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EÖTVÖS UNIVERSITY BUDAPEST

Department of Physics of Complex Systems

Spectrum Services 2007

László Dobos (ELTE)dobos@complex.elte.hu

Tamás Budavári (JHU), István Csabai (ELTE)

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MOTIVATIONS

• SDSS Data Archive Server offers very limited possibility to search among spectra

• SkyServer has nice search features, but does not contain the spectra

• Observed spectra are in many formats:– binning– wavelength scale (air / vacuum)– extinction correction– file format

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SPECTRUM & FILTER SERVICES

• Database of spectra• Wide range of search possibilities• Preprocessing spectra on the fly• Data analysis• Access to data in many file formats• Plot spectra• Web interface• Web service to program against

• Filter service:database of optical instrument band-pass curves

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AVAILABLE SPECTRA

• Repository of observed and theoretical spectra– SDSS DR1-DR5 (1M spectra in DR5 only)– 2dF (250k)– BaSeL stellar library– Bruzual-Charlot stochastic burst model library

(100k)

• 'My Spectrum' is a public repository where users can upload their own measurements or save results of spectrum processing.

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SEARCH POSSIBILITIES

• Cone search - search by coordinates and radius

• ID search - if you know the database identifier (ie. from SkyServer)

• Object search - by a list of coordinates• Redshift search• Advanced search - with many basic options

• Region search - gives back spectra of objects in a complex, arbitrary area

• Similarity search - based on PCA

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3. REGION SEARCH

• The new Footprint Service allows defining complex regions on the sphere

• Spectrum Services link to the Footprint Service to get region description

• Spectra observed in the given region can be retrieved from the database

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4. SIMILAR SPECTRUM SEARCH

• Spectra are expanded on a predefined basisPCA (see Ching-Wa's talk) or model spectra

• Coefficients are stored in a multi-dimensional database

• Database is indexed by special spatial indices

• N-Nearest neighbour search in the coefficient space

• Not necessarily physical, still interesting

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GALAXIES

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PREPROCESSING TOOLS

• General functions to convert spectra to the same format to use in analysis

• Functions:– Correction for galactic extinction– Rest frame– Normalization– Rebinning– Vacuum - Air wavelength conversion

• Download preprocessed spectra (XML, VOTable, ASCII)

• Store them in 'MySpectrum' for later use

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ANALYSIS TOOLS

• Composite spectrum:– average, median

• Convolution with filters from Filter Servicesynthetic magnitude calculation

• Continuum and line fitting

• The new version will be really fast:– Parallel computation on multiple processor– optimized LAPACK libraries

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SUMMARY & FUTURE WORKS

• Spectrum database and public repository• Web site & web service• Integration with other VO services:

– Filter Service, Footprint Service

• Preprocessing and analyzis tools

• Improved line fitting algorithm• Make similarity search public• Latest VO standard implementation

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URLs OF INTEREST

• Spectrum Serviceshttp://voservices.net/spectrum

• Filter Servicehttp://voservices.net/filter

• Footprint Servicehttp://voservices.net/footprint

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Distribution of SDSS objects in the space of SDSS galaxy eigenspectra

Galaxies

Stars

QSOs

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WEB INTERFACE

• For interactive use by humans• Concept: try the functions on the web page,

but use the web service for batch processing

• Register / login• Search and display results in a nice format• 'Wizards' to guide users through the pages

of many parameters of scientific functions• Download spectra in XML, VOTable, ASCII• (No implementation of the latest DM yet)

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2. SPEEDING UP SPECTRUM SERVICES

• Objective:processing hundreds of thousands of

spectra• Moved to .Net 2.0 - Better computing performance

• Streamlined processing of spectra– Minimal memory usage– No upper limit for number of spectra

• Multi-processor support– parallel execution of processing routines

• Optimized LAPACK integration:– MKL (intel), ACML (AMD)

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4.1 THE ECOEFF SPACE

• DR4 galaxy eigenspectra used as basis(Yip et. al 2002) from gappy PCA algorithm

• All spectra (even stars and QSOs) are expressed on this basis

• Our method: minimal χ2 fitting (with masks etc.)

• Applied to:– SDSS DR5– Charlot's stochastic 100k spectrum set

• Objective: find physical parameters very quickly