31 research outputs found
Thermal Jeans fragmentation within 1000 AU in OMC-1S
We present subarcsecond 1.3 mm continuum ALMA observations towards the Orion
Molecular Cloud 1 South (OMC-1S) region, down to a spatial resolution of 74 AU,
which reveal a total of 31 continuum sources. We also present subarcsecond 7 mm
continuum VLA observations of the same region, which allow to further study
fragmentation down to a spatial resolution of 40 AU. By applying a Mean Surface
Density of Companions method we find a characteristic spatial scale at ~560 AU,
and we use this spatial scale to define the boundary of 19 `cores' in OMC-1S as
groupings of millimeter sources. We find an additional characteristic spatial
scale at ~2900 AU, which is the typical scale of the filaments in OMC-1S,
suggesting a two-level fragmentation process. We measured the fragmentation
level within each core and find a higher fragmentation towards the southern
filament. In addition, the cores of the southern filament are also the densest
(within 1100 AU) cores in OMC-1S. This is fully consistent with previous
studies of fragmentation at spatial scales one order of magnitude larger, and
suggests that fragmentation down to 40 AU seems to be governed by thermal Jeans
processes in OMC-1S.Comment: Accepted to Ap
Gravity or turbulence? -III. Evidence of pure thermal Jeans fragmentation at ~0.1 pc scale
We combine previously published interferometric and single-dish data of
relatively nearby massive dense cores that are actively forming stars to test
whether their `fragmentation level' is controlled by turbulent or thermal
support. We find no clear correlation between the fragmentation level and
velocity dispersion, nor between the observed number of fragments and the
number of fragments expected when the gravitationally unstable mass is
calculated including various prescriptions for `turbulent support'. On the
other hand, the best correlation is found for the case of pure thermal Jeans
fragmentation, for which we infer a core formation efficiency around 13 per
cent, consistent with previous works. We conclude that the dominant factor
determining the fragmentation level of star-forming massive dense cores at 0.1
pc scale seems to be thermal Jeans fragmentation.Comment: accepted in MNRA
An SiO Toroid and Wide-angle Outflow associated with the Massive Protostar W75N(B)-VLA2
We have carried out ALMA observations of the massive star-forming region
W75N(B), which contains the massive protostars VLA1, VLA2, and VLA3.
Particularly, VLA2 is an enigmatic protostar associated with a wind-driven
HO maser shell, which has evolved from an almost isotropic outflow to a
collimated one in just 20 years. The shell expansion seemed to be halted by an
obstacle located to the northeast of VLA2. Here we present our findings from
observing the 1.3 mm continuum and HCO and SiO emission lines. Within a
region of ( au) diameter, we have detected 40 compact
mm-continuum sources, three of them coinciding with VLA1, VLA2, and VLA3. While
the HCO emission is mainly distributed in a fragmented structure around the
three massive protostars, but without any of the main HCO clumps spatially
coinciding with them, the SiO is highly concentrated on VLA2, indicating the
presence of very strong shocks generated near this protostar. The SiO emission
is clearly resolved into an elongated structure (; au390 au) perpendicular to the major axis of the wind-driven maser
shell. The structure and kinematics of the SiO emission are consistent with a
toroid and a wide-angle outflow surrounding a central mass of
M, thus supporting previous theoretical predictions regarding the
evolution of the outflow. Additionally, we have identified the expected
location and estimated the gas density of the obstacle that is hindering the
expansion of the maser shell.Comment: To be published in The Astrophysical Journal Letters. Sixteen pages,
seven figures. Updated metadat
Educación ambiental y sociedad. Saberes locales para el desarrollo y la sustentabilidad
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