SETI public: Objective Subclass Determination of Sloan Digital Sky Survey Unknown Spectral Ob

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Paper: astro-ph/0512119
Date: Mon, 5 Dec 2005 18:34:27 GMT (419kb)

Title: Objective Subclass Determination of Sloan Digital Sky Survey Unknown
Spectral Objects

Authors: David Bazell, David J. Miller, Mark SubbaRao

Comments: 19 pages; 5 figures; submitted to Ap. J
\\
We analyze a portion of the SDSS photometric catalog, consisting of
approximately 10,000 objects that have been spectroscopically classified
into
stars, galaxies, QSOs, late-type stars and unknown objects, in order to
investigate the existence and nature of subclasses of the unknown objects.
We
use a modified mixture modeling approach that makes use of both labeled and
unlabeled data and performs class discovery on the data set. This technique
discovers putative novel classes by identifying compact clusters that
largely
contain objects from the unknown class of objects. These clusters are of
possible scientific interest because they represent structured groups of
outliers, relative to the known object classes. We identify two such well
defined subclasses of the unknown object class. One subclass contains 58%
unknown objects, 40% stars, and 2% galaxies, QSOs, and late-type stars. The
other contains 91% unknown objects, 6% late-type stars, and 3% stars,
galaxies,
and QSOs. We discuss possible interpretations of these subclasses while also
noting some caution must be applied to purely color-based object
classifications. As a side benefit of this limited study we also find two
distinct classes, consisting largely of galaxies, that coincide with the
recently discussed bimodal galaxy color distribution.

\\ ( http://arXiv.org/abs/astro-ph/0512119 , 419kb)

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