Transcript spectrum & filter services

EÖTVÖS UNIVERSITY BUDAPEST
Department of Physics of Complex Systems
Spectrum Services 2007
László Dobos (ELTE)
[email protected]
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:
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binning
wavelength scale (air / vacuum)
extinction correction
file format
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SPECTRUM & FILTER SERVICES
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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
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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
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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 basis
PCA (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:
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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 Service
synthetic 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 Services
http://voservices.net/spectrum
• Filter Service
http://voservices.net/filter
• Footprint Service
http://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
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