J/A+A/692/A86 Millimetre observations of chi Cygni (Hoai+, 2024)
Millimetre observations of the S-type AGB star chi Cygni.
Variability of the emission of the inner envelope.
Hoai D.T., Winters J.M., Nhung P.T., Darriulat P., Le Bertre T.
<Astron. Astrophys. 692, A86 (2024)>
=2024A&A...692A..86H 2024A&A...692A..86H (SIMBAD/NED BibCode)
ADC_Keywords: Stars, S ; Stars, late-type ; Interferometry ; Radio lines
Keywords: stars: AGB and post-AGB - circumstellar matter -
stars: late-type - stars: individual: chi Cygni
Abstract:
New observations are presented of millimetre line emissions of the
circumstellar envelope (CSE) of the asymptotic giant branch (AGB)
star chi Cygni, using the recently upgraded NOEMA array. chi Cygni
is an S-type Mira variable, at the border between oxygen-rich and
carbon-rich stars. It has been observed for over 40 years to display
features that suggest evidence for the strong role played by
pulsation associated shock waves in the generation of its wind.
These new observations provide evidence of a bright H12CN(3-2)
line emission confined to the very close neighbourhood of the star;
however, this emission appears significantly more extended in 2024
than in 2023. The interpretation of such variability in terms of
maser emission has been considered and found to raise significant
unanswered questions. Moreover, other unexpected features are
observed in the very close neighbourhood of the star, including low
Si16O(6-5)/Si17O(6-5), 28SiO(5-4)/29SiO(5-4), and
12CO(2-1)/13CO(2-1) line emission ratios. We discuss several
features, which possibly confirm the important role played by shocks:
a measurement of the SiO(5-4)/SiO(6-5) emission ratio; the observation
of a recent mass ejection, particularly enhanced in the north-western
red-shifted octant, which has left a depression in its wake; patterns
of enhanced CO(2-1) line emission, which suggest an interpretation in
terms of episodic outflows, on a time scale of a few decades, enhanced
over solid angles associated with the surface of convective cells.
Unravelling the mechanisms underlying such newly observed features
is very challenging. Thus, a confirmation of the reported observations
with improved sensitivity and angular resolution would be highly
welcome. The observation of SiO maser emission in the (nu=1,J=6-5)
transition is reported for the first time.
Description:
Spectral maps of different molecules in chi Cygni was observed with
NOEMA using 12 antennas in the extended A- and B-configurations in
February and March 2023, and in February 2024. The spectral resolution
is 0.5km/s and the pixel size is 0.03x0.03arcsec2. The beam sizes
are ∼0.2x0.1arcsec2 in A-configuration and ∼ 0.4x0.2 in
B-configuration observations. The maps are centred on the continuum
emission position which has RA=19:50:33.87986 and Dec=32:54:49.6350.
Objects:
----------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------
19 50 33.92 +32 54 50.5 chi Cyg = HR 7564
----------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 133 10 List of fits datacubes
fits/* . 10 Individual fits datacubes
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 29 I2 --- Nz Number of slices
31- 35 I5 m/s bVRAD Lower value of VRAD interval
37- 41 I5 m/s BVRAD Upper value of VRAD interval
43- 45 I3 m/s dVRAD VRAD resolution
47- 52 I6 Kibyte size Size of FITS file
54- 71 A18 --- FileName Name of FITS file, in subdirectory fits
73-133 A61 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Do Thi Hoai, dthoai(at)vnsc.org.vn
(End) Patricia Vannier [CDS] 22-Oct-2024