Hungarian VO activities

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Hungarian VO activities

• László Dobos, István Csabai
• Eötvös University
• Tamás Budavári, Alex Szalay
• Johns Hopkins

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Topics

• Spectrum Service
• Footprint service
• Spatial Indexing of large multidimensional
  datasets

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Spectrum Service

• Database of over 1M spectraSDSS DR2-4, 2dFGRS,
  theoretical
• Access remote dataset from the web site or
  central web service
• Parallel querying of remote databases
• Intuitive web user interface
• Web services - several standards

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Spectrum Service - functions

• Composite spectrum generation
• Galactic extinction correction (Schlegel's map)
• Synthetic magnitude calculation (many filters)
• Continuum fitting (Bruzual-Charlot models)
• Line fitting (currently in improvement)

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Spectrum Services - science

• Age determination and evolution detection in LRG
  spectra by fitting Bruzual-Charlot models
• Comparing distributions of theoretical spectrum
  sets with the SDSS spectra
• We strongly encourage students and PhD students
  to use the VO tools

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Footprint service

• Spherical Geometry Library by Tamás Budavári
  (Johns Hopkins)
• Web user interface
• database of footprints of large surveys
• footprint upload
• intersect, union calculation
• visualization

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Multidimensional datasets

• Typical datasets with 200M points
• Color Index space - multidimensional
• gt100GB -gt do not fit into the memory
• Standard algorithms do not work
• Same problem with distributed datasets (VO)

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nD datasets - typical tasks

• Object types are classified by a set of linear
  inequlities in magnitude space (n dimensional
  polihedra)
• Compute a histogram of the whole parameter space
• Find similar objects
• Find clusters, outliers
• Compare the distribution of two very large
  datasets

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nD datasets - problems, idea

• No random access to the data
• In a DB server data pages on the disk - takes
  long time to access and load
• In the VO servers are distributed over the
  world, slow network
• Main idea organize data on a geometrical basis
  in the n-dimensional space
• kd-Trees, Voronoi-tessalation

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Scientific ideas

• SDSS photometry 5D 300M points finding all
  objects with similar colors source
  classification star quasar separation blue
  red galaxy locus etc.
• Karhunen-Loeve (PCA) coeffs of Bruzual-Charlot
  models 5-15D 100K-100M p Quick match with
  observed spectra

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Scientific ideas cont.

• Magnitudes of spectral synthesis models 5-10D
  100K-100M points match with observations photo-z
  physical props. from photometry check
  consitency of various models (BC-GRASIL)
• Multiresolution visualization of large number of
  points

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URLs

• http//voservices.net
• http//voservices.net/spectrum
• http//hvo.elte.hu