37,446 research outputs found
A Narrowband Imaging Survey for High Redshift Galaxies in the Near Infrared
A narrowband imaging survey of 276 square minutes of arc was carried out at
near infrared wavelengths to search for emission line objects at high
redshifts. Most of the fields contained a known quasar or radio galaxy at a
redshift that placed one of the strong, restframe optical emission lines
(H-alpha, [O III], H-beta, or [O II]) in the bandpass of the narrowband filter.
The area weighted line flux limit over the entire survey was 3.4x10e-16
erg/cm2/s (3-sigma), while the most sensitive limits reached 1.4x10e-16
erg/cm2/s. Integrating the volume covered by all four optical emission lines in
each image yields a total comoving volume surveyed of 1.4x10e5 cubic
megaparsecs. Considering only H-alpha emission in the K band (2.05 < z < 2.65),
where the survey is most sensitive, the survey covered a comoving volume of
3.0x10e4 cubic megaparsecs to a volume-weighted average star formation rate of
112 M-solar/yr (for Ho = 50 km/s/Mpc, Omega = 1). This is the most extensive
near-infrared survey which is deep enough to have a reasonable chance at
detecting strong line emission from an actively star-forming population of
galaxies, when d against simple models of galaxy formation. One emission line
candidate was identified in this survey, and subsequently confirmed
spectroscopically.Comment: To appear in the Astronomical Journal, November 1996. 23 pages,
including 2 tables and 7 figure
A non-LTE abundance analysis of the post-AGB star ROA 5701
An analysis of high-resolution Anglo-Australian Telescope (AAT)/ University
College London Echelle Spectrograph (UCLES) optical spectra for the ultraviolet
(UV)-bright star ROA 5701 in the globular cluster omega Cen (NGC 5139) is
performed, using non-local thermodynamic equilibrium (non-LTE) model
atmospheres to estimate stellar atmospheric parameters and chemical
composition. Abundances are derived for C, N, O, Mg, Si and S, and compared
with those found previously by Moehler et al. We find a general metal
underabundance relative to young B-type stars, consistent with the average
metallicity of the cluster. Our results indicate that ROA 5701 has not
undergone a gas-dust separation scenario as previously suggested. However, its
abundance pattern does imply that ROA 5701 has evolved off the AGB prior to the
onset of the third dredge-up.Comment: 9 pages, 2 figures. Accepted for publication in MNRAS (Online Early
Weak Localization Thickness Measurements of Si:P Delta-Layers
We report on our results for the characterization of Si:P delta-layers grown
by low temperature molecular beam epitaxy. Our data shows that the effective
thickness of a delta-layer can be obtained through a weak localization analysis
of electrical transport measurements performed in perpendicular and parallel
magnetic fields. An estimate of the diffusivity of phosphorous in silicon is
obtained by applying this method to several samples annealed at 850 Celsius for
intervals of zero to 15 minutes. With further refinements, this may prove to be
the most precise method of measuring delta-layer widths developed to date,
including that of Secondary Ion Mass Spectrometry analysis
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