932 research outputs found
First detection of methanol towards a post-AGB object, HD101584
The circumstellar environments of objects on the asymptotic giant branch and
beyond are rich in molecular species. Nevertheless, methanol has never been
detected in such an object, and is therefore often taken as a clear signpost
for a young stellar object. However, we report the first detection of CH3OH in
a post-AGB object, HD101584, using ALMA. Its emission, together with emissions
from CO, SiO, SO, CS, and H2CO, comes from two extreme velocity spots on either
side of the object where a high-velocity outflow appears to interact with the
surrounding medium. We have derived molecular abundances, and propose that the
detected molecular species are the effect of a post-shock chemistry where
circumstellar grains play a role. We further provide evidence that HD101584 was
a low-mass, M-type AGB star
HD101584: Circumstellar characteristics and evolutionary status
We have performed a study of the characteristics of the circumstellar
environment of the binary object HD101584, that provides information on a
likely evolutionary scenario. We have obtained and analysed ALMA observations,
complemented with observations using APEX, of a large number of molecular
lines. An analysis of the spectral energy distribution has also been performed.
Emissions from 12 molecular species (not counting isotopologues) have been
observed, and most of them mapped with angular resolutions in the range 0.1" to
0.6". Four circumstellar components are identified: i) a central compact source
of size 0.15", ii) an expanding equatorial density enhancement (a flattened
density distribution in the plane of the orbit) of size 3", iii) a bipolar
high-velocity outflow (150 km/s), and iv) an hourglass structure. The outflow
is directed almost along the line of sight. There is evidence of a second
bipolar outflow. The mass of the circumstellar gas is 0.5[D/1 kpc]^2 Msun,
about half of it lies in the equatorial density enhancement. The dust mass is
0.01[D/1 kpc]^2 Msun, and a substantial fraction of this is in the form of
large-sized, up to 1 mm, grains. The estimated kinetic age of the outflow is
770[D/1 kpc] yr. The kinetic energy and the scalar momentum of the accelerated
gas are estimated to be 7x10^(45)[D/1 kpc]^2 erg and 10^(39)[D/1 kpc]^2 g cm/s,
respectively. We provide good evidence that the binary system HD101584 is in a
post-common-envelope-evolution phase, that ended before a stellar merger.
Isotope ratios combined with stellar mass estimates suggest that the primary
star's evolution was terminated already on the first red giant branch (RGB).
Most of the energy required to drive the outflowing gas was probably released
when material fell towards the companion.Comment: Accepted for publication in A&
Optical tomography of the born-again ejecta of A 58
In a born-again planetary nebula (PN), processed H-deficient material has
been injected inside the old, H-rich nebula as a result of a very late thermal
pulse (VLTP) event. Long-slit spectra have been used to unveil the chemical and
physical differences between these two structures, but the ejection and shaping
processes remain still unclear. In order to peer into the morpho-kinematics of
the H-deficient ejecta in the born-again PN A 58, we present the first integral
field spectroscopic observations of a born-again PN as obtained with GTC
MEGARA. We detect emission from the H, He I, [O III], [N II] and [S II]
emission lines, which help us unveil the expansion patterns of the different
structures. In combination with ALMA and Hubble Space Telescope data we are
able to produce a complete view of the H-deficient ionized and molecular ejecta
in A 58. We propose an hourglass structure for the ionized material that
embraces molecular high-velocity polar components, while bisected by an
expanding toroidal molecular and dusty structure. Our results leverage the role
of a companion in shaping the VLTP ejecta in this born-again PN.Comment: 11 pages, 6 figure
Ultracompact HII regions with extended emission: The case of G43.89-0.78 and its molecular environment
The Karl Jansky Very Large Array (VLA), Owens Valley Radio Observatory
(OVRO), Atacama Large Millimetric Array (ALMA), and the infrared
\textit{Spitzer} observatories, are powerful facilities to study massive star
formation regions and related objects such as ultra--compact (UC) \hii regions,
molecular clumps, and cores. We used these telescopes to study the \uchiir
G43.89--0.78. The morphological study at arcminute scales using NVSS and
\textit{Spitzer} data shows that this region is similar to those observed in
the \textit{ bubble--like} structures revealed by \textit{Spitzer}
observations. With this result, and including a physical characterization based
on 3.6 cm data, we suggest G43.89--0.78 be classified as an \uchiir with
Extended Emission because it meets the operational definition given in this
paper comparing radio continuum data at 3.6 and 20~cm. For the ultra-compact
component, we use VLA data to obtain physical parameters at 3.6~cm confirming
this region as an \uchii region. Using ALMA observations, we detect the
presence of a dense ( cm) and small ( 2.0\arcsec;
0.08 pc) molecular clump with a mass of 220 M and average kinetic
temperature of 21~K, located near to the \uchii region. In this clump,
catalogued as G43.890--0.784, water masers also exist, possibly tracing a
bipolar outflow. We discover in this vicinity two additional clumps which we
label as G43.899--0.786 (T = 50 K; M = 11 M), and G43.888--0.787
(T = 50 K; M = 15 M).Comment: 13 pages, 8 figures, 2 tables. Accepted for publication in the
Monthly Notices of the Royal Astronomical Society Main Journal (2020
Magnetically aligned dust and SiO maser polarisation in the envelope of the red supergiant VY Canis Majoris
International audienceWe use Atacama Large Millimeter/submillimeter Array Band 5 science verification observations of the red supergiant VY CMa to study the polarization of SiO thermal/masers lines and dust continuum at ~1.7 mm wavelength. We analyse both linear and circular polarization and derive the magnetic field strength and structure, assuming the polarization of the lines originates from the Zeeman effect, and that of the dust originates from aligned dust grains. We also discuss other effects that could give rise to the observed polarization. We detect, for the first time, significant polarization (~3%) of the circumstellar dust emission at millimeter wavelengths. The polarization is uniform with an electric vector position angle of . Varying levels of linear polarization are detected for the J=4-3 28SiO v=0, 1, 2, and 29SiO v=0, 1 lines, with the strongest polarization fraction of ~30% found for the 29SiO v=1 maser. The linear polarization vectors rotate with velocity, consistent with earlier observations. We also find significant (up to ~1%) circular polarization in several lines, consistent with previous measurements. We conclude that the detection is robust against calibration and regular instrumental errors, although we cannot yet fully rule out non-standard instrumental effects. Emission from magnetically aligned grains is the most likely origin of the observed continuum polarization. This implies that the dust is embedded in a magnetic field >13 mG. The maser line polarization traces the magnetic field structure. The magnetic field in the gas and dust is consistent with an approximately toroidal field configuration, but only higher angular resolution observations will be able to reveal more detailed field structure. If the circular polarization is due to Zeeman splitting, it indicates a magnetic field strength of ~1-3 Gauss, consistent with previous maser observations
Charting Circumstellar Chemistry of Carbon-rich AGB Stars: I. ALMA 3 mm spectral surveys
AGB stars are major contributors to the chemical enrichment of the ISM
through nucleosynthesis and extensive mass loss. Most of our current knowledge
of AGB atmospheric and circumstellar chemistry, in particular in a C-rich
environment, is based on observations of the carbon star IRC+10216. We aim to
obtain a more generalised understanding of the chemistry in C-rich AGB CSEs by
studying a sample of three carbon stars, IRAS15194-5115, IRAS15082-4808, and
IRAS07454-7112, and test the archetypal status often attributed to IRC+10216.
We performed spatially resolved, unbiased spectral surveys in ALMA Band 3. We
identify a total of 132 rotational transitions from 49 molecular species. There
are two main morphologies of the brightness distributions: centrally-peaked
(e.g. HCN) and shell-like (e.g. CH). We estimated the sizes of the
molecular emitting regions using azimuthally-averaged radial profiles of the
line brightness distributions, and derived abundance estimates. Of the shell
distributions, the cyanopolyynes peak at slightly smaller radii than the
hydrocarbons, and CN and HNC show the most extended emission. The emitting
regions for each species are the smallest for IRAS07454-7112. We find that,
within the uncertainties of the analysis, the three stars present similar
abundances for most species, also compared to IRC+10216. We find that SiO is
more abundant in our three stars compared to IRC+10216. Our estimated isotopic
ratios match well the literature values for the sources. The observed
circumstellar chemistry appears very similar across our sample and compared to
that of IRC+10216, both in terms of the relative location of the emitting
regions and molecular abundances. This implies that, to a first approximation,
the chemical models tailored to IRC+10216 are able to reproduce the observed
chemistry in C-rich envelopes across roughly an order of magnitude in wind
density.Comment: 21 pages. 13 figures and 8 tables in the main text. 5 appendices
contain additional figures and tables. Appendix tables are available in
electronic form at the CDS, along with the reprocessed ALMA cubes and
spectra, at http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ or via anonymous
ftp to cdsarc.u-strasbg.fr(130.79.128.5). Accepted for publication in
Astronomy & Astrophysic
VLTI/PIONIER reveals the close environment of the evolved system HD101584
Context: The observed orbital characteristics of post-asymptotic giant branch
(post-AGB) and post-red giant branch (post-RGB) binaries are not understood. We
suspect that the missing ingredients to explain them probably lie in the
continuous interaction of the central binary with its circumstellar
environment. Aims: We aim at studying the circumbinary material in these
complex systems by investigating the connection between the innermost and
large-scale structures. Methods: We perform high-angular resolution
observations in the near-infrared continuum of HD101584, which has a complex
structure as seen at millimeter wavelengths with a disk-like morphology and a
bipolar outflow due to an episode of strong binary interaction. To account for
the complexity of the target we first perform an image reconstruction and use
this result to fit a geometrical model to extract the morphological and thermal
features of the environment. Results: The image reveals an unexpected
double-ring structure. We interpret the inner ring to be produced by emission
from dust located in the plane of the disk and the outer ring to be produced by
emission from dust that is located 1.6[D/1kpc] au above the disk plane. The
inner ring diameter (3.94[D/1kpc] au), and temperature (T=154010K) are
compatible with the dust sublimation front of the disk. The origin of the
out-of-plane ring (with a diameter of 7.39[D/1kpc] au and a temperature of
1014K) could be due to episodic ejection or a dust condensation front in
the outflow. Conclusion: The observed outer ring is possibly linked with the
blue-shifted side of the large scale outflow seen by ALMA and is tracing its
launching location to the central star. Such observations give morphological
constraints on the ejection mechanism. Additional observations are needed to
constrain the origin of the out-of-plane structure.Comment: Accepted to A&A. 14 pages, 13 figure
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