Heating rate profiles in galaxy clusters

In recent years, evidence has accumulated suggesting that the gas in galaxy clusters is heated by non-gravitational processes. Here, we calculate the heating rates required to maintain a physically motivated mass flow rate, in a sample of seven galaxy clusters. We employ the spectroscopic mass deposition rates as an observational input along with temperature and density data for each cluster. On energetic grounds, we find that thermal conduction could provide the necessary heating for A2199, Perseus, A1795 and A478. However, the suppression factor of the classical Spitzer value is a different function of radius for each cluster. Based on the observations of plasma bubbles, we also calculate the duty cycles for each active galactic nucleus (AGN), in the absence of thermal conduction, which can provide the required energy input. With the exception of Hydra-A, it appears that each of the other AGNs in our sample requires duty cycles of roughly 10⁶–10⁷ yr to provide their steady-state heating requirements. If these duty cycles are unrealistic, this may imply that many galaxy clusters must be heated by very powerful Hydra-A type events interspersed between more frequent smaller scale outbursts. The suppression factors for the thermal conductivity required for combined heating by AGN and thermal conduction are generally acceptable. However, these suppression factors still require 'fine-tuning' of the thermal conductivity as a function of radius. As a consequence of this work, we present the AGN duty cycle as a cooling flow diagnostic.     

Detectors For Space Science

The design of detector systems for flight applications requires the consideration of a number of issues unique to space instrumentation. Flight detectors must endure hostile radiation environments and thermal extremes. Paramount importance is given to reliability since inflight replacement is at best difficult and usually impossible. Flight detectors are also significant cost and design drivers since they often determine key requirements for flight instruments such as volume, mass, power consumption, heat dissipation and communications budgets. In this paper we describe the primary concerns in developing flight detector systems, and review the challenges posed by future NASA and ESA space science missions for detector development.     

Evidence and Implications of Pressure Fluctuations in the ISM

A recent survey of the fine-structure excitation of neutral carbonreveals that the interstellar medium in the Galactic plane exhibits athermal pressure, nT/k, that ranges from about 10³to 10⁴cm^-3K from one location to the next, with occasional excursions in excess of about 10⁵ cm^-3K. The large excitations for small amounts of gas indicate that some regions are either subjected to shocks or must be pressurized within time scales much shorter than the time needed to reach thermal equilibrium. These rapidfluctuations probably arise from the cascade of macroscopic mechanical energyto small scales through a turbulent cascade. One consequence of thiseffect is that changes in gas temperature can arise from near adiabaticcompressions and expansions, and this may explain why investigations of21-cm emission and absorption reveal the presence of hydrogen attemperatures well below the expected values derived from the balance ofvarious known heating and cooling processes.     

THE ELLICOTT METEORITE

Two individual specimens (total weight 15.7 kg) of a new medium octahedrite were found near Ellicott, El Paso County, Colorado. The find is only 1.2 km from the find (in 1890) of the Franceville medium octahedrite. Ellicott and Franceville are distinct meteorites, the latter exhibiting pronounced differences in shock features, kamacite band width, and Ni, Ga, Ge, and Ir contents. Ellicott is a group IA iron while Franceville is in group IIIA.     

A virtual surface concept for nested yield surface plasticity

A return mapping algorithm based on the concept of virtual surfaces is presented for stress integration in the numerical solution of boundary value problems using an elastoplastic multiple yield surface model. Both kinematic hardening and isotropic softening yield surfaces are addressed. With the implementation of virtual surfaces, the active yield surface is located before a stress update is implemented. The return mapping algorithm consists of only two steps. The first step consists of performing the intermediate update of the trial stress corresponding to the translation of all yield surfaces inside the active yield surface. Little calculation is involved in this step. The second step consists of performing the conventional explicit one-step radial return mapping of the updated trial stress on the corresponding active yield surface. The algorithm efficiency resides in the virtual surface based return mapping which preserves the elastic predictor representation of the updated trial stress, and limits iterations to at most two steps.     

Electron-impact excitation of the Cameron system (a3π → X1Σ)of CO

We have studied the excitation of the Cameron bands of carbon monoxide (a³π → X¹Σ⁺) by electron impact on CO and CO₂. This investigation was prompted by a recent study of the Martian airglow by Conway (1981) who concluded that the cross section for the dissociative excitation of the Cameron bands is seven times larger than the laboratory value reported by Ajello (1971a) and by a perplexing inconsistency between the optical cross section and CO(a³π) time-of-flight experiments. We have found now that three factors have contributed to these discrepancies: (1) spectral contamination of the (1,4) Cameron band used by Ajello to normalize the entire Cameron band cross section, (2) major revisions in the magnitude of the CO(a³π) radiative lifetime, and (3) new insights into the effects of the CO(a³π) velocity distribution on the field of view of the emission experiments. The new results largely reconcile the TOF and emission measurements, but they also suggest that the calculated photoelectron fluxes in the Martian atmosphere may be too large by a factor of 3.     

VRI photometry of late dwarf common proper motion stars

Summary From the photometric observations of a sample of late dwarf common proper motion pairs it may be inferred that about 30%–50% of such systems contain one or more additional stellar components. A small fraction of such systems have separations in excess of 5000 A.U.