21 research outputs found
PRODIGE -- Envelope to Disk with NOEMA II. Small-scale temperature structure and a streamer feeding the SVS13A protobinary using CH3CN and DCN
Aims. We present high sensitivity and high-spectral resolution NOEMA
observations of the Class 0/I binary system SVS13A, composed of the low-mass
protostars VLA4A and VLA4B with a separation of ~90 au. VLA4A is undergoing an
accretion burst that enriches the chemistry of the surrounding gas. This gives
us an excellent opportunity to probe the chemical and physical conditions as
well as the accretion process. Methods. We observe the (12K-11K) lines of CH3CN
and CH313CN, the DCN (3-2) line, and the C18O (2-1) line toward SVS13A using
NOEMA. Results. We find complex line profiles at disk scales which cannot be
explained by a single component or pure Keplerian motion. By adopting two
velocity components to model the complex line profiles, we find that the
temperatures and densities are significantly different between these two
components. This suggests that the physical conditions of the emitting gas
traced via CH3CN can change dramatically within the circumbinary disk. In
addition, combining our observations of DCN (3-2) with previous ALMA
high-angular-resolution observations, we find that the binary system (or VLA4A)
might be fed by an infalling streamer from envelope scales (~700 au). If this
is the case, this streamer contributes to the accretion of material onto the
system with a rate of at least 1.4x10-6 Msun yr-1. Conclusions. We conclude
that the CH3CN emission in SVS13A traces hot gas from a complex structure. This
complexity might be affected by a streamer that is possibly infalling and
funneling material into the central region.Comment: 20 pages, 19 figures, accepted to A&
PRODIGE -- Envelope to disk with NOEMA I. A 3000 au streamer feeding a Class I protostar
Context. In the past few years, there has been a rise in the detection of
streamers, asymmetric flows of material directed toward the protostellar disk
with material from outside the star's natal core. It is unclear how they affect
the process of mass accretion, in particular beyond the Class 0 phase. Aims. We
investigate the gas kinematics around Per-emb-50, a Class I source in the
crowded star-forming region NGC 1333. Our goal is to study how the mass infall
proceeds from envelope to disk scales in this source. Results. We discover a
streamer delivering material toward Per-emb-50 in HCO and CO
emission. The streamer's emission can be well described by the analytic
solutions for an infalling parcel of gas along a streamline with conserved
angular momentum, both in the image plane and along the line of sight
velocities. The streamer has a mean infall rate of M yr, times higher than the current accretion rate of the
protostar. SO and SO emission reveal asymmetric infall motions in the inner
envelope, additional to the streamer around Per-emb-50. Furthermore, the
presence of SO could mark the impact zone of the infalling material.
Conclusions. The streamer delivers sufficient mass to sustain the protostellar
accretion rate and might produce an accretion burst, which would explain the
protostar's high luminosity with respect to other Class I sources. Our results
highlight the importance of late infall for protostellar evolution: streamers
might provide a significant amount of mass for stellar accretion after the
Class 0 phase.Comment: 20 pages, 14 figures, accepted for publication in A&
Focused wave interactions with floating structures: A blind comparative study
The paper presents results from the Collaborative Computational Project in Wave Structure Interaction (CCP-WSI) Blind Test Series 2. Without prior access to the physical data, participants, with numerical methods ranging from low-fidelity linear models to fully non-linear Navier-Stokes (NS) solvers, simulate the interaction between focused wave events and two separate, taut-moored, floating structures: a hemispherical-bottomed cylinder and a cylinder with a moonpool. The 'blind' numerical predictions for heave, surge, pitch and mooring load, are compared against physical measurements. Dynamic time warping is used to quantify the predictive capability of participating methods. In general, NS solvers and hybrid methods give more accurate predictions; however, heave amplitude is predicted reasonably well by all methods; and a WEC-Sim implementation, with CFD-informed viscous terms, demonstrates comparable predictive capability to even the stronger NS solvers. Large variations in the solutions are observed (even among similar methods), highlighting a need for standardisation in the numerical modelling of WSI problems
SPARKS II.: Complex organic molecules in accretion shocks around a hot core precursor
Classical hot cores are rich in molecular emission, and they show a high abundance of complex organic molecules (COMs). The emergence of molecular complexity is poorly constrained in the early evolution of hot cores. Using the Atacama Large Millimeter Array we put observational constraints on the physical location of COMs in a high-mass protostellar envelope associated with the G328.2551-0.5321 clump. The protostar is single down to ~400au scales and we resolve the emission region of COMs. Using thermodynamic equilibrium modelling of the available 7.5 GHz bandwidth around ~345 GHz, we detect emission from 10 COMs, and identify a line of deuterated water (HDO). The most extended emission originates from methanol, methyl formate and formamide. Together with HDO, these molecules are found to be associated with both the accretion shocks and the inner envelope, for which we estimate a moderate temperature of 110 K. Our findings reveal a significant difference in the distribution of COMs. O-bearing COMs, such as ethanol, acetone, and ethylene glycol are almost exclusively found and show a higher abundance towards the accretion shocks with 180 K. Whereas N-bearing COMs with a CN group, such as vinyl and ethyl cyanide peak on the central position, thus the protostar and the accretion disk. This is the first observational evidence for a large column density of COMs seen towards accretion shocks at the centrifugal barrier at the inner envelope. Since the molecular composition is dominated by that of the accretion shocks and the radiatively heated hot inner region is very compact, we propose this source to be a precursor to a classical, radiatively heated hot core
Emerging molecular complexity of hot cores: accretion shocks give rise to complex organic molecules around a high-mass protostar
Sulphur-rich cold gas around the hot core precursor G328.2551-0.5321. An APEX unbiased spectral survey of the 2 mm, 1.2 mm, and 0.8 mm atmospheric windows
During star formation, the dense gas undergoes significant chemical evolution
leading to the emergence of a rich variety of molecules associated with hot
cores and hot corinos. The physical and chemical conditions are poorly
constrained; the early phases of emerging hot cores in particular represent an
unexplored territory. We provide here a full molecular inventory of a massive
protostellar core that is proposed to be a precursor of a hot core. We
performed an unbiased spectral survey towards the hot core precursor associated
with clump G328.2551-0.5321 between 159GHz and 374GHz. To identify the spectral
lines, we used rotational diagrams and radiative transfer modelling assuming
LTE. We detected 39 species and 26 isotopologues, and were able to distinguish
a warm and compact inner region, a colder more extended envelope, and the
kinematic signatures of the accretion shocks that have previously been observed
with ALMA. We associate most of the emission of the small molecules with the
cold gas, while the molecular emission of the warm gas is enriched by complex
organic molecules (COMs). We find a high abundance of S-bearing molecules in
the cold gas phase suggesting a low sulphur depletion, with a factor of > 1%.
We identify nine COMs in the warm gas, four in the cold gas, and four towards
the accretion shocks. The high abundances of S-bearing species originating from
the undisturbed gas may suggest a contribution from shocked gas at the outflow
cavity walls. The molecular composition of the warm gas is similar to that of
both hot cores and hot corinos, but the molecular abundances are closer to the
values found towards hot corinos than to values found towards hot cores.
Considering the compactness of the warm region and its moderate temperature, we
suggest that thermal desorption has not been completed towards this object yet,
representing an early phase of the emergence of hot cores.Comment: 68 pages, 59 figures. Accepted by A&A after refereeing and language
corrections. Abstract abbreviate