420 research outputs found
Gaia Data Release 1. Cross-match with external catalogues - Algorithm and results
Although the Gaia catalogue on its own will be a very powerful tool, it is
the combination of this highly accurate archive with other archives that will
truly open up amazing possibilities for astronomical research. The advanced
interoperation of archives is based on cross-matching, leaving the user with
the feeling of working with one single data archive. The data retrieval should
work not only across data archives, but also across wavelength domains. The
first step for seamless data access is the computation of the cross-match
between Gaia and external surveys. The matching of astronomical catalogues is a
complex and challenging problem both scientifically and technologically
(especially when matching large surveys like Gaia). We describe the cross-match
algorithm used to pre-compute the match of Gaia Data Release 1 (DR1) with a
selected list of large publicly available optical and IR surveys. The overall
principles of the adopted cross-match algorithm are outlined. Details are given
on the developed algorithm, including the methods used to account for position
errors, proper motions, and environment; to define the neighbours; and to
define the figure of merit used to select the most probable counterpart.
Statistics on the results are also given. The results of the cross-match are
part of the official Gaia DR1 catalogue.Comment: 18 pages, 8 figures. Accepted for publication by A&
1WHSP: an IR-based sample of 1,000 VHE -ray blazar candidates
Blazars are the dominant type of extragalactic sources at microwave and at
-ray energies. In the most energetic part of the electromagnetic
spectrum (E>100GeV) a large fraction of high Galactic latitude sources are
blazars of the High Synchrotron Peaked (HSP) type, that is BL Lac objects with
synchrotron power peaking in the UV or in the X-ray band. HSP blazars are
remarkably rare, with only a few hundreds of them expected to be above the
sensitivity limits of currently available surveys. To find these very uncommon
objects, we have devised a method that combines ALLWISE survey data with
multi-frequency selection criteria. The sample was defined starting from a
primary list of infrared colour-colour selected sources from the ALLWISE all
sky survey database, and applying further restrictions on IR-radio and IR-X-ray
flux ratios. Using a polynomial fit to the multi-frequency data (radio to
X-ray) we estimated synchrotron peak frequencies and fluxes of each object. We
assembled a sample including 992 sources, which is currently the largest
existing list of confirmed and candidates HSP blazars. All objects are expected
to radiate up to the highest -ray photon energies. In fact, 299 of
these are confirmed emitters of GeV -ray photons (based on Fermi-LAT
catalogues), and 36 have already been detected in the TeV band. The majority of
sources in the sample are within reach of the upcoming Cherenkov Telescope
Array (CTA), and many may be detectable even by the current generation of
Cherenkov telescopes during flaring episodes. The sample includes 425
previously known blazars, 151 new identifications, and 416 HSP candidates
(mostly faint sources) for which no optical spectra is available yet. The full
1WHSP catalogue is on-line at http://www.asdc.asi.it/1whsp/ providing a direct
link to the SED building tool where multifrequency data can be easily
visualised
Scanning optical pyrometer for measuring temperatures in hollow cathodes
Life-limiting processes in hollow cathodes are determined largely by the temperature of the electron emitter. To support cathode life assessment, a noncontact temperature measurement technique which employs a stepper motor-driven fiber optic probe was developed. The probe is driven inside the hollow cathode and collects light radiated by the hot interior surface of the emitter. Ratio pyrometry is used to determine the axial temperature profile. Thermocouples on the orifice plate provide measurements of the external temperature during cathode operation and are used to calibrate the pyrometer system in situ with a small oven enclosing the externally heated cathode. The diagnostic method and initial measurements of the temperature distribution in a hollow cathode are discussed
Studying the evolution of AGB stars in the Gaia epoch
We present asymptotic giant branch (AGB) models of solar metallicity, to
allow the interpretation of observations of Galactic AGB stars, whose distances
should be soon available after the first release of the Gaia catalogue. We find
an abrupt change in the AGB physical and chemical properties, occurring at the
threshold mass to ignite hot bottom burning,i.e. . Stars with
mass below reach the C-star stage and eject into the
interstellar medium gas enriched in carbon , nitrogen and . The higher
mass counterparts evolve at large luminosities, between and . The mass expelled from the massive AGB stars
shows the imprinting of proton-capture nucleosynthesis, with considerable
production of nitrogen and sodium and destruction of and . The
comparison with the most recent results from other research groups are
discussed, to evaluate the robustness of the present findings. Finally, we
compare the models with recent observations of galactic AGB stars, outlining
the possibility offered by Gaia to shed new light on the evolution properties
of this class of objects.Comment: 21 pages, 11 figure, 3 tables, accepted for publication in MNRAS
(2016 July 11
Evaluating GAIA performances on eclipsing binaries. III. Orbits and stellar parameters for UW LMi, V432 Aur and CN Lyn
The orbits and physical parameters of three detached F and G-type eclipsing
binaries have been derived combining Hipparcos H(P) photometry with 8480-8740
Ang ground-based spectroscopy, simulating the photometric+spectroscopic
observations that the GAIA mission will obtain. Tycho B(T) and V(T) light
curves are too noisy to be modeled for the three targets, and only mean Tycho
colors are retained to constrain the temperature. No previous combined
photometric+spectroscopic solution exists in literature for any of the three
targets. Quite remarkably, CN Lyn turned out to be an equal masses F5 triple
system. Distances from the orbital solutions agree within the astrometric error
with the Hipparcos parallaxes.Comment: A&A, accepted in pres
Gaia Data Release 2. Cross-match with external catalogues - Algorithms and results
Context. Although the Gaia catalogue on its own is a very powerful tool, it
is the combination of this high-accuracy archive with other archives that will
truly open up amazing possibilities for astronomical research. The advanced
interoperation of archives is based on cross-matching, leaving the user with
the feeling of working with one single data archive. The data retrieval should
work not only across data archives but also across wavelength domains. The
first step for a seamless access to the data is the computation of the
cross-match between Gaia and external surveys.
Aims. We describe the adopted algorithms and results of the pre-computed
cross-match of the Gaia Data Release 2 (DR2) catalogue with dense surveys
(Pan-STARRS1 DR1, 2MASS, SDSS DR9, GSC 2.3, URAT-1, allWISE, PPMXL, and APASS
DR9) and sparse catalogues (Hipparcos2, Tycho-2, and RAVE 5).
Methods. A new algorithm is developed specifically for sparse catalogues.
Improvements and changes with respect to the algorithm adopted for DR1 are
described in detail.
Results. The outputs of the cross-match are part of the official Gaia DR2
catalogue. The global analysis of the cross-match results is also presented.Comment: accepted for publication in A&A Gaia DR2 special issu
Functional pasta enriched with bioactive compounds and fibers in the form of highly stable SC-CO2 extracted pumpkin oleoresin/α-CD complex
Very near-field plume investigation of the D55
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76343/1/AIAA-1997-3062-753.pd
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