40 research outputs found
The Alignment of the Magnetic Field and Collimated Outflows in Star-forming Regions: the Case of NGC 2071
The magnetic field is believed to play a crucial role in the process of star
formation. From the support it provides during the initial collapse of
molecular clouds to the creation of strong collimated jets responsible for
large mass losses, current theories predict its importance in many different
stages during the formation of stars. Here we report on observational evidence
which tests one aspect that can be inferred from these theories: the alignment
between the local magnetic field and collimated bipolar outflows in such
environments. There is good evidence of an alignment in the case of NGC 2071.Comment: 11 pages, 4 figure
Probing the Magnetic Field with Molecular Ion Spectra
Observations of the effect of the magnetic field on its environment are
usually achieved with techniques which rely on the interaction with the spin of
the particles under study. Because of the relative weakness of this effect,
extraction of the field characteristics proves to be a most challenging task.
We take a totally different approach to the problem and show that the
manifestation of the magnetic field can be directly observed by means of a
comparison of the spectra of molecular ions with those of neutral molecules.
This takes advantage of the strong cyclotron interaction between the ions and
the field, but requires the presence of flows or turbulent motion in the gas.
We compare our theory to data obtained on the OMC-1, OMC-2, OMC-3 and DR21(OH)
molecular clouds.Comment: 16 pages, 3 figures, 2 table
An integral gated mode single photon detector at telecom wavelengths
We demonstrate an integral gated mode single photon detector at telecom
wavelengths. The charge number of an avalanche pulse rather than the peak
current is monitored for single-photon detection. The transient spikes in
conventional gated mode operation are canceled completely by integrating, which
enables one to improve the performance of single photon detector greatly with
the same avalanche photodiode. This method has achieved a detection efficiency
of 29.9% at the dark count probability per gate equal to 5.57E-6/gate
(1.11E-6/ns) at 1550nm.Comment: word to PDF, 3 pages with 4 figure
IRC+10216's Innermost Envelope -- The eSMA's View
We used the Extended Submillimeter Array (eSMA) in its most extended
configuration to investigate the innermost (within a radius of 290 R* from the
star) circumstellar envelope (CSE) of IRC+10216. We imaged the CSE using HCN
and other molecular lines with a beam size of 0."22 x 0."46, deeply into the
very inner edge (15 R*) of the envelope where the expansion velocity is only 3
km/s. The excitation mechanism of hot HCN and KCl maser lines is discussed. HCN
maser components are spatially resolved for the first time on an astronomical
object. We identified two discrete regions in the envelope: a region with a
radius of . 15 R*, where molecular species have just formed and the gas has
begun to be accelerated (region I) and a shell region (region II) with a radius
of 23 R* and a thickness of 15 R*, whose expansion velocity has reached up to
13 km/s, nearly the terminal velocity of 15 km/s. The SiS line detected
in region I shows a large expansion velocity of 16 km/s due to strong wing
components, indicating that the emission may arise from a shock region in the
innermost envelope. In region II, the P.A. of the most copious mass loss
direction was found to be 120 +/- 10 degrees, which may correspond to the
equatorial direction of the star. Region II contains a torus-like feature.
These two regions may have emerged due to significant differences in the size
distributions of the dust particles in the two regions.Comment: 26 pages, 8 figures, accepted for publication in The Astrophysical
Journal. Please find the pdf at
http://www.submm.caltech.edu/~hs/astroph/0904.0280.pdf and the ps file at
http://www.submm.caltech.edu/~hs/astroph/0904.0280.p
A Comprehensive Survey of Hydrogen Chloride in the Galaxy
We report new observations of the fundamental transition of HCl (at
625.918GHz) toward a sample of 25 galactic star-forming regions, molecular
clouds, and evolved stars, carried out using the Caltech Submillimeter
Observatory. Fourteen sources in the sample are also observed in the
corresponding H\tscl\ transition (at 624.978GHz). We have obtained
clear detections in all but four of the targets, often in emission. Absorptions
against bright background continuum sources are also seen in nine cases,
usually involving a delicate balance between emission and absorption features.
From RADEX modeling, we derive gas densities and HCl column densities for
sources with HCl emission. HCl is found in a wide range of environments, with
gas densities ranging from to ~cm. The HCl abundance
relative to H is in the range of . Comparing with the
chlorine abundance in the solar neighborhood, this corresponds to a chlorine
depletion factor of up to 400, assuming that HCl accounts for one third
of the total chlorine in the gas phase. The [\tfcl]/[\tscl] isotopic ratio is
rather varied, from unity to 5, mostly lower than the terrestrial value
of 3.1. Such variation is highly localized, and could be generated by the
nucleosynthesis in supernovae, which predicts a \tscl\ deficiency in most
models. The lower ratios seen in W3IRS4 and W3IRS5 likely confine the
progenitors of the supernovae to stars with relatively large mass
(\ga25M_\sun) and high metallicity (Z0.02).Comment: 11 pages, 5 figures, accepted by Ap
On the Measurement of the Magnitude and Orientation of the Magnetic Field in Molecular Clouds
We demonstrate that the combination of Zeeman, polarimetry and ion-to-neutral
molecular line width ratio measurements permits the determination of the
magnitude and orientation of the magnetic field in the weakly ionized parts of
molecular clouds. Zeeman measurements provide the strength of the magnetic
field along the line of sight, polarimetry measurements give the field
orientation in the plane of the sky and the ion-to-neutral molecular line width
ratio determines the angle between the magnetic field and the line of sight. We
apply the technique to the M17 star-forming region using a HERTZ 350 um
polarimetry map and HCO+-to-HCN molecular line width ratios to provide the
first three-dimensional view of the magnetic field in M17.Comment: 37 pages, 12 figures, 3 table
System Design and Optimisation Study on a Novel CCHP System Integrated with a Hybrid Energy Storage System and an ORC
For achieving higher energy transferring efficiency from the resources to the load, the Combined Cooling, Heating, and Power (CCHP) systems have been widely researched and applied as an efficient approach. The key idea of this study is designing a novel structure of a hybrid CCHP system and evaluating its performance. In this research, there is a hybrid energy storage unit enhancing the whole system’s operation flexibility while supplying cooling, heating, and power. An ORC system is integrated into the CCHP system which takes responsibility of absorbing the low-temperature heat source for electricity generation. There are a few research studies focusing on the CCHP systems’ performance with this structure. In order to evaluate the integrated system’s performance, investigation and optimisation work has been conducted with the approaches of experimental studies and modelling simulation. The integrated system’s configuration, the model building process of several key components, the optimisation method, and the case studies are discussed and analysed in this study. The design of the integrated system and the control strategy are displayed in detail. Several sets of dynamic energy demand profiles are selected to evaluate the performance of the integrated system. The simulation study of the system supplying selected scenarios of loads is conducted. A comprehensive evaluation report indicates that the system’s efficiency during each study process differs while supplying different loads. The results include the power supplied by each component, the energy consumed by each type of load, and the efficiency improvements. It is found that the integrated system fully satisfies the selected domestic loads and various selected scenarios of loads with high efficiency. Compared to conventional power plants or CHP systems, the system efficiency enhancement comes from higher amount of recovery waste heat. Especially, the ORC system can absorb the low-temperature heat source for electricity generation. Compared to the original following electrical load (FEL) control strategy, the optimisation process brings overall efficiency improvements. The system’s overall efficiency was increased by from 3%, 3.18%, 2.85%, 17.11%, 8.89%, and 21.7% in the second case studies. Through the whole study, the main challenge lies within the design and the energy management of the integrated system