arXiv subjects

A. Zhang

Publications and source records attributed to A. Zhang.

25 records · Page 2Linked to original sources

arXiv2012

On the central quadric ansatz: integrable models and Painleve reductions

It was observed by Tod and later by Dunajski and Tod that the Boyer-Finley (BF) and the dispersionless Kadomtsev-Petviashvili (dKP) equations possess solutions whose level surfaces are central quadrics in the space of independent variables (the so-called central quadric ansatz). It was demonstrated that generic solutions of this type are described by Painleve equations PIII and PII, respectively. The aim of our paper is threefold: -- Based on the method of hydrodynamic reductions, we classify integrable models possessing the central quadric ansatz. This leads to the five canonical forms (including BF and dKP). -- Applying the central quadric ansatz to each of the five canonical forms, we obtain all Painleve equations PI - PVI, with PVI corresponding to the generic case of our classification. -- We argue that solutions coming from the central quadric ansatz constitute a subclass of two-phase solutions provided by the method of hydrodynamic reductions.

nlin.SI↗

arXiv2011

The NStED Periodogram Service and Interface for Public CoRoT Data

As part of the NASA-CNES agreement, the NASA Star and Exoplanet Database (NStED) serves as the official US portal for the public CoRoT data products. NStED is a general purpose archive with the aim of providing support for NASA's planet finding and characterization goals. Consequently, the NASA Exoplanet Science Institute (NExScI) developed, and NStED adapted, a periodogram service for CoRoT data to determine periods of variability phenomena and create phased photometric light curves. Through the NStED periodogram interface, the user may choose three different period detection algorithms to use on any photometric time series product, or even upload and analyze their own data. Additionally, the NStED periodogram is remotely accessed by the CoRoT archive as part of its interface. NStED is available at {\bf http://nsted.ipac.caltech.edu}.

astro-ph.IM↗

arXiv2009

The LAEX and NASA portals for CoRoT public data

* Aims. We describe here the main functionalities of the LAEX (Laboratorio de Astrofisica Estelar y Exoplanetas/Laboratory for Stellar Astrophysics and Exoplanets) and NASA portals for CoRoT Public Data. The CoRoT archive at LAEX was opened to the community in January 2009 and is managed in the framework of the Spanish Virtual Observatory. NStED (NASA Star and Exoplanet Database) serves as the CoRoT portal for the US astronomical community. NStED is a general purpose stellar and exoplanet archive with the aim of providing support for NASA planet finding and characterisation goals, and the planning and support of NASA and other space missions. CoRoT data at LAEX and NStED can be accessed at http://sdc.laeff.inta.es/corotfa/ and http://nsted.ipac.caltech.edu,respectively. * Methods. Based on considerable experience with astronomical archives, the aforementioned archives are designed with the aim of delivering science-quality data in a simple and efficient way. * Results. LAEX and NStED not only provide access to CoRoT Public Data but furthermore serve a variety of observed and calculated astrophysical data. In particular, NStED provides scientifically validated information on stellar and planetary data related to the search for and characterization of extrasolar planets, and LAEX makes any information from Virtual Observatory services available to the astronomical community.

astro-ph.SR↗

arXiv2008

The NStED Stellar and Exoplanet Hosting Star Service

The NASA Star and Exoplanet Database (NStED) is a general purpose stellar archive with the aim of providing support for NASA's planet finding and characterization goals, stellar astrophysics, and the planning of NASA and other space missions. There are two principal components of NStED: a database of (currently) 140,000 nearby stars and exoplanet-hosting stars, and an archive dedicated to high precision photometric surveys for transiting exoplanets. We present a summary of the NStED stellar database, functionality, tools, and user interface. NStED currently serves the following kinds of data for 140,000 stars (where available): coordinates, multiplicity, proper motion, parallax, spectral type, multiband photometry, radial velocity, metallicity, chromospheric and coronal activity index, and rotation velocity/period. Furthermore, the following derived quantities are given wherever possible: distance, effective temperature, mass, radius, luminosity, space motions, and physical/angular dimensions of habitable zone. Queries to NStED can be made using constraints on any combination of the above parameters. In addition, NStED provides tools to derive specific inferred quantities for the stars in the database, cross-referenced with available extra-solar planetary data for those host stars. NStED can be accessed at http://nsted.ipac.caltech.edu

astro-ph↗

arXiv2008

The NStED Exoplanet Transit Survey Service

The NASA Star and Exoplanet Database (NStED) is a general purpose stellar archive with the aim of providing support for NASA's planet finding and characterization goals, stellar astrophysics, and the planning of NASA and other space missions. There are two principal components of NStED: a database of (currently) 140,000 nearby stars and exoplanet-hosting stars, and an archive dedicated to high-precision photometric surveys for transiting exoplanets. We present a summary of the latter component: the NStED Exoplanet Transit Survey Service (NStED-ETSS), along with its content, functionality, tools, and user interface. NStED-ETSS currently serves data from the TrES Survey of the Kepler Field as well as dedicated photometric surveys of four stellar clusters. NStED-ETSS aims to serve both the surveys and the broader astronomical community by archiving these data and making them available in a homogeneous format. Examples of usability of ETSS include investigation of any time-variable phenomena in data sets not studied by the original survey team, application of different techniques or algorithms for planet transit detections, combination of data from different surveys for given objects, statistical studies, etc. NStED-ETSS can be accessed at \tt{http://nsted.ipac.caltech.edu}

astro-ph↗

arXiv2004

Heavy and Light Pentaquark Chiral Lagrangian

Using the SU(3) flavor symmetry, we construct the chiral Lagrangians for the light and heavy pentaquarks. The correction from the nonzero quark is taken into account perturbatively. We derive the Gell-Mann$-$Okubo type relations for various pentaquark multiplet masses and Coleman-Glashow relations for anti-sextet heavy pentaquark magnetic moments. We study possible decays of pentaquarks into conventional hadrons. We also study the interactions between and within various pentaquark multiplets and derive their coupling constants in the symmetry limit. Possible kinematically allowed pionic decay modes are pointed out.

hep-ph↗

arXiv2004

$J^P={1/2}^-$ Pentaquarks in Jaffe and Wilczek's Diquark Model

If Jaffe and Wilczek's diquark picture for $Θ_5$ pentaquark is correct, there should also exist a $SU_F$(3) pentaquark octet and singlet with no orbital excitation between the diquark pair, hence $J^P={1/2}^-$. These states are lighter than the $Θ_5$ anti-decuplet and lie close to the orbitally excited (L=1) three-quark states in the conventional quark model. We calculate their masses and magnetic moments and discuss their possible strong decays using the chiral Lagrangian formalism. Among them two pentaquarks with nucleon quantum numbers may be narrow. Selection rules of strong decays are derived. We propose the experimental search of these nine additional $J^P={1/2}^-$ baryon states. Especially there are two additional $J^P={1/2}^-$ $Λ$ baryons around $Λ(1405)$. We also discuss the interesting possibility of interpreting $Λ(1405)$ as a pentaquark. The presence of these additional states will provide strong support of the diquark picture for the pentaquarks. If future experimental searches fail, one has to re-evaluate the relevance of this picture for the pentaquarks.

hep-ph↗