18,403 research outputs found

    CO Rovibrational Emission as a Probe of Inner Disk Structure

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    We present an analysis of CO emission lines from a sample of T Tauri, Herbig Ae/Be, and transitional disks with known inclinations in order to study the structure of inner disk molecular gas. We calculate CO inner radii by fitting line profiles with a simple parameterized model. We find that, for optically thick disks, CO inner radii are strongly correlated with the total system luminosity (stellar plus accretion) and consistent with the dust sublimation radius. Transitional disk inner radii show the same trend with luminosity, but are systematically larger. Using rotation diagram fits, we derive, for classical T Tauri disks, emitting areas consistent with a ring of width ~0.15 AU located at the CO inner radius; emitting areas for transitional disks are systematically smaller. We also measure lower rotational temperatures for transitional disks, and disks around Herbig Ae/Be stars, than for those around T Tauri stars. Finally, we find that rotational temperatures are similar to, or slightly lower than, the expected temperature of blackbody grains located at the CO inner radius, in contrast to expectations of thermal decoupling between gas and dust

    Water production in comet 81P/Wild 2 as determined by Herschel/HIFI

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    The high spectral resolution and sensitivity of Herschel/HIFI allows for the detection of multiple rotational water lines and accurate determinations of water production rates in comets. In this Letter we present HIFI observations of the fundamental 1_(10)–1_(01) (557 GHz) ortho and 1_(11)–0_(00) (1113 GHz) para rotational transitions of water in comet 81P/Wild 2 acquired in February 2010. We mapped the extent of the water line emission with five point scans. Line profiles are computed using excitation models which include excitation by collisions with electrons and neutrals and solar infrared radiation. We derive a mean water production rate of 1.0 × 10^(28) molecules s^(−1) at a heliocentric distance of 1.61 AU about 20 days before perihelion, in agreement with production rates measured from the ground using observations of the 18-cm OH lines. Furthermore, we constrain the electron density profile and gas kinetic temperature, and estimate the coma expansion velocity by fitting the water line shapes

    HIFI observations of water in the atmosphere of comet C/2008 Q3 (Garradd)

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    High-resolution far-infrared and sub-millimetre spectroscopy of water lines is an important tool to understand the physical and chemical properties of cometary atmospheres.We present observations of several rotational ortho- and para-water transitions in comet C/2008 Q3 (Garradd) performed with HIFI on Herschel. These observations have provided the first detection of the 2_(12)−1_(01) (1669 GHz) ortho and 1_(11)−0_(00) (1113 GHz) para transitions of water in a cometary spectrum. In addition, the ground-state transition 1_(10)−1_(01) at 557 GHz is detected and mapped. By detecting several water lines quasi-simultaneously and mapping their emission we can constrain the excitation parameters in the coma. Synthetic line profiles are computed using excitation models which include excitation by collisions, solar infrared radiation, and radiation trapping. We obtain the gas kinetic temperature, constrain the electron density profile, and estimate the coma expansion velocity by analyzing the map and line shapes. We derive water production rates of 1.7−2.8 × 10^(28) s^(−1) over the range r_h = 1.83−1.85 AU

    Observations of pre-stellar cores

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    Our understanding of the physical and chemical structure of pre-stellar cores, the simplest star-forming sites, has significantly improved since the last IAU Symposium on Astrochemistry (South Korea, 1999). Research done over these years has revealed that major molecular species like CO and CS systematically deplete onto dust grains at the interior of pre-stellar cores, while species like N2H+ and NH3 survive in the gas phase and can usually be detected towards the core centers. Such a selective behaviour of molecular species gives rise to a differentiated (onion-like) chemical composition, and manifests itself in molecular maps as a dichotomy between centrally peaked and ring-shaped distributions. From the point of view of star-formation studies, the identification of molecular inhomogeneities in cores helps to resolve past discrepancies between observations made using different tracers, and brings the possibility of self-consistent modelling of the core internal structure. Here I present recent work on determining the physical and chemical structure of two pre-stellar cores, L1498 and L1517B, using observations in a large number of molecules and Monte Carlo radiative transfer analysis. These two cores are typical examples of the pre-stellar core population, and their chemical composition is characterized by the presence of large freeze out holes in most molecular species. In contrast with these chemically processed objects, a new population of chemically young cores has started to emerge. The characteristics of its most extreme representative, L1521E, are briefly reviewed.Comment: 10 pages, 5 figures. To appear in IAU 231 conf. proc. "Astrochemistry: Recent Successes and Current Challenges," eds. D.C. Lis, G.A. Blake, and E. Herbs

    Effect of motion frequency spectrum on subjective comfort response

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    In order to model passenger reaction to present and future aircraft environments, it is necessary to obtain data in several ways. First, of course, is the gathering of environmental and passenger reaction data on commercial aircraft flights. In addition, detailed analyses of particular aspects of human reaction to the environment are best studied in a controllable experimental situation. Thus the use of simulators, both flight and ground based, is suggested. It is shown that there is a reasonably high probability that the low frequency end of the spectrum will not be necessary for simulation purposes. That is, the fidelity of any simulation which omits the very low frequency content will not yield results which differ significantly from the real environment. In addition, there does not appear to be significant differences between the responses obtained in the airborne simulator environment versus those obtained on commercial flights

    WSC-07: Evolving the Web Services Challenge

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    Service-oriented architecture (SOA) is an evolving architectural paradigm where businesses can expose their capabilities as modular, network-accessible software services. By decomposing capabilities into modular services, organizations can share their offerings at multiple levels of granularity while also creating unique access points for their peer organizations. The true impact of SOA will be realized when 3rd party organizations can obtain a variety of services, on-demand, and create higher-order composite business processes. The Web Services Challenge (WSC) is a forum where academic and industry researchers can share experiences of developing tools that automate the integration of web services. In the third year (i.e. WSC-07) of the Web Services Challenge, software platforms will address several new composition challenges. Requests and results will be transmitted within SOAP messages. In addition, semantic representations will be both represented in the eXtensible Markup Language (XML) and in the Web Ontology Language (OWL). Finally, composite processes will have both sequential and concurrent branches

    The millimeter and submillimeter laboratory spectrum of methyl formate in its ground symmetric torsional state

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    Over 200 rotational lines of methyl formate in its ground (v-t = 0), symmetric (A) torsional state have been measured in the frequency range 140-550 GHz. Analysis of these and lower frequency transitions permits accurate prediction (≀0.1 MHz) of over 10,000 transitions at frequencies below 600 GHz with angular momentum J ≀ 50. The measured spectral lines have permitted identification of over 100 new methyl formate lines in Orion

    High-Resolution 4.7 Micron Keck/NIRSPEC Spectra of Protostars. II. Detection of the ^(13)CO Isotope in Icy Grain Mantles

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    The high-resolution (R = 25,000) infrared M-band spectrum of the massive protostar NGC 7538 IRS 9 shows a narrow absorption feature at 4.779 ÎŒm (2092.3 cm^(-1)) that we attribute to the vibrational stretching mode of the ^(13)CO isotope in pure CO icy grain mantles. This is the first detection of ^(13)CO in icy grain mantles in the interstellar medium. The ^(13)CO band is a factor of 2.3 narrower than the apolar component of the ^(12)CO band. With this in mind, we discuss the mechanisms that broaden solid-state absorption bands. It is shown that ellipsoidally shaped pure CO grains fit the bands of both isotopes at the same time. Slightly worse but still reasonable fits are also obtained by CO embedded in N_2-rich ices and thermally processed O_2-rich ices. In addition, we report new insights into the nature and evolution of interstellar CO ices by comparing the very high resolution multicomponent solid ^(12)CO spectrum of NGC 7538 IRS 9 with that of the previously studied low-mass source L1489 IRS. The narrow absorption of apolar CO ices is present in both spectra but much stronger in NGC 7538 IRS 9. It is superposed on a smooth broad absorption feature well fitted by a combination of CO_2 and H_2O-rich laboratory CO ices. The abundances of the latter two ices, scaled to the total H_2O ice column, are the same in both sources. We thus suggest that thermal processing manifests itself as evaporation of apolar ices only and not the formation of CO_2 or polar ices. Finally, the decomposition of the ^(12)CO band is used to derive the ^(12)CO/^(13)CO abundance ratio in apolar ices. A ratio of ^(12)CO/^(13)CO = 71 ± 15 (3 σ) is deduced, in good agreement with gas-phase CO studies (~77) and the solid ^(12)CO_2/^(13)CO_2 ratio of 80 ± 11 found in the same line of sight. The implications for the chemical path along which CO_2 is formed are discussed

    The laboratory millimeter-wave spectrum of methyl formate in its ground torsional E state

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    Over 250 rotational transitions of the internal rotor methyl formate (HCOOCH_3) in its ground v_t = 0 degenerate (E) torsional substate have been measured in the millimeter-wave spectral region. These data and a number of E-state lines identified by several other workers have been analyzed using an extension of the classical principal-axis method in the high barrier limit. The resulting rotational constants allow accurate prediction of the v_t = 0 E substate methyl formate spectrum below 300 GHz between states with angular momentum J ≀ 30 and rotational energy E_(rot)≀ 350cm^(-1). The calculated transition frequencies for the E state, when combined with the results of the previous analysis of the ground-symmetric, nondegenerate state, account for over 200 of the emission lines observed toward Orion in a recent survey of the 215-265 GHz band
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