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NGC2237CXO - NGC 2237 Chandra X-Ray Point Source Catalog

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Overview

the authors have obtained high spatial resolution Chandra X-ray images of the NGC 2237 young stellar cluster on the periphery of the Rosette Nebula. They detect 168 X-ray sources, 80% of which have stellar counterparts in USNO, Two Micron All Sky Survey, and deep FLAMINGOS images. These constitute the first census of the cluster members with 0.2 <~ M <~ 2 M_sun. Star locations in near-infrared color-magnitude diagrams indicate a cluster age of around 2 Myr with a visual extinction of 1 <~ AV <~ 3 at 1.4 kpc, the distance of the Rosette Nebula's main cluster NGC 2244. The authors derive the K-band luminosity function and the X-ray luminosity function of the cluster, which indicate a population of ~ 400-600 stars. The X-ray-selected sample shows a K-excess disk frequency of 13%. The young Class II counterparts are aligned in an arc ~3 pc long suggestive of a triggered formation process induced by the O stars in NGC 2244. The diskless Class III sources are more dispersed. Several X-ray emitting stars are located inside the molecular cloud and around gaseous pillars projecting from the cloud. These stars, together with a previously unreported optical outflow originating inside the cloud, indicate that star formation is continuing at a low level and the cluster is still growing. This X-ray view of young stars on the western side of the Rosette Nebula complements the authors' earlier studies of the central cluster NGC 2244 and the embedded clusters on the eastern side of the Nebula. The large-scale distribution of the clusters and molecular material is consistent with a scenario in which the rich central NGC 2244 cluster formed first, and its expanding H II region triggered the formation of the now-unobscured satellite clusters Rosette Molecular Cloud (RMC) XA and NGC 2237. A large swept-up shell of material around the H II region is now in a second phase of collect-and-collapse fragmentation, leading to the recent formation of subclusters. Other clusters deeper in the molecular cloud appear unaffected by the Rosette Nebula expansion.

Some sources which have information from published catalogs are listed by their source_number value below, where for convenience, [OI81] = Ogura & Ishida (1981, PASJ, 33, 149), [MJD95] = Massey, Johnson, & Degioia-Eastwood (1995, ApJ, 454, 151) and [BC02] = Berghofer & Christian (2002, A&A, 384, 890):

   53 = [OI81] 14 = [MJD95] 104; spectral type B1V; pmRA=11.0 mas/yr,
        pmDE=-2.8 mas/yr;
   54 = [OI81] 10 = [MJD95] 108; spectral type B2V; pmRA=-2.3 mas/yr,
        pmDE=-11.9 mas/yr;
   61 = V539 Mon [OI81] 13 = [MJD95] 110; MSX6C G206.1821-02.3456;
        pmRA=2.8 mas/yr, pmDE=0.4 mas/yr;
   71 = [OI81] 12 = [MJD95] 102; pmRA=6.8 mas/yr, pmDE=0.6 mas/yr;
  128 = [OI81] 35 = [MJD95] 471; spectral type A2:; pmRA=-0.8 mas/yr,
        pmDE=3.6 mas/yr;
  138 = [OI81] 36 = [MJD95] 497; spectral type B5; pmRA=6.5 mas/yr,
        pmDE=2.1 mas/yr;
  141 = [MJD95] 498; pmRA=-3.0 mas/yr, pmDE=1.9 mas/yr;
  149 = [BC02] 11; known X-ray source; log(Lx(ROSAT/PSPC))=31.01 erg/s;
        pmRA=0.6 mas/yr, pmDE=-12.6 mas/yr;
  161 = [MJD95] 653; pmRA=-1.0 mas/yr, pmDE=-5.4 mas/yr

Catalog Bibcode

2010ApJ...716..474W

References

A Chandra Study of the Rosette Star-forming Complex. III. The NGC 2237 Cluster
and the Region's Star Formation History
     Wang J., Feigelson E.D., Townsley L.K., Broos P.S.,
     Roman-Zuniga C.G., Lada E., Garmire G.
    <Astrophys. J. 716, 474 (2010)>
    =2010ApJ...716..474W

Provenance

This table was created by the HEASARC in July 2010 based on electronic versions of Tables 1, 2, 3 and 4 of the reference paper which were obtained from the electronic ApJ web site. To distinguish between the 130 X-ray sources in the primary sample (Table 1 of the reference paper) and the 38 X-ray sources in the tentative sample (Table 2 of the reference paper), the HEASARC has created a parameter called source_sample which is set to 'P' for the primary sources and to 'T' for the tentative sources.

Parameters

Source_Number
A running source number in order of increasing J2000.0 Right Ascension, which uniquely identifies the X-ray source.

Source_Sample
To distinguish between the 130 X-ray sources in the primary sample (Table 1 of the reference paper) and the 38 X-ray sources in the tentative sample (Table 2 of the reference paper), the HEASARC has created this parameter which is set to 'P' for the primary sources and to 'T' for the tentative sources.

Name
The name of the X-ray source using the 'CXOU' prefix (for Chandra X-ray Observatory, Unregistered source) and the J2000 coordinates of the source in the (higher precision than standard) HHMMSS.ss+DDMMSS.s format.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000 decimal degree coordinates and to a precision of 10-6 degrees in the original table.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000 decimal degree coordinates and to a precision of 10-6 degrees 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 statistical positional error of the X-ray source, i.e., the estimated 1-sigma standard deviation of the random component of the position error, in arcseconds. This is computed as (standard deviation of PSF inside extraction region)/(number of counts extracted)0.5.

Off_Axis
The off-axis angle of the X-ray source from the nominal Chandra pointing direction, in arcminutes.

Counts
The estimated net counts extracted in the total energy band (0.5 - 8 keV) for the X-ray source.

Counts_Error
The Poisson-Based average 1-sigma error in the total-band counts for the X-ray source.

Bck_Counts
The background counts in the total-band (0.5 - 8 keV) in the X-ray source extraction region.

HB_Counts
The estimated net counts extracted in the hard energy band (2 - 8 keV) for the X-ray source.

PSF_Fraction
The fraction of the PSF (at 1.497 keV) enclosed within the extraction region for the X-ray source. Note that a reduced PSF fraction (significantly below 90%) may indicate that the source is in a crowded region.

Significance
The photometric significance of the X-ray source in the total band, computed as the net counts divided by the upper error in the net counts.

Log_Bck_Prob_Limit
This flag parameter is set to '<' if the corresponding value of log P_B (log_bck_prob) is an upper limit.

Log_Bck_Prob
The log of the probability (log P_B) that the extracted counts (total band) are solely from the background. Some sources have P_B values above the 1% threshold that defines the catalog because local background estimates can rise during the final extraction iteration after sources are removed from the catalog. Sources with P_B < 0.001 (0.1%) are considered primary sources (source_sample = 'P' for 'Primary'), while those with 0.001 (0.1%) <= P_B < 0.01 (1%) are considered tentative (source_sample = 't' for 'Tentative').

Source_Anomaly_Flag
This flag parameter is set to 'g' to indicate the presence of the following source anomaly, namely that the fractional time that the source was on a detector (FRACEXPO from mkarf) is < 0.9.

Source_Variable_Flag
This flag parameter contains codes which characterize the X-ray source variability in the total band based on the K-S statistic, as follows (no value is reported for sources with fewer than four counts or for sources in chip gaps or on field edges):

    a: no evidence for variability (P_KS > 0.05)
    b: possibly variable (0.005 < P_KS < 0.05)
    c: definitely variable (P_KS < 0.005)
  

Exposure
The effective exposure time for the X-ray source, in seconds. This is the approximate time the source would have to be observed on-axis (i.e., no telescope vignetting) on a nominal region of the detector (with no dithering over insensitive regions of the detector) in order to obtain the reported number of source counts.

Median_Energy
The background-corrected total-band median photon energy of the X-ray source photons, in keV.

Log_NH
The logarithm of the best-fit column density, log n_H, in H atoms/cm2.

Log_NH_Flag
This flag parameter is marked with a value of 'F' to indicate that the corresponding parameter value was frozen in the fit.

Log_NH_Neg_Err
The lower 90% confidence level error in the best-fit value of log n_H, in H atoms/cm2. More significant digits are used for uncertainties <0.1 in order to avoid large rounding errors; for consistency, the same number of significant digits is used for both lower and upper uncertainties. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; in such cases, the listed parameter values are unreliable.

Log_NH_Pos_Err
The upper 90% confidence level error in the best-fit value of log n_H, in H atoms/cm2. More significant digits are used for uncertainties <0.1 in order to avoid large rounding errors; for consistency, the same number of significant digits is used for both lower and upper uncertainties. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; in such cases, the listed parameter values are unreliable.

APEC_kT
The best-fit value of the plasma temperature from the APEC model, kT, in keV. All such fits used the "tbabs * apec)" model in XSPEC and assumed 0.3 solar abundances (Imanishi et al. (2001, ApJ, 557, 747), Feigelson et al. (2002, ApJ, 574, 258). In four cases (source nos. 19, 113, 162, and 163), a power-law spectral model gives a significantly better fit than a single-temperature thermal model. In these cases, this parameter gives the power-law index Gamma rather than the plasma temperature.

APEC_kT_Flag
This flag parameter is marked with a value of 'F' to indicate that the corresponding parameter value was frozen in the fit.

APEC_kT_Neg_Err
The lower 90% confidence level error in the best-fit value of the plasma temperature, kT, in keV, from the APEC model (or in the power-law slope for sources 19, 113, 162 or 163). More significant digits are used for uncertainties <0.1 in order to avoid large rounding errors; for consistency, the same number of significant digits is used for both lower and upper uncertainties. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; in such cases the listed parameter values are unreliable.

APEC_kT_Pos_Err
The upper 90% confidence level error in the best-fit value of the plasma temperature, kT, in keV, from the APEC model (or in the power-law slope for sources 19, 113, 162 or 163). More significant digits are used for uncertainties <0.1 in order to avoid large rounding errors; for consistency, the same number of significant digits is used for both lower and upper uncertainties. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; in such cases the listed parameter values are unreliable.

Log_EM
The logarithm of the model emission measure log EM derived from the best-fit APEC model, assuming a distance of 1.4 kpc to NGC 2237, in cm-3. In four cases (source nos. 19, 113, 162, and 163), a power-law spectral model gives a significantly better fit than a single-temperature thermal model. In these cases, this parameter gives the power-law normalization rather than the plasma log EM.

Log_EM_Neg_Err
The lower 90% confidence level error in the best-fit value of the logarithm of the plasma emission measure, log EM, in cm-3, from the APEC model (or in the power-law normalization for sources 19, 113, 162 or 163). More significant digits are used for uncertainties <0.1 in order to avoid large rounding errors; for consistency, the same number of significant digits is used for both lower and upper uncertainties. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; in such cases the listed parameter values are unreliable.

Log_EM_Pos_Err
The upper 90% confidence level error in the best-fit value of the logarithm of the plasma emission measure, log EM, in cm-3, from the APEC model (or in the power-law normalization for sources 19, 113, 162 or 163). More significant digits are used for uncertainties <0.1 in order to avoid large rounding errors; for consistency, the same number of significant digits is used for both lower and upper uncertainties. Uncertainties are missing when XSPEC was unable to compute them or when their values were so large that the parameter is effectively unconstrained. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of luminosities; in such cases the listed parameter values are unreliable.

Log_SB_Lx_Obs
The logarithm of the observed soft-band (0.5 - 2 keV) luminosity of the X-ray source, assuming a distance of 1.4 kpc, in erg/s (omitted when log n_H > 22.5 cm-2, since the soft-band emission is essentially unmeasurable in such cases).

Log_HB_Lx_Obs
The logarithm of the observed hard-band (2 - 8 keV) luminosity of the X-ray source, assuming a distance of 1.4 kpc, in erg/s.

Log_HB_Lx
The logarithm of the absorption-corrected hard-band (2 - 8 keV) luminosity of the X-ray source, assuming a distance of 1.4 kpc, in erg/s.

Log_Lx_Obs
The logarithm of the observed total-band (0.5 - 8 keV) luminosity of the X-ray source assuming a distance of 1.4 kpc, in erg/s.

Log_Lx
The logarithm of the absorption-corrected total-band (0.5 - 8 keV) luminosity of the X-ray source assuming a distance of 1.4 kpc, in erg/s. This is omitted when log n_H > 22.5 cm-2, since the soft-band emission is essentially unmeasurable in such cases.

USNO_Name
The USNO B1.0 source designation of the stellar counterpart to the X-ray source.

Bmag
The B-band magnitude of the stellar counterpart to the X-ray source. The errors of the BRI magnitudes are <0.02 mag in general for stars with V < 17 mag and become >0.05 mag for fainter stars V > 19 mag Berghofer & Christian 2002, A&A, 384, 890).

Rmag
The R-band magnitude of the stellar counterpart to the X-ray source. The errors of the BRI magnitudes are <0.02 mag in general for stars with V < 17 mag and become >0.05 mag for fainter stars V > 19 mag Berghofer & Christian 2002, A&A, 384, 890).

Imag
The I-band magnitude of the stellar counterpart to the X-ray source. The errors of the BRI magnitudes are <0.02 mag in general for stars with V < 17 mag and become >0.05 mag for fainter stars V > 19 mag Berghofer & Christian 2002, A&A, 384, 890).

TwoMASS_Name
The designation of the 2MASS counterpart to the X-ray source.

Flamingos_ID
The FLAMINGOS source identifier of the near-IR counterpart to the X-ray source (see Section 3.1 of the reference paper for more details).

Jmag
The FLAMINGOS, else 2MASS, J-band magnitude of the near-IR counterpart to the X-ray source. The mean photometric uncertainties in FLAMINGOS are 0.058 +/- 0.012, 0.064 +/- 0.018, and 0.056 +/- 0.014 for J, H, and K, respectively (Roman-Zuniga et al. (2008, ApJ, 672, 861). The typical errors are much smaller for brighter stars (e.g., sigma_J = 0.02 mag for stars with J < 16 mag.

Hmag
The FLAMINGOS, else 2MASS, H-band magnitude of the near-IR counterpart to the X-ray source. The mean photometric uncertainties in FLAMINGOS are 0.058 +/- 0.012, 0.064 +/- 0.018, and 0.056 +/- 0.014 for J, H, and K, respectively (Roman-Zuniga et al. (2008, ApJ, 672, 861). The typical errors are much smaller for brighter stars (e.g., sigma_J = 0.02 mag for stars with J < 16 mag.

Kmag
The FLAMINGOS, else 2MASS, K-band magnitude of the near-IR counterpart to the X-ray source. The mean photometric uncertainties in FLAMINGOS are 0.058 +/- 0.012, 0.064 +/- 0.018, and 0.056 +/- 0.014 for J, H, and K, respectively (Roman-Zuniga et al. (2008, ApJ, 672, 861). The typical errors are much smaller for brighter stars (e.g., sigma_J = 0.02 mag for stars with J < 16 mag.

TwoMASS_Flags
The 2MASS source Photmetric Quality (Contamination and Confusion) flag values for the likely 2MASS counterpart to the X-ray source (see Cutri et al. (2003, The IRSA 2MASS All-Sky Point Source Catalog, NASA/IPAC Infrared Science Archive, http://irsa.ipac.caltech.edu/applications/Gator ).


Contact Person

Questions regarding the NGC2237CXO database table can be addressed to the HEASARC User Hotline.

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