7,134 research outputs found
Galaxy-Targeting Approach Optimized for Finding the Radio Afterglows of Gravitational Wave Sources
Kilonovae and radio afterglows of neutron star merger events have been
identified as the two most promising counterparts, of these gravitational wave
sources, that can provide arcsecond localization. While several new and
existing optical search facilities have been dedicated to finding kilonovae,
factors such as dust obscuration and the daytime sky may thwart these searches
in a significant fraction of gavitational wave events. Radio-only searches,
being almost immune to these factors, are equally capable of finding the
counterparts and in fact offer a complementary discovery approach, despite the
modest fields of view for many of the present-day radio interferometers. Such
interferometers will be able to carry out competitive searches for the
electromagnetic counterparts through the galaxy targeting approach. Adapting
and improving on an existing algorithm by Rana et al. 2017. we present here a
method that optimizes the placement of radio antenna pointings, integration
time, and antenna slew. We simulate 3D gravitational wave localizations to find
the efficacy of our algorithm; with substantial improvements in slew overhead
and containment probability coverage, our algorithm performs significantly
better than simple galaxy-rank-ordered observations. We propose that telescopes
such as the Very Large Array, MeerKAT, Australia Telescope Compact Array and
the Gaint Meterwave Radio Telescope, having fields of view 1 deg
and searching for the counterparts of nearby GW events over tens of square
degrees or larger, will especially benefit from this optimized galaxy-targeting
approach for electromagnetic counterpart searches.Comment: 13 pages, 7 figures, Submitted to Ap
Are crowdsourced datasets suitable for specialized routing services? Case study of Openstreetmap for routing of people with limited mobility
Nowadays, Volunteered Geographic Information (VGI) has increasingly gained attractiveness to both amateur users and professionals. Using data generated from the crowd has become a hot topic for several application domains including transportation. However, there are concerns regarding the quality of such datasets. As one of the most famous crowdsourced mapping platforms, we analyze the fitness for use of OpenStreetMap (OSM) database for routing and navigation of people with limited mobility. We assess the completeness of OSM data regarding sidewalk information. Relevant attributes for sidewalk information such as sidewalk width, incline, surface texture, etc. are considered, and through both extrinsic and intrinsic quality analysis methods, we present the results of fitness for use of OSM data for routing services of disabled persons. Based on empirical results, it is concluded that OSM data of relatively large spatial extents inside all studied cities could be an acceptable region of interest to test and evaluate wheelchair routing and navigation services, as long as other data quality parameters such as positional accuracy and logical consistency are checked and proved to be acceptable. We present an extended version of OSMatrix web service and explore how it is employed to perform spatial and temporal analysis of sidewalk data completeness in OSM. The tool is beneficial for piloting activities, whereas the pilot site planners can query OpenStreetMap and visualize the degree of sidewalk data availability in a certain region of interest. This would allow identifying the areas that data are mostly missing and plan for data collection events. Furthermore, empirical results of data completeness for several OSM data indicators and their potential relation to sidewalk data completeness are presented and discussed. Finally, the article ends with an outlook for future research study in this area
The ROSAT-ESO Flux-Limited X-Ray (REFLEX) Galaxy Cluster Survey III: The Power Spectrum
We present a measure of the power spectrum on scales from 15 to 800 Mpc/h
using the ROSAT-ESO Flux-Limited X-Ray(REFLEX) galaxy cluster catalogue. The
REFLEX survey provides a sample of the 452 X-ray brightest southern clusters of
galaxies with the nominal flux limit S=3.0 10^{-12}erg/s/cm2 for the ROSAT
energy band (0.1-2.4)keV. Several tests are performed showing no significant
incompletenesses of the REFLEX clusters with X-ray luminosities brighter than
10^{43}erg/s up to scales of about 800 Mpc/h. They also indicate that cosmic
variance might be more important than previous studies suggest. We regard this
as a warning not to draw general cosmological conclusions from cluster samples
with a size smaller than REFLEX. Power spectra, P(k), of comoving cluster
number densities are estimated for flux- and volume-limited subsamples. The
most important result is the detection of a broad maximum within the comoving
wavenumber range 0.022<k<0.030 h/Mpc. The data suggest an increase of the power
spectral amplitude with X-ray luminosity. Compared to optically selected
cluster samples the REFLEX P(k)is flatter for wavenumbers k<0.05 h/Mpc thus
shifting the maximum of P(k) to larger scales. The smooth maximum is not
consistent with the narrow peak detected at k=0.05 h/Mpc using the Abell/ACO
richness data. In the range 0.02<k<0.4 h/Mpc general agreement is found
between the slope of the REFLEX P(k) and those obtained with optically selected
galaxies. A semi-analytic description of the biased nonlinear power spectrum in
redshift space gives the best agreement for low-density Cold Dark Matter models
with or without a cosmological constant.Comment: 22 pages, 20 figures, (A&A accepted), also available at
http://www.xray.mpe.mpg.de/theorie/REFLEX
Brown dwarf census with the Dark Energy Survey year 3 data and the thin disc scale height of early L types
27 pages, 18 figuresIn this paper we present a catalogue of 11 745 brown dwarfs with spectral types ranging from L0 to T9, photometrically classified using data from the Dark Energy Survey (DES) year 3 release matched to the Vista Hemisphere Survey (VHS) DR3 and Wide-field Infrared Survey Explorer (WISE) data, covering ≈2400 deg2 up to iAB = 22. The classification method follows the same phototype method previously applied to SDSS-UKIDSS-WISE data. The most significant difference comes from the use of DES data instead of SDSS, which allow us to classify almost an order of magnitude more brown dwarfs than any previous search and reaching distances beyond 400 pc for the earliest types. Next, we also present and validate the GalmodBD simulation, which produces brown dwarf number counts as a function of structural parameters with realistic photometric properties of a given survey. We use this simulation to estimate the completeness and purity of our photometric LT catalogue down to iAB = 22, as well as to compare to the observed number of LT types. We put constraints on the thin disc scale height for the early L (L0–L3) population to be around 450 pc, in agreement with previous findings. For completeness, we also publish in a separate table a catalogue of 20 863 M dwarfs that passed our colour cut with spectral types greater than M6. Both the LT and the late M catalogues are found at DES release page https://des.ncsa.illinois.edu/releases/other/y3-mlt.Peer reviewedFinal Published versio
Integrating distributed data streams
Abstract unavailable please refer to PD
The Palomar/Keck Adaptive Optics Survey of Young Solar Analogs: Evidence for a Universal Companion Mass Function
We present results from an adaptive optics survey for substellar and stellar
companions to Sun-like stars. The survey targeted 266 F5-K5 stars in the 3Myr
to 3Gyr age range with distances of 10-190pc. Results from the survey include
the discovery of two brown dwarf companions (HD49197B and HD203030B), 24 new
stellar binaries, and a triple system. We infer that the frequency of
0.012-0.072Msun brown dwarfs in 28-1590AU orbits around young solar analogs is
3.2% (+3.1%,-2.7%; 2sigma limits). The result demonstrates that the deficiency
of substellar companions at wide orbital separations from Sun-like stars is
less pronounced than in the radial velocity "brown dwarf desert." We infer that
the mass distribution of companions in 28-1590AU orbits around solar-mass stars
follows a continuous dN/dM_2 ~ M_2^(-0.4) relation over the 0.01-1.0Msun
secondary mass range. While this functional form is similar to that for
<0.1Msun isolated objects, over the entire 0.01-1.0Msun range the mass
functions of companions and of isolated objects differ significantly. Based on
this conclusion and on similar results from other direct imaging and radial
velocity companion surveys in the literature, we argue that the companion mass
function follows the same universal form over the entire range between 0-1590AU
in orbital semi-major axis and 0.01-20Msun in companion mass. In this context,
the relative dearth of substellar versus stellar secondaries at all orbital
separations arises naturally from the inferred form of the companion mass
function.Comment: Final version accepted by ApJ Supplements. 50 pages, including 12
tables + 16 figures. Version with full tables available at
http://www.astro.sunysb.edu/metchev/PUBLICATIONS/cmf.pd
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