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NGC2264CX2 - NGC 2264 Chandra X-Ray Point Source Catalog 2

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Overview

With the goal of improving the member census of the NGC 2264 star-forming region and studying the origin of X-ray activity in young pre-main sequence (PMS) stars, the authors analyzed a deep, 100 ks long, Chandra ACIS observation covering a 17' x 17' field in the 3 Myr old star-forming region (SFR) NGC 2264. The preferential detection in X-rays of low-mass PMS stars gives strong indications of their membership. The authors study X-ray activity as a function of stellar and circumstellar characteristics by correlating the X-ray luminosities, temperatures, and absorptions with optical and near-infrared (NIR) data from the literature.

The authors detected 420 X-ray point sources in the observation above a 4.6-sigma significance threshold using the PWDetect software. Optical and NIR counterparts were found in the literature for 85% of the sources. The authors argue that more than 90% of these counterparts are NGC 2264 members, thereby significantly increasing the known low-mass cluster population by about 100 objects. Among the sources without counterpart, about 50% are probably associated with members, several of which are expected to be previously unknown protostellar objects. With regard to activity, several previous findings are confirmed: X-ray luminosity is related to stellar mass, although with a large scatter; L_x/L_bol is close to, but almost invariably below, the saturation level of 10-3, especially when considering the quiescent X-ray emission. A comparison between classical T Tauri stars (CTTS) and weak-line T Tauri stars (WTTS) shows several differences: CTTS have, at any given mass, activity levels that are both lower and more scattered than WTTS; emission from CTTS may also be more time variable and is on average slightly harder than for WTTS. However, there is evidence in some CTTS of extremely cool, ~0.1 - 0.2 keV, plasma which the authors speculate is due to plasma heated by accretion shocks.

The X-ray spectra of the 199 sources with more than 50 detected photons were analyzed by the authors. Spectral fits were performed with XSPEC 11.3 and with several shell and TCL scripts to automate the process. For each source, they fit the data in the [0.5 - 7.0] keV energy interval with several model spectra: one and two isothermal components (APEC), subject to photoelectric absorption from interstellar and circumstellar material (WABS). Plasma abundances for one-temperature (1T) models were fixed at 0.3 times the solar abundances, while they were both fixed at that value and treated as a free parameter for the two-temperature (2T) models. The absorbing column densities, N_H, were both left as a free parameter and fixed at values corresponding to the optically/NIR determined extinctions, when available: N_H =1.6 x 1021 A_V.

This table contains the X-ray, optical and NIR data for the 420 detected X-ray sources; it does not contain the master catalog of 1598 optical/NIR sources within the ACIS FOV which was presented in Table 3 of the reference paper, available at ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+A/455/903/table3.dat


Catalog Bibcode

2006A&A...455..903F

References

ACIS-I observations of NGC 2264. Membership and X-ray properties of PMS stars.
    Flaccomio E., Micela G., Sciortino S.
   <Astron. Astrophys., 455, 903-921 (2006)>
   =2006A&A...455..903F    (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in March 2007 based on CDS catalog J/A+AJ/455/903 files table1.dat, table4.dat and table6.dat.

Parameters

Source_Number
A running number for the X-ray source in order of increasing J2000.0 Right Ascension.

Name
The name of the X-ray source using the '[FMS2006b]' prefix followed by the source number, as recommended by the CDS Dictionary of Nomenclature of Celestial Objects.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 seconds of time in the original table.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 arcseconds in the original table.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Error_Radius
The uncertainty in the position of the X-ray source, in arcseconds.

Off_Axis
The distance of the X-ray source from the Chandra optical axis, in arcminutes.

Counts
The background-subtracted source counts in the 0.2- 7 keV band as derived by PWDetect directly from the wavelet transform of the data.

Exposure
The effective exposure time at the source position, averaged over the PSF, as computed by PWDetect from an exposure map created with standard CIAO tools assuming an input energy of 2.0 keV.

SNR
The statistical significance of the X-ray source detection.

Prob_Constant
The Kolmogorov-Smirnov Test probability that the distribution of photon arrival times is compatible with a constant count-rate. Given the sample size (420 sources), a value below 0.001 (obtained for 72 sources) indicates the light-curve is almost certainly variable, while a <0.01 value (87 sources) indicates probable variability, although up to ~ 4 = 420 x 0.01) of the variable sources might actually be constant.

NH
The equivalent hydrogen absorption column density N_H towards the X-ray source, in H atoms cm-2.

NH_Type
The source for the N_H estimate: 'Av' if derived from the inferred visual extinction for a star of known spectral type, 'JHK' if estimated by dereddening the location of the star in the (J-H) vs. (H-K) diagram, or 'X' if derived from the X-ray spectral analysis.

Spectral_Model
The spectral model used in the spectral analysis of the X-ray source, as follows:

          1T = one-temperature model with plasma abundances fixed at
               0.3 times the solar abundances, N_H fixed at values
               corresponding to the optically/NIR determined extinctions,
               when available: N_H = 1.6 x 1021 x AV
          2T = two-temperature models with both Plasma abundances fixed at
               0.3 times the solar abundances and treated as a free parameter
               NH fixed at values corresponding to the optically/NIR
               determined extinctions, when available: N_H = 1.6 x 1021 A_V
        2Tab = two-temperature models with both free N_H and free abundances
  

Ic_Mag
The Cousins I magnitude I_C of the optical/NIR counterpart to the X-ray source.

RI_Color
The Cousins R-I color index of the optical/NIR counterpart to the X-ray source.

Jmag
The J magnitude of the optical/NIR counterpart to the X-ray source.

Hmag
The H magnitude of the optical/NIR counterpart to the X-ray source.

Kmag
The K magnitude of the optical/NIR counterpart to the X-ray source.

Spect_Type
The MK spectral type of the optical/NIR counterpart to the X-ray source.

A_Vmag
The absorption in the V band A_V for the optical/NIR counterpart to the X-ray source.

A_Vmag_Jhk
The absorption in the V band for the optical/NIR counterpart to the X-ray source as derived from dereddening the location of the star in the (J-H) vs. (H-K) diagram.

Log_T_Eff
The logarithm of the effective temperature, in K, of the stellar counterpart to the X-ray source, derived for stars with spectral types using the relations compiled by Kenyon & Hartmann (1995, ApJS, 101, 117) and, for the temperatures of M stars, the intermediate-gravity scale of Luhman (1999, ApJ, 525, 466).

Log_L_Bol
The logarithm of the bolometric luminosity, in solar luminosities, of the stellar counterpart to the X-ray source, derived for stars with spectral types using the relation log L_bol = -0.4 [I_c - BC_I - A_V/1.63 - DM(760 pc)], where BC is the bolometric corrrection and DM(760 pc) is the distance modulus for the assumed distance to NGC 2264, i.e., 5 x (log 760 - 1) = 9.40 magnitudes.

Stellar_Mass
The mass, in solar masses, of the stellar counterpart to the X-ray source, derived from the theoretical H-R Diagram (Fig. 5 in the reference paper) through interpolation of the Siess et al. (2000, A&A, 358, 593 = SDF) evolutionary tracks.

Log_Stellar_Age
The logarithm of the age, in yr, of the stellar counterpart to the X-ray source, derived from the theoretical H-R Diagram (Fig. 5 in the reference paper) through interpolation of the Siess et al. (2000, A&A, 358, 593 = SDF) evolutionary tracks.

Rotational_Period
The rotational period, in days, of the stellar counterpart to the X-ray source.

Spectral_Model_Flag
This flag parameter indicates the existence of a note on the particular spectral model used, as follows:

             a = Abund.= 1.43 (0.42 - 5.00)
             b = Abund.= 0.84 (0.50 - 1.26)
             c = Abund.= 0.94 (0.38 - 2.69)
  

Null_Probability
The null probability that the observed spectrum is described by the quoted spectral model

NH_Lower
The lower value of the best-fit interval for N_H, in atom cm-2.

NH_Upper
The upper value of the best-fit interval for N_H, in atom cm-2.

Te_Plasma_1
The plasma temperature kT_1, in keV, of the APEC model component in the 1T models, and of the lower temperature component in the 2T models.

Te_Plasma_1_Lower
The lower value of the best-fit interval for kT_1, in keV.

Te_Plasma_1_Upper
The upper value of the best-fit interval for kT_1, in keV.

Log_Norm_1
The logarithm of the normalization, log norm_1, of the APEC model component in the 1T models, and of the lower temperature component in the 2T models.

Log_Norm_1_Lower
The lower value of the best-fit interval for log_norm_1.

Log_Norm_1_Upper
The upper value of the best-fit interval for log_norm_1.

Te_Plasma_2
The plasma temperature kT_2, in keV, of the higher temperature component in the 2T models in keV.

Te_Plasma_2_Lower
The lower value of the best-fit interval for kT_2, in keV.

Te_Plasma_2_Upper
The upper value of the best-fit interval for kT_2, in keV.

Log_Norm_2
The logarithm of the normalization, log norm_2, of the higher temperature component in the 2T models.

Log_Norm_2_Lower
The lower value of the best-fit interval for log_norm_2.

Log_Norm_2_Upper
The upper value of the best-fit interval for log_norm_2.

Flux
The observed (absorbed) flux of the X-ray source in the 0.5 - 7.0 keV band, in erg/s/cm2.

Flux_Corr
The absorption-corrected flux of the X-ray source in the 0.5 - 7.0 keV band, in erg/s/cm2.

Class
The HEASARC Browse object classification of the stellar counterpart based on the spectral type.


Contact Person

Questions regarding the NGC2264CX2 database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 28-Aug-2012