J/MNRAS/535/1586 High polarization standard observations (Cotton+, 2024)
Polarization position angle standard stars: a reassessment of θ and its
variability for seventeen stars based on a decade of observations.
Cotton D.V., Bailey J., Kedziora-Chudczer L., Bott K., De Horta A.,
Filcek N., Marshall J.P., Melville G., Buzasi D.L., Boiko I., Borsato N.W.,
Perkins J., Opitz D., Melrose S., Gruening G., Evensberget D., Zhao J.
<Mon. Not. R. Astron. Soc. 535, 1586-1615 (2024)>
=2024MNRAS.535.1586C 2024MNRAS.535.1586C (SIMBAD/NED BibCode)
ADC_Keywords: Stars, standard ; Polarization
Keywords: instrumentation: polarimeters - techniques: polarimetric -
stars: supergiants
Abstract:
Observations of polarization position angle (θ) standards made
from 2014 to 2023 with the High Precision Polarimetric Instrument
(HIPPI) and other HIPPI-class polarimeters in both hemispheres are
used to investigate their variability. Multi-band data were first used
to thoroughly recalibrate the instrument performance by bench-marking
against carefully selected literature data. A novel Co-ordinate
Difference Matrix (CDM) approach - which combines pairs of points -
was then used to amalgamate monochromatic (g' band) observations from
many observing runs and re-determine θ for 17 standard stars.
The CDM algorithm was then integrated into a fitting routine and used
to establish the impact of stellar variability on the measured
position angle scatter. The approach yields variability detections for
stars on long time scales that appear stable over short runs. The best
position angle standards are l Car, o Sco, HD 154445, HD 161056 and
ι1 Sco which are stable to ≤0.123deg. Position angle
variability of 0.27-0.82 deg, significant at the 3-σ level, is
found for 5 standards, including the Luminous Blue Variable HD 160529
and all but one of the other B/A-type supergiants (HD 80558, HD
111613, HD 183143 and 55 Cyg), most of which also appear likely to be
variable in polarization magnitude (p) - there is no preferred
orientation for the polarization in these objects, which are all
classified as α Cygni variables. Despite this we make six key
recommendations for observers - relating to data acquisition,
processing and reporting - that will allow them to use these standards
to achieve <0.1deg precision in the telescope position angle with
similar instrumentation, and allow data sets to be combined more
accurately.
Description:
A catalogue of high polarization standard observations made with
HIPPI-class instruments between 2014 and 2023. The details of each
observation are given in obs.dat with details common to observations
within a sub-run, such as the Telescope and instrument set-up details,
given in the runs.dat file.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 37 17 List of studied stars
runs.dat 68 89 Summary of observing runs
obs.dat 129 583 High polarization standard observations
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Object HD catalogue number
11- 12 I2 h RAh Simbad right ascension (J2000)
14- 15 I2 min RAm Simbad right ascension (J2000)
17- 21 F5.2 s RAs Simbad right ascension (J2000)
23 A1 --- DE- Simbad Declination sign (J2000)
24- 25 I2 deg DEd Simbad Declination (J2000)
27- 28 I2 arcmin DEm Simbad Declination (J2000)
30- 33 F4.1 arcsec DEs Simbad Declination (J2000)
35- 37 I3 --- Nobs Number of observations on obs.dat table
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Byte-by-byte Description of file: runs.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Run Run designation: [X]YYYYMMM[S] (1)
11- 20 A10 "date" UTStart UT Start date of observation: YYYY-MM-DD
22- 31 A10 "date" UTEnd UT End date of observation: YYYY-MM-DD
33- 42 A10 --- Inst Instrment name: HIPPI, HIPPI-2 or Mini-HIPPI
44- 49 A6 --- Mod-Er Modulator and performance era: MMM-EN (2)
51- 54 A4 --- Tel Telescope: AAT, PIN, GN, OOS, UNSW or WSU
56- 59 F4.1 --- fTel Telescope f-number
61- 62 A2 --- BL Barlow lens used: x2 or NA (3)
64- 68 F5.3 deg TPAe Adopted error in telescope position angle
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Note (1): X may be m for Mini-HIPPI run or 'N' for the northern copy of HIPPI-2.
S indicates a sub-run (alpha) or a second run (numeric) begun that month.
Note (2): Run 2018AUG is given as BNS-EN, this refers to:
E5: 2018AUG 2018-08-16 - 2018-08-23
E6: 2018AUG 2018-08-24 - 2018-08-27
E7: 2018AUG 2018-08-29 - 2018-09-02
Note (3): For effective f-number multiply BL by ftel.
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Byte-by-byte Description of file: obs.dat
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Bytes Format Units Label Explanations
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1- 19 A19 "datime" Obs.date Observation mid-point: YYYY-MM-DDThh:mm:ss
21- 24 I4 s Dwell Observation dwell time
26- 34 A9 --- Run Run designation: [X]YYYYMMM[S] (1)
36- 44 A9 --- Object HD catalogue number
46- 50 F5.1 arcsec ApDiam Aperture diameter
52- 55 A4 --- Sky Sky timing at each PA (2)
57- 61 A5 --- Filter Filter (3)
63 A1 --- PMT [B/R] Blue (B) or Red (R) sensitive PMT
65- 69 F5.1 nm WLeff Effective wavelength
71- 78 F8.6 --- Eff 1/efficiency correction applied
80- 83 I4 s ExpTime Exposure time
85- 91 F7.1 ppm pobs Polarization magnitude of observation
93- 97 F5.1 ppm e_pobs Error in pobs from measurement statistics
99-105 F7.3 deg PAobs Position angle of observation, 2020 Equinox
107-111 F5.3 deg e_PAobs Position angle error from measurement
statistics
113-119 F7.1 ppm ppred Predicted polarization magnitude
121-127 F7.3 deg PApred Predicted position angle
129 A1 --- Notes [S/M] Notes (4)
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Note (1): X may be m for Mini-HIPPI run or 'N' for the northern copy of HIPPI-2.
S indicates a sub-run (alpha) or a second run (numeric) begun that month.
See runs.dat for information pertaining to each run.
Note (2): Listed in order: 0 45 90 135;
T = Trailing sky
L = Leading sky
B = Bracketing skies
D = Dark only, no sky
N = No sky or dark
Note (3): Filters code as follows:
U = Bessel U
425SP = 425 nm short-pass
500SP = 500 nm short-pass
g' = SDSS g'
V = Bessel V
Vp = Pixelteq 390 to 750nm
r' = SDSS r'
650LP = 650 nm long-pass
Clear = no filter
Note (4): Notes as follows:
S = single detector
M = marked filter
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Acknowledgements:
Daniel V. Cotton, dc(at)mira.org
(End) Patricia Vannier [CDS] 18-Oct-2024