696 research outputs found
A Galactic Plane Relative Extinction Map from 2MASS
We present three 14400 square degree relative extinction maps of the Galactic
Plane (|b|<20degrees) obtained from 2MASS using accumulative star counts (Wolf
diagrams). This method is independent of the colour of the stars and the
variation of extinction with wavelength. Stars were counted in 3.5'x3.5' boxes,
every 20". 1x1degree surrounding fields were chosen for reference, hence the
maps represent local extinction enhancements and ignore any contribution from
the ISM or very large clouds. Data reduction was performed on a Beowulf-type
cluster (in approximately 120 hours). Such a cluster is ideal for this type of
work as areas of the sky can be independently processed in parallel. We studied
how extinction depends on wavelength in all of the high extinction regions
detected and within selected dark clouds. On average a power law opacity index
(\beta) of 1.0 to 1.8 in the NIR was deduced. The index however differed
significantly from region to region and even within individual dark clouds.
That said, generally it was found to be constant, or to increase, with
wavelength within a particular region.Comment: 4 pages, 2 figures, A&A Letters accepted, version with high
resolution figures at http://www.dias.ie/~d
Optical spectra of selected Chamaeleon I young stellar objects
We present optical spectra of eight candidate brown dwarfs and a previously
known T Tauri star (Sz 33) of the Chamaeleon I dark cloud. We derived spectral
types based on the strength of the TiO or VO absorption bands present in the
spectra of these objects as well as on the PC3 index of Martin et al. (1999).
Photometric data from the literature are used to estimate the bolometric
luminosities for these sources. We apply D'Antona & Mazzitelli (1997) pre-main
sequence evolutionary tracks and isochrones to derive masses and ages. Based on
the presence of Halpha in emission, we confirm that most of the candidates are
young objects. Our sample however includes two sources for which we can only
provide upper limits for the emission in Halpha; whereas these two objects are
most likely foreground/background stars, higher resolution spectra are required
to confirm their true nature. Among the likely cloud members, we detect one new
sub-stellar object and three transition stellar/sub-stellar sources.Comment: 22 pages - manuscript forma
Quasistatic crack growth based on viscous approximation: a model with branching and kinking.
Employing the technique of vanishing viscosity and time rescaling, we show the existence of quasistatic evolutions of cracks in brittle materials in the setting of antiplane shear. The crack path is not prescribed a priori and is chosen in an admissible class of piecewise regular sets that allows for branching and kinking
Performance of the First ANTARES Detector Line
In this paper we report on the data recorded with the first Antares detector
line. The line was deployed on the 14th of February 2006 and was connected to
the readout two weeks later. Environmental data for one and a half years of
running are shown. Measurements of atmospheric muons from data taken from
selected runs during the first six months of operation are presented.
Performance figures in terms of time residuals and angular resolution are
given. Finally the angular distribution of atmospheric muons is presented and
from this the depth profile of the muon intensity is derived.Comment: 14 pages, 9 figure
Status and Recent Results of the Acoustic Neutrino Detection Test System AMADEUS
The AMADEUS system is an integral part of the ANTARES neutrino telescope in
the Mediterranean Sea. The project aims at the investigation of techniques for
acoustic neutrino detection in the deep sea. Installed at a depth of more than
2000m, the acoustic sensors of AMADEUS are based on piezo-ceramics elements for
the broad-band recording of signals with frequencies ranging up to 125kHz.
AMADEUS was completed in May 2008 and comprises six "acoustic clusters", each
one holding six acoustic sensors that are arranged at distances of roughly 1m
from each other. The clusters are installed with inter-spacings ranging from
15m to 340m. Acoustic data are continuously acquired and processed at a
computer cluster where online filter algorithms are applied to select a
high-purity sample of neutrino-like signals. 1.6 TB of data were recorded in
2008 and 3.2 TB in 2009. In order to assess the background of neutrino-like
signals in the deep sea, the characteristics of ambient noise and transient
signals have been investigated. In this article, the AMADEUS system will be
described and recent results will be presented.Comment: 7 pages, 8 figures. Proceedings of ARENA 2010, the 4th International
Workshop on Acoustic and Radio EeV Neutrino Detection Activitie
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