172 research outputs found
Antithetic Conjuncts in Written English
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68390/2/10.1177_003368827901000204.pd
The COMPLETE Survey of Outflows in Perseus
We present a study on the impact of molecular outflows in the Perseus
molecular cloud complex using the COMPLETE survey large-scale 12CO(1-0) and
13CO(1-0) maps. We used three-dimensional isosurface models generated in
RA-DEC-Velocity space to visualize the maps. This rendering of the molecular
line data allowed for a rapid and efficient way to search for molecular
outflows over a large (~ 16 sq. deg.) area. Our outflow-searching technique
detected previously known molecular outflows as well as new candidate outflows.
Most of these new outflow-related high-velocity features lie in regions that
have been poorly studied before. These new outflow candidates more than double
the amount of outflow mass, momentum, and kinetic energy in the Perseus cloud
complex. Our results indicate that outflows have significant impact on the
environment immediately surrounding localized regions of active star formation,
but lack the energy needed to feed the observed turbulence in the entire
Perseus complex. This implies that other energy sources, in addition to
protostellar outflows, are responsible for turbulence on a global cloud scale
in Perseus. We studied the impact of outflows in six regions with active star
formation within Perseus of sizes in the range of 1 to 4 pc. We find that
outflows have enough power to maintain the turbulence in these regions and
enough momentum to disperse and unbind some mass from them. We found no
correlation between outflow strength and star formation efficiency for the six
different regions we studied, contrary to results of recent numerical
simulations. The low fraction of gas that potentially could be ejected due to
outflows suggests that additional mechanisms other than cloud dispersal by
outflows are needed to explain low star formation efficiencies in clusters.Comment: Published in The Astrophysical Journa
An Ammonia Spectral Atlas of Dense Cores in Perseus
We present ammonia observations of 193 dense cores and core candidates in the
Perseus molecular cloud made using the Robert F. Byrd Green Bank Telescope. We
simultaneously observed the NH3(1,1), NH3(2,2), CCS (2_1 -> 1_0) and CC34S (2_1
-> 1_0) transitions near 23 GHz for each of the targets with a spectral
resolution of dv ~ 0.024 km/s. We find ammonia emission associated with nearly
all of the (sub)millimeter sources as well as at several positions with no
associated continuum emission. For each detection, we have measured physical
properties by fitting a simple model to every spectral line simultaneously.
Where appropriate, we have refined the model by accounting for low optical
depths, multiple components along the line of sight and imperfect coupling to
the GBT beam. For the cores in Perseus, we find a typical kinetic temperature
of T=11 K, a typical column density of N(NH3)~ 10^14.5 /cm^2 and velocity
dispersions ranging from sigma_v = 0.07 km/s to 0.7 km/s. However, many cores
with velocity dispersions > 0.2 km/s show evidence for multiple velocity
components along the line of sight.Comment: 19 pages; Accepted to ApJS; version with high resolution figures
available at http://www.cfa.harvard.edu/COMPLETE/papers/nh3-paper1.pdf ;
online data at
http://www.cfa.harvard.edu/COMPLETE/data_html_pages/GBT_NH3.htm
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Perception, Cognition, and Effectiveness of Visualizations with Applications in Science and Engineering
Visualization is a powerful tool for data exploration and analysis. With data ever-increasing in quantity and becoming integrated into our daily lives, having effective visualizations is necessary. But how does one design an effective visualization? To answer this question we need to understand how humans perceive, process, and understand visualizations. Through visualization evaluation studies we can gain deeper insight into the basic perception and cognition theory of visualizations, both through domain-specific case studies as well as generalized laboratory experiments.Engineering and Applied Science
The COMPLETE Survey of Star-Forming Regions: Phase I Data
We present an overview of data available for the Ophiuchus and Perseus
molecular clouds from ``Phase I'' of the COMPLETE Survey of Star-Forming
Regions. This survey provides a range of data complementary to the Spitzer
Legacy Program ``From Molecular Cores to Planet Forming Disks.'' Phase I
includes: Extinction maps derived from 2MASS near-infrared data using the NICER
algorithm; extinction and temperature maps derived from IRAS 60 and 100um
emission; HI maps of atomic gas; 12CO and 13CO maps of molecular gas; and
submillimetre continuum images of emission from dust in dense cores. Not
unexpectedly, the morphology of the regions appears quite different depending
on the column-density tracer which is used, with IRAS tracing mainly warmer
dust and CO being biased by chemical, excitation and optical depth effects.
Histograms of column-density distribution are presented, showing that
extinction as derived from 2MASS/NICER gives the closest match to a log-normal
distribution as is predicted by numerical simulations. All the data presented
in this paper, and links to more detailed publications on their implications
are publically available at the COMPLETE website.Comment: Accepted by AJ. Full resolution version available from:
http://www.cfa.harvard.edu/COMPLETE/papers/complete_phase1.pd
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