7,147 research outputs found
The magnetic field in the NGC 2024 FIR 5 dense core
We used the Submillimeter Array (SMA) to observe the thermal polarized dust
emission from the protostellar source NGC 2024 FIR 5. The polarized emission
outlines a partial hourglass morphology for the plane-of-sky component of the
core magnetic field. Our data are consistent with previous BIMA maps, and the
overall magnetic field geometries obtained with both instruments are similar.
We resolve the main core into two components, FIR 5A and FIR 5B. A possible
explanation for the asymmetrical field lies in depolarization effects due to
the lack of internal heating from FIR 5B source, which may be in a prestellar
evolutionary state. The field strength was estimated to be 2.2 mG, in agreement
with previous BIMA data. We discuss the influence of a nearby H{\sc ii} region
over the field lines at scales of pc. Although the hot component is
probably compressing the molecular gas where the dust core is embedded, it is
unlikely that the radiation pressure exceeds the magnetic tension. Finally, a
complex outflow morphology is observed in CO (3 2) maps. Unlike
previous maps, several features associated with dust condensations other than
FIR 5 are detected.Comment: 48 pages, 12 figures, accepted for publication in The Astrophysical
Journa
On the distribution of an effective channel estimator for multi-cell massive MIMO
Accurate channel estimation is of utmost importance for massive MIMO systems to provide significant improvements in spectral and energy efficiency. In this work, we present a study on the distribution of a simple but yet effective and practical channel estimator for multi-cell massive MIMO systems suffering from pilot-contamination. The proposed channel estimator performs well under moderate to aggressive pilot contamination scenarios without previous knowledge of the inter-cell large-scale channel coefficients and noise power, asymptotically approximating the performance of the linear MMSE estimator as the number of antennas increases. We prove that the distribution of the proposed channel estimator can be accurately approximated by the circularly-symmetric complex normal distribution, when the number of antennas, M, deployed at the base station is greater than 10
- …