J/MNRAS/466/2948 Polarimetry of 53 post-AGB stars (Akras+, 2017)
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., Panoglou D.
<Mon. Not. R. Astron. Soc., 466, 2948-2982 (2017)>
=2017MNRAS.466.2948A 2017MNRAS.466.2948A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Polarization
Keywords: polarization - circumstellar matter - binaries: general -
stars: AGB and post-AGB
Abstract:
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%
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%), lowly polarized (1%<DoP<4%), moderately polarized (4%<DoP<8%)
and highly polarized (DoP>8%). 23 out of the 53 (66%) belong to the
first group, 10 (19%) to the second, five ( %) to the third and only
three (6%) to the last group. Approximately 34%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.
Description:
A sample of 53 post-AGB stars was selected from De Ruyter et al.
(2006A&A...448..641D 2006A&A...448..641D) and the Torun catalogue of Galactic post-AGB
and relative objects (Szczerba et al. 2007, Cat. J/A+A/469/799, 2012,
Proc, IAU Symp. 283, 506) by applying the following criteria to all
the programme stars: (i) they exhibit a near-IR excess in their SED
profiles, which may be associated with the thermal emission of hot
dust grains (Evans, 1985MNRAS.217..493L 1985MNRAS.217..493L) and provides a signature of a
dusty circumstellar disc/torus (De Ruyter et al., 2006A&A...448..641D 2006A&A...448..641D)
and (ii) they are bright enough at optical wavelengths to perform
accurate linear polarimetry from the 0.84-m telescope at the
Observatorio Astronomico Nacional in Sierra de San Pedro Martir,
Mexico. In Table 1, we list for the stars of our sample their
coordinates, their classification type and information about their
binarity.
Linear polarization measurements were performed with the 0.84-m f/15
telescope of the Observatorio Astronomico Nacional in the Sierra de
San Pedro Martir, Mexico, using the POLIMA polarimeter in conjunction
with a 2048x2048 CCD camera (13x13um pixels), which results in a scale
of 0.44-arcsec/pix The polarimeter consists of a rotating
Glan-Taylor prism driven by a stepper motor. As the polarimeter is a
single-beam device with a very slow modulation, good photometric
conditions are required for accurate polarimetry. The observations
were performed between 2012 January and December at/or near the new
Moon phase. The broad-band filters U, B, V, R and I were used with
exposure times from 5 to 180s.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 93 53 Log file of the observations
tableb1.dat 107 421 Intrinsic degree of polarization, PA of the
polarization vectors, total degree of polarization
and ISP of all the stars in our sample
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See also:
J/A+A/469/799 : Torun catalog of post-AGB and related objects (Szczerba+, 2007)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 A16 --- Name Name (mainly IRAS name)
19- 32 A14 --- OName Other name
35- 39 F5.1 deg GLON Galactic longitude
41- 45 F5.1 deg GLAT Galactic latitude
47- 48 I2 h RAh Right ascension (J2000)
50- 51 I2 min RAm Right ascension (J2000)
53- 56 F4.1 s RAs Right ascension (J2000)
58 A1 --- DE- Declination sign (J2000)
59- 60 I2 deg DEd Declination (J2000)
62- 63 I2 arcmin DEm Declination (J2000)
65- 68 F4.1 arcsec DEs Declination (J2000)
70- 77 A8 --- Type Type
79- 89 A11 --- Bin Note on binarity
90- 93 A4 --- Ref Reference (1)
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Note (1): References as follows:
1 = De Ruyter et al. (2006A&A...448..641D 2006A&A...448..641D)
2 = Van Winckel, Waelkens & Waters (1995)
3 = Hrivnak et al. (2008, Cat. J/AJ/136/1557)
4 = Hrivnak et al. (2011ApJ...734...25H 2011ApJ...734...25H)
5 = Van Winckel et al. (2012, Cat. J/A+A/542/A53)
6 = Gielen et al. (2008A&A...490..725G 2008A&A...490..725G)
7 = Waters et al. (1993A&A...269..242W 1993A&A...269..242W)
8 = Kreiner (2004, Cat. J/AcA/54/207)
9 = Castro-Carrizo et al. (2012A&A...545A...1C 2012A&A...545A...1C)
10 = Van Winckel et al. (1998A&A...336L..17V 1998A&A...336L..17V)
11 = Kodaira, Greenstein & Oke (1970ApJ...159..485K 1970ApJ...159..485K)
12 = Reyniers (2002, PhD thesis, Katholieke University, Leuven)
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Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 A16 --- Name Name
18- 22 F5.1 deg PAISP Intrinsic degree of polarization
24- 27 F4.1 deg e_PAISP rms uncertainty on PAISP
30- 38 F9.4 d JD Julian date (JD-2450000)
40 A1 --- Filt Filter
42- 46 F5.2 % DoP ?=- Polarization degree corrected for the ISM
and bias noise
48- 51 F4.2 % e_DoP ? rms uncertainty on DoP
53- 57 F5.1 deg PA ?=- Position angle corrected for the ISM and
bias noise
59- 62 F4.1 deg e_PA ? rms uncertainty on PA
64- 68 F5.2 % PMAS Observed polarization degree measurements
after correction for the bias noise
70- 73 F4.2 % e_PMAS rms uncertainty on PMAS
75- 79 F5.2 % Pobs Observed polarization degree measurements
before correction for the bias noise
81- 84 F4.2 % e_Pobs rms uncertainty on Pobs
86- 91 F6.2 deg PAobs Observed position angle
93- 97 F5.2 deg e_PAobs rms uncertainty on PAobs
99-102 F4.2 % ISP Interstellar degree of polarization
104-107 F4.2 % e_ISP rms uncertainty on ISP
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 17-Oct-2019