
1- 10 A10 --- Name Star name 12- 13 I2 h RAh Right ascension (J2000) 15- 16 I2 min RAm Right ascension (J2000) 18- 22 F5.2 s RAs Right ascension (J2000) 24 A1 --- DE- Declination sign (J2000) 25- 26 I2 deg DEd Declination (J2000) 28- 29 I2 arcmin DEm Declination (J2000) 31- 34 F4.1 arcsec DEs Declination (J2000) 36- 53 A18 --- AFOSC Name of the file with AFOSC data in subdirectory files 55- 73 A19 --- CAFOS Name of the file with CAFOS data in subdirectory files 75- 92 A18 --- FORS2 Name of the file with FORS2 data in subdirectory files
Byte-by-byte Description of file: files/*
Bytes Format Units Label Explanations
1- 4 I4 0.1nm lambda Wavelength in Angstroem 6- 20 E15.9 % Q Stokes Q in percent 22- 35 E14.9 % e_Q Error of Stokes Q in percent 37- 51 E15.9 % U Stokes U in percent 53- 66 E14.9 % e_U Error of Stokes U in percent 68- 81 E14.9 % Pol Degree of polarization in percent 83- 96 E14.9 % e_Pol Error of degree of polarization in percent 98-111 E14.9 deg PolPA Polarization angle in degree 113-126 E14.9 deg e_PolPA Error of polarization angle in degree
Acknowledgements: Aleksandar Cikota, acikota(at)
(End) Patricia Vannier [CDS] 21-Mar-2018
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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