723 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&
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
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
Nobeyama Cygnus-X Survey: Physical Properties of CO clumps in DR-6(W), DR-9 and DR-13S regions
Cygnus-X is considered a region of interest for high-energy astrophysics,
since the Cygnus OB2 association has been confirmed as a PeVatron in the Cygnus
cocoon. In this research note, we present new high-resolution (16'')
CO(J=10) and CO (J=10) observations
obtained with the Nobeyama 45-m radiotelescope, to complement the Nobeyama
Cygnus-X Survey. We discovered 19 new CO clumps associated with the
star-forming regions DR-6W, DR-9, and DR13S. We present the physical parameters
of these clumps, which are consistent with the neighboring covered regions. We
confirm the clumpy nature of these regions and of a filament located between
DR6 and DR6W. These results strongly suggest that star formation occurs in
these regions with clumps of sizes 10 pc, masses 10
M, and H densities of 10 cm.Comment: 8 pages, 3 Figures, 1 Table. https://pos.sissa.it/444/631/pd
The ALMA Survey of 70 Dark High-mass Clumps in Early Stages (ASHES). II: Molecular Outflows in the Extreme Early Stages of Protocluster Formation
We present a study of outflows at extremely early stages of high-mass star
formation obtained from the ALMA Survey of 70 dark High-mass clumps
in Early Stages (ASHES). Twelve massive 3.670 dark prestellar
clump candidates were observed with the Atacama Large Millimeter/submillimeter
Array (ALMA) in Band 6. Forty-three outflows are identified toward 41 out of
301 dense cores using the CO and SiO emission lines, yielding a detection rate
of 14%. We discover 6 episodic molecular outflows associated with low- to
high-mass cores, indicating that episodic outflows (and therefore episodic
accretion) begin at extremely early stages of protostellar evolution for a
range of core masses. The time span between consecutive ejection events is much
smaller than those found in more evolved stages, which indicates that the
ejection episodicity timescale is likely not constant over time. The estimated
outflow dynamical timescale appears to increase with core masses, which likely
indicates that more massive cores have longer accretion timescales than less
massive cores. The lower accretion rates in these 70 dark objects
compared to the more evolved protostars indicate that the accretion rates
increase with time. The total outflow energy rate is smaller than the turbulent
energy dissipation rate, which suggests that outflow induced turbulence cannot
sustain the internal clump turbulence at the current epoch. We often detect
thermal SiO emission within these 70 dark clumps that is unrelated
to CO outflows. This SiO emission could be produced by collisions, intersection
flows, undetected protostars, or other motions.Comment: 32 pages, 9 figures, 4 tables, accepted for publication in Ap
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