448 research outputs found
Windows through the Dusty Disks Surrounding the Youngest Low Mass Protostellar Objects
The formation and evolution of young low mass stars are characterized by
important processes of mass loss and accretion ocurring in the innermost
regions of their placentary circumstellar disks. Because of the large
obscuration of these disks at optical and infrared wavelengths in the early
protostellar stages (Class 0 Sources), they were previously detected only at
radio wavelengths using interferometric techniques. We have detected with the
Infrared Space Observatory (ISO) the mid-infrared emission associated with the
Class 0 protostar VLA1 in the HH1-2 region located in the Orion nebula. The
emission arises in the three wavelength windows at 5.3, 6.6 and 7.5 micras
where the absorption due to ices and silicates has a local minimum that exposes
the central parts of the youngest protostellar systems to mid-infrared
investigations. The mid-infrared emission arises from a central source with 4
AU diameter at an averaged temperature of 700 K, deeply embedded in a dense
region with a visual extinction of Av=80-100mag.Comment: The article is here and on pres
Uniform random colored complexes
We present here random distributions on -edge-colored, bipartite
graphs with a fixed number of vertices . These graphs are dual to
-dimensional orientable colored complexes. We investigate the behavior of
quantities related to those random graphs, such as their number of connected
components or the number of vertices of their dual complexes, as . The techniques involved in the study of these quantities also yield a
Central Limit Theorem for the genus of a uniform map of order , as .Comment: 36 pages, 9 figures, minor additions and correction
Mass spectrometry imaging of levofloxacin distribution in TB-infected pulmonary lesions by MALDI-MSI and continuous liquid microjunction surface sampling
A multi-modal mass spectrometry imaging (MSI) and profiling approach has been applied to assess the partitioning of the anti-TB fluoroquinolone levofloxacin into pulmonary lesions. Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) and a commercial liquid microjunction surface sampling technology (LMJ-SSP), or flowprobe, have been used to both spatially profile and image drug distributions in lung tissue sections from TB-infected rabbits following oral administration of a single human-equivalent dose., Levofloxacin levels were highest at 6 h post-dose in normal lung, cellular granuloma, and necrotic caseum compartments. The drug accumulated in the cellular granuloma regions with lower amounts partitioning into central caseous compartments. Flowprobe imaging at 630 μm (limited by the probe tip diameter) enabled visualization of drug distribution into lesion compartments, including limited differentiation of relative drug abundance in cellular versus caseous regions of the lesions., MALDI-MSI analysis at 75 μm provided more detailed drug distribution, which clearly accumulated in the cellular region immediately surrounding the central caseum core. Imaging and profiling data acquired by flowprobe and MALDI-MSI were validated by quantitative LC/MS/MS analysis of lung and granuloma homogenates taken from the same animals., The results of the investigation show flowprobe imaging and sampling as a rapid and sensitive alternative to MALDI-MSI for profiling drug distributions into tissues when spatial resolution of data below the threshold of the probe diameter is not required
Detection of Formaldehyde Towards the Extreme Carbon Star IRC+10216
We report the detection of H2CO (formaldehyde) around the carbon-rich AGB
star, IRC+10216. We find a fractional abundance with respect to molecular
hydrogen of x(H2CO)= (1.3 {+1.5}{-0.8}) x 10^{-8}. This corresponds to a
formaldehyde abundance with respect to water vapor of x(H2CO)/x(H2O)=(1.1 +/-
0.2) x 10^{-2}, in line with the formaldehyde abundances found in Solar System
comets, and indicates that the putative extrasolar cometary system around
IRC+10216 may have a similar chemical composition to Solar System comets.
However, we also failed to detect CH3OH (methanol) around IRC+10216 and our
upper limit of x(CH3OH)/x(H2O) < 7.7 x 10^{-4}, (3 sigma), indicates that
methanol is substantially underabundant in IRC+10216, compared to Solar System
comets. We also conclude, based on offset observations, that formaldehyde has
an extended source in the envelope of IRC+10216 and may be produced by the
photodissociation of a parent molecule, similar to the production mechanism for
formaldehyde in Solar System comet comae. Preliminary mapping observations also
indicate a possible asymmetry in the spatial distribution of formaldehyde
around IRC+10216, but higher signal-to-noise observations are required to
confirm this finding. This study is based on observations carried out with the
IRAM 30m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and
IGN (Spain). (abridged)Comment: accepted to ApJ, 45 pages, 11 figure
Spatially resolved detection of crystallized water ice in a TTauri object
We search for frozen water and its processing around young stellar objects
(YSOs of class I/II). We try to detect potential, regional differences in water
ice evolution within YSOs, which is relevant to understanding the chemical
structure of the progenitors of protoplanetary systems and the evolution of
solid materials. Water plays an important role as a reaction bed for rich
chemistry and is an indispensable requirement for life as known on Earth. We
present our analysis of NAOS-CONICA/VLT spectroscopy of water ice at 3um for
the TTauri star YLW 16A in the rho-Ophiuchi molecular cloud. We obtained
spectra for different regions of the circumstellar environment. The observed
absorption profiles are deconvolved with the mass extinction profiles of
amorphous and crystallized ice measured in laboratory. We take into account
both absorption and scattering by ice grains. Water ice in YLW 16A is detected
with optical depths of between tau=1.8 and tau=2.5. The profiles that are
measured can be fitted predominantly by the extinction profiles of small grains
(0.1um - 0.3um) with a small contribution from large grains (<10%). However, an
unambiguous trace of grain growth cannot be found. We detected crystallized
water ice spectra that have their origin in different regions of the
circumstellar environment of the TTauri star YLW 16A. The crystallinity
increases in the upper layers of the circumstellar disk, while only amorphous
grains exist in the bipolar envelope. As in studies of silicate grains in
TTauri objects, the higher crystallinity in the upper layers of the outer disk
regions implies that water ice crystallizes and remains crystallized close to
the disk atmosphere where water ice is shielded against hard irradiation.Comment: 17 pages, 13 figures, 4 tables; accepted by Astronomy and
Astrophysic
The circumstellar environment of T Tau S at high spatial and spectral resolution
We have obtained the first high spatial (0.05'') and spectral (R~35000)
resolution 2 micron spectrum of the T Tau S tight binary system using adaptive
optics on the Keck II telescope. We have also obtained the first 3.8 and 4.7
micron images that resolve the three components of the T Tau multiple system,
as well as new 1.6 and 2.2 micron images. Together with its very red
near-infrared colors, the spectrum of T Tau Sb shows that this T Tauri star is
extincted by a roughly constant extinction of Av~15 mag, which is probably the
0.7''x0.5'' circumbinary structure recently observed in absorption in the
ultraviolet. T Tau Sa, which is also observed through this screen and is
actively accreting, further possesses a small edge-on disk that is evidenced by
warm (390 K), narrow overtone CO rovibrational absorption features in our
spectrum. We find that T Tau Sa is most likely an intermediate-mass star
surrounded by a semi-transparent 2-3 AU-radius disk whose asymmetries and short
Keplerian rotation explain the large photometric variability of the source on
relatively short timescales. We also show that molecular hydrogen emission
exclusively arises from the gas that surrounds T Tau S and that its spatial and
kinematic structure, while providing suggestive evidence for a jet-like
structure, is highly complex.Comment: accepted for publication in the Astrophysical Journal; 41 pages, 10
figure
Interstellar deuterated ammonia: From NH3 to ND3
We use spectra and maps of NH2D, ND2H, and ND3, obtained with the CSO, IRAM
30m and Arecibo telescopes, to study deuteration processes in dense cores. The
data include the first detection of the hyperfine structure of ND2H. The
emission of ND2H and ND3 does not seem to peak at the positions of the embedded
protostars, but instead at offset positions, where outflow interactions may
occur. A constant ammonia fractionation ratio in star-forming regions is
generally assumed to be consistent with an origin on dust grains. However, in
the pre-stellar cores studied here, the fractionation varies significantly when
going from NH3 to ND3. We present a steady state model of the gas-phase
chemistry for these sources, which includes passive depletion onto dust grains
and multiply saturated deuterated species up to five deuterium atoms (e.g.
CD5+). The observed column density ratios of all four ammonia isotopologues are
reproduced within a factor of 3 for a gas temperature of 10 K. We also predict
that deuterium fractionation remains significant at temperatures up to 20 K. ND
and NHD, which have rotational transitions in the submillimeter domain are
predicted to be abundant.Comment: 14 pages, 12 figures, 12 table
Sub-arcsec imaging of the AB Aur molecular disk and envelope at millimeter wavelengths: a non Keplerian disk
We present sub-arcsecond images of AB Auriga obtained with the IRAM Plateau
de Bure interferometer in the isotopologues of CO, and in continuum at 3 and
1.3 mm. Instead of being centrally peaked, the continuum emission is dominated
by a bright, asymmetric (spiral-like) feature at about 140 AU from the central
star. The large scale molecular structure suggests the AB Aur disk is inclined
between 23 and 43 degrees, but the strong asymmetry of the continuum and
molecular emission prevents an accurate determination of the inclination of the
inner parts. We find significant non-Keplerian motion, with a best fit exponent
for the rotation velocity law of 0.41 +/- 0.01, but no evidence for radial
motions. The disk has an inner hole about 70 AU in radius. The disk is warm and
shows no evidence of depletion of CO. The dust properties suggest the dust is
less evolved than in typical T Tauri disks. Both the spiral-like feature and
the departure from purely Keplerian motions indicates the AB Aur disk is not in
quasi-equilibrium. Disk self-gravity is insufficient to create the
perturbation. This behavior may be related either to an early phase of star
formation in which the Keplerian regime is not yet fully established and/or to
a disturbance of yet unknown origin. An alternate, but unproven, possibility is
that of a low mass companion located about 40 AU from AB Aur.Comment: 10 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
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