J/A+A/642/A93 EP Aqr ALMA and SPHERE observations (Homan+, 2020)
A detailed view on the circumstellar environment of the M-type AGB star
EP Aquarii. I. High-resolution ALMA and SPHERE observations.
Homan W., Cannon E., Montarges M., Richards A.M.S., Millar T.J., Decin L.
<Astron. Astrophys. 642, A93 (2020)>
=2020A&A...642A..93H 2020A&A...642A..93H (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Millimetric/submm sources ; Radio sources
Keywords: stars: AGB and post-AGB - circumstellar matter - stars: mass-loss -
submillimeter: stars
Abstract:
Cool evolved stars are known to be significant contributors to the
enrichment of the interstellar medium through their dense and dusty
stellar winds. High resolution observations of these outflows have
shown them to possess high degrees of morphological complexity. We
observed the asymptotic giant branch (AGB) star EP Aquarii with ALMA
in band 6 and VLT/SPHERE/ZIMPOL in four filters the visible. Both
instruments had an angular resolution of 0.025". These are follow-up
observations to the lower-resolution 2016 ALMA analysis of EP Aquarii,
which revealed that its wind possesses a nearly face-on,
spiral-harbouring equatorial density enhancement, with a nearly
pole-on bi-conical outflow. At the base of the spiral, the SiO
emission revealed a distinct emission void approximately 0.4" to the
west of the continuum brightness peak, which was proposed to be linked
to the presence of a companion. The new ALMA data better resolve the
inner wind and reveal that its morphology as observed in CO is
consistent with hydrodynamical companion-induced perturbations.
Assuming that photodissociation by the UV-field of the companion is
responsible for the emission void in SiO, we deduced the spectral
properties of the tentative companion from the size of the hole. We
conclude that the most probable companion candidate is a white dwarf
with a mass between 0.65 and 0.8M☉, though a solar-like
companion could not be definitively excluded. The radial SiO emission
shows periodic, low-amplitude perturbations. We tentatively propose
that they could be the consequence of the interaction of the AGB wind
with another much closer low-mass companion. The polarised
SPHERE/ZIMPOL data show a circular signal surrounding the AGB star
with a radius of ∼0.1". Decreased signal along a PA of 138°
suggests that the dust is confined to an inclined ring-like structure,
consistent with the previously determined wind morphology.
Description:
ALMA band 6 CO and SiO and continuum, combined dataset between ∼160
and ∼22 milliarcsecnds observations.
EP Aquarii was observed by ALMA in Band 6 for project code
2018.1.00750.S (PI W. Homan) using the extended configuration C43-10,
hereafter referred to as TM0. These observations complement data taken
in three configurations at lower resolutions, described by Homan et
al. (2018b), and aspects of data reduction common to all observations
are described there. EP Aqr was observed at R.A. 21:46:31.88046,
Dec. -02:12:45.5471. The antenna configuration consisted of 46
antennae, and covered baseline lengths between 83 and 16196m, which
are sensitive to angular scales up to 0.48". As the phase reference
source we used J2156-0037 (position R.A. 21:56:14.758,
Dec. 00:37:04.594), and the QSO targets J2232+1143 and J2253+1608 were
used as bandpass calibrators. The target: phase reference switching
cycle was about 80 sec, with about 50 sec on target, for a total of 99
minutes on target, and the angular separation was 3. J2206-0031 was
observed as a check source at 22:06:43.282598 -00.31.02.49604, 246.5
from the reference source. During observations, the precipitable water
vapour (PWV) was between 1 and 2.6 mm.
All details can be found in the paper.
Objects:
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RA (2000) DE Designation(s)
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21 46 31.85 -02 12 45.9 EP Aqr = HD 207076
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 171 3 List of fits image and datacubes
fits/* . 3 Individual fits image and datacubes
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 32 I3 --- Nz ? Number of slices, for the datacubes
34- 56 A23 "datime" Obs.date Observation date
58- 64 F7.3 GHz Freq Observed frequency of lower value of frequency
interval for the datacubes
66- 72 F7.3 GHz BFreq ? Upper value of frequency interval
for the datacubes
74- 79 I6 Hz dFreq ? Frequency resolution for the datacubes
81- 88 I8 Kibyte size Size of FITS file
90-134 A45 --- FileName Name of FITS file, in subdirectory fits
136-171 A36 --- Title Title of the FITS file
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Acknowledgements:
Ward Homan, ward.homan(at)kuleuven.be
(End) Patricia Vannier [CDS] 20-Aug-2020