7 research outputs found

    IRS Scan-mapping of the Wasp-waist Nebula (IRAS 16253–2429). I. Derivation of Shock Conditions from H_2 Emission and Discovery of 11.3 μm PAH Absorption

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    The outflow driven by the Class 0 protostar, IRAS 16253–2429, is associated with bipolar cavities visible in scattered mid-infrared light, which we refer to as the Wasp-Waist Nebula. InfraRed Spectometer (IRS) scan mapping with the Spitzer Space Telescope of a ~1' × 2' area centered on the protostar was carried out. The outflow is imaged in six pure rotational (0-0 S(2) through 0-0 S(7)) H_2 lines, revealing a distinct, S-shaped morphology in all maps. A source map in the 11.3 μm polycyclic aromatic hydrocarbon (PAH) feature is presented in which the protostellar envelope appears in absorption. This is the first detection of absorption in the 11.3 μm PAH feature. Spatially resolved excitation analysis of positions in the blue- and redshifted outflow lobes, with extinction-corrections determined from archival Spitzer 8 μm imaging, shows remarkably constant temperatures of ~1000 K in the shocked gas. The radiated luminosity in the observed H_2 transitions is found to be 1.94 ± 0.05 × 10^(–5) L_⊙ in the redshifted lobe and 1.86 ± 0.04 × 10^(–5) L_⊙ in the blueshifted lobe. These values are comparable to the mechanical luminosity of the flow. By contrast, the mass of hot (T ~ 1000 K) H_2 gas is 7.95 ± 0.19 × 10^(–7) M_⊙ in the redshifted lobe and 5.78 ± 0.17 × 10^(–7) M_⊙ in the blueshifted lobe. This is just a tiny fraction, of order 10^(–3), of the gas in the cold (30 K), swept-up gas mass derived from millimeter CO observations. The H_2 ortho/para ratio of 3:1 found at all mapped points in this flow suggests previous passages of shocks through the gas. Comparison of the H_2 data with detailed shock models of Wilgenbus et al. shows the emitting gas is passing through Jump (J-type) shocks. Pre-shock densities of 10^4 cm^(–3)≤ n _H ≤ 10^5 cm^(–3) are inferred for the redshifted lobe and n _H ≤ 10^3 cm^(–3) for the blueshifted lobe. Shock velocities are 5 km s^(–1) ≤ v_s ≤ 10 km s^(–1) for the redshifted gas and v_s = 10 km s^(–1) for the blueshifted gas. Initial transverse (to the shock) magnetic field strengths for the redshifted lobe are in the range 10-32 μG, and just 3 μG for the blueshifted lobe. A cookbook for using the CUBISM contributed software for IRS spectral mapping data is presented in the Appendix

    Protostellar Outflows in L1340

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    We have searched the L1340 A, B, and C clouds for shocks from protostellar outflows using the H_2 2.122 μm near-infrared line as a shock tracer. Substantial outflow activity has been found in each of the three regions of the cloud (L1340 A, L1340 B, and L1340 C). We find 42 distinct shock complexes (16 in L1340 A, 11 in L1340 B, and 15 in L1340 C). We were able to link 17 of those shock complexes into 12 distinct outflows and identify candidate source stars for each. We examine the properties (A_V, T_(bol), and L_(bol)) of the source protostars and compare them to the properties of the general population of Class 0/I and flat spectral energy distribution protostars and find that there is an indication, albeit at low statistical significance, that the outflow-driving protostars are drawn from a population with lower A_V, higher L_(bol), and lower T_(bol) than the general population of protostars

    Spitzer Warm Mission Transition and Operations

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    Following the successful dynamic planning and implementation of IRAC Warm Instrument Characterization activities, transition to Spitzer Warm Mission operations has gone smoothly. Operation teams procedures and processes required minimal adaptation and the overall composition of the Mission Operation System retained the same functionality it had during the Cryogenic Mission. While the warm mission scheduling has been simplified because all observations are now being made with a single instrument, several other differences have increased the complexity. The bulk of the observations executed to date have been from ten large Exploration Science programs that, combined, have more complex constraints, more observing requests, and more exo-planet observations with durations of up to 145 hours. Communication with the observatory is also becoming more challenging as the Spitzer DSN antenna allocations have been reduced from two tracking passes per day to a single pass impacting both uplink and downlink activities. While IRAC is now operating with only two channels, the data collection rate is roughly 60% of the four-channel rate leaving a somewhat higher average volume collected between the less frequent passes. Also, the maximum downlink data rate is decreasing as the distance to Spitzer increases requiring longer passes. Nevertheless, with well over 90% of the time spent on science observations, efficiency has equaled or exceeded that achieved during the cryogenic mission

    Protostellar Outflows in L1340

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    We have searched the L1340 A, B, and C clouds for shocks from protostellar outflows using the H_2 2.122 μm near-infrared line as a shock tracer. Substantial outflow activity has been found in each of the three regions of the cloud (L1340 A, L1340 B, and L1340 C). We find 42 distinct shock complexes (16 in L1340 A, 11 in L1340 B, and 15 in L1340 C). We were able to link 17 of those shock complexes into 12 distinct outflows and identify candidate source stars for each. We examine the properties (A_V, T_(bol), and L_(bol)) of the source protostars and compare them to the properties of the general population of Class 0/I and flat spectral energy distribution protostars and find that there is an indication, albeit at low statistical significance, that the outflow-driving protostars are drawn from a population with lower A_V, higher L_(bol), and lower T_(bol) than the general population of protostars

    Spitzer Space Telescope observatory planning and scheduling team

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    Launched as the space infrared telescope facility (SIRTF) in August, 2003 and renamed in early 2004, the Spitzer space telescope is performing an extended series of science observations at wavelengths ranging from 3 to 180 microns. The California Institute of Technology is the home of the Spitzer Science Center (SSC) and operates the science operations system (SOS), which supports science operations of the observatory. A key function supported by the SOS is the long-range planning and short-term scheduling of the observatory. This paper describes the role and function of the SSC observatory planning and scheduling team (OPST), its operational interfaces, processes, and tools

    A Mid-Infrared Study of the Class 0 Cluster in LDN 1448

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    We present ground-based mid-infrared observations of Class 0 protostars in LDN 1448. Of the five known protostars in this cloud, we detected two, L1448N:A and L1448C, at 12.5, 17.9, 20.8, and 24.5 microns, and a third, L1448 IRS 2, at 24.5 microns. We present high-resolution images of the detected sources, and photometry or upper limits for all five Class 0 sources in this cloud. With these data, we are able to augment existing spectral energy distributions (SEDs) for all five objects and place them on an evolutionary status diagram.Comment: Accepted by the Astronomical Journal; 26 pages, 9 figure

    Unsaturated Hydraulic Conductivity Estimation of a Forest Soil Assuming a Stochastic-Convective Process

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    Measurement of soil hydraulic conductivity requires considerable time and effort, which makes it difficult to characterize this important parameter across larger areas, especially remote forest regions. Forest soils are frequently texturally coarser than those in agricultural areas, making them more probable candidates for applications building on the stochastic-convective hypothesis. We developed a method for measuring unsaturated soil hydraulic conductivity based on the analysis of a dye tracer resident concentration profile. In the experiment, partially saturated, steady-state water flow was established in a forest allophanic soil by a sprinkler operating at 50 mm h^(–1), after which the water application was switched to a 10 mg L^(–1) Brilliant Blue FCF solution. The tracer was applied continuously until its cumulative infiltration reached 125 mm, after which the stained soil profile was exposed and photographed. The picture was subjected to an image analysis procedure designed to obtain the resident concentration profile of the tracer. The concentration was fitted to the solution of the convective lognormal transfer function, whose parameters were used in further calculations using functional relationships derived from the stochastic-convective framework. The resulting hydraulic conductivity as a function of soil water content agreed within an order of magnitude with the relationship obtained by the instantaneous profile method. While the Mualem–van Genuchten model better reproduced the shape of that relationship, it strongly underestimated the hydraulic conductivity across the soil water content interval of interest (0.1–0.4). Finally, ways to improve the predictive capacity of the stochastic-convective approach in terms of the general trends of the functional relationship were proposed
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