J/A+A/699/A22 pi1 Gru SPHERE images (Montarges+, 2025)
An accreting dwarf star orbiting the S-type giant star pi1 Gru.
Montarges M., Malfait J., Esseldeurs M., de Koter A., Baron F., Kervella P.,
Danilovich T., Richards A.M.S., Sahai R., McDonald I., Khouri T., Shetye S.,
Zijlstra A., Van de Sande M., El Mellah I., Herpin F., Siess L., Etoka S.,
Gobrecht D., Marinho L., Wallstroem S.H.J., Wong K.T., Yates J.
<Astron. Astrophys. 699, A22 (2025)>
=2025A&A...699A..22M 2025A&A...699A..22M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Stars, M-type ; Stars, late-type ; Morphology ;
Optical ; Polarization
Keywords: stars: AGB and post-AGB - binaries: close - circumstellar matter -
stars: imaging - stars: mass-loss - stars: individual: pi1 Gru
Abstract:
At the end of their lives, when low- to intermediate-mass stars reach
the asymptotic giant branch (AGB), their photosphere expands up to a
few hundred times and a strong stellar wind develops. This allows for
various types of interactions with celestial bodies in their close
circumstellar environment, including mass- and angular-momentum
transfer.
We aim to characterize the properties of the inner companion of the
S-type AGB star pi1 Gru, and to identify plausible future evolution
scenarios for this triple system.
We observed pi1 Gru with ALMA and VLT/SPHERE. In addition, we
collected archival photometry data and used the Hipparcos-Gaia proper
motion anomaly. We derive the best orbital parameters from Bayesian
inference.
The inner companion, pi1 Gru C was located at 37.4±2.0mas from the
primary in June-July 2019 (projected separation of 6.05±0.55au at
161.7±11.7pc). The best orbital solution gives a companion mass of
0.86+0.22-0.20M☉ (using the derived mass of the primary),
and a semi-major axis of 7.05+0.54-0.57au. This leads to an
orbital period of 11.0+1.7-1.5yr. The best solution is an
elliptical orbit with eccentricity e=0.35+0.18-0.17, but a
circular orbit cannot be totally excluded. The close companion can
either be a K1V(F9.5V/K7V) star or a white dwarf. The ultraviolet and
millimeter continuum photometry are consistent with the presence of an
accretion disk around the close companion. The ultraviolet emission
could then either originate in hot spots in an overall cooler disk, or
also from a hot disk in case the companion is a white dwarf.
Though the close companion and the AGB star are interacting, and an
accretion disk is observed around the companion, the mass-accretion
rate is too low to cause a Ia supernova but could produce nove every
∼900yr. Short wavelength spatially resolved observations are needed to
further constrain the nature of the C companion. Searches for close-in
companions similar to this system will help to better understand the
physics of mass- and angular-momentum transfer, and orbital evolution
in the late evolutionary stages.
Description:
Reduced VLT/SPHERE images (intensity/polarimetry/degree of linear
polarization/polarization angle) for pi1 Gru in July 2015, September
2015, July 2021
Objects:
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RA (2000) DE Designation(s)
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22 22 44.20 -45 56 52.7 pi1 Gru = HR 8521
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 201 10 List of fits images
fits/* . 10 Individual fits images
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See also:
J/A+A/671/A96 : ATOMIUM - VLT/SPHERE overview (Montarges+, 2023)
https://almascience.eso.org/alma-data/lp/atomium : ATOMIUM Home Page
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- 25 F6.4 arcsec/pix scale Scale of the image
27- 29 I3 --- Nx Number of pixels along X-axis
31- 33 I3 --- Ny Number of pixels along Y-axis
35- 57 A23 "datime" Obs.date Observation date
59- 61 I3 Kibyte size Size of FITS file
63-144 A82 --- FileName Name of FITS file, in subdirectory fits
146-201 A56 --- Title Title of the file
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Acknowledgements:
Miguel Montarges, miguel.montarges(at)obspm.fr
(End) Patricia Vannier [CDS] 29-Apr-2025