1,834 research outputs found
A Census of Object Types and Redshift Estimates in the SDSS Photometric Catalog from a Trained Decision-Tree Classifier
We have applied ClassX, an oblique decision tree classifier optimized for
astronomical analysis, to the homogeneous multicolor imaging data base of the
Sloan Digital Sky Survey (SDSS), training the software on subsets of SDSS
objects whose nature is precisely known via spectroscopy. We find that the
software, using photometric data only, correctly classifies a very large
fraction of the objects with existing SDSS spectra, both stellar and
extragalactic. ClassX also accurately predicts the redshifts of both normal and
active galaxies in SDSS. To illustrate ClassX applications in SDSS research, we
(a) derive the object content of the SDSS DR2 photometric catalog and (b)
provide a sample catalog of resolved SDSS objects that contains a large number
of candidate AGN galaxies, 27,000, along with 63,000 candidate normal galaxies
at magnitudes substantially fainter than typical magnitudes of SDSS
spectroscopic objects. The surface density of AGN selected by ClassX to i~19 is
in agreement with that quoted by SDSS. When ClassX is applied to the
photometric data fainter than the SDSS spectroscopic limit, the inferred
surface density of AGN rises sharply, as expected. The ability of the
classifier to accurately constrain the redshifts of huge numbers (ultimately ~
10^7) of active galaxies in the photometric data base promises new insights
into fundamental issues of AGN research, such as the evolution of the AGN
luminosity function with cosmic time, the starburst--AGN connection, and
AGN--galactic morphology relationships.Comment: Accepted for publication in The Astronomical Journal, Vol. 130, 2005;
33 pages, 10 figures, 5 tables, AASTeX v5.0. Table 5 will be electronic in
the published journal, but available now at
http://www-int.stsci.edu/~margon/table5.ascii and
http://www-int.stsci.edu/~margon/table5.ascii.g
Extreme Ultraviolet Emission from Clusters of Galaxies: Inverse Compton Radiation from a Relic Population of Cosmic Ray Electrons?
We suggest that the luminous extreme ultraviolet (EUV) emission which has
been detected recently from clusters of galaxies is Inverse Compton (IC)
scattering of Cosmic Microwave Background (CMB) radiation by low energy cosmic
ray electrons in the intracluster medium. The cosmic ray electrons would have
Lorentz factors of gamma ~ 300, and would lose energy primarily by emitting EUV
radiation. These particles have lifetimes comparable to the Hubble time; thus,
the electrons might represent a relic population of cosmic rays produced by
nonthermal activity over the history of the cluster. The IC model naturally
explains the observed increase in the ratio of EUV to X-ray emission with
radius in clusters. The required energy in cosmic ray electrons is typically
1--10% of the thermal energy content of the intracluster gas. We suggest that
the cosmic ray electrons might have been produced by supernovae in galaxies, by
radio galaxies, or by particle acceleration in intracluster shocks.Comment: ApJ Letters, in press, 4 pages with 1 embedded figure, Latex in
emulateapj styl
Running a distributed virtual observatory: US Virtual Astronomical Observatory operations
Operation of the US Virtual Astronomical Observatory shares some issues with
modern physical observatories, e.g., intimidating data volumes and rapid
technological change, and must also address unique concerns like the lack of
direct control of the underlying and scattered data resources, and the
distributed nature of the observatory itself. In this paper we discuss how the
VAO has addressed these challenges to provide the astronomical community with a
coherent set of science-enabling tools and services. The distributed nature of
our virtual observatory-with data and personnel spanning geographic,
institutional and regime boundaries-is simultaneously a major operational
headache and the primary science motivation for the VAO. Most astronomy today
uses data from many resources. Facilitation of matching heterogeneous datasets
is a fundamental reason for the virtual observatory. Key aspects of our
approach include continuous monitoring and validation of VAO and VO services
and the datasets provided by the community, monitoring of user requests to
optimize access, caching for large datasets, and providing distributed storage
services that allow user to collect results near large data repositories. Some
elements are now fully implemented, while others are planned for subsequent
years. The distributed nature of the VAO requires careful attention to what can
be a straightforward operation at a conventional observatory, e.g., the
organization of the web site or the collection and combined analysis of logs.
Many of these strategies use and extend protocols developed by the
international virtual observatory community.Comment: 7 pages with 2 figures included within PD
Phase diagram and magnetic collective excitations of the Hubbard model in graphene sheets and layers
We discuss the magnetic phases of the Hubbard model for the honeycomb lattice
both in two and three spatial dimensions. A ground state phase diagram is
obtained depending on the interaction strength
U and electronic density n. We find a first order phase transition between
ferromagnetic regions where the spin is maximally polarized (Nagaoka
ferromagnetism) and regions with smaller magnetization (weak ferromagnetism).
When taking into account the possibility of spiral states, we find that the
lowest critical U is obtained for an ordering momentum different from zero. The
evolution of the ordering momentum with doping is discussed. The magnetic
excitations (spin waves) in the antiferromagnetic insulating phase are
calculated from the random-phase-approximation for the spin susceptibility. We
also compute the spin fluctuation correction to the mean field magnetization by
virtual emission/absorpion of spin waves. In the large limit, the
renormalized magnetization agrees qualitatively with the Holstein-Primakoff
theory of the Heisenberg antiferromagnet, although the latter approach produces
a larger renormalization
Ferromagnetism in a hard-core boson model
The problem of ferromagnetism -- associated with a ground state with maximal
total spin -- is discussed in the framework of a hard-core model, which forbids
the occupancy at each site with more than one particle. It is shown that the
emergence of ferromagnetism on finite square lattices crucially depends on the
statistics of the particles. Fermions (electrons) lead to the well-known
instabilities for finite hole densities, whereas for bosons (with spin)
ferromagnetism appears to be stable for all hole densities.Comment: 8 pages, 7 figures, RevTex
SDSS AGNs with X-ray Emission from ROSAT PSPC Pointed Observations
We present a sample of 1744 type 1 active galactic nuclei (AGNs) from the
Sloan Digital Sky Survey (SDSS DR4) spectroscopic catalog with X-ray
counterparts in the White-Giommi-Angelini Catalog (WGACAT) of ROSAT PSPC
pointed observations. Of 1744 X-ray sources, 1410 (80.9%) are new AGN
identifications. Of 4574 SDSS DR4 AGNs for which we found radio matches in the
catalog of radio sources from the FIRST catalog, 224 turned up in our sample of
SDSS X-ray AGNs. The sample objects are given in a catalog that contains
optical and X-ray parameters along with radio emission parameters where
available. We illustrate the content of our catalog and its potential for AGN
science by providing statistical relationships for the catalog data. The
potential of the morphological information is emphasized by confronting the
statistics of optically resolved and unresolved AGNs. The immediate properties
of the catalog objects include significant correlation of X-ray and optical
fluxes, which is consistent with expectations. Also expected is the decrease of
X-ray flux toward higher redshifts. The X-ray to optical flux ratio for the
unresolved AGNs exhibits a decline toward higher redshifts, in agreement with
previous results. The resolved AGNs, however, display the opposite trend. At a
given optical brightness, X-ray fluxes of radio-quiet AGNs by a factor of 2. We
caution, however, that because of the variety of selection effects present in
both the WGACAT and the SDSS, the interpretation of any relationships based on
our sample of X-ray AGNs requires a careful analysis of these effects.Comment: 34 pages, 18 figure
Check list of ground-dwelling ant diversity (Hymenoptera: Formicidae) of the Iguazú National Park with a comparison at regional scale
We describe the ant fauna of Iguazú National Park (INP), a region of high biodiversity andendemism in northeastern Argentina that includes the southernmost protected area ofthe Atlantic Forest (AF). Ants were sampled over seven periods from 1998 to 2011 usinga variety of techniques. We also surveyed museum collections and the scientific literatureto obtain additional records of ants from INP. In addition to providing a species list, wecompare ant composition of INP to other sites in the Upper Paraná, Serra do Mar CoastalForest and Araucaria ecoregion of AF. A total of 172 ant species belonging to 56 genera arereported; 56 species are new records for Misiones Province and 39 species are reportedfrom Argentina for the first time. Alto Paraná and Canindeyú departments in Paraguaypresent the most similar ant fauna to INP. Serra da Bodoquena in Brazil and Pilcomayoin Argentina showed higher similarity with the Upper Paraná AF ecoregion, despite thatSerra da Bodoquena is composed of a mix of ecoregions. Ant diversity was lower in UpperParaná than in Serra do Mar Coastal Forest ecoregion. This difference may result fromhigher primary productivity and a greater altitudinal variation in the coastal region.Fil: Hanisch, Priscila Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; ArgentinaFil: Calcaterra, Luis Alberto. Fundación para el Estudio de Especies Invasivas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Leponce, M.. Royal Belgian Institute of Natural Sciences. Aquatic and Terrestrial Ecology unit; BélgicaFil: Achury, R.. University of Illinois at Urbana; Estados UnidosFil: Suarez, A. V.. University of Illinois at Urbana; Estados UnidosFil: Silva, R. R.. Museu Paraense Emílio Goeldi; BrasilFil: Paris, Carolina Ivon. Universidad de Buenos Aires; Argentin
The Energy Spectrum of Primary Cosmic Ray Electrons in Clusters of Galaxies and Inverse Compton Emission
Models for the evolution of the integrated energy spectrum of primary cosmic
ray electrons in clusters of galaxies have been calculated, including the
effects of losses due to inverse Compton (IC), synchrotron, and bremsstrahlung
emission, and Coulomb losses to the intracluster medium (ICM). The combined
time scale for these losses reaches a maximum of ~3e9 yr for electrons with a
Lorentz factor ~300. Only clusters in which there has been a substantial
injection of relativistic electrons since z <~ 1 will have any significant
population of primary cosmic ray electrons at present. In typical models, there
is a broad peak in the electron energy distribution extending to gamma~300, and
a steep drop in the electron population beyond this. In clusters with current
particle injection, there is a power-law tail of higher energy electrons with
an abundance determined by the current rate of injection. A significant
population of electrons with gamma~300, associated with the peak in the
particle loss time, is a generic feature of the models. The IC and synchrotron
emission from these models was calculated. In the models, EUV and soft X-ray
emission are nearly ubiquitous. This emission is produced by electrons with
gamma~300. The spectra are predicted to drop rapidly in going from the EUV to
the X-ray band. The IC emission also extends down the UV, optical, and IR bands
with a fairly flat spectrum. Hard X-ray (HXR) and diffuse radio emission due to
high energy electrons (gamma~10e4) is present only in clusters which have
current particle acceleration. Assuming that the electrons are accelerated in
ICM shocks, one would only expect diffuse HXR/radio emission in clusters which
are currently undergoing a large merger.Comment: Accepted for publication in the Astrophysical Journal, with minor
revisons to wording for clarity and one additional reference. 19 pages with
16 embedded Postscript figures in emulateapj.sty. Abbreviated abstract belo
Estudo da regeneração florestal de uma área de caíva com extração de erva-mate e pastejo animal no Planalto Norte Catarinense.
Caívas são remanescentes de florestas nativas com diferentes níveis de adensamento florestal, cujos estratos herbáceos são compostos por pastagens nativas, extensivamente pastejadas. Essas áreas de caívas, ainda que em diferentes estágios sucessionais, são importantes referências ambientais para diversas espécies da fauna e da flora local e ocupam, aproximadamente 13% da área do Planalto Norte Catarinense. Por serem áreas antropizadas, sua manutenção depende, em grande parte, do potencial de regeneração das espécies florestais presentes. Este trabalho teve por objetivo realizar o levantamento fitossociológico da regeneração de uma caíva, com área total de 10 ha, que vem sendo utilizada para extração de erva-mate nativa e pastejo animal há mais de 60 anos. O levantamento foi realizado em novembro e dezembro de 2010, em uma área experimental de 4.320 m2 demarcada dentro da caíva, onde foram alocadas 27 parcelas amostrais de 144m² cada. Todos os indivíduos arbustivos inferiores a 50 cm de altura, presentes nas parcelas, foram medidos e identificados. A identificação taxonômica foi realizada em campo com o apoio de um mateiro com experiência. A ordenação das famílias e gêneros foi baseada no APG III e a nomenclatura das espécies foi verificada nos arquivos on-line de Missouri Botanical Garden. Para análise fitossociológica foram realizadas as análises de frequência e dominância, absoluta e relativa. As plântulas foram agrupadas por altura, nos níveis de 0-10; 11-20; 21-40 e >41 cm. Na ordenação por altura, a maior concentração de plântulas ocorreu no extrato de 21-40 cm, sendo que foram encontradas 52% das plântulas neste extrato. Dentre as 1.641 plântulas amostradas foram identificadas 31 espécies, 19 famílias e 29 gêneros botânicos. Das espécies com maior densidade destacaram-se Zanthoxylum sp. (mamica de cadela), Allophylus edulis (vacum), Myrcia sp. (guamirim), Ilex microdonta Reissek (congonha), Mosiera prismatica (cerninho). Com relação à freqüência, as espécies que mais se destacaram foram: Zanthoxylum sp. (mamica de cadela), Allophylus edulis (vacum), Myrcia sp. (guamirim), Ilex microdonta Reissek (congonha), Ocotea sp. (canela). A quantidade e diversidade de espécies das plântulas levantadas na área amostral indicam que o processo de regeneração das áreas de caíva é intenso e atende a demanda para manutenção das características das caívas da região
Estrutura e composição florística de uma área de caíva com extração de erva-mate e pastejo animal no Planalto Norte Catarinense.
Caívas são remanescentes de Floresta Ombrófila Mista que se apresentam como fragmentos florestais de tamanhos variados nas propriedades rurais. A somatória desses fragmentos contribui para a formação da paisagem característica do Planalto Norte Catarinense (PNC) e parte do Centro-Sul Paranaense, formando um mosaico de áreas de cultivo intercaladas por áreas de florestas. Apesar de não ser computada especificamente nos censos agropecuários, sua estimativa é que estão presentes em aproximadamente 39% dos estabelecimentos rurais, ocupando em torno de 70.000 hectares no PNC. O presente trabalho teve como objetivo caracterizar a estrutura e composição florística de uma área de caíva cuja utilização, há mais de 60 anos, tem sido a extração de erva-mate nativa e o pastejo animal por rebanho bovino. A área experimental com 4.320 m2 foi demarcada dentro de uma caíva de aproximadamente 10 ha, localizada em uma propriedade rural no município de Canoinhas. Foram alocadas 27 parcelas amostrais com 144 m² cada, onde foi realizado o levantamento na área total da parcela. Foram medidos e identificados todos os indivíduos com DAP ? 5 cm e calculados os parâmetros fitossociológicos de densidade, frequência, dominância e valor de importância. Verificou-se a ocorrência de 418 indivíduos arbóreos, 12 famílias botânicas e 21 espécies. As famílias com maior número de espécies foram Myrtaceae (4), Aquifoliaceae (3) e Lauraceae (3); e as famílias com maior número de indivíduos foram Aquifoliaceae (240), Myrtaceae (83) e Annonaceae (43). O índice de diversidade de Shannon foi de 3,18, indicando considerável diversidade florística. As espécies que contribuíram para os maiores valores de importância foram: Ilex paraguariensis, Mosiera prismatica, Ocotea porosa e Rollinia rugulosa. Esses resultados confirmam que as caívas representam uma importante reserva de espécies de árvore nativas, mesmo sendo manejadas há longo tempo
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