Mon. Not. R. Astron. Soc., 466, 2948-2982 (2017/April-2)
Multi-band polarimetry of post-asymptotic giant branch stars - I. Optical measurements.
AKRAS S., RAMIREZ VELEZ J.C., NANOURIS N., RAMOS-LARIOS G., LOPEZ J.M., HIRIART D. and PANOGLOU D.
Abstract (from CDS):
We present new optical broad-band (UBVRI) aperture polarimetric observations of 53 post-asymptotic giant branch (AGB) stars selected to exhibit a large near-infrared excess. 24 out of the 53 stars (45 per cent of our sample) are presented for the first time. A statistical analysis shows four distinctive groups of polarized post-AGB stars: unpolarized or very lowly polarized (degree of polarization or DoP < 1 per cent), lowly polarized (1 per cent < DoP < 4 per cent), moderately polarized (4 per cent < DoP < 8 per cent) and highly polarized (DoP > 8 per cent). 23 out of the 53 (66 per cent) belong to the first group, 10 (19 per cent) to the second, five (9 per cent) to the third and only three (6 per cent) to the last group. Approximately 34 per cent of our sample was found to be unpolarized objects, which is close to the percentage of round planetary nebulae. On average, the low and moderate groups show a wavelength-dependent polarization that increases towards shorter wavelengths, implying an intrinsic origin of the polarization, which signifies a Rayleigh-like scattering spectrum typical for non-symmetrical envelopes composed principally of small dust grains. The moderately polarized stars exhibit higher K - W3 and W1 - W3 colour indices compared with the group of lowly polarized stars, suggesting a possible relation between DoP and mass-loss rate. Moreover, they are found to be systematically colder (redder in B - V), which may be associated with the condensation process close to these stars that results in a higher degree of polarization. We also provide evidence that multiple scattering in optically thin polar outflows is the mechanism that gives high DoP in post-AGB stars with bipolar or multi-polar envelopes.
© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Polarization - circumstellar matter - binaries: general - stars: AGB and post-AGB - stars: AGB and post-AGB
VizieR on-line data:
<Available at CDS (J/MNRAS/466/2948): table1.dat tableb1.dat>
Misprints: GLMP 177 = GLMP 117, IRAS 06167-1036 = IRAS 06176-1036, IRAS 06338+5338 = IRAS 06338+5333, IRAS 11427+0800 = IRAS 11472-0800, IRAS 18181+2149 = IRAS 18281+2149, IRAS 22327+1731 = IRAS 22327-1731, LS V +1015 = LS VI +1015, QY Sqe = QY Sge, Rec Rectangle = Red Rectangle, V5112 Sqr = V5112 Sgr.
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