2 research outputs found
Study of the atmospheric conditions at Cerro Armazones using astronomical data
Aims: We studied the precipitable water vapour (PWV) content near Cerro
Armazones and discuss the potential use of our technique of modelling the
telluric absorbtion lines for the investigation of other molecular layers. The
site is designated for the European Extremely Large Telescope (E-ELT) and the
nearby planned site for the Cherenkov Telescope Array (CTA). Methods:
Spectroscopic data from the Bochum Echelle Spectroscopic Observer (BESO)
instrument were investigated by using line-by-line radiative transfer model
(LBLRTM) radiative transfer models for the Earths atmosphere with the telluric
absorption correction tool molecfit. All observations from the archive in the
period from December 2008 to the end of 2014 were investigated. The dataset
completely covers the El Nino event registered in the period 2009-2010. Models
of the 3D Global Data Assimilation System (GDAS) were used for further
comparison. Moreover, for those days with coincidence of data from a similar
study with VLT/X-shooter and microwave radiometer LHATPRO data at Cerro
Paranal, a direct comparison is presented. Results: This analysis shows that
the site has systematically lower PWV values, even after accounting for the
decrease in PWV expected from the higher altitude of the site with respect to
Cerro Paranal, using the average atmosphere found with radiosondes. We found
that GDAS data are not a suitable method for predicting of local atmospheric
conditions - they usually systematically overestimate the PWV values. Due to
the large sample, we were furthermore able to characterize the site with
respect to symmetry across the sky and variation with the years and within the
seasons. This kind of technique of studying the atmospheric conditions is shown
to be a promising step into a possible monitoring equipment for CTA.Comment: Accepted for publication in Astronomy and Astrophysics, 7 pages, 9
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Spectral and morphological analysis of the remnant of Supernova 1987A with ALMA & ATCA
We present a comprehensive spectral and morphological analysis of the remnant
of Supernova (SN) 1987A with the Australia Telescope Compact Array (ATCA) and
the Atacama Large Millimeter/submillimeter Array (ALMA). The non-thermal and
thermal components of the radio emission are investigated in images from 94 to
672 GHz ( 3.2 mm to 450 m), with the assistance of a
high-resolution 44 GHz synchrotron template from the ATCA, and a dust template
from ALMA observations at 672 GHz. An analysis of the emission distribution
over the equatorial ring in images from 44 to 345 GHz highlights a gradual
decrease of the east-to-west asymmetry ratio with frequency. We attribute this
to the shorter synchrotron lifetime at high frequencies. Across the transition
from radio to far infrared, both the synchrotron/dust-subtracted images and the
spectral energy distribution (SED) suggest additional emission beside the main
synchrotron component () and the thermal component
originating from dust grains at K. This excess could be due to
free-free flux or emission from grains of colder dust. However, a second
flat-spectrum synchrotron component appears to better fit the SED, implying
that the emission could be attributed to a pulsar wind nebula (PWN). The
residual emission is mainly localised west of the SN site, as the spectral
analysis yields across the western regions,
with around the central region. If there is a PWN in the remnant
interior, these data suggest that the pulsar may be offset westward from the SN
position.Comment: ApJ accepted. 21 pages, emulateapj. References update