2,557 research outputs found
Advances in Spectral Classification
In this article we give an overview of the developments in the field of
spectral classification and its continued importance in the fields of stellar
and galactic evolution. The extension of MK system to cool stars as well as
refined classification of the hot stars using the new data obtained from modern
ground based facilities and space missions has been described. A brief summary
of automated methods of spectral classifications developed for the quick and
objective classification of the ongoing and future surveys is presented. A new
spectral class encoding system developed for exploitation of databases is
described. Recent large scale spectral classification catalogues are listed.Comment: To appear in BASI, 33 pages, 9 figure
Distributed downlink multi-cell processing requiring reduced-rate back-haul data exchange
Different-complexity Multi-Cell Processing (MCP) schemes employing Distributed Signal-to-Interference-Leakage-plus-Noise-Ratio (SILNR) precoding techniques are proposed, which require reduced back-haul data exchange in comparison to the conventional MCP structure. Our results demonstrate that the proposed structures are capable of increasing the achievable cell-edge throughput and offering different geographic rate profile distributions as well as meeting different delay requirements
Abundance Analyses of Field RV Stars, V: DS Aquarii, UY Arae, TW Camelopardis, BT Librae, U Moncerotis, TT Ophiuchi, and RV Tauri
Abundance analyses are presented and discussed for eight RV Tauri variables.
The RV B star UY Ara shows the abundance anomalies seen in other RV B stars,
namely elements that condense into grains at high temperature are underabundant
but elements of low condensation temperature are much less underabundant. This
pattern is ascribed to a separation of dust from gas with accretion of gas but
not dust by the atmosphere. Abundances for two RV C stars with earlier results
for other RV C stars show that these intrinsically metal-poor stars do not show
effects of dust-gas separation. Analyses of five RV A stars show that these
cooler stars are very largely unaffected by dust-gas separation. It is proposed
that the deeper convective envelope of cooler stars dilutes anomalies resulting
from dust-gas separation - the dusty wind off the RV Tauri variable or a dusty
circumbinary disk - are reviewed and observational tests are suggested.Comment: 42 pages, 6 figures, 8 tables, this may be listed as ApJ in pres
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