4,397 research outputs found
Light Curve Patterns and Seismology of a White Dwarf with Complex Pulsation
The ZZ Ceti star KUV 02464+3239 was observed over a whole season at the
mountain station of Konkoly Observatory. A rigorous frequency analysis revealed
6 certain periods between 619 and 1250 seconds, with no shorter period modes
present. We use the observed periods, published effective temperature and
surface gravity, along with the model grid code of Bischoff-Kim, Montgomery and
Winget (2008) to perform a seismological analysis. We find acceptable model
fits with masses between 0.60 and 0.70 M_Sun. The hydrogen layer mass of the
acceptable models are almost always between 10^-4 and 10^-6 M_*. In addition to
our seismological results, we also show our analysis of individual light curve
segments. Considering the non-sinusoidal shape of the light curve and the
Fourier spectra of segments showing large amplitude variations, the importance
of non-linear effects in the pulsation is clearly seen.Comment: 5 pages, 6 figures, in "Stellar Pulsation: Challenges for Theory and
Observation", Eds. J. Guzik and P. A. Bradley, AIP
Sudbury project (University of Muenster-Ontario Geological Survey): Field studies 1984-1989 - summary of results
In cooperation between the Ontario Geological Survey and the Institute of Geology and Institute of Planetology, geological, petrological, and geochemical studies were carried out on impact-related phenomena of the Sudbury structure during the last decade. The main results of the field studies are briefly reviewed. Footwall rocks, sublayer, and lower sections of the Sudbury Igneous Complex (SIC) were mainly mapped and sampled in the northern (Levack Township) and western (Trillabelle and Sultana Properties) parts of the north range. Within these mapping areas Sudbury Breccias (SB) and Footwall Breccias (FB) were studied; SB were also investigated along extended profiles beyond the north and south ranges up to 55 km from the SIC. The Onaping Formation (OF) and the upper section of the SIC were studied both in the north range (Morgan and Dowling Townships) and in the southern east range (Capreol and McLennan Townships)
Optically probing symmetry breaking in the chiral magnet Cu2OSeO3
We report on the linear optical properties of the chiral magnet Cu2OSeO3,
specifically associated with the absence of inversion symmetry, the chiral
crystallographic structure, and magnetic order. Through spectroscopic
ellipsometry, we observe local crystal-field excitations below the
charge-transfer gap. These crystal-field excitations are optically allowed due
to the lack of inversion symmetry at the Cu sites. Optical polarization
rotation measurements were used to study the structural chirality and magnetic
order. The temperature dependence of the natural optical rotation, originating
in the chiral crystal structure, provides evidence for a finite
magneto-electric effect in the helimagnetic phase. We find a large
magneto-optical susceptibility on the order of V(540nm)~10^4 rad/(T*m) in the
helimagnetic phase and a maximum Faraday rotation of ~165deg/mm in the
ferrimagnetic phase. The large value of V can be explained by considering spin
cluster formation and the relative ease of domain reorientation in this
metamagnetic material. The magneto-optical activity allows us to map the
magnetic phase diagram, including the skyrmion lattice phase. In addition to
this, we probe and discuss the nature of the various magnetic phase transitions
in Cu2OSeO3.Comment: 9 pages, 10 figure
Characterizing the pulsations of the ZZ Ceti star KUV 02464+3239
We present the results on period search and modeling of the cool DAV star KUV
02464+3239. Our observations resolved the multiperiodic pulsational behaviour
of the star. In agreement with its position near the red edge of the DAV
instability strip, it shows large amplitude, long period pulsation modes, and
has a strongly non-sinusoidal light curve. We determined 6 frequencies as
normal modes and revealed remarkable short-term amplitude variations. A
rigorous test was performed for the possible source of amplitude variation:
beating of modes, effect of noise, unresolved frequencies or rotational
triplets. Among the best-fit models resulting from a grid search, we selected 3
that gave l=1 solutions for the largest amplitude modes. These models had
masses of 0.645, 0.650 and 0.680 M_Sun. The 3 `favoured' models have M_H
between 2.5x10^-5 - 6.3x10^-6 M_* and give 14.2 - 14.8 mas seismological
parallax. The 0.645 M_Sun (11400 K) model also matches the spectroscopic log g
and T_eff within 1 sigma. We investigated the possibility of mode trapping and
concluded that while it can explain high amplitude modes, it is not required.Comment: 11 pages, 8 figures, accepted for publication in MNRA
GeoCLEF 2006: the CLEF 2006 Ccross-language geographic information retrieval track overview
After being a pilot track in 2005, GeoCLEF advanced to be a regular track within CLEF 2006. The
purpose of GeoCLEF is to test and evaluate cross-language geographic information retrieval (GIR): retrieval for
topics with a geographic specification. For GeoCLEF 2006, twenty-five search topics were defined by the
organizing groups for searching English, German, Portuguese and Spanish document collections. Topics were
translated into English, German, Portuguese, Spanish and Japanese. Several topics in 2006 were significantly
more geographically challenging than in 2005. Seventeen groups submitted 149 runs (up from eleven groups and
117 runs in GeoCLEF 2005). The groups used a variety of approaches, including geographic bounding boxes,
named entity extraction and external knowledge bases (geographic thesauri and ontologies and gazetteers)
Challenges to evaluation of multilingual geographic information retrieval in GeoCLEF
This is the third year of the evaluation of
geographic information retrieval (GeoCLEF)
within the Cross-Language Evaluation Forum
(CLEF). GeoCLEF 2006 presented topics and
documents in four languages (English,
German, Portuguese and Spanish). After two
years of evaluation we are beginning to
understand the challenges to both Geographic
Information Retrieval from text and of
evaluation of the results of geographic
information retrieval. This poster enumerates
some of these challenges to evaluation and
comments on the limitations encountered in the
first two evaluations
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