4,032 research outputs found
Origin of the wide-angle hot H2 in DG Tauri: New insight from SINFONI spectro-imaging
We wish to test the origins proposed for the extended hot H2 at 2000K around
the atomic jet from the T Tauri star DGTau, in order to constrain the
wide-angle wind structure and the possible presence of an MHD disk wind. We
present flux calibrated IFS observations in H2 1-0 S(1) obtained with
SINFONI/VLT. Thanks to spatial deconvolution by the PSF and to accurate
correction for uneven slit illumination, we performed a thorough analysis and
modeled the morphology, kinematics, and surface brightness. We also compared
our results with studies in [FeII], [OI], and FUV-pumped H2. The
limb-brightened H2 emission in the blue lobe is strikingly similar to
FUV-pumped H2 imaged 6yr later, confirming that they trace the same hot gas and
setting an upper limit of 12km/s on any expansion proper motion. The wide-angle
H2 rims are at lower blueshifts than probed by narrow long-slit spectra. We
confirm that they extend to larger angle and to lower speed the onion-like
velocity structure observed in optical atomic lines. The latter is shown to be
steady over more/equal than 4yr but undetected in [FeII] by SINFONI, probably
due to strong iron depletion. The H2 rim thickness less/equal than 14AU rules
out excitation by C-shocks, and J-shock speeds are constrained to 10km/s. We
find that explaining the H2 wide-angle emission with a shocked layer requires
either a recent outburst (15yr) into a pre-existing ambient outflow or an
excessive wind mass flux. A slow photoevaporative wind from the dense
irradiated disk surface and an MHD disk wind heated by ambipolar diffusion seem
to be more promising and need to be modeled in more detail
Chemistry of a newly detected circumbinary disk in Ophiuchus
(Abridged) Astronomers recently started discovering exoplanets around binary
systems. Therefore, understanding the formation and evolution of circumbinary
disks is crucial for a complete scenario of planet formation. The aim of this
paper is to present the detection of a circumbinary disk around Oph-IRS67 and
analyse its structure. We present high-angular-resolution (0.4", 60 AU)
observations of C17O, H13CO+ , C34S, SO2, C2H and c-C3H2 molecular transitions
with ALMA at 0.8 mm. The spectrally and spatially resolved maps reveal the
kinematics of the circumbinary disk as well as its chemistry. Molecular
abundances are estimated using RADEX. The continuum emission reveals the
presence of a circumbinary disk around the two sources. This disk has a
diameter of ~620 AU and is well traced by C17O and H13CO+ emission. C2H and
c-C3H2 trace a higher-density region which is spatially offset from the sources
(~430 AU). Finally, SO2 shows compact emission around one of the sources,
Oph-IRS67 B. The molecular transitions which trace the circumbinary disk are
consistent with a Keplerian profile on disk scales (< 200 AU) and an infalling
profile for envelope scales (> 200 AU). The Keplerian fit leads to a mass of
2.2 Msun. Inferred CO abundances w.r.t. H2 are comparable to the canonical ISM
value of 2.7e-4. This study proves the first detection of the circumbinary disk
associated with Oph-IRS67. The disk is chemically differentiated from the
nearby high-density region. The lack of methanol emission suggests the extended
disk dominates the mass budget in the inner- most regions of the protostellar
envelope, generating a flat density profile where less material is exposed to
high temperatures. Thus, complex organic molecules would be associated with
lower column densities. Finally, Oph-IRS67 is a promising candidate for the
detection of both circumstellar disks with higher-angular-resolution
observations.Comment: 19 pages, 14 figures, 6 table
Physical and chemical fingerprint of protostellar disc formation
(Abridged) The purpose of this paper is to explore and compare the physical
and chemical structure of Class I low-mass protostellar sources on
protoplanetary disc scales. We present a study of the dust and gas emission
towards a representative sample of 12 Class I protostars from the Ophiuchus
molecular cloud with the Atacama Large Millimeter/submillimeter Array (ALMA).
The continuum at 0.87 mm and molecular transitions from C17O, C34S, H13CO+,
CH3OH, SO2 , and C2H were observed at high angular resolution (0.4", ~60 au
diameter) towards each source. Disc and stellar masses are estimated from the
continuum flux and position-velocity diagrams, and six of the sources show
disc-like structures. Towards the more luminous sources, compact emission and
large line widths are seen for transitions of SO2 that probe warm gas (Eu ~200
K). In contrast, C17O emission is detected towards the least evolved and less
luminous systems. No emission of CH3OH is detected towards any of the continuum
peaks, indicating an absence of warm CH3OH gas towards these sources. A
power-law relation is seen between the stellar mass and the bolometric
luminosity, corresponding to a mass accretion rate of (2.4 +/- 0.6) x 10^-7
Msun/year for the Class I sources. This mass accretion rate is lower than the
expected value if the accretion is constant in time and rather points to a
scenario of accretion occurring in bursts. The differentiation between C17O and
SO2 suggests that they trace different physical components: C17O traces the
densest and colder regions of the disc-envelope system, while SO2 may be
associated with regions of higher temperature, such as accretion shocks. The
lack of warm CH3OH emission suggests that there is no hot-core-like region
around any of the sources and that the CH3OH column density averaged over the
disc is low.Comment: 20 pages, 16 figures, 8 table
Evidence for a single hydrogen molecule connected by an atomic chain
Stable, single-molecule conducting-bridge configurations are typically
identified from peak structures in a conductance histogram. In previous work on
Pt with H at cryogenic temperatures it has been shown that a peak near 1
identifies a single molecule Pt-H-Pt bridge. The histogram shows
an additional structure with lower conductance that has not been identified.
Here, we show that it is likely due to a hydrogen decorated Pt chain in contact
with the H molecular bridge.Comment: 4 pages, 4 figure
Imaging Oxygen Distribution in Marine Sediments. The Importance of Bioturbation and Sediment Heterogeneity
The influence of sediment oxygen heterogeneity, due to bioturbation, on diffusive oxygen flux was investigated. Laboratory experiments were carried out with 3 macrobenthic species presenting different bioturbation behaviour patterns:the polychaetes Nereis diversicolor and Nereis virens, both constructing ventilated galleries in the sediment column, and the gastropod Cyclope neritea, a burrowing species which does not build any structure. Oxygen two-dimensional distribution in sediments was quantified by means of the optical planar optode technique. Diffusive oxygen fluxes (mean and integrated) and a variability index were calculated on the captured oxygen images. All species increased sediment oxygen heterogeneity compared to the controls without animals. This was particularly noticeable with the polychaetes because of the construction of more or less complex burrows. Integrated diffusive oxygen flux increased with oxygen heterogeneity due to the production of interface available for solute exchanges between overlying water and sediments. This work shows that sediment heterogeneity is an important feature of the control of oxygen exchanges at the sediment–water interface
Quantum Interaction : the Construction of Quantum Field defined as a Bilinear Form
We construct the solution of the quantum wave equation
as a bilinear form which can
be expanded over Wick polynomials of the free -field, and where
is defined as the normal ordered product with
respect to the free -field. The constructed solution is correctly defined
as a bilinear form on , where is a
dense linear subspace in the Fock space of the free -field. On
the diagonal Wick symbol of this bilinear form
satisfies the nonlinear classical wave equation.Comment: 32 pages, LaTe
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