137 research outputs found
Rotationally-Driven Fragmentation for the Formation of the Binary Protostellar System L1551 IRS 5
Either bulk rotation or local turbulence is widely invoked to drive
fragmentation in collapsing cores so as to produce multiple star systems. Even
when the two mechanisms predict different manners in which the stellar spins
and orbits are aligned, subsequent internal or external interactions can drive
multiple systems towards or away from alignment thus masking their formation
process. Here, we demonstrate that the geometrical and dynamical relationship
between the binary system and its surrounding bulk envelope provide the crucial
distinction between fragmentation models. We find that the circumstellar disks
of the binary protostellar system L1551 IRS 5 are closely parallel not just
with each other but also with their surrounding flattened envelope.
Measurements of the relative proper motion of the binary components spanning
nearly 30 yr indicate an orbital motion in the same sense as the envelope
rotation. Eliminating orbital solutions whereby the circumstellar disks would
be tidally truncated to sizes smaller than are observed, the remaining
solutions favor a circular or low-eccentricity orbit tilted by up to
25 from the circumstellar disks. Turbulence-driven fragmentation
can generate local angular momentum to produce a coplanar binary system, but
which bears no particular relationship with its surrounding envelope. Instead,
the observed properties conform with predictions for rotationally-driven
fragmentation. If the fragments were produced at different heights or on
opposite sides of the midplane in the flattened central region of a rotating
core, the resulting protostars would then exhibit circumstellar disks parallel
with the surrounding envelope but tilted from the orbital plane as is observed.Comment: Accepted for publication in Ap
Millimeter- and Submillimeter-Wave Observations of the OMC-2/3 Region. II. Observational Evidence for Outflow-Triggered Star Formation in the OMC-2 FIR 3/4 Region
We have carried out the observations of the OMC-2 FIR 3/4 region with the NMA
and ASTE in the HCO (1--0), CO (3--2, 1--0), SiO (=0,
=2--1), CS (2--1), and CHOH (=7--6) lines and in the 3.3 mm
continuum emission. Our NMA observations in the HCO emission have
revealed 0.07 pc-scale dense gas associated with FIR 4. The CO
(3--2,1--0) emission shows high-velocity blue and red shifted components at the
both north-east and south-west of FIR 3, suggesting a molecular outflow nearly
along the plane of the sky driven by FIR 3. The SiO and the CHOH emission
are detected around the interface between the outflow and the dense gas.
Furthermore, the CO (1--0) emission shows an L-shaped structure in the
P-V diagram. These results imply presence of the shock due to the interaction
between the molecular outflow driven by FIR 3 and the dense gas associated with
FIR 4. Moreover, our high angular-resolution observations of FIR 4 in the 3.3
mm continuum emission have first found that FIR 4 consists of eleven dusty
cores. The separation among these cores is on the same order of the Jeans
length, suggesting that the fragmentation into these cores has been caused by
the gravitational instability. The time scale of the fragmentation is similar
to the time scale of the interaction between the molecular outflow and the
dense gas. We suggest that the interaction between the molecular outflow from
FIR 3 and the dense gas associated with FIR 4 triggered the fragmentation into
these dusty cores, and hence the next generation the cluster formation.Comment: 13 pages, 9 figures. Accepted by Ap
Molecular Evolution in Collapsing Prestellar Cores
We have investigated the evolution and distribution of molecules in
collapsing prestellar cores via numerical chemical models, adopting the
Larson-Penston solution and its delayed analogues to study collapse. Molecular
abundances and distributions in a collapsing core are determined by the balance
among the dynamical, chemical and adsorption time scales. When the central
density n_H of a prestellar core with the Larson-Penston flow rises to 3 10^6
cm^{-3}, the CCS and CO column densities are calculated to show central holes
of radius 7000 AU and 4000 AU, respectively, while the column density of N2H+
is centrally peaked. These predictions are consistent with observations of
L1544. If the dynamical time scale of the core is larger than that of the
Larson-Penston solution owing to magnetic fields, rotation, or turbulence, the
column densities of CO and CCS are smaller, and their holes are larger than in
the Larson-Penston core with the same central gas density. On the other hand,
N2H+ and NH3 are more abundant in the more slowly collapsing core. Therefore,
molecular distributions can probe the collapse time scale of prestellar cores.
Deuterium fractionation has also been studied via numerical calculations. The
deuterium fraction in molecules increases as a core evolves and molecular
depletion onto grains proceeds. When the central density of the core is n_H=3
10^6 cm^{-3}, the ratio DCO+/HCO+ at the center is in the range 0.06-0.27,
depending on the collapse time scale and adsorption energy; this range is in
reasonable agreement with the observed value in L1544.Comment: 21 pages, 17 figure
New Panoramic View of CO and 1.1 mm Continuum Emission in the Orion A Molecular Cloud. I. Survey Overview and Possible External Triggers of Star Formation
We present new, wide and deep images in the 1.1 mm continuum and the
CO (=1-0) emission toward the northern part of the Orion A Giant
Molecular Cloud (Orion-A GMC). The 1.1 mm data were taken with the AzTEC camera
mounted on the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope
in Chile, and the CO (=1-0) data were with the 25 beam receiver
(BEARS) on the NRO 45 m telescope in the On-The-Fly (OTF) mode. The present
AzTEC observations are the widest (\timeform{1.D7}
\timeform{2.D3}, corresponding to 12 pc 17 pc) and the
highest-sensitivity (9 mJy beam) 1.1 mm dust-continuum imaging of
the Orion-A GMC with an effective spatial resolution of 40\arcsec. The
CO (=1-0) image was taken over the northern \timeform{1D.2}
\times\timeform{1D.2} (corresponding 9 pc 9 pc) area with a
sensitivity of 0.93 K in , a velocity resolution of 1.0 km
s, and an effective spatial resolution of 21\arcsec. With these data,
together with the MSX 8 m, Spitzer 24 m and the 2MASS data, we have
investigated the detailed structure and kinematics of molecular gas associated
with the Orion-A GMC and have found evidence for interactions between molecular
clouds and the external forces that may trigger star formation. Two types of
possible triggers were revealed; 1) Collision of the diffuse gas on the cloud
surface, particularly at the eastern side of the OMC-2/3 region, and 2)
Irradiation of UV on the pre-existing filaments and dense molecular cloud
cores. Our wide-field and high-sensitivity imaging have provided the first
comprehensive view of the potential sites of triggered star formation in the
Orion-A GMC.Comment: 32 pages, 20 figures, accepted for publication in PAS
Interaction between the Outflow and the Core in IRAM 04191+1522
We have carried out mapping observations of the molecular core associated
with the young Class 0 protostar, IRAM 04191+1522, in the CH3OH (JK=2K-1K) and
C34S (J=2-1) lines using the 45 m telescope at Nobeyama Radio Observatory. As
well as an elongated envelope associated with the protostellar formation (size
\~0.07 pc x 0.04 pc, mass ~ 2.3 Mo), two compact (~ 0.03 pc) condensations were
found in the CH3OH line at the southern edge of the elongated envelope, where
the blueshifted CO outflow emerging from the protostar is located. In contrast
to the elongated envelope, those compact CH3OH condensations show much larger
line width (up to 2.0 km s-1) with centroid velocities blueshifted by ~ 0.8 km
s-1. The compact condensations have momenta (~ 0.06 Mo km s-1) comparable to
that of the blueshifted molecular outflow. These results suggest that the
compact condensations are probably formed in the course of interaction between
the outflow and the ambient gas surrounding the protostar, and that such
interaction may cause dissipation of a part of the ambient gas. No drastic,
localized enhancement of the CH3OH abundance is, however, observed toward the
compact condensations, implying that there seems to be no significant shock
heating at the compact condensations. This may be because the CO outflow
velocity (< 10 km s-1) is too low to cause effective heating to release CH3OH
on dust grains into gas phase.Comment: 22 pages, 7 gif figures, uses aastex.cl
Co-existence of acute myeloid leukemia with multilineage dysplasia and Epstein-Barr virus-associated T-cell lymphoproliferative disorder in a patient with rheumatoid arthritis: a case report
Rheumatoid arthritis (RA) is an autoimmune disease mediated by inflammatory processes mainly at the joints. Recently, awareness of Epstein-Barr virus (EBV)-associated T-cell lymphoproliferative disorder (T-LPD) has been heightened for its association with methotraxate usage in RA patients. In the contrary, acute myeloid leukemia with multilineage dysplasia (AML-MLD) has never been documented to be present concomitantly with the above two conditions. In this report we present a case of an autopsy-proven co-existence of AML-MLD and EBV-associated T-LPD in a patient with RA
O2-Filled Swimbladder Employs Monocarboxylate Transporters for the Generation of O2 by Lactate-Induced Root Effect Hemoglobin
The swimbladder volume is regulated by O2 transfer between the luminal space and the blood In the swimbladder, lactic acid generation by anaerobic glycolysis in the gas gland epithelial cells and its recycling through the rete mirabile bundles of countercurrent capillaries are essential for local blood acidification and oxygen liberation from hemoglobin by the “Root effect.” While O2 generation is critical for fish flotation, the molecular mechanism of the secretion and recycling of lactic acid in this critical process is not clear. To clarify molecules that are involved in the blood acidification and visualize the route of lactic acid movement, we analyzed the expression of 17 members of the H+/monocarboxylate transporter (MCT) family in the fugu genome and found that only MCT1b and MCT4b are highly expressed in the fugu swimbladder. Electrophysiological analyses demonstrated that MCT1b is a high-affinity lactate transporter whereas MCT4b is a low-affinity/high-conductance lactate transporter. Immunohistochemistry demonstrated that (i) MCT4b expresses in gas gland cells together with the glycolytic enzyme GAPDH at high level and mediate lactic acid secretion by gas gland cells, and (ii) MCT1b expresses in arterial, but not venous, capillary endothelial cells in rete mirabile and mediates recycling of lactic acid in the rete mirabile by solute-specific transcellular transport. These results clarified the mechanism of the blood acidification in the swimbladder by spatially organized two lactic acid transporters MCT4b and MCT1b
Cuf2 Is a Novel Meiosis-Specific Regulatory Factor of Meiosis Maturation
Meiosis is the specialized form of the cell cycle by which diploid cells produce the haploid gametes required for sexual reproduction. Initiation and progression through meiosis requires that the expression of the meiotic genes is precisely controlled so as to provide the correct gene products at the correct times. During meiosis, four temporal gene clusters are either induced or repressed by a cascade of transcription factors
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