426 research outputs found
Assessing molecular outflows and turbulence in the protostellar cluster Serpens South
Molecular outflows driven by protostellar cluster members likely impact their
surroundings and contribute to turbulence, affecting subsequent star formation.
The very young Serpens South cluster consists of a particularly high density
and fraction of protostars, yielding a relevant case study for protostellar
outflows and their impact on the cluster environment. We combined CO
observations of this region using the Combined Array for Research in
Millimeter-wave Astronomy (CARMA) and the Institut de Radioastronomie
Millim\'{e}trique (IRAM) 30 m single dish telescope. The combined map allows us
to probe CO outflows within the central, most active region at size scales of
0.01 pc to 0.8 pc. We account for effects of line opacity and excitation
temperature variations by incorporating CO and CO data for the
and transitions (using Atacama Pathfinder Experiment and
Caltech Submillimeter Observatory observations for the higher CO transitions),
and we calculate mass, momentum, and energy of the molecular outflows in this
region. The outflow mass loss rate, force, and luminosity, compared with
diagnostics of turbulence and gravity, suggest that outflows drive a sufficient
amount of energy to sustain turbulence, but not enough energy to substantially
counter the gravitational potential energy and disrupt the clump. Further, we
compare Serpens South with the slightly more evolved cluster NGC 1333, and we
propose an empirical scenario for outflow-cluster interaction at different
evolutionary stages.Comment: 26 pages, 15 figures, accepted for publication in the Astrophysical
Journa
A cochain level proof of Adem relations in the mod 2 Steenrod algebra
In 1947, N.E. Steenrod defined the Steenrod Squares, which are mod 2 cohomology operations, using explicit cochain formulae for cup-i products of cocycles. He later recast the construction in more general homological terms, using group homology and acyclic model methods, rather than explicit cochain formulae, to define mod p operations for all primes p. Steenrod's student J. Adem applied the homological point of view to prove fundamental relations, known as the Adem relations, in the algebra of cohomology operations generated by the Steenrod operations. In this paper we give a proof of the mod 2 Adem relations at the cochain level. Specifically, given a mod 2 cocycle, we produce explicit cochain formulae whose coboundaries are the Adem relations among compositions of Steenrod Squares applied to the cocycle, using Steenrod's original cochain definition of the Square operations
Persistence Steenrod modules
It has long been envisioned that the strength of the barcode invariant offiltered cellular complexes could be increased using cohomology operations.Leveraging recent advances in the computation of Steenrod squares, we introducea new family of computable invariants on mod 2 persistent cohomology termed-barcodes. We present a complete algorithmic pipeline for theircomputation and illustrate their real-world applicability using the space ofconformations of the cyclo-octane molecule.<br
Rotating filament in Orion B: Do cores inherit their angular momentum from their parent filament?
Angular momentum is one of the most important physical quantities that govern
star formation. The initial angular momentum of a core may be responsible for
its fragmentation and can have an influence on the size of the protoplanetary
disk. To understand how cores obtain their initial angular momentum, it is
important to study the angular momentum of filaments where they form. While
theoretical studies on filament rotation have been explored, there exist very
few observational measurements of the specific angular momentum in star-forming
filaments. We present high-resolution N2D+ ALMA observations of the LBS 23
(HH24-HH26) region in Orion B, which provide one of the most reliable
measurements of the specific angular momentum in a star-forming filament. We
find the total specific angular momentum (), the
dependence of the specific angular momentum with radius (j(r) ), and the ratio of rotational energy to gravitational energy
() comparable to those observed in rotating cores with
sizes similar to our filament width ( 0.04 pc) in other star-forming
regions. Our filament angular momentum profile is consistent with rotation
acquired from ambient turbulence and with simulations that show cores and their
host filaments develop simultaneously due to the multi-scale growth of
nonlinear perturbation generated by turbulence.Comment: accepted by ApJ, 2020.12.
Gamma-ray emission from massive young stellar objects
Massive stars form in dense and massive molecular cores. The exact formation
mechanism is unclear, but it is possible that some massive stars are formed by
processes similar to those that produce the low-mass stars, with
accretion/ejection phenomena occurring at some point of the evolution of the
protostar. This picture seems to be supported by the detection of a collimated
stellar wind emanating from the massive protostar IRAS 16547-4247. A triple
radio source is associated with the protostar: a compact core and two radio
lobes. The emission of the southern lobe is clearly non-thermal. Such emission
is interpreted as synchrotron radiation produced by relativistic electrons
locally accelerated at the termination point of a thermal jet. Since the
ambient medium is determined by the properties of the molecular cloud in which
the whole system is embedded, we can expect high densities of particles and
infrared photons. Because of the confirmed presence of relativistic electrons,
inverse Compton and relativistic Bremsstrahlung interactions are unavoidable.
Proton-proton collision should also occur, producing an injection of neutral
pions. In this paper we aim at making quantitative predictions of the spectral
energy distribution of the non-thermal spots generated by massive young stellar
objects, with emphasis on the particular case of IRAS 16547-4247. We present
spectral energy distributions for the southern lobe of this source, for a
variety of conditions. We show that high-energy emission might be detectable
from this object in the gamma-ray domain (MeV to TeV). The source may also be
detectable at X-rays through long exposures with current X-ray instruments.Comment: 8 pages, 6 figures, accepted for publication in A&
ALMA Cycle 1 Observations of the HH46/47 Molecular Outflow: Structure, Entrainment and Core Impact
We present ALMA Cycle 1 observations of the HH46/47 molecular outflow using
combined 12m array and ACA observations. The improved angular resolution and
sensitivity of our multi-line maps reveal structures that help us study the
entrainment process in much more detail and allow us to obtain more precise
estimates of outflow properties than previous observations. We use 13CO(1-0)
and C18O(1-0) emission to correct for the 12CO(1-0) optical depth to accurately
estimate the outflow mass, momentum and kinetic energy. This correction
increases the estimates of the mass, momentum and kinetic energy by factors of
about 9, 5 and 2, respectively, with respect to estimates assuming optically
thin emission. The new 13CO and C18O data also allow us to trace denser and
slower outflow material than that traced by the 12CO maps, and they reveal an
outflow cavity wall at very low velocities (as low as 0.2km/s with respect to
the cores central velocity). Adding with the slower material traced only by
13CO and C18O, there is another factor of 3 increase in the mass estimate and
50% increase in the momentum estimate. The estimated outflow properties
indicate that the outflow is capable of dispersing the parent core within the
typical lifetime of the embedded phase of a low-mass protostar, and that it is
responsible for a core-to-star efficiency of 1/4 to 1/3. We find that the
outflow cavity wall is composed of multiple shells associated with a series of
jet bow-shock events. Within about 3000AU of the protostar the 13CO and C18O
emission trace a circumstellar envelope with both rotation and infall motions,
which we compare with a simple analytic model. The CS(2-1) emission reveals
tentative evidence of a slowly-moving rotating outflow, which we suggest is
entrained not only poloidally but also toroidally by a disk wind that is
launched from relatively large radii from the source.Comment: Accepted for publication in ApJ. 26 pages, 20 figure
ADSORPTION ESSAYS OF PALLADIUM IN MODIFIED SILICA GEL WITH THIOURONIUM GROUPS: EXPERIMENTAL AND THEORICAL STUDIES
Indexación: Web of Science; ScieloThe silylant 3-cloropropyltriethoxysilyl was anchored over silica gel in anhydrous conditions in order to react with thiourea to obtain modified silica gel with thiouronium. The aim to obtain an inorganic support that is able to hijack metals from the VIII group such as palladium. The product was characterized by Sbet and FTIR infrared spectroscopy. For the determination of the structure in the modified silica gel NMR spectra of silicon and carbon were preformed in solid state. The coordination form of the modified silica gel to the metal was studied computationally in the context of the DFT theory, using the ADF code. This was a collaborative work with "Fundación Chile" for the recuperation of precious metals from the mining industry.http://ref.scielo.org/gk7rm
AMBER on the VLTI: data processing and calibration issues
We present here the current performances of the AMBER / VLTI instrument for
standard use and compare these with the offered modes of the instrument. We
show that the instrument is able to reach its specified precision only for
medium and high spectral resolution modes, differential observables and bright
objects. For absolute observables, the current achievable accuracy is strongly
limited by the vibrations of the Unit Telescopes, and also by the observing
procedure which does not take into account the night-long transfer function
monitoring. For low-resolution mode, the current limitation is more in the data
reduction side, since several effects negligible at medium spectral resolution
are not taken into account in the current pipeline. Finally, for faint objects
(SNR around 1 per spectral channel), electromagnetic interferences in the VLTI
interferometric laboratory with the detector electronics prevents currently to
get unbiased measurements. Ideas are under study to correct in the data
processing side this effect, but a hardware fix should be investigated
seriously since it limits seriously the effective limiting magnitude of the
instrument.Comment: 10 page
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