J/ApJ/659/585 X-ray classification of young star clusters (Hojnacki+, 2007)
An X-ray spectral classification algorithm with application to young stellar
clusters.
Hojnacki S.M., Kastner J.H., Micela G., Feigelson E.D., Lalonde S.M.
<Astrophys. J., 659, 585-598 (2007)>
=2007ApJ...659..585H 2007ApJ...659..585H
ADC_Keywords: Clusters, open ; X-ray sources
Keywords: methods: statistical - open clusters and associations: general -
stars: early-type - stars: pre-main-sequence - X-rays: stars
Abstract:
A large volume of low signal-to-noise, multidimensional data is
available from the CCD imaging spectrometers aboard the Chandra X-Ray
Observatory and the X-Ray Multimirror Mission (XMM-Newton). To make
progress analyzing this data, it is essential to develop methods to
sort, classify, and characterize the vast library of X-ray spectra in
a nonparametric fashion (complementary to current parametric model
fits). We have developed a spectral classification algorithm that
handles large volumes of data and operates independently of the
requirement of spectral model fits.
We use proven multivariate statistical techniques including principal
component analysis and an ensemble classifier consisting of
agglomerative hierarchical clustering and K-means clustering applied
for the first time for spectral classification. The algorithm
positions the sources in a multidimensional spectral sequence and then
groups the ordered sources into clusters based on their spectra. These
clusters appear more distinct for sources with harder observed
spectra. The apparent diversity of source spectra is reduced to a
three-dimensional locus in principal component space, with spectral
outliers falling outside this locus.
The algorithm was applied to a sample of 444 strong sources selected
from the 1616 X-ray emitting sources detected in deep Chandra imaging
spectroscopy of the Orion Nebula Cluster.
Description:
Data from the COUP (Getman et al., 2005, Cat. J/ApJS/160/319)
observations (ObsIDs 4395, 3744, 4373, 4374, 4396, and 3498) of the
ONC were used as the input data set for development of the X-ray
source classification algorithm.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 77 444 Properties of the 444 COUP sources
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See also:
J/ApJS/160/319 : COUP: observations and source lists (Getman+, 2005)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- COUP COUP source number (1)
6- 7 I2 --- Class [1-17] X-ray spectral class (see paper)
9- 14 F6.2 --- HR2 ? Hardness ratio 2 (0.5-1.7 vs. 1.7-2.8keV) (1)
16- 21 F6.2 --- HR3 Hardness ratio 3 (1.7-2.8 vs. 2.8-8.0keV) (1)
23- 28 F6.2 [cm-2] NH Log Hydrogen column density (1)
30- 35 F6.2 keV kT1 Energy of first plasma component (1)
37- 42 F6.2 keV kT2 ? Energy of second plasma component (1)
44- 49 F6.2 --- T1/T2 ? Ratio of first and second plasma components
51- 56 F6.3 [K] Teff ? Log of the stellar effective temperature (1)
58- 63 F6.1 0.1nm EWCa ? Equivalent width of CaII line in Angstroms (1)
65- 70 F6.2 mag AV ? The visual absorption (1)
72- 77 F6.2 mag DelK ? The Δ(I-K) near-infrared excess (1)
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Note (1): From Getman et al. (2005, Cat. J/ApJS/160/319).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 25-Jan-2009