1,242 research outputs found
A study of the social expectations and desires of psychiatric patients.
Includes 7 figures and 25 tables.
Thesis (M.S.)--Boston Universit
The HII region G35.673-00.847: another case of triggered star formation?
As part of a systematic study that we are performing with the aim to increase
the observational evidence of triggered star formation in the surroundings of
HII regions, we analyze the ISM around the HII region G35.673-00.847, a poorly
studied source. Using data from large-scale surveys: Two Micron All Sky Survey,
Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), MIPSGAL,
Galactic Ring Survey (GRS), VLA Galactic Plane Survey (VGPS), and NRAO VLA Sky
Survey (NVSS) we performed a multiwavelength study of G35.673-00.847 and its
surroundings. The mid IR emission, shows that G35.673-00.847 has an almost
semi-ring like shape with a cut towards the galactic west. The radius of this
semi-ring is about 1.5' (~1.6 pc, at the distance of ~3.7 kpc). The distance
was estimated from an HI absorption study and from the analysis of the
molecular gas. Indeed, we find a molecular shell composed by several clumps
distributed around the HII region, suggesting that its expansion is collecting
the surrounding material. We find several YSO candidates over the molecular
shell. Finally, comparing the HII region dynamical age and the fragmentation
time of the molecular shell, we discard the collect and collapse as the
mechanism responsible for the YSOs formation, suggesting other processes such
as radiative driven implosion and/or small-scale Jeans gravitational
instabilities.Comment: Accepted for publication in A&A, 18 October 2010. Some figures were
degraded to reduce file siz
2-D and 3-D Radiation Transfer Models of High-Mass Star Formation
2-D and 3-D radiation transfer models of forming stars generally produce
bluer 1-10 micron colors than 1-D models of the same evolutionary state and
envelope mass. Therefore, 1-D models of the shortwave radiation will generally
estimate a lower envelope mass and later evolutionary state than
multidimensional models. 1-D models are probably reasonable for very young
sources, or longwave analysis (wavelengths > 100 microns). In our 3-D models of
high-mass stars in clumpy molecular clouds, we find no correlation between the
depth of the 10 micron silicate feature and the longwave (> 100 micron) SED
(which sets the envelope mass), even when the average optical extinction of the
envelope is >100 magnitudes. This is in agreement with the observations of
Faison et al. (1998) of several UltraCompact HII (UCHII) regions, suggesting
that many of these sources are more evolved than embedded protostars.
We have calculated a large grid of 2-D models and find substantial overlap
between different evolutionary states in the mid-IR color-color diagrams. We
have developed a model fitter to work in conjunction with the grid to analyze
large datasets. This grid and fitter will be expanded and tested in 2005 and
released to the public in 2006.Comment: 10 pages, 8 figures, to appear in the proceedings of IAU Symp 227,
Massive Star Birth: A Crossroads of Astrophysics, (Cesaroni R., Churchwell
E., Felli M., Walmsley C. editors
A self-consistent model of Galactic stellar and dust infrared emission and the abundance of polycyclic aromatic hydrocarbons
We present a self-consistent three-dimensional Monte-Carlo radiative transfer
model of the stellar and dust emission in the Milky-Way, and have computed
synthetic observations of the 3.6 to 100 microns emission in the Galactic
mid-plane. In order to compare the model to observations, we use the GLIMPSE,
MIPSGAL, and IRAS surveys to construct total emission spectra, as well as
longitude and latitude profiles for the emission. The distribution of stars and
dust is taken from the SKY model, and the dust emissivities includes an
approximation of the emission from polycyclic aromatic hydrocarbons in addition
to thermal emission. The model emission is in broad agreement with the
observations, but a few modifications are needed to obtain a good fit. Firstly,
by adjusting the model to include two major and two minor spiral arms rather
than four equal spiral arms, the fit to the longitude profiles for |l|>30
degrees can be improved. Secondly, introducing a deficit in the dust
distribution in the inner Galaxy results in a better fit to the shape of the
IRAS longitude profiles at 60 and 100 microns. With these modifications, the
model fits the observed profiles well, although it systematically
under-estimates the 5.8 and 8.0 microns fluxes. One way to resolve this
discrepancy is to increase the abundance of PAH molecules by 50% compared to
the original model, although we note that changes to the dust distribution or
radiation field may provide alternative solutions. Finally, we use the model to
quantify which stellar populations contribute the most to the heating of
different dust types, and which stellar populations and dust types contribute
the most to the emission at different wavelengths.Comment: Published in A&A. This version has been revised (compared to the
published version) to include additional references to previous work. Scripts
to reproduce the results in this paper can be found as supplementary material
on the A&A site, or at https://github.com/hyperion-rt/paper-galaxy-rt-mode
The environment of the infrared dust bubble N65: a mutiwavelength study
AIMS: We investigate the environment of the infrared dust bubble N65 and
search for evidence of triggered star formation in its surroundings. METHODS:
We performed a multiwavelength study of the region around N65 with data taken
from large-scale surveys: Two Micron All Sky Survey, GLIMPSE, MIPSGAL, SCUBA,
and GRS. We analyzed the distribution of the molecular gas and dust in the
environment of N65 and performed infrared photometry and spectral analysis of
point sources to search for young stellar objects and identify the ionizing
star candidates. RESULTS: We found a molecular cloud that appears to be
fragmented into smaller clumps along the N65 PDR. This indicates that the
so-called collect and collapse process may be occurring. Several young stellar
objects are distributed among the molecular clumps. They may represent a second
generation of stars whose formation was triggered by the bubble expanding into
the molecular gas. We dentified O-type stars inside N65, which are the most
reliable ionizing star candidates.Comment: 15 pages, 10 figures, accepted for publication in A&A. Figures
degraded to reduce file siz
Does globalisation affect crime? theory and evidence
Globalization skeptics argue that trade liberalization has high social costs, including an increase in expropriative behavior such as civil-conflict, coercion of labor and crime. We show that a theoretical relationship between trade and expropriation exists, but the sign differs for developed and developing economies. We verify this empirically using data on crime rates. Specifically we find trade liberalization,as measured by both higher openness and lower import duty rates, tends to increase burglaries and theft in very labor abundant countries. For other countries, however,we find that trade liberalization has either a small negative effect on crime,or no effect, depending on the country’s capital abundance
The tyranny of distance and the gravity of resources
To what extent does geography remain an important determinant of comparative advantage and factor incomes in resource markets? We estimate gravity models for resources and find that some minerals and fuels, particularly Iron Ore and Gas, do have very high elasticities of trade with respect to distance. To assess the implications of this we then consider a simple counterfactual where location advantages are eliminated. We find that for a few countries, including Australia and New Zealand, distance barriers have a large impact of their market share
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