Molecular Cloud Formation behind Shock Waves
Motivated by our previous paper, in which we argued for the formation of molecular clouds from large-scale flows in the diffuse Galactic interstellar medium, we examine the formation of molecular gas behind shocks in atomic gas using a one-dimensional chemical/dynamical model. In our analysis we place particular emphasis on constraints placed on the dynamical evolution by the chemistry. The most important result of this study is to stress the importance of shielding the moleculargas from the destructive effects of UVradiation. For shock ram pressures comparable to or exceeding typical local interstellar medium pressures, self-shielding controls the formation time of molecular hydrogen, but CO formation requires shielding of the interstellar radiation field by dust grains. We find that for typical parameters the molecular hydrogen fractional abundance can become significant well before CO forms. The timescale for (CO) molecular cloud formation is not set by the H2 formation rate on grains, but rather by the timescale for accumulating a sufficient column density or extinction, AV k0:7. The local ratio of atomic to molecular gas (4:1), coupled with short estimates for the lifetimes of molecular clouds (3‐5 Myr), suggests that the timescales for accumulating molecular clouds from atomic material typically must be no longer than about 12‐20 Myr. Based on the shielding requirement, this implies that the typical product of preshock density and velocity must benvk20 cm � 3 km s � 1 . In turn, depending on the shock velocity, this implies shock ram pressures that are a few times the typical estimated local turbulent gas pressure and comparable to the total pressures(gasplusmagneticpluscosmicrays).CoupledwiththerapidformationofCOonceshieldingissufficient, flow-driven formation of molecular clouds in the local interstellar medium can occur sufficiently rapidly to account for observations. We also provide detailed predictions of atomic and molecular emission and absorption that track the formation of a molecular cloud from a purely atomic medium, with a view toward helping to verify cloud formation by shock waves. However, our predictions suggest that the detection of the pre-CO stages will be challenging. Finally, we provide an analytic solution for time-dependent H2 formation that may be of use in numerical hydrodynamic calculations. Subject headingg ISM: clouds — ISM: evolution — ISM: kinematics and dynamics — ISM: molecules — shock waves — stars: formation

title: Ejecta, Dust, and Synchrotron Radiation in SNR B0540–69.3: A More Crab-Like Remnant than the Crab
abstract: We present near- and mid-infrared observations of the pulsar-wind nebula (PWN) SNR B0540?69.3 and its associated supernova remnant made with the Spitzer Space Telescope. We report detections of the PWN with all four IRAC bands, the 24 ?m band of MIPS, and the Infrared Spectrograph (IRS). We find no evidence of IR emission from the X-ray/radio shell surrounding the PWN resulting from the forward shock of the supernova blast wave. The flux of the PWN itself is dominated by synchrotron emission at shorter (IRAC) wavelengths, with a warm dust component longward of 20 ?m. We show that this dust continuum can be explained by a small amount [~ -->(1?3) ? 10?3 -->M?] of dust at a temperature of ~50-65 K, heated by the shock wave generated by the PWN being driven into the inner edge of the ejecta. This is evidently dust synthesized in the supernova. We also report the detection of several lines in the spectrum of the PWN and present kinematic information about the PWN as determined from these lines. Kinematics are consistent with previous optical studies of this object. Line strengths are also broadly consistent with what one expects from optical line strengths. We find that lines arise from slow (~20 km s?1) shocks driven into oxygen-rich clumps in the shell swept up by an iron-nickel bubble, which have a density contrast of ~100-200 relative to the bulk of the ejecta, and that faster shocks (~250 km s?1) in the hydrogen envelope are required to heat dust grains to observed temperatures. We infer from estimates of heavy-element ejecta abundances that the progenitor star was likely in the range of 20-25 -->M?.

title: A DETAILED ANALYSIS OF A CYGNUS LOOP SHOCK-CLOUD INTERACTION
abstract: The XA region of the Cygnus Loop is a complex zone of radiative and nonradiatve shocks interacting with interstellar clouds. We combine five far ultraviolet spectral observations from the Hopkins Ultraviolet Telescope (HUT), a grid of 24 IUE spectra, and a high-resolution long-slit Hα spectrum to study the spatial emission line variations across the region. These spectral data are placed in context using ground-based optical emission-line images of the region and a far-UV image obtained by the Ultraviolet Imaging Telescope (UIT). The presence of high-ionization species (O VI, N V, and C IV) indicates a shock velocity near 170 km s-1 while other diagnostics indicate vsh ≈ 140 km s-1. It is likely that a large range of shock velocities may exist at a spatial scale smaller than we are able to resolve. By comparing C IV λ1550, C III λ977, and C III] λ1909, we explore resonance scattering across the region. We find that a significant column depth is present at all positions, including those not near bright optical or UV filaments. Analysis of the O VI doublet ratio suggests an average optical depth of about unity in that ion, while flux measurements of [Si VIII] λ1443 suggest a hot component in the region at just below 106 K. Given the brightness of the O VI emission and the age of the interaction, we rule out the mixing-layer interpretation of the UV emission. Furthermore, we formulate a picture of the XA region as that of an encounter of the blast wave with a finger of dense gas protruding inward from the pre-supernova cavity.

title: ULTRAVIOLET SPECTROSCOPY OF NARROW CORONAL MASS EJECTIONS
abstract: We present Ultraviolet Coronagraph Spectrometer (UVCS) observations of five narrow coronal mass ejections (CMEs) that were among 15 narrow CMEs originally selected by Gilbert and coworkers. Two events (1999 March 27, April 15) were "structured," i.e., in white-light data they exhibited well-defined interior features, and three (1999 May 9, May 21, June 3) were "unstructured," i.e., appeared featureless. In UVCS data the events were seen as 4°-13° wide enhancements of the strongest coronal lines H I Lyα and O VI λλ1032, 1037. We derived electron densities for several of the events from the Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2 white-light observations. They are comparable to or smaller than densities inferred for other CMEs. We modeled the observable properties of examples of the structured (1999 April 15) and unstructured (1999 May 9) narrow CMEs at different heights in the corona between 1.5 and 2 R☉. The derived electron temperatures, densities, and outflow speeds are similar for those two types of ejections. They were compared with properties of polar coronal jets and other CMEs. We discuss different scenarios of narrow CME formation as either a jet formed by reconnection onto open field lines or a CME ejected by expansion of closed field structures. Overall, we conclude that the existing observations do not definitively place the narrow CMEs into the jet or the CME picture, but the acceleration of the 1999 April 15 event resembles acceleration seen in many CMEs, rather than constant speeds or deceleration observed in jets.

title: SIMULTANEOUS CHANDRA AND RXTE SPECTROSCOPY OF THE MICROQUASAR H 1743 − 22 : CLUES TO DISK WIND AND JET FORMATION FROM A VARIABLE IONIZED OUTFLOW
abstract: We observed the bright phase of the 2003 outburst of the Galac tic black hole candidate H 1743 − 22 in Xrays simultaneously withChandra andRXTE on four occasions. The Chandra/HETGS spectra reveal narrow, variable (He-like) Fe XXV and (H-like) Fe XXVI resonance abs orption lines. In the first observation, the Fe XXVI line has a FWHM of 1800± 400 km/s and a blue-shift of 700 ± 200 km/s, suggesting that the highly ionized medium is an outflow. Moreover, the Fe XXV line is obse rved to vary significantly on a timescale of a few hundred seconds in the first observation, which correspo nds to the Keplerian orbital period at approximately 104 rg (whererg = GM/c2). Our models for the absorption geometry suggest that a comb ination of geometric effects and changing ionizing flux are required to account fo r he large changes in line flux observed between observations, and that the absorption likely occurs at a rad ius less than 10 4 rg for a 10M⊙ black hole. Viable models for the absorption geometry include cyclic absorpti n due to an accretion disk structure, absorption in a clumpy outflowing disk wind, or possibly a combination of the se two. If the wind in H 1743 −322 has unity filling factor, the highest implied mass outflow rate is 20% of the Edd ington mass accretion rate. This wind may be a hot precursor to the Seyfert-like, outflowing “warm absorber” g eometries recently found in the Galactic black holes GX 339-4 and XTE J1650 −500. We discuss these findings in the context of ionized Fe abs orption lines found in the spectra of other Galactic sources, and connections to warm absorbers, winds, and jets in other accreting systems.

title: OBSERVATIONS AND INTERPRETATION OF A LOW CORONAL SHOCK WAVE OBSERVED IN THE EUV BY THE SDO/AIA
abstract: Taking advantage of both the high temporal and spatial resolutions of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we studied a limb coronal shock wave and its associated extreme ultraviolet (EUV) wave that occurred on 2010 June 13. Our main findings are: (1) the shock wave appeared clearly only in the channels centered at 193 angstrom and 211 angstrom as a dome-like enhancement propagating ahead of its associated semi-spherical coronal mass ejection (CME) bubble; (2) the density compression of the shock is 1.56 according to radio data and the temperature of the shock is around 2.8 MK; (3) the shock wave first appeared at 05: 38 UT, 2 minutes after the associated flare has started and 1 minute after its associated CME bubble appeared; (4) the top of the dome-like shock wave set out from about 1.23 R-circle dot and the thickness of the shocked layer is similar to 2 x 10(4) km; (5) the speed of the shock wave is consistent with a slight decrease from about 600 km s(-1) to 550 km s(-1); and (6) the lateral expansion of the shock wave suggests a constant speed around 400 km s(-1), which varies at different heights and directions. Our findings support the view that the coronal shock wave is driven by the CME bubble, and the on-limb EUV wave is consistent with a fast wave or at least includes the fast wave component.

title: Radiation effects in detector electronics
abstract: Radiation effects produced in electronics for detectors operated at intense high-energy particle accelerators are reviewed. Both displacement damage in semiconductor material and long-lived ionization effects produced by charge trapping in dielectrics near interfaces are potentially serious. Hardening and test methods must recognize the particular circuit's functional requirements. The dominant defects and appropriate hardening method depend on the important parameter (e.g., offset, leakage, noise) as well as the operating frequency.