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XMMOBSTARS - XMM-Newton OB Stars Catalog

HEASARC
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Overview

Following the advent of increasingly sensitive X-ray observatories, deep observations of early-type stars became possible. However, the results for only a few objects or clusters have until now been reported and there has been no large survey comparable to that based upon the ROSAT All-Sky Survey (RASS). A limited survey of X-ray sources, consisting of all public XMM observations (2XMMi) and slew survey data (XMMSL1), is now available. The X-ray counterparts to hot, massive stars have been searched for in these catalogs. About 300 OB stars were detected with XMM. Half of them were bright enough for a spectral analysis to be possible, and we make available the detailed spectral properties that were derived. The X-ray spectra of O stars are represented well by low (< 1 keV) temperature components and seem to indicate that an absorption column is present in addition to the interstellar contribution. The X-ray fluxes are well correlated with the bolometric fluxes, with a scatter comparable to that of the RASS studies and thus larger than found previously with XMM for some individual clusters. These results contrast with those of B stars that exhibit a large scatter in the L_X - L_BOL relation, no additional absorption being found, and the fits indicate a plasma at higher temperatures. Variability (either within one exposure or between multiple exposures) was also investigated whenever possible: short-term variations are far more rare than long-term ones (the former affects a few percent of the sample, while the latter concerns between one third and two thirds of the sources).

This is a catalog of X-ray emitters amongst early-type stars following a correlation between the Reed (2003, AJ, 125, 2531) Catalog of galactic OB Stars and the 2XMMi Catalog (Watson et al. 2009, A&A, 493, 339). See the reference paper for more details.


Catalog Bibcode

2009A&A...506.1055N

References

Hot stars observed by XMM-Newton. I. The catalog and the properties of OB stars
    Naze Y.
    <Astron. Astrophys. 506, 1055 (2009)>
    =2009A&A...506.1055N        (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in November 2009 based on CDS table J/A+A/506/1055 file table1.dat.

HEASARC Implementation

This HEASARC table is based on Table 1 from the reference paper, being the primary table of 2XMM and 2XMMi X-ray sources which the author cross-correlated against the Reed Catalog of OB Stars. It does not contain the data from Table 5 in the paper ('The Spectral Properties of the Detected Hot Stars') nor from Table 7 ('Additional X-Ray Detections of Hot Stars Using the XMM Slew Survey').

Parameters

Source_Flag
This flag parameter has possible values from 1-6 which indicate the type of star, coded as follows:

             1 -> S = 0, O stars (35 objects)
             2 -> S = 0, B stars (91 objects)
             3 -> S = 0, WR stars (7 objects)
             4 -> S != 0, O stars (98 objects)
             5 -> S != 0, B stars (70 objects)
             6 -> S != 0, WR stars (9 objects)
  
where S is the value of the 2XMMi quality flag, which is set to 0 if the X-ray source has no problematic issues, and to 1-4 if it might be spurious. Experience has shown that hot stars in clusters are generally detected with a non-zero quality flag, because of the presence of numerous neighbors. To be as complete as possible, the author did not exclude sources based on non-zero quality flag values.

Component_ID
This parameter contains a letter [a-e] in case two OB stars correspond to the same X-ray source. Both stars in such a pair have been given the same value for this parameter. There are 5 such pairs:

    a -> BD -12 4982
    b -> HD 33742/33743
    c -> HD 93129 A/B
    d -> BD -12 4975
    e -> Cyg OB2-22 A/B
  

Alt_Name
This parameter contains the information which was used to query the 2XMMi Catalog, i.e., either the preferred name in the Reed OB Stars Catalog (Reed 2003) or the coordinates of the OB star in the Reed Catalog.

Reed_Id_Number
The identification number (also known as the ALS number) of the OB star in the Reed Catalog (CDS Catalog <V/125>).

Name
The usual name of the OB star, e.g., HD, BD, CPD, etc.

RA
The Right Ascension of the XMM-Newton source in the selected equinox, based on the position-based 2XMMi source name, and hence derived from the truncated J2000.0 equatorial coordinates specified with a precision of 0.1 seconds of time.

Dec
The Declination of the XMM-Newton source in the selected equinox, based on the position-based 2XMMi source name, and hence derived from the truncated J2000.0 equatorial coordinates specified with a precision of 1 arcsecond.

LII
The Galactic Longitude of the XMM-Newton source.

BII
The Galactic Latitude of the XMM-Newton source.

Spect_Type_Flag
This flag parameter is set to 'S' to indicate that the source spectral type was taken from SIMBAD.

Spect_Type
The (MK) spectral type of the OB star, which was chosen to be the most recent one from the Reed Catalog, except for the Wolf-Rayet stars (WRs) where the clssification of the VIIth WR Catalog (van der Hucht 2001, New Astron. Rev. 45, 135) was used. If no type was available in the Reed Catalog, then the spectral type from Simbad was used, and the value of the spect_type_flag parameter was set to 'S' (changed from the '~' character used in the original table).

Binary_Flag
This flag parameter is set to 'Y' to indicate that the OB star is in a binary system. A star was classified as a binary if either the spectral type available in the Reed catalog indicated the presence of a companion or if the star was a known binary in the 9th Binary Catalog (Pourbaix et al. 2004, A&A, 424, 727) and/or in Gies (2003, in 'A Massive Star Odyssey: from Main Sequence to Supernova': Proc. IAU Symp. 212, 91).

Photometry_Flag
This flag parameter is set to 'S' to indicate that the source photometric data were taken from SIMBAD.

Vmag
The V magnitude of the OB star. The photometric data correspond to the most recent values in the Reed Catalog, or, if unavailable, to the Simbad values (in the latter case, the value of the photometry_flag parameter was set to 'S' (changed from the '~' character used in the original table).

BV_Color
The B-V color index of the OB star. The photometric data correspond to the most recent values in the Reed Catalog, or, if unavailable, to the Simbad values (in the latter case, the value of the photometry_flag parameter was set to 'S' (changed from the '~' character used in the original table).

NH
The interstellar absorption column density N_H, in cm-2, towards the OB star. For the WR stars, these were taken from Oskinova et al. (2005, MNRAS, 361, 679) for WN stars. For O and B stars, these characteristics were calculated whenever a precise spectral type (i.e., not only 'O star' or 'B star') and magnitude values were known. The interstellar column was derived from Bohlin's formula (N_H = 5.8 x 1021 x E(B-V) cm-2, Bohlin et al. 1978, ApJ, 224, 132), where the color excesses were calculated from the difference between the observed colors and the instrinsic ones.

Log_Fbol
The logarithm of the OB star's bolometric flux, log f_BOL, in erg s-1 cm-2. For the WR stars, these were taken from Oskinova et al. (2005, MNRAS, 361, 679) for WN stars. For O and B stars, these characteristics were calculated whenever a precise spectral type (i.e., not only 'O star' or 'B star') and magnitude values were known. Because of the scarcity of accurate distances to many OB stars, bolometric fluxes were preferred to bolometric luminosities. They were calculated using the usual formulae, yielding:

   log f_BOL = -4.61 -[V - 3.1 x E(B-V) + BC]/2.5
  
where f_BOL is in erg cm-2 s-1. Intrinsic colors and bolometric corrections (BC) were taken, for the considered spectral types, from Martins and Plez (2006, A&A, 457, 637) for O stars and from the Schmidt-Kaler Handbook (1982) for B stars. In the case of binaries, the intrinsic properties (colour, BC) of the primary star were used.

B.C. Reed has remarked that the identification of the star ALS 1855 with the star ALS 15858 in Simbad is wrong, and that they are actually two stars. This would mean that the total bolometric flux, in the logarithmic scale, for these two objects would be -6.81, leading to a decrease of the log(L_X/L_BOL) ratio by 0.23 dex (i.e. log(L_X/L_BOL) = -6.47). This did not change the conclusions that were presented in the reference paper, notice.

Offset
The angular distance between the X-ray source position and that of its stellar counterpart, in arcseconds.

XMM_Name
The position-based part of the IAU-style designation of the 2XMM(i) source. The prefix could be either '2XMM' or '2XMMi': to determine which, the user should check the XMMSSC table at the position of the source in question.

PN_Filter
The filter used for the EPIC-pn observation of the XMM source.

M1_Filter
The filter used for the EPIC-MOS1 observation of the XMM source.

M2_Filter
The filter used for the EPIC-MOS2 observation of the XMM source.

PN_XID_Rate
The count rate of the X-ray source in the 0.5 - 4.5 keV (XID) energy range, in ct/s, as measured by the EPIC-pn camera (for counts with patterns 0-4 for the pn and 0-12 for the MOS cameras).

PN_XID_Rate_Error
The uncertainty in the EPIC-pn count rate for the X-ray source, in ct/s.

M1_XID_Rate
The count rate of the X-ray source in the 0.5 - 4.5 keV (XID) energy range, in ct/s, as measured by the EPIC-MOS1 camera (for counts with patterns 0-4 for the pn and 0-12 for the MOS cameras).

M1_XID_Rate_Error
The uncertainty in the EPIC-MOS1 count rate for the X-ray source, in ct/s.

M2_XID_Rate
The count rate of the X-ray source in the 0.5 - 4.5 keV (XID) energy range, in ct/s, as measured by the EPIC-MOS2 camera (for counts with patterns 0-4 for the pn and 0-12 for the MOS cameras).

M2_XID_Rate_Error
The uncertainty in the EPIC-MOS2 count rate for the X-ray source, in ct/s.

PN_HR1
The XMM hardness ratio HR1 for bands 1 and 2 of the X-ray source as measured in the EPIC-pn camera. New energy bands were used in the 2XMM processing compared to 1XMM. The following are the basic energy bands:

  1       =       0.2 -   0.5 keV
  2       =       0.5 -   1.0 keV                 (formerly part of band 2)
  3       =       1.0 -   2.0 keV                 (formerly part of band 2)
  4       =       2.0 -   4.5 keV                 (formerly band 3)
  5       =       4.5 -  12.0 keV                 (formerly bands 4 and 5)
  
while these are the broad energy bands:
  6       =       0.2 -   2.0 keV                 soft band, no images made
  7       =       2.0 -  12.0 keV                 hard band, no images made
  8       =       0.2 -  12.0 keV                 total band
  9       =       0.5 -   4.5 keV                 XID band
  

The hardness ratios for each camera are derived by the SAS task emldetect. They are defined as the ratio between the bands A and B:

              HR(A,B) = (band B - band A) / (band A + band B).
  

Note that in the case where the rate in one band is 0.0 (i.e., too faint to be detected in this band) the hardness ratio will be -1 or +1 which is only a lower or upper limit, respectively. In cases where the rate in both bands is zero, the hardness ratio is undefined (NULL).

There are four hardness ratios (n) using the following bands:

  HR1:    bands 1 & 2
  HR2:    bands 2 & 3
  HR3:    bands 3 & 4
  HR4:    bands 4 & 5
  

EPIC hardness ratios are calculated by the SAS task srcmatch and are averaged over all three cameras (PN, M1, M2). Note that no energy conversion factor was used and that the EPIC hardness ratios are de facto not hardness ratios but an equivalent number helpful to characterise the hardness of a source.

PN_HR1_Error
The uncertainty in the EPIC-pn hardness ratio for bands 1 and 2. Errors are the 1-sigma error on the hardness ratio as derived by the SAS task emldetect.

PN_HR2
The XMM hardness ratio HR2 for bands 2 and 3 of the X-ray source as measured in the EPIC-pn camera. See the pn_hr1 parameter description above for more information.

PN_HR2_Error
The uncertainty in the EPIC-pn hardness ratio for bands 2 and 3. Errors are the 1-sigma error on the hardness ratio as derived by the SAS task emldetect.

PN_HR3
The XMM hardness ratio HR3 for bands 3 and 4 of the X-ray source as measured in the EPIC-pn camera. See the pn_hr1 parameter description above for more information.

PN_HR3_Error
The uncertainty in the EPIC-pn hardness ratio for bands 3 and 4. Errors are the 1-sigma error on the hardness ratio as derived by the SAS task emldetect.

PN_HR4
The XMM hardness ratio HR4 for bands 4 and 5 of the X-ray source as measured in the EPIC-pn camera. See the pn_hr1 parameter description above for more information.

PN_HR4_Error
The uncertainty in the EPIC-pn hardness ratio for bands 4 and 5. Errors are the 1-sigma error on the hardness ratio as derived by the SAS task emldetect.

M1_HR1
The XMM hardness ratio HR1 for bands 1 and 2 of the X-ray source as measured in the EPIC-MOS1 camera. See the pn_hr1 parameter description above for more information.

M1_HR1_Error
The uncertainty in the EPIC-MOS1 hardness ratio for bands 1 and 2. Errors are the 1-sigma error on the hardness ratio as derived by the SAS task emldetect.

M1_HR2
The XMM hardness ratio HR2 for bands 2 and 3 of the X-ray source as measured in the EPIC-MOS1 camera. See the pn_hr1 parameter description above for more information.

M1_HR2_Error
The uncertainty in the EPIC-MOS1 hardness ratio for bands 2 and 3. Errors are the 1-sigma error on the hardness ratio as derived by the SAS task emldetect.

M1_HR3
The XMM hardness ratio HR3 for bands 3 and 4 of the X-ray source as measured in the EPIC-MOS1 camera. See the pn_hr1 parameter description above for more information.

M1_HR3_Error
The uncertainty in the EPIC-MOS1 hardness ratio for bands 3 and 4. Errors are the 1-sigma error on the hardness ratio as derived by the SAS task emldetect.

M1_HR4
The XMM hardness ratio HR4 for bands 4 and 5 of the X-ray source as measured in the EPIC-MOS1 camera. See the pn_hr1 parameter description above for more information.

M1_HR4_Error
The uncertainty in the EPIC-MOS1 hardness ratio for bands 4 and 5. Errors are the 1-sigma error on the hardness ratio as derived by the SAS task emldetect.

M2_HR1
The XMM hardness ratio HR1 for bands 1 and 2 of the X-ray source as measured in the EPIC-MOS2 camera. See the pn_hr1 parameter description above for more information.

M2_HR1_Error
The uncertainty in the EPIC-MOS2 hardness ratio for bands 1 and 2. Errors are the 1-sigma error on the hardness ratio as derived by the SAS task emldetect.

M2_HR2
The XMM hardness ratio HR2 for bands 2 and 3 of the X-ray source as measured in the EPIC-MOS2 camera. See the pn_hr1 parameter description above for more information.

M2_HR2_Error
The uncertainty in the EPIC-MOS2 hardness ratio for bands 2 and 3. Errors are the 1-sigma error on the hardness ratio as derived by the SAS task emldetect.

M2_HR3
The XMM hardness ratio HR3 for bands 3 and 4 of the X-ray source as measured in the EPIC-MOS2 camera. See the pn_hr1 parameter description above for more information.

M2_HR3_Error
The uncertainty in the EPIC-MOS2 hardness ratio for bands 3 and 4. Errors are the 1-sigma error on the hardness ratio as derived by the SAS task emldetect.

M2_HR4
The XMM hardness ratio HR4 for bands 4 and 5 of the X-ray source as measured in the EPIC-MOS2 camera. See the pn_hr1 parameter description above for more information.

M2_HR4_Error
The uncertainty in the EPIC-MOS2 hardness ratio for bands 4 and 5. Errors are the 1-sigma error on the hardness ratio as derived by the SAS task emldetect.

Detection_Likelihood
The total detection likelihood for the EPIC X-ray source.

Quality_Flag
The overall quality flag S for the EPIC X-ray source, ranging from 0 = 'Best' to 1-4 = 'Possibly Spurious'. See the source_flag parameter description above for more information.

Stv_Flag
The EPIC short-term variability flag, where a value of 1 means variable. This parameter corresponds directly to the variability flag found in the 2XMMi Catalog, i.e., it is defined to be 1 if the source was found to be variable with a significance level of 0.001% following a chi-squared test performed on the time series of the individual exposures. For hot stars, as could be expected, very few objects vary within one exposure (<10%). Three sources display a flare, which is quite typical of low-mass, pre-main-sequence stars: HD37016 (B2.5V), HD33904 (B9III), and HD 37479 (sigma Ori E, B1/2V, whose flare decay has a rather long time constant). In addition, HD120991 (B2Ve) exhibits a clear increase of its count rate during the observation. For the other stars, there is no obvious flare, and the variations cannot easily be differentiated from those of the background signal.

Ltv_Flag
The EPIC long-term variability flag. Long-term variability, for example between exposures, can occur, but the 2XMMi Catalog does not check for its presence. This long-term variability flag was thus calculated for this present catalog: it is set to be 2 if there are not enough exposures (0 or 1 observation for all combinations of filters/instruments), to 1 if a chi-squared test detected variations in the count rate (in at least one combination of filters/instruments) with a significance level of 1%, and otherwise is set to 0. As is obvious from Table 4 in the reference paper, this type of variability is far more common in hot stars, with few differences between single and binary OB stars.

N_Detections
The number of individual detections of the X-ray source by XMM.

Flux
The unabsorbed flux of the X-ray source in the 0.5 - 10. keV band, in erg s-1 cm-2.

Log_Lx_Lbol
The logarithm of the ratio of the X-ray to the bolometric luminosities (or, equivalently, fluxes), Log(L_X/L_BOL), where the X-ray band is the 0.5 - 10.0 keV energy range.

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


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 17-Nov-2009