J/A+A/671/A96 ATOMIUM - VLT/SPHERE overview (Montarges+, 2023)
The VLT/SPHERE view of the ATOMIUM cool evolved star sample.
I. Overview: Sample characterization through polarization analysis.
Montarges M., Cannon E., de Koter A., Khouri T., Lagadec E., Kervella P.,
Decin L., McDonald I., Homan W., Waters L.B.F.M., Sahai R., Gottlieb C.A.,
Malfait J., Maes S., Pimpanuwat B., Jeste M., Danilovich T., De Ceuster F.,
Van de Sande M., Gobrecht D., Wallstroem S.H.J., Wong K.T., El Mellah I.,
Bolte J., Herpin F., Richards A.M.S., Baudry A., Etoka S., Gray M.D.,
Millar T.J., Menten K.M., Mueller H.S.P., Plane J.M.C., Yates J.,
Zijlstra A.
<Astron. Astrophys. 671, A96 (2023)>
=2023A&A...671A..96M 2023A&A...671A..96M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Stars, M-type ; Stars, late-type ;
Stars, supergiant ; Morphology ; Optical ; Polarization
Keywords: stars: AGB and post-AGB - supergiants - stars: mass-loss -
stars: imaging - circumstellar matter - stars: evolution
Abstract:
Low- and intermediate-mass asymptotic giant stars and massive red
supergiant stars are important contributors to the chemical enrichment
of the Universe. They are among the most efficient dust factories of
the Galaxy, harboring chemically rich circumstellar environments. Yet,
the processes that lead to dust formation or the large-scale shaping
of the mass loss still escape attempts at modeling.
Through the ATOMIUM project, we aim to present a consistent view of a
sample of 17 nearby cool evolved stars. Our goals are to unveil the
dust-nucleation sites and morphologies of the circumstellar envelope
of such stars and to probe ambient environments with various
conditions. This will further enhance our understanding of the roles
of stellar convection and pulsations, and that of companions in
shaping the dusty circumstellar medium. Methods. Here we present and
analyze VLT/SPHERE-ZIMPOL polarimetric maps obtained in the visible
(645-820nm) of 14 out of the 17 ATOMIUM sources. They were obtained
contemporaneously with the ALMA high spatial resolution data. To help
interpret the polarized signal, we produced synthetic maps of light
scattering by dust, through 3D radiative transfer simulations with the
RADMC3D code.
The degree of linear polarization (DoLP) observed by ZIMPOL spreads
across several optical filters. We infer that it primarily probes dust
located just outside of the point spread function of the central
source, and in or near the plane of the sky. The polarized signal is
mainly produced by structures with a total optical depth close to
unity in the line of sight, and it represents only a fraction of the
total circumstellar dust. The maximum DoLP ranges from 0.03-0.38
microns depending on the source, fractions that can be reproduced by
our 3D pilot models for grains composed of olivine, melilite,
corundum, enstatite, or forsterite. The spatial structure of the DoLP
shows a diverse set of shapes, including clumps, arcs, and full
envelopes. Only for three sources do we note a correlation between the
ALMA CO v=0, J=2-1 and SiO v=0, J=5-4 lines, which trace the gas
density, and the DoLP, which traces the dust.
The clumpiness of the DoLP and the lack of a consistent correlation
between the gas and the dust location show that, in the inner
environment, dust formation occurs at very specific sites. This has
potential consequences for the derived mass-loss rates and dust-to-gas
ratio in the inner region of the circumstellar environment. Except for
pi.01 Gru and perhaps GY Aql, we do not detect interactions between
the circumstellar wind and the hypothesized companions that shape the
wind at larger scales. This suggests that the orbits of any other
companions are tilted out of the plane of the sky.
Description:
Reduced VLT/SPHERE images (intensity/polarimetry/degree of linear
polarization/polarization angle) for the main sources and their
associated PSF
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 52 14 List of studied stars
list.dat 214 58 List of fits images
fits/* . 58 Individual fits images
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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- 7 A7 --- Name Star name
10- 11 I2 h RAh Right ascension (J2000)
13- 14 I2 min RAm Right ascension (J2000)
16- 20 F5.2 s RAs Right ascension (J2000)
22 A1 --- DE- Declination sign (J2000)
23- 24 I2 deg DEd Declination (J2000)
26- 27 I2 arcmin DEm Declination (J2000)
29- 32 F4.1 arcsec DEs Declination (J2000)
34- 42 A9 --- PSF1 Name of star for associated PSF
44- 52 A9 --- PSF2 Name of star for associated PSF
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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- 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
63-136 A74 --- FileName Name of FITS file, in subdirectory fits
138-214 A77 --- Title Title of the FITS file
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Acknowledgements:
Miguel Montarges, miguel.montarges(at)observatoiredeparis.psl.eu
(End) Patricia Vannier [CDS] 13-Feb-2023