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Diagnostic Applications for Micro-Synchrophasor Measurements
This report articulates and justifies the preliminary selection of diagnostic applications for data from micro-synchrophasors (µPMUs) in electric power distribution systems that will be further studied and developed within the scope of the three-year ARPA-e award titled Micro-synchrophasors for Distribution Systems
Envelope structure of deeply embedded young stellar objects in the Serpens Molecular Cloud
Aperture synthesis and single-dish (sub) millimeter molecular lines and
continuum observations reveal in great detail the envelope structure of deeply
embedded young stellar objects (SMM1, SMM2, SMM3, SMM4) in the densely
star-forming Serpens Molecular Cloud. Resolved millimeter continuum emission
constrains the density structure to a radial power law with index -2.0 +/- 0.5,
and envelope masses of 8.7, 3.0, and 5.3 M_sol for SMM1, SMM3, and SMM4. The
core SMM2 does not seem to have a central condensation and may not have formed
a star yet. The molecular line observations can be described by the same
envelope model, if an additional, small amount of warm (100 K) material is
included. This probably corresponds to the inner few hundred AU of the envelope
were the temperature is high. In the interferometer beam, the molecular lines
reveal the inner regions of the envelopes, as well as interaction of the
outflow with the surrounding envelope. Bright HCO+ and HCN emission outlines
the cavities, while SiO and SO trace the direct impact of the outflow on
ambient gas. Taken together, these observations provide a first comprehensive
view of the physical and chemical structure of the envelopes of deeply embedded
young stellar objects in a clustered environment on scales between 1000 and
10,000 AU.Comment: 46 pages, incl. 12 postscript figures, uses ApJ latex and psfig
macro
Chemical Modelling of Young Stellar Objects, I. Method and Benchmarks
Upcoming facilities such as the Herschel Space Observatory or ALMA will
deliver a wealth of molecular line observations of young stellar objects
(YSOs). Based on line fluxes, chemical abundances can then be estimated by
radiative transfer calculations. To derive physical properties from abundances,
the chemical network needs to be modeled and fitted to the observations. This
modeling process is however computationally exceedingly demanding, particularly
if in addition to density and temperature, far UV (FUV) irradiation, X-rays,
and multi-dimensional geometry have to be considered.
We develop a fast tool, suitable for various applications of chemical
modeling in YSOs. A grid of the chemical composition of the gas having a
density, temperature, FUV irradiation and X-ray flux is pre-calculated as a
function of time. A specific interpolation approach is developed to reduce the
database to a feasible size. Published models of AFGL 2591 are used to verify
the accuracy of the method. A second benchmark test is carried out for FUV
sensitive molecules. The novel method for chemical modeling is more than
250,000 times faster than direct modeling and agrees within a mean factor of
1.35. The tool is distributed for public use.
In the course of devloping the method, the chemical evolution is explored: We
find that X-ray chemistry in envelopes of YSOs can be reproduced by means of an
enhanced cosmic-ray ionization rate. We further find that the abundance of CH+
in low-density gas with high ionization can be enhanced by the recombination of
doubly ionized carbon (C++) and suggest a new value for the initial abundance
of the main sulphur carrier in the hot-core.Comment: Accepted by ApJS. 24 pages, 15 figures. A version with higher
resolution images is available from
http://www.astro.phys.ethz.ch/staff/simonbr/papgridI.pdf . Online data
available at http://www.astro.phys.ethz.ch/chemgrid.html . Second paper of
this series of papers available at arXiv:0906.058
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