476 research outputs found
The Discovery of Vibrationally-Excited H_2 in the Molecular Cloud near GRB 080607
GRB 080607 has provided the first strong observational signatures of
molecular absorption bands toward any galaxy hosting a gamma-ray burst. Despite
the identification of dozens of features as belonging to various atomic and
molecular (H_2 and CO) carriers, many more absorption features remained
unidentified. Here we report on a search among these features for absorption
from vibrationally-excited H_2, a species that was predicted to be produced by
the UV flash of a GRB impinging on a molecular cloud. Following a detailed
comparison between our spectroscopy and static, as well as dynamic, models of
H_2* absorption, we conclude that a column density of 10^{17.5+-0.2} cm^{-2} of
H_2* was produced along the line of sight toward GRB 080607. Depending on the
assumed amount of dust extinction between the molecular cloud and the GRB, the
model distance between the two is found to be in the range 230--940 pc. Such a
range is consistent with a conservative lower limit of 100 pc estimated from
the presence of Mg I in the same data. These distances show that substantial
molecular material is found within hundreds of pc from GRB 080607, part of the
distribution of clouds within the GRB host galaxy.Comment: Submitted to ApJL, 6 pages emulate
Constraining the Environment of CH+ Formation with CH3+ Observations
The formation of CH+ in the interstellar medium has long been an outstanding
problem in chemical models. In order to probe the physical conditions of the
ISM in which CH+ forms, we propose the use of CH3+ observations. The pathway to
forming CH3+ begins with CH+, and a steady state analysis of CH3+ and the
reaction intermediary CH2+ results in a relationship between the CH+ and CH3+
abundances. This relationship depends on the molecular hydrogen fraction, f_H2,
and gas temperature, T, so observations of CH+ and CH3+ can be used to infer
the properties of the gas in which both species reside. We present observations
of both molecules along the diffuse cloud sight line toward Cyg OB2 No. 12.
Using our computed column densities and upper limits, we put constraints on the
f_H2 vs. T parameter space in which CH+ and CH3+ form. We find that average,
static, diffuse molecular cloud conditions (i.e. f_H2>0.2, T~60 K) are excluded
by our analysis. However, current theory suggests that non-equilibrium effects
drive the reaction C+ + H_2 --> CH+ + H, endothermic by 4640 K. If we consider
a higher effective temperature due to collisions between neutrals and
accelerated ions, the CH3+ partition function predicts that the overall
population will be spread out into several excited rotational levels. As a
result, observations of more CH3+ transitions with higher signal-to-noise
ratios are necessary to place any constraints on models where magnetic
acceleration of ions drives the formation of CH+.Comment: 7 pages, 3 figures, 2 tables, accepted for publication in Ap
Diffuse Atomic and Molecular Gas near IC443
We present an analysis of results on absorption from Ca II, Ca I, K I, and
the molecules CH+, CH, C2, and CN that probes gas interacting with the
supernova remnant IC443. The eleven directions sample material across the
visible nebula and beyond its eastern edge. Most of the neutral material,
including the diatomic molecules, is associated with the ambient cloud detected
via H I and CO emission. Analysis of excitation and chemistry yields gas
densities that are typical of diffuse molecular gas. The low density gas probed
by Ca II extends over a large range in velocities, from -120 to +80 km/s in the
most extreme cases. This gas is distributed among several velocity components,
unlike the situation for the shocked molecular clumps, whose emission occurs
over much the same range but as very broad features. The extent of the
high-velocity absorption suggests a shock velocity of 100 km/s for the
expanding nebula.Comment: To be published in Ap
Sakurai's Object: characterizing the near-infrared CO ejecta between 2003 and 2007
We present observations of Sakurai's Object obtained at 1–5 μm between 2003 and 2007. By fitting a radiative transfer model to an echelle spectrum of CO fundamental absorption features around 4.7 μm, we determine the excitation conditions in the line-forming region. We find 12C/13C = 3.5+2.0−1.5, consistent with CO originating in ejecta processed by the very late thermal pulse, rather than in the pre-existing planetary nebula. We demonstrate the existence of 2.2 × 10−6≤MCO≤ 2.7 × 10−6 M⊙ of CO ejecta outside the dust, forming a high-velocity wind of 500 ± 80 km s−1. We find evidence for significant weakening of the CO band and cooling of the dust around the central star between 2003 and 2005. The gas and dust temperatures are implausibly high for stellar radiation to be the sole contributor
Measurement of Total (p,Pi) Cross Sections Through Residual Activity
This work was supported by the National Science Foundation Grants NSF PHY 78-22774 A03, NSF PHY 81-14339, and by Indiana Universit
Chemical Analysis of a Diffuse Cloud along a Line of Sight Toward W51: Molecular Fraction and Cosmic-Ray Ionization Rate
Absorption lines from the molecules OH+, H2O+, and H3+ have been observed in
a diffuse molecular cloud along a line of sight near W51 IRS2. We present the
first chemical analysis that combines the information provided by all three of
these species. Together, OH+ and H2O+ are used to determine the molecular
hydrogen fraction in the outskirts of the observed cloud, as well as the
cosmic-ray ionization rate of atomic hydrogen. H3+ is used to infer the
cosmic-ray ionization rate of H2 in the molecular interior of the cloud, which
we find to be zeta_2=(4.8+-3.4)x10^-16 per second. Combining the results from
all three species we find an efficiency factor---defined as the ratio of the
formation rate of OH+ to the cosmic-ray ionization rate of H---of
epsilon=0.07+-0.04, much lower than predicted by chemical models. This is an
important step in the future use of OH+ and H2O+ on their own as tracers of the
cosmic-ray ionization rate.Comment: 21 pages, 1 figure, 4 table
Nigerian scam e-mails and the charms of capital
So-called '419' or 'advance-fee' e-mail frauds have proved remarkably successful. Global losses to these scams are believed to run to billions of dollars. Although it can be assumed that the promise of personal gain which these e-mails hold out is part of what motivates victims, there is more than greed at issue here. How is it that the seemingly incredible offers given in these unsolicited messages can find an audience willing to treat them as credible? The essay offers a speculative thesis in answer to this question. Firstly, it is argued, these scams are adept at exploiting common presuppositions in British and American culture regarding Africa and the relationships that are assumed to exist between their nations and those in the global south. Secondly, part of the appeal of these e-mails lies in the fact that they appear to reveal the processes by which wealth is created and distributed in the global economy. They thus speak to their readers’ attempts to map or conceptualise the otherwise inscrutable processes of that economy. In the conclusion the essay looks at the contradictions in the official state response to this phenomena
Activation Measurements of the 7-Li(p,n)7-Be Reaction from 60-480 MeV
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Some discussions on functionalist housing and its economics in Romania by Lhe late 1950s and early 1960s
This paper proposes an analysis of the Romanian architectural practices in the late 1950's and early 1960's by considering the availability of financial resources. I premise that echoes of Moscow's approaches to the built environment overlapped the Bucharest politicians' priorities, whose lack of constancy in economic decision-making exacerbated itself as the urban construction programs advanced. From the Romanian authorities' point of view, therefore, raising the mass housing profitability could save important financial resources for other investments in heavy industry, while maintaining the appearance of a social state. Similarities between Soviet and Romanian modernist building projects suggested a coherent approach to housing throughout the bloc. However, this article will show that functionalist architectural modernism -cheap and fast to erect- also proved beneficial for Gheorghe Gheorghiu-Dej's economic plans, which questions urban construction projects' political agendas and the professional tensions between architects and economists. Therefore, investigating the functionalist architecture opens up several lines of inquiry: to what extent Nikita Khrushchev's housing program was transferred in Romania; the tortuous policies of the Romanian state's leadership in the field of housing as well as how local bureaucratic or professional actors appropriated, interpreted and adjusted such programs; and, the economic costs of the new functionalist approach to urban dwelling. In this way, this article reads the making of functionalist mass housing programs by the late 1950s to assess the Soviets' part in building the Romanian cities. To this end, the article contributes to the recent scholarly literature on multiple modernities
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