216 research outputs found
L1551NE - Discovery of a Binary Companion
L1551NE is a very young (class 0 or I) low-mass protostar located close to
the well-studied L1551 IRS5. We present here evidence, from 1.3mm continuum
interferometric observations at ~1'' resolution, for a binary companion to
L1551NE. The companion, whose 1.3mm flux density is ~1/3 that of the primary
component, is located 1.43'' (~230 A.U. at 160pc) to the southeast. The
millimeterwave emission from the primary component may have been just barely
resolved, with deconvolved size ~0.82"x0.70" (~131x112 A.U.). The companion
emission was unresolved (<100 A.U.). The pair is embedded within a flattened
circum-binary envelope of size ~5.4'' x 2.3'' (~860 x 370 A.U.). The masses of
the three components (i.e. from the cicumstellar material of the primary star
and its companion, and the envelope) are approximately 0.044, 0.014 and 0.023
Mo respectively.Comment: 8 pages, 1 figur
Detection of Infall Signatures Towards Serpens SMM4
We present the detection of kinematic infall signatures towards the Class 0
protostellar system SMM4 in the Serpens cloud core. We have observed the dense
molecular gas towards the embedded source using millimeter and submillimeter
line transitions of density sensitive molecular tracers. High signal-to-noise
ratio maps obtained in HCO+ J=1-0, J=3-2, and J=4-3, and CS J=2-1 show the
blue-bulge infall signature. The blue-bulge infall signature can be observed in
the centroid velocity maps of protostellar objects when infall dominates over
rotation. The line profiles of HCO+ and CS exhibit the characteristic blue
asymmetric line profile signature consistent with infall. In addition, HCO+ and
CS optical depth profiles obtained using isotopic observations show a red
asymmetry also consistent with an infall interpretation. Using
three-dimensional radiative transfer models based on the rotating, collapse
model of Terebey, Shu and Cassen, we derive infall parameters of the source. To
determine the direction and orientation of molecular outflows in the larger
Serpens cluster, wide-field mapping of CO J=1-0 emission was also performed.Comment: 27 pages, 7 figures, to appear in Ap
Chemical chronology of the Southern Coalsack
We demonstrate how the observed H2O ice column densities toward three dense
globules in the Southern Coalsack could be used to constrain the ages of these
sources. We derive ages of ~10^5 yr, in agreement with dynamical studies of
these objects. We have modelled the chemical evolution of the globules, and
show how the molecular abundances are controlled by both the gas density and
the initial chemical conditions as the globules formed. Based on our derived
ages, we predict the column densities of several species of interest. These
predictions should be straightforward to test by performing molecular line
observationsComment: 10 pages, 4 figures, in press at MNRA
A sensitive submillimetre survey of broad absorption line quasars
The definitive version is available at www.blackwell-synergy.com--Copyright Blackwell Publishing DOI : 10.1111/j.1365-2966.2006.11200.xPeer reviewe
Star Formation in the Northern Cloud Complex of NGC 2264
We have made continuum and spectral line observations of several outflow
sources in the Mon OB1 dark cloud (NGC 2264) using the Heinrich Hertz Telescope
(HHT) and ARO 12m millimeter-wave telescope. This study explores the kinematics
and outflow energetics of the young stellar systems observed and assesses the
impact star formation is having on the surrounding cloud environment. Our data
set incorporates 12CO(3-2), 13CO(3-2), and 12CO(1-0) observations of outflows
associated with the sources IRAS 06382+1017 and IRAS 06381+1039, known as IRAS
25 and 27, respectively, in the northern cloud complex. Complementary 870
micron continuum maps were made with the HHT 19 channel bolometer array. Our
results indicate that there is a weak (approximately less than 0.5%) coupling
between outflow kinetic energy and turbulent energy of the cloud. An analysis
of the energy balance in the IRAS 25 and 27 cores suggests they are maintaining
their dynamical integrity except where outflowing material directly interacts
with the core, such as along the outflow axes.Comment: 28 pages including 6 figures, to be published in ApJ 01 July 2006,
v645, 1 issu
A Sub-millimeterwave ``Flare'' from GG Tau?
We have monitored the millimeter and submillimeter emission from the young
stellar object GG Tau, a T Tauri binary system surrounded by a massive
circumbinary disk. We find that between 1992 and 1994, the flux has increased
significantly at 800, 1100, and 1300 microns, resulting in a steepening of the
observed spectral energy distribution at those wavelengths. Such an increase
appears consistent with a modest increase in disk luminosity (a factor of two).
The increase in the effective disk temperature might arise from a slight change
in the disk heating processes. Alternatively, the flux increase may reflect a
sudden change in the underlying dust optical properties.Comment: 15 pages, AASTex v.4.0 format, four postscript figures, four tables,
to appear in The Astrophysical Journa
Results of the engineering run of the coherent neutrino nucleus interaction experiment (CONNIE)
The CONNIE detector prototype is operating at a distance of 30 m from the core of a 3.8 GWth nuclear reactor with the goal of establishing Charge-Coupled Devices (CCD) as a new technology for the detection of coherent elastic neutrino-nucleus scattering. We report on the results of the engineering run with an active mass of 4 g of silicon. The CCD array is described, and the performance observed during the first year is discussed. A compact passive shield was deployed around the detector, producing an order of magnitude reduction in the background rate. The remaining background observed during the run was stable, and dominated by internal contamination in the detector packaging materials. The in-situ calibration of the detector using X-ray lines from fluorescence demonstrates good stability of the readout system. The event rates with the reactor ON and OFF are compared, and no excess is observed coming from nuclear fission at the power plant. The upper limit for the neutrino event rate is set two orders of magnitude above the expectations for the standard model. The results demonstrate the cryogenic CCD-based detector can be remotely operated at the reactor site with stable noise below2 e RMS and stable background rates. The success of the engineering test provides a clear path for the upgraded 100 g detector to be deployed during 2016.Fil: Aguilar Arevalo, A.. Universidad Nacional Autónoma de México; MéxicoFil: Bertou, Xavier Pierre Louis. Comisión Nacional de Energía Atómica; Argentina. Comisión Nacional de Energía Atómica. Fundación José A. Balseiro; ArgentinaFil: Bonifazi, C.. Universidade Federal do Rio de Janeiro; BrasilFil: Butner, M.. Fermi National Accelerator Laboratory; Estados UnidosFil: Cancelo, G.. Fermi National Accelerator Laboratory; Estados UnidosFil: Castañeda Vazquez, A.. Universidad Nacional Autónoma de México; MéxicoFil: Cervantes Vergara, B.. Universidad Nacional Autónoma de México; MéxicoFil: Chavez, C. R.. Universidad Nacional de Asunción; ParaguayFil: Da Motta, H.. Centro Brasileiro de Pesquisas Físicas; BrasilFil: D'Olivo, J. C.. Universidad Nacional Autónoma de México; MéxicoFil: Dos Anjos, J.. Centro Brasileiro de Pesquisas Físicas; BrasilFil: Estrada, J.. Fermi National Accelerator Laboratory; Estados UnidosFil: Fernández Moroni, Guillermo. Universidad Nacional del Sur. Departamento de Ingeniería Eléctrica y de Computadoras. Instituto ; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ford, R.. Fermi National Accelerator Laboratory; Estados UnidosFil: Foguel, A.. Centro Brasileiro de Pesquisas Físicas; Brasil. Universidade Federal do Rio de Janeiro; BrasilFil: Hernandez Torres, K. P.. Universidad Nacional Autónoma de México; MéxicoFil: Izraelevitch, F.. Fermi National Accelerator Laboratory; Estados UnidosFil: Kavner, A.. University of Michigan; Estados UnidosFil: Kilminster, B.. Universitat Zurich; SuizaFil: Kuk, K.. Fermi National Accelerator Laboratory; Estados UnidosFil: Lima Jr, H. P.. Centro Brasileiro de Pesquisas Físicas; BrasilFil: Makler, M.. Centro Brasileiro de Pesquisas Físicas; BrasilFil: Molina, J.. Universidad Nacional de Asunción; ParaguayFil: Moreno Granados, G.. Universidad Nacional Autónoma de México; MéxicoFil: Moro, Juan Manuel. Universidad Nacional del Sur. Departamento de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Paolini, Eduardo Emilio. Universidad Nacional del Sur. Departamento de Ingeniería Eléctrica y de Computadoras. Instituto ; ArgentinaFil: Sofo Haro, Miguel Francisco. Comision Nacional de Energia Atomica. Gerencia D/area de Energia Nuclear; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tiffenberg, Javier Sebastian. Fermi National Accelerator Laboratory; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Trillaud, F.. Universidad Nacional Autónoma de México; MéxicoFil: Wagner, S.. Centro Brasileiro de Pesquisas Físicas; Brasil. Pontificia Universidade Católica do Rio Grande do Sul; Brasi
Inferences from the kinematic properties of 6.7 GHz methanol masers
Context. It is now well established that the strong and widespread 6.7 GHz
methanol masers are associated with young high mass stars. A still
unsolved question is where in the circumstellar environment the masers
arise.
Aims.We address this question by considering an ensemble of rest frame
maser velocities of 337 maser features.
Methods. The CS(2-1) spectra of 63 methanol maser sources were used to derive
systemic velocities and velocity dispersion of the thermal gas. Using
the systemic velocities and the velocities of the 337 maser features
in the 63 sources, a single distribution of rest frame maser
velocities was constructed. This distribution as well as other
kinematic information about the masers are used to evaluate four
proposed scenarios for where the masers might arise in the
circumstellar environment.
Results.It is shown that kinematically the masers are not associated with hot
cores. We also argue that the scenario in which the masers are
associated with an external generated planar shock that propagates into
a rotating core cannot explain the observed kinematic properties of the
masers. It was found that a simple Keplerian-like disk model is consistent
with the observed distribution of rest frame maser
velocities. Although outflows have the potential to explain the data,
it was not possible to fully test this possibility due to the diverse
nature of outflows
Sustainability Assessment of Coal-Fired Power Plants with Carbon Capture and Storage
Carbon capture and sequestration (CCS) has the ability to dramatically reduce carbon dioxide (CO2) emissions from power production. Most studies find the potential for 70 to 80 percent reductions in CO2 emissions on a life-cycle basis, depending on the technology. Because of this potential, utilities and policymakers are considering the wide-spread implementation of CCS technology on new and existing coal plants to dramatically curb greenhouse gas (GHG) emissions from the power generation sector. However, the implementation of CCS systems will have many other social, economic, and environmental impacts beyond curbing GHG emissions that must be considered to achieve sustainable energy generation. For example, emissions of nitrogen oxides (NOx), sulfur oxides (SOx), and particulate matter (PM) are also important environmental concerns for coal-fired power plants. For example, several studies have shown that eutrophication is expected to double and acidification would increase due to increases in NOx emissions for a coal plant with CCS provided by monoethanolamine (MEA) scrubbing. Potential for human health risks is also expected to increase due to increased heavy metals in water from increased coal mining and MEA hazardous waste, although there is currently not enough information to relate this potential to actual realized health impacts. In addition to environmental and human health impacts, supply chain impacts and other social, economic, or strategic impacts will be important to consider. A thorough review of the literature for life-cycle analyses of power generation processes using CCS technology via the MEA absorption process, and other energy generation technologies as applicable, yielded large variability in methods and core metrics. Nonetheless, a few key areas of impact for CCS were developed from the studies that we reviewed. These are: the impact of MEA generation on increased eutrophication and acidification from ammonia emissions and increased toxicity from MEA production and the impact of increased coal use including the increased generation of NOx from combustion and transportation, impacts of increased mining of coal and limestone, and the disposal of toxic fly ash and boiler ash waste streams. Overall, the implementing CCS technology could contribute to a dramatic decrease in global GHG emissions, while most other environmental and human health impact categories increase only slightly on a global scale. However, the impacts on human toxicity and ecotoxicity have not been studied as extensively and could have more severe impacts on a regional or local scale. More research is needed to draw strong conclusions with respect to the specific relative impact of different CCS technologies. Specifically, a more robust data set that disaggregates data in terms of component processes and treats a more comprehensive set of environmental impacts categories from a life-cycle perspective is needed. In addition, the current LCA framework lacks the required temporal and spatial scales to determine the risk of environmental impact from carbon sequestration. Appropriate factors to use when assessing the risk of water acidification (groundwater/oceans/aquifers depending on sequestration site), risk of increased human toxicity impact from large accidental releases from pipeline or wells, and the legal and public policy risk associated with licensing CO2 sequestration sites are also not currently addressed. In addition to identifying potential environmental, social, or risk-related issues that could impede the large-scale deployment of CCS, performing LCA-based studies on energy generation technologies can suggest places to focus our efforts to achieve technically feasible, economically viable, and environmentally conscious energy generation technologies for maximum impact
- …