4,014 research outputs found
Circumbinary Molecular Rings Around Young Stars in Orion
We present high angular resolution 1.3 mm continuum, methyl cyanide molecular
line, and 7 mm continuum observations made with the Submillimeter Array and the
Very Large Array, toward the most highly obscured and southern part of the
massive star forming region OMC1S located behind the Orion Nebula. We find two
flattened and rotating molecular structures with sizes of a few hundred
astronomical units suggestive of circumbinary molecular rings produced by the
presence of two stars with very compact circumstellar disks with sizes and
separations of about 50 AU, associated with the young stellar objects 139-409
and 134-411. Furthermore, these two circumbinary rotating rings are related to
two compact and bright {\it hot molecular cores}. The dynamic mass of the
binary systems obtained from our data are 4 M for 139-409 and
0.5 M for 134-411. This result supports the idea that
intermediate-mass stars will form through {\it circumstellar disks} and
jets/outflows, as the low mass stars do. Furthermore, when intermediate-mass
stars are in multiple systems they seem to form a circumbinary ring similar to
those seen in young, multiple low-mass systems (e.g., GG Tau and UY Aur).Comment: Accepted by Astronomy and Astrophysic
Strongly misaligned triple system in SR 24 revealed by ALMA
We report the detection of the 1.3 mm continuum and the molecular emission of the disks of the young triple system SR24 by analyzing ALMA (The Atacama Large Millimeter/Submillimter Array) subarcsecond archival observations. We estimate the mass of the disks (0.025 M ⊙ and 4 Ă— 10‑5 M ⊕ for SR24S and SR24N, respectively) and the dynamical mass of the protostars (1.5 M ⊙ and 1.1 M ⊙). A kinematic model of the SR24S disk to fit its C18O (2-1) emission allows us to develop an observational method to determine the tilt of a rotating and accreting disk. We derive the size, inclination, position angle, and sense of rotation of each disk, finding that they are strongly misaligned (108^circ ) and possibly rotate in opposite directions as seen from Earth, in projection. We compare the ALMA observations with 12CO SMA archival observations, which are more sensitive to extended structures. We find three extended structures and estimate their masses: a molecular bridge joining the disks of the system, a molecular gas reservoir associated with SR24N, and a gas streamer associated with SR24S. Finally, we discuss the possible origin of the misaligned SR24 system, concluding that a closer inspection of the northern gas reservoir is needed to better understand it. Fil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. GobernaciĂłn. ComisiĂłn de Investigaciones CientĂficas. Instituto Argentino de RadioastronomĂa. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto Argentino de RadioastronomĂa; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Zapata, L. A.. Universidad Nacional AutĂłnoma de MĂ©xico; MĂ©xicoFil: Gabbasov, R.. Universidad AutĂłnoma del Estado de Hidalgo; MĂ©xic
Analysis of Nd3+:glass, solar-pumped, high-powr laser systems
The operating characteristics of Nd(3+):glass lasers energized by a solar concentrator were analyzed for the hosts YAG, silicate glass, and phosphate glass. The modeling is based on the slab zigzag laser geometry and assumes that chemical hardening methods for glass are successful in increasing glass hardness by a factor of 4. On this basis, it was found that a realistic 1-MW solar-pumped laser might be constructed from phosphate glass 4 sq m in area and 2 mm thick. If YAG were the host medium, a 1-MW solar-pumped laser need only be 0.5 sq m in area and 0.5 cm thick, which is already possible. In addition, Nd(3+) doped glass fibers were found to be excellent solar-pumped laser candidates. The small diameter of fibers eliminates thermal stress problems, and if their diameter is kept small (10 microns), they propagate a Gaussian single mode which can be expanded and transmitted long distances in space. Fiber lasers could then be used for communications in space or could be bundled and the individual beams summed or phase-matched for high-power operation
Spectroscopic measurements of solar wind generation
Spectroscopically observable quantities are described which are sensitive to the primary plasma parameters of the solar wind's source region. The method is discussed in which those observable quantities are used as constraints in the construction of empirical models of various coronal structures. Simulated observations are used to examine the fractional contributions to observed spectral intensities from coronal structures of interest which co-exist with other coronal structures along simulated lines-of-sight. The sensitivity of spectroscopic observables to the physical parameters within each of those structures is discussed
BOOTSTRAPPING IN VECTOR AUTOREGRESSIONS: AN APPLICATION TO THE PORK SECTOR
Standard bootstrap method is used to generate confidence intervals (CIs) of impulse response functions of VAR and SVAR models in the pork sector. In the VAR model, the bootstrap method does not produce significant different results from Monte Carlo simulations. In the SVAR analysis, on the other hand, the bootstrap CIs are significantly different from Monte Carlo CIs after a six period forecast intervals. This suggests that the choice of method used to measure reliability of IRFs is not trivial. Furthermore, bootstrap CIs in SVAR model seem to be more stable than MC CIs, which tend to be wider in the longer horizons.Research Methods/ Statistical Methods,
The APEX-CHAMP+ view of the Orion Molecular Cloud 1 core - Constraining the excitation with submillimeter CO multi-line observations
A high density portion of the Orion Molecular Cloud 1 (OMC-1) contains the
prominent, warm Kleinmann-Low (KL) nebula that is internally powered by an
energetic event plus a farther region in which intermediate to high mass stars
are forming. Its outside is affected by ultraviolet radiation from the
neighboring Orion Nebula Cluster and forms the archetypical photon-dominated
region (PDR) with the prominent bar feature. Its nearness makes the OMC-1 core
region a touchstone for research on the dense molecular interstellar medium and
PDRs. Using the Atacama Pathfinder Experiment telescope (APEX), we have imaged
the line emission from the multiple transitions of several carbon monoxide (CO)
isotopologues over the OMC-1 core region. Our observations employed the 2x7
pixel submillimeter CHAMP+ array to produce maps (~ 300 arcsec x 350 arcsec) of
12CO, 13CO, and C18O from mid-J transitions (J=6-5 to 8-7). We also obtained
the 13CO and C18O J=3-2 images toward this region. The 12CO line emission shows
a well-defined structure which is shaped and excited by a variety of phenomena,
including the energetic photons from hot, massive stars in the nearby Orion
Nebula's central Trapezium cluster, active high- and intermediate-mass star
formation, and a past energetic event that excites the KL nebula. Radiative
transfer modeling of the various isotopologic CO lines implies typical H2
densities in the OMC-1 core region of ~10^4-10^6 cm^-3 and generally elevated
temperatures (~ 50-250 K). We estimate a warm gas mass in the OMC-1 core region
of 86-285 solar masses.Comment: 11 pages, 9 figures, accepted by A&
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