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NGC3293CXO - NGC 3293 Chandra X-Ray Point Source Catalog



NGC 3293 is a young stellar cluster at the northwestern periphery of the Carina Nebula Complex that has remained poorly explored until now. The authors wanted to characterize the stellar population of NGC 3293 in order to evaluate key parameters of the cluster population like the age and the mass function, and to test claims of an abnormal initial mass function (IMF) and a deficit of <= 2.5*Msun stars. Thus, they performed a deep (71 ksec) X-ray observation of NGC 3293 with Chandra in which they detected 1026 individual X-ray point sources. These X-ray data directly probe the low-mass (M <= 2*Msun) stellar population by means of the strong X-ray emission of young low-mass stars. The authors have identified counterparts for 74% of the X-ray sources in their deep near-infrared images.

These data clearly show that NGC 3293 hosts a large population of ~ 1*Msun stars, refuting claims of a lack of M <= 2.5*Msun stars. The analysis of the color-magnitude diagram suggests an age of ~8-10 Myr for the low-mass population of the cluster. There are at least 511 X-ray detected stars with color-magnitude positions that are consistent with young stellar members within 7 arcminutes from the cluster center. The number ratio of X-ray detected stars in the 1-2 solar mass range versus the M >= 5*Msun stars (known from optical spectroscopy) is well consistent with the expectation from a normal field initial mass function. Most of the early B-type stars and ~20% of the later B-type stars are detected as X-ray sources.

These data shows that NGC 3293 is one of the most populous stellar clusters in the entire Carina Nebula Complex (only excelled by Tr 14, and very similar to Tr 16 and Tr 15). The cluster has probably harbored several O-type stars, the supernova explosions of which may have had an important impact on the early evolution of the Carina Nebula Complex.

The authors used the Chandra X-ray Observatory to perform a deep pointing of the cluster NGC 3293 with the Imaging Array of the Chandra Advanced CCD Imaging Spectrometer (ACIS-I). The 71-ksec observation was performed as an open time project with ObsID 16648 (PI: T. Preibisch) during Chandra Observing Cycle 15 in October 2015 (start date: 2015-10-07 T10:14:23, end date: 2015-10-08 T06:43:28). The imaging array ACIS-I provides a field of view of 17' x 17' on the sky (which corresponds to a scale of 11.3 x 11.3pc at the cluster distance of 2.3 kpc), and has a pixel size of 0.492". The aimpoint of the observation was RA(J2000) = 10h 35m 50.07s, Dec(J2000) = -58o 14' 00", which is close to the optical center of the cluster (see Fig. 1 in the reference paper). The pointing roll angle (i.e., the orientation of the detector with respect to the celestial North direction) was 140.19o. In addition to ACIS-I, one CCD detector (CCD 7 = S3) of the spectroscopic array ACIS-S was also operational during this pointing. It covers an 8.3' x 8.3' area on the sky southwest of the cluster center. While the ACIS-I chips are front-illuminated (FI), the S3 chip is back-illuminated (BI), and thus its response extends to energies below that accessible by the FI chips. This causes a substantially higher level of background in the S3 chip. Furthermore, the PSF is seriously degraded at the rather large off-axis angles of the S3 chip. These two effects led to a considerably higher detection limit for point sources in the area covered by the S3 chip compared to the region covered by the ACIS-I array. Nevertheless, the S3 data were included in the data analysis and source detection, and contributed four point sources to the total source list.

At the distance of 2.3 kpc, the expected ACIS point source sensitivity limit for a three-count detection on-axis in a 71-ks observation corresponds to a minimum X-ray luminosity of Lx ~ 1029.7 erg s-1 in the 0.5-8.0 keV energy band, assuming an extinction of AV ~ 1 mag (NH ~ 2 x 1021 cm-2) typical for the stars in the central region of NGC 3293, and a thermal plasma with kT = 1 keV (which is a typical value for young stars). Using the empirical relation between X-ray luminosity and stellar mass and the temporal evolution of X-ray luminosity from the sample of young stars in the Orion Nebula Cluster, which was very well studied in the Chandra Orion Ultradeep Project (Preibisch et al. 2005, ApJS, 160, 401; Preibisch & Feigelson 2005, ApJS, 160, 390), the authors expected to detect ~90% of the ~ 1*Msun stars in the central region of the young cluster NGC 3293.

The X-ray properties of the 97 B-type stars in the ACIS-I field towards the cluster (24 of which are detected as X-ray sources) are not included in this HEASARC table, but are listed in Table 3 of the reference paper, which is also reproduced below:

ESL No.* Star Name     X-ray    Spectral Type   X-ray Luminosity (Lx)   log (Lx/Lbol)
                       Src No.                      erg/s

   49                           B2.5 V           < 4.33e+30                  < -5.88
   33    HDE 303073             B8 III           < 7.15e+30                  < -6.31
   65    ALS 20075              B5 III-V         < 2.12e+30                  < -5.88
   77                           B6-7 V           < 1.42e+30                  < -5.91
   96    ALS 20084              B6-7 III         < 9.09e+29                  < -5.96
   87                    47     B5 V               4.62e+30                    -5.11
   38                           B2.5 V           < 7.16e+29                  < -6.94
   68                    78     B9 III             4.79e+30
   72                           B8 IIp           < 6.87e+29
   69                           B5 V             < 3.89e+29                  < -6.47
   22    HDE 303075             B0.5-1.5n        < 6.22e+29                  < -7.77
  109                           B5 V             < 5.05e+29                  < -6.06
   93                           B6-7 V           < 5.16e+29                  < -6.17
  116                           B6-7 V           < 4.74e+29                  < -5.88
   73                           B6-7 V           < 3.87e+29                  < -6.38
   10    CPD-57 3500    395     B1 III             7.35e+29                    -7.89
  121    ALS 20096              B8: III          < 4.84e+29
   50                           B3 Vn            < 5.01e+29                  < -6.71
    2    HD 91943       418     B0.7 Ib            4.11e+30                    -8.15
   41    V438 Car               B2.5 V           < 3.94e+29                  < -7.21
   48    CPD-57 3505    461     B2.5 V             1.39e+30                    -6.67
    3    CPD-57 3506A   490     B1 III             5.37e+30                    -7.63
  125                           B8 III-V         < 8.62e+29                  < -5.48
   19    V405 Car       523     B1 V               6.77e+29                    -7.88
   34    CPD-57 3509    535     B2 IIIh            6.71e+29                    -7.54
    1    HD 91969       542     B0 Iab             2.78e+31                    -7.52
  106                   565     B6-7 V             1.20e+30                    -5.54
   53    CPD-57 3512            B3 V             < 3.61e+29                  < -6.70
   98                   598     B8 III-V           1.31e+30                    -5.65
   30    CPD-57 3514    601     B2 V               1.99e+30                    -6.64
  123                   604     B8 III             3.79e+30                    -4.98
    8    HD 91983       626     B1 III             1.36e+30                    -7.78
   32    CPD-57 3518            B0.5-B1.5 Vn     < 1.20e+30                  < -7.14
   61                           B5 V             < 3.87e+29                  < -6.56
    5    CPD-57 3521    679    B1 III              3.45e+30                    -7.61
   28    CPD-57 3520            B2 V             < 4.16e+29                  < -7.46
  113                           B6-7 V           < 4.09e+29                  < -6.01
   11    CPD-57 3526    703     B1:                2.29e+30
    6    CPD-57 3526B   710     B1 III             2.29e+30                    -7.73
   84                           B5 V             < 3.99e+29                  < -6.33
   31    CPD-57 3528            B2 V             < 1.50e+30                  < -6.66
   29    CPD-57 3531            B0.5-B1.5 Vn     < 5.99e+29                  < -7.56
   59                           B5 III-Vn        < 8.23e+29                  < -6.61
   80                           B5 V             < 1.31e+30                  < -5.98
   13     HD 92024      831     B1 III             6.59e+29                    -7.82
  108                   850     B6-7 V             3.65e+30                    -5.09
   95                   884     B6-7 V             1.49e+30                    -5.66
   67                           B3 V             < 1.20e+30                  < -6.42
   97                           B6-7 III         < 6.34e+29                  < -6.01
   94                   927     B5 V               4.42e+30                    -5.35
   85                           B5 V             < 1.47e+30                  < -5.80
    4    CPD-57 3523    697     B1 III             3.40e+30                    -7.57
    7    HD 92044       908     B1 III             2.20e+30                    -7.94
   14    CPD-57 3524A   704     B0.5 IIIn          5.46e+30                    -7.27
* The ESL number is the source number of the star as given in Evans et al. (2005, A&A, 437, 467).

Catalog Bibcode



Chandra X-ray observation of the young stellar cluster NGC 3293 in the
Carina Nebula Complex.
    Preibisch T., Flaischlen S., Gaczkowski B., Townsley L., Broos P.
    <Astron. Astrophys. 605, A85 (2017)>
    =2017A&A...605A..85P        (SIMBAD/NED BibCode)


This table was created by the HEASARC in September 2017 based upon the CDS Catalog J/A+A/605/A85 files table1.dat and table2.dat.


A unique sequential identification number for each detected Chandra source in this catalog.

The IAU-style position-based designation of the Chandra X-Ray Source in the field of NGC 3293, viz., CXONGC3293, as registered with the Dictionary of Nomenclature of Celestial Objects, using the prefix 'CXONGC3293' for 'Chandra X-ray Observatory, NGC 3293' and the J2000.0 Right Ascension and Declination truncated to 0.01 seconds of time in RA and to 0.1 arcsecond in Declination.

The Right Ascension of the Chandra X-ray source in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 10-6 degrees in the original table.

The Declination of the Chandra X-ray source in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 10-6 degrees in the original table.

The Galactic Longitude of the Chandra X-ray source.

The Galactic Latitude of the Chandra X-ray source.

The positional error of the Chandra source, in arcseconds.

The off-axis angle in units of arcminutes, which is the separation between the source position and the aim point of the observation (see Overview above).

The net counts for the Chandra source in the total energy band (0.5-8 keV).

The 1-sigma uncertainty in the net counts for the Chandra source in the total energy band (0.5-8 keV).

The background counts expected in the source extraction region.

The net counts for the Chandra source in the hard energy band (2.0-8 keV).

The fraction of the PSF (at 1.497 keV) that is enclosed within the source extraction region.

The photometric significance of the Chandra source.

This flag parameter is set to '<' if the corresponding probability is an upper limit.

The logarithm of the probability that the counts extracted from the source region are solely from the background, otherwise known as the 'no-source' probability. The choice of the source significance limit for the definition of the final sample of X-ray sources is always a compromise: a strict limit will miss true X-ray sources, whereas a more generous limit will enhance the risk of including spurious sources into the sample. The limiting value used here of 0.01 allows the detection of sources with just ~3 counts.

This flag parameter, if populated, indicates the presence of source anomalies. The values of the source anomalies flag are as follows:

      g = fractional time that source was on a detector is <0.9
      p = source piled up
      s = source on readout streak
      a = photometry and spectrum contain > 10% afterglow events

This flag parameter contains a variability characterization based on the K-S statistic calculation in AE. The values of the variability flag are as follows (where PKS is the probability of being constant):

      a = no evidence for variability (0.05 < PKS)
      b = possibly variable (0.005 <PKS <0.05)
      c = definitely variable (PKS <0.005)
No value is reported for sources with fewer than four counts or for sources in chip gaps or on field edges

The background-corrected median photon energy of the Chandra source, in keV.

The J2000.0 position-based designation of the near-infrared counterpart to the X-ray source from either the VISTA (Visible and Infrared Survey Telescope for Astronomy) Carina Nebula Survey (VCNS) Source Catalog (Preibisch et al. 2014, A&A, 572, A116) or the 2MASS Catalog (CDS Cat. B/2mass).

The J2000.0 position-based designation of the optical counterpart to the X-ray source from either the VST Photometric H-Alpha Survey of the Southern Galactic Plane and Bulge (VPHAS+) Data Release 2 (DR2) Point Source Catalog or from the VLT (Very Large Telescope) Survey Telescope (VST) images that were taken as part of the VPHAS+ survey (Drew et al. 2014, MNRAS, 440, 2036, CDS Cat. II/341).

The optical counterpart identifier in the VST VPHAS-DR2 Point Source Catalog.

Contact Person

Questions regarding the NGC3293CXO database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Monday, 25-Sep-2017 15:44:41 EDT