J/ApJS/269/10 Classif. of Chandra X-ray sources in Cygnus OB2 (Kashyap+, 2023)
Classification of Chandra X-ray sources in Cygnus OB2.
Kashyap V.L., Guarcello M.G., Wright N.J., Drake J.J., Flaccomio E.,
Aldcroft T.L., Albacete Colombo J.F., Briggs K., Damiani F., Drew J.E.,
Martin E.L., Micela G., Naylor T., Sciortino S.
<Astrophys. J. Suppl. Ser., 269, 10 (2023)>
=2023ApJS..269...10K 2023ApJS..269...10K
ADC_Keywords: X-ray sources
Keywords: Star forming regions ; Catalogs ; Astrostatistics ;
Astrostatistics techniques ; Bayesian statistics ;
Open star clusters ; OB associations ; X-ray stars ; Standard stars
Abstract:
We have devised a predominantly Naive Bayes-based method to classify
X-ray sources detected by Chandra in the Cygnus OB2 association into
members, foreground objects, and background objects. We employ a
variety of X-ray, optical, and infrared characteristics to construct
likelihoods using training sets defined by well-measured sources.
Combinations of optical photometry from the Sloan Digital Sky Survey
(riz) and Isaac Newton Telescope Photometric Hα Survey
(rIiIHα), infrared magnitudes from United Kingdom Infrared
Telescope Deep Sky Survey and Two-Micron All Sky Survey (JHK), X-ray
quantiles and hardness ratios, and estimates of extinction Av are used
to compute the relative probabilities that a given source belongs to
one of the classes. Principal component analysis is used to isolate
the best axes for separating the classes for the photometric data, and
Gaussian component separation is used for X-ray hardness and
extinction. Errors in the measurements are accounted for by modeling
as Gaussians and integrating over likelihoods approximated as quartic
polynomials. We evaluate the accuracy of the classification by
inspection and reclassify a number of sources based on infrared
magnitudes, the presence of disks, and spectral hardness induced by
flaring. We also consider systematic errors due to extinction. Of the
7924 X-ray detections, 5501 have a total of 5597 optical/infrared
matches, including 78 with multiple counterparts. We find that ∼6100
objects are likely association members, ∼1400 are background objects,
and ∼500 are foreground objects, with an accuracy of 96%, 93%, and
80%, respectively, with an overall classification accuracy of
approximately 95%.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 62 8020 Catalog of classifications
--------------------------------------------------------------------------------
See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
II/319 : UKIDSS-DR9 LAS, GCS and DXS Surveys (Lawrence+ 2012)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/AJ/101/1408 : Massive stars in Cyg OB2. (Massey+ 1991)
J/A+A/474/495 : X flares from CygOB2 young stars (Albacete Colombo+, 2007)
J/ApJ/663/320 : IR-through-UV extinction curve (Fitzpatrick+, 2007)
J/ApJ/659/585 : X-ray classif. of young star clusters (Hojnacki+, 2007)
J/ApJS/184/84 : X-ray sources in Cyg OB2 region (Wright+, 2009)
J/ApJ/720/679 : Optical spectroscopy in Cygnus X region (Beerer+, 2010)
J/A+A/521/A18 : Blue stars with disk phot. in NGC 6611 (Guarcello+, 2010)
J/ApJ/713/871 : Sources in Cyg-OB2 from X-ray (Wright+, 2010)
J/ApJS/194/4 : Classification of CCCP X-ray sources (Broos+, 2011)
J/ApJS/202/19 : riz photometry in Cyg OB2 (Guarcello+, 2012)
J/ApJ/773/135 : Disk-bearing stars in Cygnus OB2 (Guarcello+, 2013)
J/ApJS/209/28 : MYStIX Wide-Field NIR data: crowded fields (King+, 2013)
J/ApJS/209/27 : MYStIX: the Chandra X-ray sources (Kuhn+, 2013)
J/MNRAS/449/741 : The massive star population of Cygnus OB2 (Wright+, 2015)
J/MNRAS/485/1085 : Classification of emission-line galaxies (Stampoulis+, 2019)
J/ApJS/269/7 : Chandra Cyg OB2 Legacy Survey: X-ray Catalog (Wright+ 2023)
J/ApJS/269/9 : Opt-IR xids of Chandra sources in CygOB2 (Guarcello+, 2023)
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- [WDG2023] [1/7924] Source number as in
Wright+ 2023, J/ApJS/269/7 (1)
6- 13 A8 --- Match Optical/IR match? ("Multiple": 174 occurrences,
"Yes": 5423 occurrences, or "No")
15- 18 F4.2 --- pFore [0/1] Probability value of being a foreground
member
20- 23 F4.2 --- pMemb [0/1] Probability value of being a member
25- 28 F4.2 --- pBack [0/1] Probability value of being a background
member
30- 40 A11 --- Class Classification ("background": 1360 occurrences,
"foreground": 491 occurrences or
"member":6169 occurrences)
42- 62 A21 --- n_Class Additional note(s) on Class (2)
--------------------------------------------------------------------------------
Note (1): Used within the Chandra Cygnus OB2 Legacy Survey
Note (2): Note as follows:
Box = Matched to a Gaia DR2 source within position error;
ddag = Classification changed by inspection;
star = Used as part of training set;
blacksquare = Final classification inconsistent with Gaia distance.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 26-Jan-2024