J/MNRAS/396/223 QSO candidates selection in VO era (D'Abrusco+, 2009)
Quasar candidates selection in the Virtual Observatory era.
D'Abrusco R., Longo G., Walton N.A.
<Mon. Not. R. Astron. Soc., 396, 223-262 (2009)>
=2009MNRAS.396..223D 2009MNRAS.396..223D
ADC_Keywords: QSOs ; Surveys ; Photometry, SDSS
Keywords: methods: data analysis - methods: observational -
methods: statistical - catalogues - surveys - quasars: general
Abstract:
We present a method for the photometric selection of candidate quasars
in multiband surveys. The method makes use of a priori knowledge
derived from a subsample of spectroscopic confirmed quasi-stellar
objects (QSOs) to map the parameter space. The disentanglement of QSOs
candidates and stars is performed in the colour space through the
combined use of two algorithms, the probabilistic principal surfaces
and the negative entropy clustering, which are for the first time used
in an astronomical context. Both methods have been implemented in the
voneural package on the Astrogrid Virtual Observatory platform. Even
though they belong to the class of the unsupervised clustering tools,
the performances of the method are optimized by using the available
sample of confirmed quasars and it is therefore possible to learn from
any improvement in the available 'base of knowledge'. The method
has been applied and tested on both optical and optical plus
near-infrared data extracted from the visible Sloan Digital Sky Survey
(SDSS) and infrared United Kingdom Infrared Deep Sky Survey-Large Area
Survey public data bases. In all cases, the experiments lead to high
values of both efficiency and completeness, comparable if not better
than the methods already known in the literature. A catalogue of
optical candidate QSOs extracted from the SDSS Data Release 7 Legacy
photometric data set has been produced.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 25 37 List of the stripe files
data/* . 37 Ascii stripe files
fits/* . 37 Files in FITS format
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See also:
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
http://www.sdss.org : SDSS Home Page
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- FileName Name of the file in subdirectory data
16- 20 I5 --- Nqsos Number of QSOs in the file
24- 25 I2 --- Stripe [9/86] Stripe number
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Byte-by-byte Description of file: data/*
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Bytes Format Units Label Explanations
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1- 7 I7 --- Seq Candidate ID
9- 26 A18 --- objID SDSS objID of the source
28- 36 F9.5 deg RAdeg Right ascension in decimal degrees (J2000)
38- 46 F9.5 deg DEdeg Declination in decimal degrees (J2000)
48- 53 F6.3 mag umag PSF magnitude in SDSS/u' band
55- 60 F6.3 mag gmag PSF magnitude in SDSS/g' band
62- 67 F6.3 mag rmag PSF magnitude in SDSS/r' band
69- 74 F6.3 mag imag PSF magnitude in SDSS/i' band
76- 81 F6.3 mag zmag PSF magnitude in SDSS/z' band
83- 84 I2 --- cl [1,10] Cluster index (generation number of
'goal-successful' cluster)
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History:
Copied at http://voneural.na.infn.it/qso.html
(End) Patricia Vannier [CDS] 31-Jan-2011