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Limits on Chromospheres and Convection among the Main-Sequence A Stars
Ayres, Thomas R.; Redfield, Seth; Simon, Theodore +1 more
In deeply convective stars, the nonthermal energy required to heat the chromosphere ultimately is supplied by turbulent magnetoconvection. Because the early and middle A stars have very shallow convective layers, they are not expected to produce enough magnetoconvective power to sustain luminous chromospheres or hot coronae. Here we describe a sea…
The Interacting Dwarf Galaxy NGC 3077: The Interplay of Atomic and Molecular Gas with Violent Star Formation
Scoville, Nick; Walter, Fabian; Martin, Crystal +1 more
We present a comprehensive multiwavelength study of the nearby interacting dwarf galaxy NGC 3077 (member of the M81 triplet). High-resolution VLA H I observations show that most of the atomic gas (~90%) around NGC 3077 is situated in a prominent tidal arm with a complex velocity structure. Little H I (~5×107 Msolar) is associ…
Four-point Cluster application of magnetic field analysis tools: The discontinuity analyzer
Balogh, A.; Glassmeier, K. -H.; Dunlop, M. W.
The Cluster spacecraft have collected 3-D information on magnetic field structures at small to medium scales (100-1000 km) in the Earth's dayside magnetosphere, magnetosheath, and near solar wind. We focus here on the first application of the discontinuity analyzer analysis technique (determination of the geometry and motion of magnetic discontinu…
Fundamental Properties and Distances of Large Magellanic Cloud Eclipsing Binaries. III. EROS 1044
Fitzpatrick, Edward L.; Guinan, Edward F.; Udalski, Andrzej +2 more
We present results from a detailed analysis of a third eclipsing binary (EB) system in the Large Magellanic Cloud, EROS 1044 (~B2 IV-V+~B2 III-IV). Our study combines the ``classical'' EB study of light and radial velocity curves with detailed modeling of the observed spectral energy distribution and yields an essentially complete picture of the s…
Optically Faint Counterparts to the Infrared Space Observatory FIRBACK 170 Micron Population: Discovery of Cold, Luminous Galaxies at High Redshift
Smail, I.; Ivison, R. J.; Helou, G. +3 more
We present Keck spectroscopy and UKIRT near-IR imaging observations of two 170 µm-selected sources from the Infrared Space Observatory (ISO) FIRBACK survey that have faint counterparts in the optical and r-K~5. Both sources were expected to lie at z>1, based on their far-infrared, submillimeter, and radio fluxes, assuming a spectral energ…
High-resolution X-ray imaging and spectroscopy of the core of NGC 4945 with XMM-Newton and Chandra
Schurch, N. J.; Warwick, R. S.; Roberts, T. P.
We utilize the complementary capabilities of XMM-Newton and Chandra to conduct a detailed imaging and spectral study of the nearby galaxy NGC 4945 focusing on its nucleus and immediate surroundings (within ~ kpc of the nucleus). A complex morphology is revealed including a predominantly hard, but partially resolved, nuclear source plus a spectrall…
Dust in I Zw 18 from Hubble Space Telescope Narrowband Imaging
Cannon, John M.; Skillman, Evan D.; Garnett, Donald R. +1 more
We present new WFPC2 narrowband imaging of the blue compact dwarf galaxy I Zw 18, which is host to the lowest metallicity H II regions known. Images at Hα and Hβ are combined with archival broadband images to allow the study of the ionized gas distribution and morphology. Analysis of the Hα/Hβ flux ratio reveals significant enhancements in some ar…
Modeling the heliospheric current sheet: Solar cycle variations
Riley, Pete; Linker, J. A.; Mikić, Z.
In this report we employ an empirically driven, three-dimensional MHD model to explore the evolution of the heliospheric current sheet (HCS) during the course of the solar cycle. We compare our results with a simpler ``constant-speed'' approach for mapping the HCS outward into the solar wind to demonstrate that dynamic effects can substantially de…
N-Band Observations of Henize 2-10: Unveiling the Dusty Engine of a Starburst Galaxy
Johnson, Kelsey E.; Vacca, William D.; Conti, Peter S.
As part of an ongoing program to better understand the early stages of massive star cluster evolution and the physical conditions for their formation, we have obtained J, H, K', and N (10.8 µm) images of the nuclear region of the starburst galaxy He 2-10. The N-band images were obtained with the Gemini North Telescope. In only 10 minutes of …
Evolution of very small particles in the southern part of Orion B observed by ISOCAM
Perault, M.; Olofsson, G.; Boulanger, F. +19 more
We present ISOCAM observations (5-18 mu m) of the southern part of Orion B, including the reflection nebula NGC 2023 and the Horsehead nebula illuminated by the B star HD 37903 and the O star sigma Orionis, respectively. Due to the limited radiation field, the emission in these wavelengths is due to very small particles which are heated each time …