22,041 research outputs found
Postprocessing techniques for 3D non-linear structures
How graphics postprocessing techniques are currently used to examine the results of 3-D nonlinear analyses, some new techniques which take advantage of recent technology, and how these results relate to both the finite element model and its geometric parent are reviewed
Archival research on absorption lines in violently star-forming galaxies
A computerized analysis of a starburst model is discussed. The model proposes that the absorption line equivalent width should scale with the level of star forming activity. Archival International Ultraviolet Explorer (IUE) data on IUE spectra of luminous blue galaxies were compared with previous IUE observations of extragalactic HII regions and low luminosity galaxies. The comparisons are summarized and causes for offsets are discussed
The small-scale Structure of the Magellanic Stream as a Foundation for Galaxy Evolution
The Magellanic Stream (MS) is the nearest example of a gaseous trail formed
by interacting galaxies. While the substantial gas masses in these kinds of
circumgalactic structures are postulated to represent important sources of fuel
for future star formation, the mechanisms whereby this material might be
accreted back into galaxies remain unclear. Recent neutral hydrogen (HI)
observations have demonstrated that the northern portion of the MS, which
probably has been interacting with the Milky Way's hot gaseous halo for close
to 1000~Myr, has a larger spatial extent than previously recognized, while also
containing significant amounts of small-scale structure. After a brief
consideration of the large-scale kinematics of the MS as traced by the
recently-discovered extension of the MS, we explore the aging process of the MS
gas through the operation of various hydrodynamic instabilities and
interstellar turbulence. This in turn leads to consideration of processes
whereby MS material survives as cool gas, and yet also evidently fails to form
stars. Parallels between the MS and extragalactic tidal features are briefly
discussed with an emphasis on steps toward establishing what the MS reveals
about the critical role of local processes in determining the evolution of
these kinds of systems
Near-IR Spectroscopy of a Young Super-Star Cluster in NGC 6946: Chemical Abundances and Abundance Patterns
Using the NIRSPEC spectrograph at Keck II, we have obtained H and K-band
echelle spectra for a young (10-15 Myr), luminous (MV=-13.2) super-star cluster
in the nearby spiral galaxy NGC 6946. From spectral synthesis and equivalent
width measurements we obtain for the first time accurate abundances and
abundance patterns in an extragalactic super-star cluster. We find
[Fe/H]=-0.45+/-0.08 dex, an average alpha-enhancement of +0.22+/-0.1 dex, and a
relatively low 12C/13C~ 8+/-2 isotopic ratio. We also measure a velocity
dispersion of ~9.1 km/s, in agreement with previous estimates. We conclude that
integrated high-dispersion spectroscopy of massive star clusters is a promising
alternative to other methods for abundance analysis in extragalactic young
stellar populations.Comment: 5 pages, incl. 2 figures. Accepted for publication in MNRAS Letters.
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Cell receptor-independent infection by a neurotropic murine coronavirus.
The cellular receptors for a coronavirus, mouse hepatitis virus (MHV), have been recently identified as one or more members of the carcinoembryonic antigen (CEA) family. The neurotropic JHM strain of MHV (MHV-JHM) possesses a highly fusogenic surface (S) glycoprotein. This protein is now shown to promote the spread of MHV into cells lacking the specific CEA-related MHV receptor. Resistant cells are recruited into MHV-induced syncytium with consequent production of progeny virus. Cell-to-cell spread of virus via membrane fusion without the requirement for specific cell surface receptor offers a novel way for virus to spread within infected hosts
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