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LMCN11CXO - LMC N11 Giant HII Region Chandra X-Ray Point Source Catalog

HEASARC
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Overview

A very sensitive X-ray investigation of the giant H II region N11 in the Large Magellanic Cloud (LMC) was performed using the Chandra X-ray Observatory in which 165 point sources were detected. The 300-ks observation reveals X-ray sources with luminosities (if at the 50 kpc distance of the LMC) down to 1032 erg s-1, increasing the number of known point sources in the field by more than a factor of five. Among these detections are 13 massive stars (3 compact groups of massive stars, 9 O stars, and one early B star) with log(LX/LBOL) ~ -6.5 to -7, which may suggest that they are highly magnetic or colliding-wind systems. On the other hand, the stacked signal for regions corresponding to undetected O stars yields log(LX/LBOL) ~ -7.3, i.e., an emission level comparable to similar Galactic stars despite the lower metallicity. Other point sources coincide with 11 foreground stars, 6 late-B/A stars in N11, and many background objects. This observation also uncovers the extent and detailed spatial properties of the soft, diffuse emission regions, but the presence of some hotter plasma in their spectra suggests contamination by the unresolved stellar population.

The Chandra ACIS-I observations of N11 were made in six separate segments within two months in 2007. As summarized in Table 1, the exposure time of each segment was 42-49 ks and the roll angle ranged from 130 to 188 degrees Cleaning of significant background flares, together with a correction for the dead time of the six observations, resulted in a total of 280 ks useful exposure for the subsequent analysis. A combination of source detection algorithms (wavelet, sliding-box, and maximum likelihood centroid fitting) were applied to unsmoothed data in three bands: soft (S): 0.5-2.0 keV, hard (H): 2-8 keV, and total (T): 0.5-8 keV. The final source list contains 165 sources with local false detection probability P < 10-6 in at least one band (Poisson statistics were used in calculating the significance of a source detection above the local count background). The source detection, though optimized for point-like sources, includes a few strong peaks of diffuse X-ray emission, chiefly associated with the SNR N11L, which lies about ~7' west of the field center.

The authors calculated the net (background-subtracted) count rates in four sub-bands (S1 = 0.5-1.0 keV, S2 = 1-2 keV, H1 = 2-4 keV and H2 = 4-8 keV, which were later added to form the count rates in the broader bands (S, H, and T). Source counts for each sub-band were then extracted within the 70% energy-encircled radius (EER) of the PSF, whose size depends on the off-axis angle of the source in the exposure and of the energy band under consideration. A background correction was also applied. Finally, count rates were derived by dividing source net counts by their effective exposure times (values at the source positions in the exposure map of the energy band under consideration), leading to equivalent on-axis values. It should be noted that the presented count rates have thus been corrected for the full PSF and for the effective exposure, which accounts not only for the telescope vignetting, but also for the degradation of the detector sensitivity over time. Therefore, the actual number of counts in a detection aperture is not simply a count rate multiplied by an exposure of 280 ks. The difference could be up to a factor of ~2, depending on a source's spectral shape.

The authors searched for counterparts to their X-ray sources in several catalogs: the USNO-B1.0 Catalog (Monet et al. 2003), the Guide Star Catalog V2.3.2 (GSC, Lasker et al. 2008), the 2MASS All-Sky Catalog of Point Sources (Cutri et al. 2003), the Magellanic Clouds Photometric Survey (MCPS; Zaritsky et al. 2004, AJ, 128, 1606), the IRSF Magellanic Clouds Point Source Catalog (Kato et al. 2007, PASJ, 59, 615)), the DENIS Catalogue toward Magellanic Clouds (DCMC; Cioni et al. 2000, A&AS, 144, 235), and JHKs photometry of N11 young stellar objects ([HKN2006]; Hatano et al. 2006, AJ, 132, 2653). A best correlation radius of 1" was found to be optimal and was thus used to derive the final list of optical and infrared counterparts to the Chandra X-ray sources: 71 of the 165 sources have at least one counterpart within 1".

The HEASARC has modified the counterpart names given in this table compared to those given in the reference paper so that they comply with the forms recommended by the CDS Dictionary of Nomenclature of Celestial Objects.


Catalog Bibcode

2014ApJS..213...23N

References

A Deep Chandra Observation of the Giant H II Region N11. I. X-Ray Sources in
the Field
    Naze Y., Wang Q.D., Chu Y.-H., Gruendl R., Oskinova L.
   <Astrophys. J. Suppl. Ser., 213, 23 (2014)>
   =2014ApJS..213...23N    (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in August 2014 based primarily on the contents of Tables 2, 3 and 4 from the reference paper, machine-readable versions of which were obtained from the ApJS web site. Some information from Table 8 of the reference paper, viz., a number of the spectral types quoted for individual stars, was also used in populating the HEASARC-created class parameter.

Parameters

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

Alt_Name
An alternative catalog-based source designation created by the HEASARC in the style recommended by the CDS Dictionary of Nomenclature of Celestial Objects, viz., '[NWC2014] nnn', where the prefix stands for Naze, Wang, Chu 2014 and nnn is the source number.

Name
The Chandra source designation using the standard 'CXOU' prefix for unregistered Chandra X-ray sources and the J2000.0 equatorial coordinates (JHHMMSS.ss+DDMMSS.s). Note that is 1 additional place in precision more than is commonly used for Chandra source names.

RA
The Right Ascension of the X-ray source in the selected equinox. This was (implicitly) given in J2000.0 coordinates to a precision of 0.01 seconds of time in the names which were given to these sources.

Dec
The Declination of the X-ray source in the selected equinox. This was (implicitly) given in J2000.0 coordinates to a precision of 0.1 arcseconds in the names which were given to these sources.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Error_Radius
The 1-sigma positional uncertainty of the X-ray source, in arcseconds, calculated from the maximum likelihood centroid and an approximate off-axis angle (r) dependent systematic error term, viz., 0.2" + 1.4" * (r/8') (an approximation to Figure 4 of Feigelson et al. 2002, ApJ< 574, 258), which are added in quadrature. Note that they may be overestimated; see Getman et al. (2005, ApJS, 160, 319, in particular Figure 9).

Count_Rate
The equivalent on-axis source total-band (0.5-8.0 keV) count rate of the X-ray source, in ct/s (converted by the HEASARC from the ct/ks units given in the original table as published), being the sum of the exposure-corrected count rates in the four narrow bands, S1, S2, H1 and H2 (see Overview above for the band definitions).

Count_Rate_Error
The uncertainty in the equivalent on-axis source total-band (0.5-8.0 keV) count rate of the X-ray source, in ct/s (converted by the HEASARC from the ct/ks units given in the original table as published).

Hardness_Ratio_1
The hardness ratio HR1 of the X-ray source, defined as HR1 = (H-S2)/(H+S2), where H and S2 are the net (background-subtracted) count rates in the hard band (2-8 keV) and the S2 sub-band (1-2 keV), respectively. Values for this parameter are listed only for values with uncertainties less than 0.2.

Hardness_Ratio_1_Error
The uncertainty in the hardness ratio HR1 of the X-ray source.

Hardness_Ratio_2
The hardness ratio HR2 of the X-ray source, defined as HR2 = (S2-S1)/(S), where S, S1 and S2 are the net (background-subtracted) count rates in the soft band (0.5-2.0 keV) and the S1 (0.5-1.0 keV) and S2 (1-2 keV) sub-bands, respectively. Values for this parameter are listed only for values with uncertainties less than 0.2.

Hardness_Ratio_2_Error
The uncertainty in the hardness ratio HR2 of the X-ray source.

Off_Axis
The off-axis angle of the X-ray source, in arcminutes.

Counts
The raw counts of the X-ray source in the detection aperture.

Bck_Counts
The estimated background counts in the detection aperture of the X-ray source.

Exposure
The effective exposure time, in seconds, at the X-ray source position (converted by the HEASARC from the ks units given in the original table as published).

Position_Band
This flag parameter is labeled with H, S or T to indicate which detection band was used to derive the most accurate source position: H=2.0-8.0 keV, S=0.5-2.0 keV or T=0.5-8.0 keV.

Source_Flag
This flag parameter is set to 'M' (changed by the HEASARC from the '*' value used in the original reference) to indicate that the X-ray source is associated with a massive star, the properties of which are listed in table 6 of the reference paper.

CXO_2MASS_Offset
The positional offset between the Chandra source and its 2MASS counterpart, in arcseconds.

TwoMASS_Name
The name of the 2MASS counterpart to the Chandra source.

CXO_DCMC_Offset
The positional offset between the Chandra source and its DCMC counterpart (see Overview above), in arcseconds.

DCMC_Name
The name of the DCMC counterpart (see Overview above) to the Chandra source.

CXO_GSC2p3_Offset
The positional offset between the Chandra source and its GSC-2.3 counterpart, in arcseconds.

GSC2p3_Name
The name of the GSC-2.3 counterpart to the Chandra source.

CXO_HKN2006_Offset
The positional offset between the Chandra source and its Hatano et al. 2006 (HKN2006) counterpart (see Overview above), in arcseconds.

HKN2006_Name
The name of the Hatano et al. 2006 (HKN2006) counterpart (see Overview above) counterpart to the Chandra source, e.g., '[HKN2006] type NN', where type can be either 'OB' or 'HAeBe' and reflects Hatano et al.'s source classification, an OB star or a Herbig Ae/Be star, respectively.

CXO_IRSF_Offset
The positional offset between the Chandra source and its IRSF counterpart (see Overview above), in arcseconds. There are additional IRSF components within 1" for sources 24, 36, 38, 77, 106, 123, and 164: only the closest counterpart is listed herein.

IRSF_Name
The name of the IRSF counterpart (see Overview above) to the Chandra source.

CXO_MCPS_Offset
The positional offset between the Chandra source and its MCPS counterpart (see Overview above), in arcseconds.

CXO_USNOB1_Offset
The positional offset between the Chandra source and its USNO-B1.0 counterpart, in arcseconds.

USNOB1_Name
The name of the USNO-B1.0 counterpart to the Chandra source.

S_II_Flag
This flag parameter is set to 'Y' if a counterpart was found within 1" of the X-ray source position in the authors' dedicated [Si II] 6716 + 6731 Angstrom images taken with the MOSAIC camera on the Blanco 4-m Telescope at CTIO, else is set to 'N'.

Spitzer_3p6_um_Flag
This flag parameter is set to 'Y' if a 3.6-um counterpart was found in Spitzer observations of this region, else is set to 'N'. The Spitzer images and photometry of point sources in N11 are taken from the previous work by Gruendl & Chu (2009, ApJS, 184, 172).

Spitzer_8p0_um_Flag
This flag parameter is set to 'Y' if an 8.0-um counterpart was found in Spitzer observations of this region, else is set to 'N'. The Spitzer images and photometry of point sources in N11 are taken from the previous work by Gruendl & Chu (2009, ApJS, 184, 172).

CXO_Spitzer_Offset
The positional offset between the Chandra source and its Spitzer infrared counterpart, in arcseconds.

Spitzer_Name
The name of the Spitzer infrared counterpart to the Chandra source, using the '[GC2009]' prefix recommended by the CDS Dictionary of Nomenclature of Celestial Objects for objects listed in Gruendl & Chu (2009, ApJS, 184, 172). Detections in only two Spitzer channels are noted, but a few named sources have detections only in the other channels. Some sources are quoted with a positive detection 'Y' in the values of the spitzer_3p6_um_flag and spitzer_8p0_um_flag parameters, but do not have a name listed for their Spitzer counterpart: this happens because the automated detection misses some sources, especially faint ones in high-background regions.

Comment
Comments on the X-ray source and/or its counterparts in the optical or infrared.

Source_Type
The suggested nature of the source and, in some cases, its counterpart name. (See Tables 6 and 7 of the reference paper for more information on those Chandra sources which the authors have identified as OB stars in N11).

Class
The HEASARC Browse object classification of the source, based on the information given in the source_type parameter, supplemented for a small number of sources which are identified with massive stars in N11 with the spectral types for these objects given in Table 6 of the reference paper.


Contact Person

Questions regarding the LMCN11CXO database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 14-Aug-2014