Kathleen A. Barger

Complex impedance measurements of calorimeters and bolometers : Correction for stray impedances

Impedance measurements provide a useful probe of the physics of bolometers and calorimeters. We describe a method for measuring the complex impedance of these devices. In previous work, stray impedances and readout electronics of the measurement apparatus have resulted in artifacts in the impedance data. The technique allows experimenters to find an independent Thevenin or Norton equivalent circuit for each frequency. This method allows experimenters to easily isolate the device impedance from the effects of parasitic impedances and frequency dependent gains in amplifiers.

On the Metallicity and Origin of the Smith High-Velocity Cloud

The Smith Cloud is a gaseous high-velocity cloud (HVC) in an advanced state of accretion, only 2.9 kpc below the Galactic plane and due to impact the disk in 27 Myr. It is unique among HVCs in having a known distance (12.4+/-1.3 kpc) and a well-constrained 3D velocity (296 km/s), but its origin has long remained a mystery. Here we present the first absorption-line measurements of its metallicity, using HST/COS UV spectra of three AGN lying behind the Cloud together with Green Bank Telescope 21 cm spectra of the same directions. Using Voigt-profile fitting of the S II 1250, 1253, 1259 triplet together with ionization corrections derived from photoionization modeling, we derive the sulfur abundance in each direction; a weighted average of the three measurements gives [S/H]=-0.28+/-0.14, or 0.53+0.21-0.15 solar metallicity. The finding that the Smith Cloud is metal-enriched lends support to scenarios where it represents recycled Galactic material rather than the remnant of a dwarf galaxy or accreting intergalactic gas. The metallicity and trajectory of the Cloud are both indicative of an origin in the outer disk. However, its large mass and prograde kinematics remain to be fully explained. If the cloud has accreted cooling gas from the corona during its fountain trajectory, as predicted in recent theoretical work, its current mass would be higher than its launch mass, alleviating the mass concern.

Observed limits on charge exchange contributions to the diffuse X-ray background

We present a high resolution spectrum of the diffuse X-ray background from 0.1 to 1 keV for a ~1 region of the sky centered at l=90, b=+60 using a 36-pixel array of microcalorimeters flown on a sounding rocket. With an energy resolution of 11 eV FWHM below 1 keV, the spectrums observed line ratios help separate charge exchange contributions originating within the heliosphere from thermal emission of hot gas in the interstellar medium. The X-ray sensitivity below 1 keV was reduced by about a factor of four from contamination that occurred early in the flight, limiting the significance of the results. The observed centroid of helium-like O VII is 568+2-3 eV at 90% confidence. Since the centroid expected for thermal emission is 568.4 eV while for charge exchange is 564.2 eV, thermal emission appears to dominate for this line complex, consistent with much of the high-latitude O VII emission originating in 2-3 x 10^6 K gas in the Galactic halo. On the other hand, the observed ratio of C VI Ly gamma to Ly alpha is 0.3+-0.2. The expected ratios are 0.04 for thermal emission and 0.24 for charge exchange, indicating that charge exchange must contribute strongly to this line and therefore potentially to the rest of the ROSAT R12 band usually associated with 10^6 K emission from the Local Hot Bubble. The limited statistics of this experiment and systematic uncertainties due to the contamination require only >32% thermal emission for O VII and >20% from charge exchange for C VI at the 90% confidence level. An experimental gold coating on the silicon substrate of the array greatly reduced extraneous signals induced on nearby pixels from cosmic rays passing through the substrate, reducing the triggered event rate by a factor of 15 from a previous flight of the instrument.

DOWN-THE-BARREL AND TRANSVERSE OBSERVATIONS OF THE LARGE MAGELLANIC CLOUD: EVIDENCE FOR A SYMMETRIC GALACTIC WIND ON THE NEAR AND FAR SIDES OF THE GALAXY*

We compare the properties of gas flows on both the near and far side of the Large Magellanic Cloud (LMC) disk using Hubble Space Telescope UV absorption-line observations toward an AGN behind (transverse) and a star within (down-the-barrel) the LMC disk at an impact parameter of 3.2 kpc. We find that even in this relatively quiescent region gas flows away from the disk at speeds up to

Warm Ionized Medium throughout the Sagittarius–Carina Arm

\sim

Chemical Abundances in the Leading Arm of the Magellanic Stream

100 km/s in broad and symmetrical absorption in the low and high ions. The symmetric absorption profiles combined with previous surveys showing little evidence that the ejected gas returns to the LMC and provide compelling evidence that the LMC drives a global, large-scale outflow across its disk, which is the likely result of a recent burst of star formation in the LMC. We find that the outflowing gas is multiphase, ionized by both photoionization (SiII and SiIII) and collisional ionization (SiIV and CIV). We estimate a total mass and outflow rate to be

New Constraints on the Nature and Origin of the Leading Arm of the Magellanic Stream

>10^7

THE COS/UVES ABSORPTION SURVEY OF THE MAGELLANIC STREAM. III. IONIZATION, TOTAL MASS, AND INFLOW RATE ONTO THE MILKY WAY*

Msun and

WARM IONIZED GAS REVEALED IN THE MAGELLANIC BRIDGE TIDAL REMNANT: CONSTRAINING THE BARYON CONTENT AND THE ESCAPING IONIZING PHOTONS AROUND DWARF GALAXIES

>0.4

The X-ray Quantum Calorimeter Sounding Rocket Experiment: Improvements for the Next Flight

Msun/yr. Since the velocity of this large-scale outflow does not reach the LMC escape velocity, the gas removal is likely aided by either ram-pressure stripping with the Milky Way halo or tidal interactions with the surrounding galaxies, implying that the environment of LMC-like or dwarf galaxies plays an important role in their ultimate gas starvation. Finally we reassess the mass and plausible origins of the high-velocity complex toward the LMC given its newly-determined distance that places it in the lower Milky Way halo and sky-coverage that shows it extends well beyond the LMC disk.