73 research outputs found
Ultracompact HII regions with extended emission: The case of G43.89-0.78 and its molecular environment
The Karl Jansky Very Large Array (VLA), Owens Valley Radio Observatory
(OVRO), Atacama Large Millimetric Array (ALMA), and the infrared
\textit{Spitzer} observatories, are powerful facilities to study massive star
formation regions and related objects such as ultra--compact (UC) \hii regions,
molecular clumps, and cores. We used these telescopes to study the \uchiir
G43.89--0.78. The morphological study at arcminute scales using NVSS and
\textit{Spitzer} data shows that this region is similar to those observed in
the \textit{ bubble--like} structures revealed by \textit{Spitzer}
observations. With this result, and including a physical characterization based
on 3.6 cm data, we suggest G43.89--0.78 be classified as an \uchiir with
Extended Emission because it meets the operational definition given in this
paper comparing radio continuum data at 3.6 and 20~cm. For the ultra-compact
component, we use VLA data to obtain physical parameters at 3.6~cm confirming
this region as an \uchii region. Using ALMA observations, we detect the
presence of a dense ( cm) and small ( 2.0\arcsec;
0.08 pc) molecular clump with a mass of 220 M and average kinetic
temperature of 21~K, located near to the \uchii region. In this clump,
catalogued as G43.890--0.784, water masers also exist, possibly tracing a
bipolar outflow. We discover in this vicinity two additional clumps which we
label as G43.899--0.786 (T = 50 K; M = 11 M), and G43.888--0.787
(T = 50 K; M = 15 M).Comment: 13 pages, 8 figures, 2 tables. Accepted for publication in the
Monthly Notices of the Royal Astronomical Society Main Journal (2020
From Ultracompact to Extended HII Regions. II: Cloud Gravity and Stellar Motion
The dynamical evolution of HII regions with and without stellar motion in
dense, structured molecular clouds is studied. Clouds are modeled in
hydrostatic equilibrium, with gaussian central cores and external halos that
obey r**-2 and r**-3 density power laws. The cloud gravity is included as a
time-independent, external force. Stellar velocities of 0, 2, 8, and 12 km/s
are considered. When stellar motion is included, stars move from the central
core to the edge of the cloud, producing transitions from ultracompact to
extended HII regions as the stars move into lower density regions. The opposite
behavior occurs when stars move toward the cloud cores. The main conclusion of
our study is that ultracompact HII regions are pressure-confined entities while
they remain embedded within dense cores. The confinement comes from ram and/or
ambient pressures. The survival of ultracompact regions depends on the position
of the star with respect to the core, the stellar life-time, and the core
crossing time. Stars with velocities less than the cloud dispersion velocity
can produce cometary shapes smaller than 0.1 pc at times of 20,000 yr or more.
The sequence Ultracompact to Compact to Extended HII region shows a variety of
unpredictable structures due to ionization-shock front instability. Some
ultracompact HII regions with a core-halo morphology might be explained by
self-blocking effects, when stars overtake and ionize leading, piled-up clumps
of neutral gas. We use thermal energy to support the cloud against gravity; the
results remain the same if other types of isotropic cloud support are used.Comment: 27 pages, 7 ps figures, 5 png figures; submitted to Astrophysical
Journa
Compact Radio Sources in Orion: New Detections, Time Variability, and Objects in OMC-1S
We present the analysis of four 3.6 cm radio continuum archival observations
of Orion obtained using the Very Large Array in its A-configuration, with
angular resolution. The observations were made during the period
1994-1997. In a region of , we detect a total of 77 compact radio
sources. Of the total of detected sources, 54 are detected in one or more of
the individual observations and 36 of these show time variability (by more than
30%) between the observed epochs. A deep image made from averaging all data
shows an additional 23 faint sources, in the range of 0.1 to 0.3 mJy. Of the
total of 77 sources, 39 are new centimeter detections. However, only 9 of the
77 sources do not have a previously reported counterpart at near-infrared,
optical, or X-ray wavelengths. In particular, we detect three faint sources in
the OMC-1S region that may be related to the sources that power the multiple
outflows that emanate from this part of the Orion nebula. %We discuss the
nature of these sources and its relation with the %near-infrared, optical, and
X-ray objects in the region.Comment: 29 pages, 9 figure
Partial Resistance to Peroxisome Proliferator–Activated Receptor-α Agonists in ZDF Rats Is Associated With Defective Hepatic Mitochondrial Metabolism
OBJECTIVE—Fluxes through mitochondrial pathways are defective in insulin-resistant skeletal muscle, but it is unclear whether similar mitochondrial defects play a role in the liver during insulin resistance and/or diabetes. The purpose of this study is to determine whether abnormal mitochondrial metabolism plays a role in the dysregulation of both hepatic fat and glucose metabolism during diabetes
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