J/A+A/677/A96 Photopolarimetry of semi-regular variable V CVn (Neilson, 2023)
A multiyear photopolarimetric study of the semi-regular variable V CVn and
identification of analogue sources.
Neilson H., Steenken N., Simpson J., Ignace R., Shrestha M., Erba C.,
Henson G.
<Astron. Astrophys. 677, A96 (2023)>
=2023A&A...677A..96N 2023A&A...677A..96N (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Polarization ; Optical
Keywords: polarization - stars: winds, outflows - circumstellar matter -
stars: AGB and post-AGB
Abstract:
The semi-regular variable star V Canum Venaticorum (V CVn) is well
known for its unusual linear polarization position angle (PA).
Decades of observing V CVn reveal a nearly constant PA spanning
hundreds of pulsation cycles. This phenomenon has persisted through
variability that has varied by two magnitudes in optical brightness
and through variability in the polarization amplitude over 0.3% and
6.9%. Additionally, the polarization fraction of V CVn varies
inversely with brightness.
This paper presents polarization measurements obtained over three
pulsation cycles. We find that the polarization maximum does not
always occur precisely at the same time as the brightness minimum.
Instead, we observe a small lead or lag in relation to the brightness
minimum, spanning a period of a few days up to three weeks.
Furthermore, the PA sometimes exhibits a non-negligible rotation,
especially at lower polarization levels.
To elucidate the unusual optical behavior of V CVn, we present a list
of literature sources that also exhibit polarization variability with
a roughly fixed PA. We find this correlation occurs in stars with high
tangential space velocities, for instance, 'runaway' stars,
suggesting that the long-term constant PA is related to how the
circumstellar gas is shaped by the star's high-speed motion through
the interstellar medium.
Description:
Optical polarization observations and photometry of V CVn
were carried out independently by two of the co-authors (Steenken and
Simpson; hereafter 'observers') operating
Schmidt-Cassegrain-Telescopes (SCT). The observers were located in
Munich, Germany (Steenken, Ob1) and in Parton, Scotland (Simpson,
Ob2). Both telescopes have dual-beam polarimeters with V-band filters
and cooled CCD cameras mounted at the Cassegrain focus. Customary SCTs
were used, with OB1 having a focal length of 2800mm and aperture of
280mm, and OB2 using a two different SCTs with focal lengths of 1500
and 2000mm and apertures of 150 and 200mm (Ob2) on a German
equatorial mount. Object centering and autoguiding was achieved with
separate guide scopes and guiding cameras.
All raw FITS files are available on https://zenodo.org/record/7997101 .
Objects:
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RA (2000) DE Designation(s)
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13 19 27.76 +45 31 37.6 V CVn = HD 11589
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea.dat 67 227 Photopolarimetry journal of pulsation cycle
2020-2022 (tables A2-A6)
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Byte-by-byte Description of file: tablea.dat
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Bytes Format Units Label Explanations
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1- 9 F9.1 d JD Julian date
11- 16 F6.4 --- P Polarization (intrinsic, V-Band)
18- 22 F5.1 deg PA Polarization Angle
24- 30 F7.4 --- Q Stokes Q (intrinsic, V-Band)
32- 37 F6.4 --- e_Q Error on Q
39- 45 F7.4 --- U Stokes U (intrinsic, V-Band)
47- 52 F6.4 --- e_U Error on U
54- 57 F4.2 mag Vmag V magnitude
59- 62 F4.2 mag e_Vmag Error on Vmag
64- 65 I2 s ExpTime Exposure Time
67 I1 --- ObsCode [1/2] 1 = Steenken, 2 = Simpson
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Acknowledgements:
Nicolaus Steenken, nicolaus(at)steenken.info
John Simpson, john.jean.simpson(at)gmail.com
(End) Patricia Vannier [CDS] 22-May-2023