45 research outputs found
Lower Roxbury redevelopment
Thesis (M.Arch.) Massachusetts Institute of Technology. Dept. of Architecture, 1956.Accompanying drawings held by MIT Museum.Bibliography: leaf [103].by Arthur John Mudry and Flemming Steen Seiersen.M.Arch
Model for Cameron band emission in comets: A case for EPOXI mission target comet 103P/Hartley 2
The CO2 production rate has been derived in comets using the Cameron band
(a3Pi - X1Sigma) emission of CO molecule assuming that photodissociative
excitation of CO2 is the main production mechanism of CO in a3Pi metastable
state. We have devoloped a model for the production and loss of CO(a3Pi) which
has been applied to comet 103P/Hartley 2: the target of EPOXI mission. Our
model calculations show that photoelectron impact excitation of CO and
dissociative excitation of CO2 can together contribute about 60-90% to the
Cameron band emission. The modeled brightness of (0-0) Cameron band emission on
comet Hartley 2 is consistent with Hubble Space Telescope observations for 3-5%
CO2 (depending on model input solar flux) and 0.5% CO relative to water, where
photoelectron impact contribution is about 50-75%. We suggest that estimation
of CO2 abundances on comets using Cameron band emission may be reconsidered. We
predict the height integrated column brightness of Cameron band of ~1300 R
during EPOXI mission encounter period.Comment: 3 figure
Model for the Production of CO Cameron band emission in Comet 1P/Halley
The abundance of CO2 in comets has been derived using CO Cameron band (a3pi
--> X1Sigma+) emission assuming that photodissociative excitation of CO2 is the
main production process of CO(a3pi). On comet 1P/Halley the Cameron (1-0) band
has been observed by International Ultraviolet Explorer (IUE) on several days
in March 1986. A coupled chemistry-emission model is developed for comet
1P/Halley to assess the importance of various production and loss mechanisms of
CO(a3pi) and to calculate the intensity of Cameron band emission on different
days of IUE observation. Two different solar EUV flux models, EUVAC of Richards
et al. (1994) and SOLAR2000 of Tobiska (2004), and different relative
abundances of CO and CO2, are used to evaluate the role of photon and
photoelectron in producing CO molecule in a3pi state in the cometary coma. It
is found that in comet 1P/Halley 60--70% of the total intensity of the Cameron
band emission is contributed by electron impact excitation of CO and CO2, while
the contribution from photodissociative excitation of CO2 is small (20--30%).
Thus, in the comets where CO and CO2 relative abundances are comparable, the
Cameron band emission is largely governed by electron impact excitation of CO,
and not by the photodissociative excitation of CO2 as assumed earlier. Model
calculated Cameron band 1-0 emission intensity (40 R) is consistent with the
observed IUE slit-averaged brightness (37 +/- 6 R) using EUVAC model solar flux
on 13 March 1986, and also on other days of observations. Since electron impact
excitation is the major production mechanism, the Cameron emission can be used
to derive photoelectron density in the inner coma rather than the CO2
abundance.Comment: 40 pages 8 figure
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Measuring the Unknown Forces that Drive Neutron Star Mergers
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