6,722 research outputs found
Explosive Disintegration of a Massive Young Stellar System in Orion
Young massive stars in the center of crowded star clusters are expected to
undergo close dynamical encounters that could lead to energetic, explosive
events. However, there has so far never been clear observational evidence of
such a remarkable phenomenon. We here report new interferometric observations
made with the Submillimeter Array (SMA) that indicate the well known enigmatic
wide-angle outflow located in the Orion BN/KL star-forming region to have been
produced by such a violent explosion during the disruption of a massive young
stellar system, and that this was caused by a close dynamical interaction about
500 years ago. This outflow thus belongs to a totally different family of
molecular flows which is not related to the classical bipolar flows that are
generated by stars during their formation process. Our molecular data allow us
to create a 3D view of the debris flow and to link this directly to the well
known Orion H "fingers" farther outComment: Accepted by ApJ Letters The 3D movie can be found in:
ftp://ftp.mpifr-bonn.mpg.de/outgoing/lzapata/movie.gi
Searching for compact radio sources associated to UCHII regions
Ultra-Compact (UC)HII regions represent a very early stage of massive star
formation whose structure and evolution are not yet fully understood.
Interferometric observations in recent years show that some UCHII regions have
associated compact sources of uncertain nature. Based on this, we carried out
VLA 1.3 cm observations in the A configuration of selected UCHII regions in
order to report additional cases of compact sources embedded in UCHII regions.
From the observations, we find 13 compact sources associated to 9 UCHII
regions. Although we cannot establish an unambiguous nature for the newly
detected sources, we assess some of their observational properties. According
to the results, we can distinguish between two types of compact sources. One
type corresponds to sources that probably are deeply embedded in the dense
ionized gas of the UCHII region. These sources are being photo-evaporated by
the exciting star of the region and will last for 10 yr. They may play
a crucial role in the evolution of the UCHII region as the photo-evaporated
material could replenish the expanding plasma and might provide a solution to
the so-called lifetime problem for these regions. The second type of compact
sources is not associated with the densest ionized gas of the region. A few of
these sources appear resolved and may be photo-evaporating objects such as
those of the first type but with significantly lower mass depletion rates. The
rest of sources of this second type appear unresolved and their properties are
varied. We speculate on the similarity between the sources of the second type
and those of the Orion population of radio sources.Comment: 33 pages, 6 figures, 4 tables. Accepted for publication in Ap
Associations between sedentary time, physical activity and bone health among older people using compositional data analysis
Introduction : Aging is associated with a progressive decrease in bone mass (BM), and being physical active is one of the main strategies to combat this continuous loss. Nonetheless, because daily time is limited, time spent on each movement behavior is co-dependent. The aim of this study was to determine the relationship between BM and movement behaviors in elderly people using compositional data analysis.
Methods : We analyzed 871 older people [395 men (76.9 +/- 5.3y) and 476 women (76.7 +/- 4.7y)]. Time spent in sedentary behavior (SB), light physical activity (LPA) and moderate-to-vigorous physical activity (MVPA), was assessed using accelerometry. BM was determined by bone densitometry (DXA). The sample was divided according to sex and bone health indicators.
Results : The combined effect of all movement behaviors (PA and SB) was significantly associated with whole body, leg and femoral region BM in the whole sample (p<0.05), with leg and pelvic BM (p<0.05) in men and, with whole body, arm and leg BM (p<0.05) in women. In men, arm and pelvic BM were negatively associated with SB and whole body, pelvic and leg BM were positively associated with MVPA (p<0.05). In women, whole body and leg BM were positively associated with SB. Arm and whole body BM were positively associated and leg BM was negatively associated with LPA and arm BM was negatively associated with MVPA (p<0.05). Women without bone fractures spent less time in SB and more in LPA and MVPA than the subgroup with bone fractures.
Conclusion : We identified that the positive effect of MVPA relative to the other behaviors on bone mass is the strongest overall effect in men. Furthermore, women might decrease bone fracture risk through PA increase and SB reduction, despite the fact that no clear benefits of PA for bone mass were found
VLA Detection of the Ionized Stellar Winds Arising from Massive Stars in the Galactic Center Arches Cluster
The Galactic center Arches stellar cluster, detected and studied until now
only in the near-infrared, is comprised of at least one hundred massive (M>20
Msun) stars. Here we report the detection at centimeter wavelengths of radio
continuum emission from eight radio sources associated with the cluster. Seven
of these radio sources have rising spectral indices between 4.9 and 8.5 GHz and
coincide spatially with the brightest stars in the cluster, as determine from
JHK photometry and Brackett alpha and Brackett Gamma spectroscopy. Our results
confirm the presence of powerful ionized winds in these stars. The eighth radio
source has a nonthermal spectrum and its nature is yet unclear, but it could be
associated with a lower mass young star in the cluster.Comment: 6 pages, 2 embedded figures, accepted to ApJLetter
- âŠ