5,826 research outputs found
Patient problems encountered by psychiatric nurses
Thesis (M.S.)--Boston Universit
A modular set of synthetic spectral energy distributions for young stellar objects
In this paper, I present a new set of synthetic spectral energy distributions
(SEDs) for young stellar objects (YSOs) spanning a wide range of evolutionary
stages, from the youngest deeply embedded protostars to pre-main-sequence stars
with few or no disks. These models include significant improvements on the
previous generation of published models: in particular, the new models cover a
much wider and more uniform region of parameter space, do not include highly
model-dependent parameters, and include a number of improvements that make them
more suited to modeling far-infrared and sub-mm observations of forming stars.
Rather than all being part of a single monolithic set of models, the new models
are split up into sets of varying complexity. The aim of the new set of models
is not to provide the most physically realistic models for young stars, but
rather to provide deliberately simplified models for initial modeling, which
allows a wide range of parameter space to be explored. I present the design of
the model set, and show examples of fitting these models to real observations
to show how the new grid design can help us better understand what can be
determined from limited unresolved observations. The models, as well as a
Python-based fitting tool are publicly available to the community.Comment: Accepted for publication in Astronomy and Astrophysics. The models
are available at http://doi.org/10.5281/zenodo.16673
The present-day star formation rate of the Milky-Way determined from Spitzer detected young stellar objects
We present initial results from a population synthesis model aimed at
determining the star formation rate of the Milky-Way. We find that a total star
formation rate of 0.68 to 1.45 Msun/yr is able to reproduce the observed number
of young stellar objects in the Spitzer/IRAC GLIMPSE survey of the Galactic
plane, assuming simple prescriptions for the 3D Galactic distributions of YSOs
and interstellar dust, and using model SEDs to predict the brightness and color
of the synthetic YSOs at different wavelengths. This is the first Galaxy-wide
measurement derived from pre-main-sequence objects themselves, rather than
global observables such as the total radio continuum, Halpha, or FIR flux. The
value obtained is slightly lower than, but generally consistent with previously
determined values. We will extend this method in the future to fit the
brightness, color, and angular distribution of YSOs, and simultaneously make
use of multiple surveys, to place constraints on the input assumptions, and
reduce uncertainties in the star formation rate estimate. Ultimately, this will
be one of the most accurate methods for determining the Galactic star formation
rate, as it makes use of stars of all masses (limited only by sensitivity)
rather than solely massive stars or indirect tracers of massive stars.Comment: 12 pages, 3 figures, Published in the Astrophysical Journal Letter
A study to determine the extent of instruction of individual income taxes to bookkeeping students in the secondary schools of New England
Thesis (Ed.M.)--Boston Universit
Multiscale Analysis of the Gradient of Linear Polarisation
We propose a new multiscale method to calculate the amplitude of the gradient
of the linear polarisation vector using a wavelet-based formalism. We
demonstrate this method using a field of the Canadian Galactic Plane Survey
(CGPS) and show that the filamentary structure typically seen in gradients of
linear polarisation maps depends strongly on the instrumental resolution. Our
analysis reveals that different networks of filaments are present on different
angular scales. The wavelet formalism allows us to calculate the power spectrum
of the fluctuations seen in gradients of linear polarisation maps and to
determine the scaling behaviour of this quantity. The power spectrum is found
to follow a power law with gamma ~ 2.1. We identify a small drop in power
between scales of 80 < l < 300 arcmin, which corresponds well to the overlap in
the u-v plane between the Effelsberg 100-m telescope and the DRAO 26-m
telescope data. We suggest that this drop is due to undersampling present in
the 26-m telescope data. In addition, the wavelet coefficient distributions
show higher skewness on smaller scales than at larger scales. The spatial
distribution of the outliers in the tails of these distributions creates a
coherent subset of filaments correlated across multiple scales, which trace the
sharpest changes in the polarisation vector P within the field. We suggest that
these structures may be associated with highly compressive shocks in the
medium. The power spectrum of the field excluding these outliers shows a
steeper power law with gamma ~ 2.5.Comment: 12 pages, 12 figure
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