84 research outputs found
Chop Sticks and Geisha...
How would you like, says your Japanese host, at the end of a viciously hot summer day of sightseeing in Kyoto, to take dinner in true Japanese fashion tonight
The Iowa Homemaker vol.13, no.4
Chop Sticks and Geishea⊠By Mitchell V. Charnley
Coeds Choose Clever Clothes⊠By Virginia Kirstein
âTwas a Lucky Guess⊠By Gladys M. Johnson
Flowers in a Pumpkin Shell⊠By Ruth Coo
Comparative chemistry of diffuse clouds III: sulfur-bearing molecules
Using data from IRAM's Plateau de Bure Interferometer and 30 m Telescope, we
discuss the mm-wave absorption lines of CS, SO, H2S and HCS+ which arise in
diffuse clouds occulting several extragalactic continuum sources. Typical
relative abundances are X(CS)/X(HCO+) ~ 2, X(CS)/X(SO) ~ 2, X(CS)/X(H2S) ~ 6
and X(CS)/X(HCS+) ~ 13.Comment: Accepted by A&A 2002-Jan-1
Chemistry as a probe of the structures and evolution of massive star forming regions
We present detailed thermal and gas-phase chemical models for the envelope of
the massive star-forming region AFGL 2591. Time- and space-dependent chemistry
are used to study the physical structure proposed by van der Tak et al. (1999;
2000), and the chemical evolution of this region. The model is compared with
observations for 29 species covering a wide range of conditions within the
source. Taking appropriate care when comparing models with both emission and
absorption measurements, we find that the majority of the chemical structure
can be well-explained. In particular, we find that the nitrogen and hydrocarbon
chemistry can be significantly affected by temperature, with the possibility of
high-temperature pathways to HCN. While we cannot determine the sulphur
reservoir, the observations can be explained by models with the majority of the
sulphur in CS in the cold gas, SO in the warm gas, and atomic sulphur in
the warmest gas. The observed abundances of ions such as HCO and NH
and the cold gas-phase production of HCN constrain the cosmic-ray ionization
rate to s, to within a factor of three.
Finally, we find that the model and observations can simultaneously agree at a
reasonable level and often to within a factor of three for , with a strong preference for yrs since the collapse and formation of the central
luminosity source.Comment: 18 pages, 16 figure
Media Appropriation and Explicitation
<p>This paper presents a novel characterization of new media art together with an exploration of some key aspects of its practice: I propose that new media artâs defining characteristics are media appropriation and explicitation. With media appropriation I refer to the dialectal inscription into the art practice of the knowledge that allows for some particular technological production. I also propose that new media artâs language is constructed in part via the explicitation of certain aspects of more âtraditionalâ art, and that this explicitation allows for a construction of a new vocabulary. Examples of this are the explicitation of randomness, interaction, programming, or of the role that tools and instruments play, among others.</p
Sulphur chemistry in the envelopes of massive young stars
The sulphur chemistry in nine regions in the earliest stages of high-mass
star formation is studied through single-dish submillimeter spectroscopy. The
line profiles indicate that 10-50% of the SO and SO2 emission arises in
high-velocity gas, either infalling or outflowing. For the low-velocity gas,
excitation temperatures are 25 K for H2S, 50 K for SO, H2CS, NS and HCS+, and
100 K for OCS and SO2, indicating that most observed emission traces the outer
parts (T<100 K) of the molecular envelopes, except high-excitation OCS and SO2
lines. Abundances in the outer envelopes, calculated with a Monte Carlo
program, using the physical structures of the sources derived from previous
submillimeter continuum and CS line data, are ~10^-8 for OCS, ~10^-9 for H2S,
H2CS, SO and SO2, and ~10^-10 for HCS+ and NS. In the inner envelopes (T>100 K)
of six sources, the SO2 abundance is enhanced by factors of ~100-1000. This
region of hot, abundant SO2 has been seen before in infrared absorption, and
must be small, <~ 0.2 arcsec (180 AU radius). The derived abundance profiles
are consistent with models of envelope chemistry which invoke ice evaporation
at T~100$ K. Shock chemistry is unlikely to contribute. A major sulphur carrier
in the ices is probably OCS, not H2S as most models assume. The
source-to-source abundance variations of most molecules by factors of ~10 do
not correlate with previous systematic tracers of envelope heating. Without
observations of H2S and SO lines probing warm (>~ 100 K) gas, sulphur-bearing
molecules cannot be used as evolutionary tracers during star formation.Comment: Accepted by A&A, 14 pages, 5 figure
Gas-phase H2O and CO2 toward massive protostars
We present a study of gas-phase H2O and CO2 toward a sample of 14 massive
protostars with the Short Wavelength Spectrometer (SWS) on board the Infrared
Space Observatory (ISO). Modeling of the H2O spectra using a homogeneous model
with a constant excitation temperature T_ex shows that the H2O abundances
increase with temperature, up to a few times 10^-5 with respect to H2 for the
hottest sources (T_ex ~500 K). This is still a factor of 10 lower than the H2O
ice abundances observed toward cold sources in which evaporation is not
significant (Keane et al. 2001). Gas-phase CO2 is not abundant in our sources.
The abundances are nearly constant for T_ex>~100 K at a value of a few times
10^-7, much lower than the solid-state abundances of ~1--3 times 10^-6
(Gerakines et al. 1999). For both H2O and CO2 the gas/solid ratio increases
with temperature, but the increase is much stronger for H2O than for CO2,
suggesting a different type of chemistry. In addition to the homogeneous
models, a power law model has been developed for one of our sources, based on
the physical structure of this region as determined from submillimeter data by
van der Tak et al. (1999). The resulting H2O model spectrum gives a good fit to
the data.Comment: Published in the Proceedings of the `ISO beyond the Peaks' Workshop,
eds. A. Salama, M.F. Kessler, K. Leech & B. Schulz. ESA-SP 456, p67 (2000), 4
pages including 6 figure
Astrochemistry of Sub-Millimeter Sources in Orion: Studying the Variations of Molecular Tracers with Changing Physical Conditions
Cornerstone molecules (CO, H_2CO, CH_3OH, HCN, HNC, CN, CS, SO) were observed
toward seven sub-millimeter bright sources in the Orion molecular cloud in
order to quantify the range of conditions for which individual molecular line
tracers provide physical and chemical information. Five of the sources observed
were protostellar, ranging in energetics from 1 - 500L_sun, while the other two
sources were located at a shock front and within a photodissociation region
(PDR).
Statistical equilibrium calculations were used to deduce from the measured
line strengths the physical conditions within each source and the abundance of
each molecule. In all cases except the shock and the PDR, the abundance of CO
with respect to H_2 appears significantly below (factor of ten) the general
molecular cloud value of 10^-4. {Formaldehyde measurements were used to
estimate a mean temperature and density for the gas in each source. Evidence
was found for trends between the derived abundance of CO, H_2CO, CH_3OH, and CS
and the energetics of the source, with hotter sources having higher
abundances.} Determining whether this is due to a linear progression of
abundance with temperature or sharp jumps at particular temperatures will
require more detailed modeling. The observed methanol transitions require high
temperatures (T>50 K), and thus energetic sources, within all but one of the
observed protostellar sources. The same conclusion is obtained from
observations of the CS 7-6 transition. Analysis of the HCN and HNC 4-3
transitions provides further support for high densities n> 10^7 cm^-3 in all
the protostellar sources.Comment: 36 pages, 8 figures, Astronomy and Astrophysics in pres
High mass star formation in the IRAS 17233-3606 region: a new nearby and bright hot core in the southern sky
We present molecular line observations of the massive star forming region
IRAS 17233-3606 aimed at studying the molecular core associated with the
source. The observations were made using the Atacama Pathfinder Experiment
telescope in the CO (3-2) and HCO^+ (4-3) transitions, and in the CH_3OH
(6_K-5_K), (7_K-6_K) and CH_3CN (16_K-15_K) bands. For the CO(3-2) and HCO^+
(4-3) transitions, we obtained maps with a size of 70''\times 70''. The typical
angular resolution of the data is ~18''. Our observations reveal an
exceptionally rich molecular spectrum, a signpost of hot core activity.
Comparisons with two other prominent southern hot cores were made through
observations in the same frequency setups. We also detected a bipolar outflow
in CO (3-2) and HCO^+ (4-3) lines. Modelling reveals a hot core of size ~3''
and a temperature of 150 K in the IRAS17233-3606 region. The parameters of the
molecular outflow are derived through the analysis of the CO (3-2) emission,
and are typical of outflows driven by high-mass young stellar objects.Comment: 9 pages, 10 figures (plus 8 figures as Online material), accepted by
A&
The JCMT Spectral Legacy Survey: physical structure of the molecular envelope of the high-mass protostar AFGL2591
The understanding of the formation process of massive stars (>8 Msun) is
limited, due to theoretical complications and observational challenges.
We investigate the physical structure of the large-scale (~10^4-10^5 AU)
molecular envelope of the high-mass protostar AFGL2591 using spectral imaging
in the 330-373 GHz regime from the JCMT Spectral Legacy Survey. Out of ~160
spectral features, this paper uses the 35 that are spatially resolved.
The observed spatial distributions of a selection of six species are compared
with radiative transfer models based on a static spherically symmetric
structure, a dynamic spherical structure, and a static flattened structure. The
maps of CO and its isotopic variations exhibit elongated geometries on scales
of ~100", and smaller scale substructure is found in maps of N2H+, o-H2CO, CS,
SO2, CCH, and methanol lines. A velocity gradient is apparent in maps of all
molecular lines presented here, except SO, SO2, and H2CO. We find two emission
peaks in warm (Eup~200K) methanol separated by 12", indicative of a secondary
heating source in the envelope.
The spherical models are able to explain the distribution of emission for the
optically thin H13CO+ and C34S, but not for the optically thick HCN, HCO+, and
CS, nor for the optically thin C17O. The introduction of velocity structure
mitigates the optical depth effects, but does not fully explain the
observations, especially in the spectral dimension. A static flattened envelope
viewed at a small inclination angle does slightly better.
We conclude that a geometry of the envelope other than an isotropic static
sphere is needed to circumvent line optical depth effects. We propose that this
could be achieved in envelope models with an outflow cavity and/or
inhomogeneous structure at scales smaller than ~10^4 AU. The picture of
inhomogeneity is supported by observed substructure in at least six species.Comment: 17 pages; accepted for publication in A&
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