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SIGORIXMM - Sigma Orionis Cluster XMM-Newton X-Ray Point Source Catalog


This table contains some of the results of an analysis of the full EPIC field in an XMM-Newton observation of the young (~2 - 4 Myr) cluster around the hot star sigma Orionis.The authors have detected 175 X-ray sources, 88 of which have been identified with cluster members, including very low-mass stars down to the substellar limit. They detected eleven new possible candidate members from the 2MASS (CDS Cat. <II/246>) catalog. The authors find that late-type stars have a median log L_X/L_bol ~ -3.3, i.e. very close to the saturation limit. They detected significant variability in ~ 40% of late-type members or candidates, including 10 flaring sources; rotational modulation was detected in one K-type star and possibly in another 3 or 4 stars. Spectral analysis of the brightest sources shows typical quiescent temperatures in the range T_1 ~ 0.3 - 0.8 keV and T_2 ~ 1 - 3 keV, with subsolar abundances Z ~ 0.1 - 0.3 solar, similar to what is found in other star-forming regions and associations. The authors find no significant difference in the spectral properties of classical and weak-lined T Tauri stars, although classical T Tauri stars tend to be less X-ray luminous than weak-lined T Tauri stars.

XMM-Newton observations of the sigma Ori cluster, centered on the hot star sigma Ori AB, were carried out as part of the Guaranteed Time of Roberto Pallavicini using both the EPIC MOS and PN cameras and the RGS instrument. The observation (ID 0101440301) started at 21:47 UT on March 23, 2002 and ended at 9:58 UT on March 24, 2002, for a total duration of 43 ks. The EPIC cameras were operated in Full Frame mode using the thick filter.

This table contains the combined list of 88 X-ray sources positionally (<= 5") associated with confirmed or candidate cluster members, and 66 X-ray sources with no such positional associations, detected above a significance thereshold of 5 sigma. The two X-ray sources (source numbers 67 and 167) with 2 posssible positional associations are listed twice, once for each positional association, with the X-ray information repeated. Thus, there are 156 entries in this HEASARC table.

Catalog Bibcode



XMM-Newton observations of the sigma Orionis cluster.
II. Spatial and spectral analysis of the full EPIC field.
    Franciosini E., Pallavicini R., Sanz-Forcada J.
   <Astron. Astrophys., 446, 501-513 (2006)>


This table was created by the HEASARC in May 2007 based on CDS catalog J/A+A/446/501 files tablea1.dat and tableb.dat.


A running source number (called NX in the reference paper) in order of increasing J2000.0 Right Ascension, which uniquely identifies the X-ray source.

The name of the X-ray source using the '[FPS2006] NX' prefix (where FPS2006 refers to Franciosini, Pallavicini, Sanz-Forcada 2006, and NX is the name of the source number parameter in the reference paper), togther with the X-ray source number, as recommended by the CDS Dictionary of Nomenclature of Celestial Objects.

This flag is set to 'Y' to indicate the 2 X-ray sources (source numbers 59 and 130) which have been detected only on one MOS, else is set to 'N'.

To create this Browse table, the HEASARC has combined rows from two tables in the reference paper, Table A.1 which listed 88 X-ray sources which had at least one cluster member or candidate member within 5" (2 of the 88 X-ray sources have 2 counterparts each, and are listed twice, once for each counterpart), and Table B which listed 66 X-ray sources which have no optical counterparts. To distinguish these two groups, the HEASARC has created this flag parameter, which is set to 'Y' for the entries from Table A.1 and to 'N' for the entries from Table B.

The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.01 seconds of time in the original table.

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.

The Galactic Longitude of the X-ray source.

The Galactic Latitude of the X-ray source.

The statiscal significance of the X-ray source detection.

The MOS-equivalent count rate of the X-ray source, in ct/s, derived from the source detection algorithm run on the summed MOS1+MOS2+PN dataset in the 0.3-7.8 keV energy band.

The rms uncertainty in the X-ray source count rate, in ct/s.

The name of the optical counterpart to the X-ray source. Optical identifications are from the following sources:

       --  4772-  1 r05..., p05... = Wolk (1996, Ph.D. Thesis,
                                     Univ. New York at Stony Brook)
       --  rHHMMSS-DDMMa = [W96] rJHHMMSS+DDMMa in Simbad
       --  pHHMMSS-DDMMa = [W96] pJHHMMSS+DDMMa in Simbad
       --  4771-NNNN = [W96] 4771-NNNN in Simbad
       --  SE NNN = Scholz & Eisloffel (2004, CDS Cat. <J/A+A/419/249>)
                    [SE2004] NNN in Simbad
       --  SWW NNN = Sherry et al. (2004, CDS Cat. <J/AJ/128/2316>) where
                     NNN is the "recno" of J/AJ/128/2316/table4 in VizieR
       --  S Ori, J05... = Bejar et al. (2004, CDS Cat. <J/other/AN/325/705>,
                  2001ApJ...556..830B, 1999ApJ...521..671B)
                  Caballero et al. (2004A&A...424..857C)
                  Zapatero Osorio et al. (2002A&A...384..937Z): note that the
                  authors have dropped the S Ori prefix in front of the J05...
              S Ori J05... = [BMZ2001] S Ori J05... in Simbad
              S Ori NN = [BZR99] S Ori NN in Simbad
       --  K = Kenyon et al. (2005, CDS Cat. <J/MNRAS/356/89>)
               [KJN2005] NN in simbad
       --  B = Burningham et al. (2005, CDS Cat. <J/MNRAS/356/1583>)
               [BNL2005] F.FF NNNN in Simbad

This parameter flags the following notes about specific optical counterparts:

        c = Source #3 in Paper I (Sanz-Forcada et al., 2004A&A...421..715S)
        d = Source #4 in Paper I (Sanz-Forcada et al., 2004A&A...421..715S)
        e = Source detected on the PN only. The reported count rates are PN
            count rates. L_X was derived using the conversion factor for PN
            (see Sect. 3.1 of the reference paper).

The offset between the X-ray source and its optical counterpart's position, in arcseconds.

The I magnitude of the optical/near-IR counterpart to the X-ray source.

The R-I color index of the optical/near-IR counterpart to the X-ray source.

The I-J color index of the optical/near-IR counterpart to the X-ray source.

The spectral type of the optical/near-IR counterpart to the X-ray source. Spectroscopically-determined spectral types from the literature are marked by having a value of 'L' for the spect_type_flag parameter. The other spectral types have been estimated from the R-I, V-I or I-J colours using the relations by Kenyon & Hartmann (1995, CDS Cat. <J/ApJS101/117>) and Leggett et al. (2001ApJ...548..908L).

This flag parameter is set to 'L' if the spectral type was taken from the literature.

The logarithm of the unabsorbed X-ray luminosity of the cluster member or candidate, in the 0.3 - 8 keV energy band, in erg/s. This was computed using a conversion factor in based on the results of the PN and MOS1 spectral fits of late-type stars (see Sect. 4 of the reference paper). The conversion factor was determined by comparing the count rates obtained from the Wavelet algorithm on the summed dataset with the unabsorbed X-ray flux derived from the best-fit models, excluding the few sources with absorption higher than the mean value of N_H = 2.7 x 10^20 cm^-2, derived from the mean reddening E(B-V) = 0.05, and then taking the median value. The derived conversion factor, valid for the summed and MOS datasets, is CF =6.6 x 10^-12 erg cm^-2 ct^-1, with an uncertainty of ~ 15% (1-sigma standard deviation). For the source detected only in the PN the authors derived in the same way a median conversion factor CF = 2.1 x 10^-12 erg cm^-2 ct^-1 for the PN count rates. They applied these factors to all stars for which no spectral analysis can be performed, assuming that all of them have the mean absorption, since individual absorption measures are generally not available. For stars having N_H ~ 1 - 2 x 10^21 cm^-2, as found for some sources, this will underestimate the X-ray luminosity by a factor of ~ 1.5. For the stars with spectral fits the authors used instead the fluxes determined from the PN or MOS1 (if PN is not available) best-fit models. reported in Table 3 of the reference paper and in Sanz-Forcada et al. (2004A&A...421..715S). Finally, X-ray luminosities have been derived using the Hipparcos cluster distance of 352 pc.

The sensitivity in the center of the field (from 3-sigma upper limits) is L_X ~ 2 x 10^28 erg s^-1, and decreases to ~ 4 x 10^28 erg s^-1 at 13' offaxis, and to ~ 7 x 10^28 erg s^-1 when only a MOS source is present.

This flag parameter is set to 'F' to mark values of the X-ray luminosity which have been derived from the PN or MOS1 spectral fits reported in Table 3 of the reference paper and in Sanz-Forcada et al. (2004A&A...421..715S).

This flag parameter indicates the type of T Tauri star that the optical counterpart is believed to be, using the following categories:

        C  = probable Classical T Tauri Stars (CTTS)
        C? = possible Classical T Tauri Stars (CTTS)
        W  = probable Weak-lined T Tauri Stars (WTTS)
        W? = possible Weak-lined T Tauri Stars (WTTS)

The HEASARC Browse object classification based on the value of the spect_type parameter, if available.

Contact Person

Questions regarding the SIGORIXMM database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk