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J/ApJ/725/2485      X-rays from the star-forming complex W40      (Kuhn+, 2010)
A Chandra observation of the obscured star-forming complex W40.
    Kuhn M.A., Getman K.V., Feigelson E.D., Reipurth B., Rodney S.A.,
    Garmire G.P.
   <Astrophys. J., 725, 2485-2506 (2010)>
   =2010ApJ...725.2485K
ADC_Keywords: Clusters, open ; H II regions ; X-ray sources ;
              Cross identifications ; Photometry, infrared ; YSOs
Keywords: ISM: individual objects (W40) - X-rays: stars -
          open clusters and associations: individual (W40) -
          protoplanetary disks - stars: formation - stars: pre-main sequence

Abstract:
    The young stellar cluster illuminating the W40 HII region, one of the
    nearest massive star-forming regions, has been observed with the ACIS
    detector on board the Chandra X-ray Observatory. Due to its high
    obscuration, this is a poorly studied stellar cluster with only a
    handful of bright stars visible in the optical band, including three
    OB stars identified as primary excitation sources. We detect 225 X-ray
    sources, of which 85% are confidently identified as young stellar
    members of the region. Two potential distances of the cluster, 260pc
    and 600pc, are used in the paper.

Description:
    The Chandra X-ray Observatory (CXO) observed W40 for ∼38ks during
    2007 August using the ACIS camera. The observation has a nominal
    pointing of RA=18:31:23.8 and DEC=-2:05:59 (J2000), the approximate
    center of the W40 cluster, and a roll angle of 251°. Data from the
    imaging array (ACIS-I) are analyzed.

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
table1.dat        98      225   Basic source properties
table2.dat       132      225   IR and radio counterparts to Chandra sources
table3.dat        73       39   Additional non X-ray cluster members
table4.dat       127      225   X-ray spectroscopy


See also:
 B/chandra : The Chandra Archive Log (CXC, 1999-2012)
 II/246    : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
 J/AJ/140/968   : A cluster of compact radio sources in W40 (Rodriguez+, 2010)
 J/ApJS/163/306 : Chandra study of the Cep B star-forming region (Getman+, 2006)


Byte-by-byte Description of file: table1.dat

   Bytes Format Units    Label    Explanations

   1-  3  I3    ---      Seq      X-ray catalog sequence number; RA sorted
   5- 22  A18   ---      CXOW40   IAU designation (HHMMSS.ss+DDMMSS.s; J2000)
  24- 33  F10.6 deg      RAdeg    Right ascension in decimal degrees (J2000)
  35- 43  F9.6  deg      DEdeg    Declination in decimal degrees (J2000)
  45- 47  F3.1  arcsec   ePos     [0/1.5] Positional error (1)
  49- 52  F4.1  arcmin   theta    Off-axis angle θ
  54- 59  F6.1  ct       NCt      Extracted net counts in full band (0.5-8keV)
  61- 64  F4.1  ct       e_NCt    Average 1σ error in NCt
  66- 69  F4.1  ct       BCt      Background counts in the extraction region
  71- 75  F5.1  ct       HCt      Extracted net counts in hard band (2-8keV)
  77- 80  F4.2  ---      PSF      PSF fraction enclosed within extraction
                                  region (2)
  82- 85  F4.1  ---      Signi    Source significance (3)
      87  I1    ---      Anom     [0/1] Source anomalies (4)
      89  I1    ---      Var      [1/4] Variability characterization (5)
  91- 94  F4.1  ks       Exp      Effective exposure (6)
  96- 98  F3.1  keV      Emed     Median energy of net counts in full
                                  (0.5-8keV) band

Note (1): Estimated standard deviation of the random component of the position
          error, (σx2+σy2)0.5. The single-axis
          position errors, σx and σy, are estimated from the
          single-axis standard deviations of the PSF inside the extraction
          region and the number of counts extracted.
Note (2): A reduced PSF fraction (significantly below 90%) may indicate that
          the source is in a crowded region.
Note (3): Computed as net counts divided by the upper error on net counts.

Note (4):
    1 = fractional time that source was on a detector (FRACEXPO from mkarf)
        is <0.9.
Note (5): Based on K-S statistic (full band) as follows:
    2 = no evidence for variability (0.05<PKS);
    3 = possibly variable (0.005<PKS<0.05);
    4 = definitely variable (PKS<0.005).
    1 = source has with fewer than four counts or is located in a chip gap or
        on a field edge.
Note (6): Approximate time the source would have to be observed at the aimpoint
          of the ACIS-I detector in Cycle 8 to obtain the reported number of
          net counts.


Byte-by-byte Description of file: table2.dat

   Bytes Format Units   Label     Explanations

   1-  3  I3    ---     Seq       X-ray catalog sequence number
   5- 22  A18   ---     CXOW40    IAU designation (HHMMSS.ss+DDMMSS.s)
  24- 39  A16   ---     2MASS     2MASS source designation ("9999999999999999"
                                  when no information)
  41- 45  F5.1  arcsec  Offset    [0/2.6]?=-99 Chandra-2MASS positional offset
  47- 52  F6.2  mag     Jmag      ?=-99 2MASS J-band magnitude
  54- 59  F6.2  mag     e_Jmag    ?=-99 Error on Jmag
  61- 66  F6.2  mag     Hmag      ?=-99 2MASS H-band magnitude
  68- 73  F6.2  mag     e_Hmag    ?=-99 Error on Hmag
  75- 80  F6.2  mag     Ksmag     ?=-99 2MASS KS-band magnitude
  82- 87  F6.2  mag     e_Ksmag   ?=-99 Error on Ksmag
  89- 94  A6    ---     qual      2MASS photometry quality and confusion flag
                                  ("999999" when no information)
  96-103  A8    ---     Mm        Membership class (G1)
 105-110  F6.2  mag     Av        ?=-99 Visual absorption from J vs. J-H diagram
 113-118  F6.2  Msun    Mass      ?=-99 Stellar mass from J vs. J-H diagram
 120-125  F6.2  Msun    e_Mass    ?=-99 Error on mass from J vs. J-H diagram
     128  I1    ---     U         [0/3] UKIRT counterparts (7)
 130-132  I3    ---     VLA       [1/20]?=-99 VLA source (Rodriguez et al. 2010,
                                  Cat. J/AJ/140/968, <[RRR2010] W40-VLA NN> in
                                  Simbad)

Note (7): UKIRT flag as follows:
    0 = no source;
    1 = single source present;
    2 = outside Field of View;
    3 = double source present.


Byte-by-byte Description of file: table3.dat

   Bytes Format Units   Label     Explanations

   1- 16  A16   ---     Name      2MASS name (HHMMSSss+DDMMSSs) or OS 3a
  18- 22  F5.2  mag     Jmag      2MASS J-band magnitude
  24- 27  F4.2  mag     e_Jmag    Jmag uncertainty
  29- 33  F5.2  mag     Hmag      2MASS H-band magnitude
  35- 38  F4.2  mag     e_Hmag    Hmag uncertainty
  40- 44  F5.2  mag     Ksmag     2MASS Ks-band magnitude
  46- 49  F4.2  mag     e_Ksmag   Ksmag uncertainty
  51- 56  A6    ---     qual      2MASS photometry quality and confusion flag
  58- 62  F5.2  mag     Av        Visual absorption (1)
  64- 68  F5.2  Msun    Mass      Stellar mass (1)
  70- 73  F4.2  Msun    e_Mass    Mass uncertainty

Note (1): Visual absorption and stellar mass derived from the color-magnitude
          J vs J-H diagram assuming distance of 600pc and age of 1Myr.


Byte-by-byte Description of file: table4.dat

   Bytes Format Units   Label     Explanations

   1-  3  I3    ---     Seq       X-ray catalog sequence number; RA sorted
   5- 22  A18   ---     CXOW40    IAU designation
  24- 30  F7.2  ct      NCt       Extracted net counts in full band
  32- 35  F4.2  keV     Emed      Median energy of net counts in full band
  37- 44  A8    ---     Mm        Membership class (G1)
  46- 50  F5.2  [10-7W] Lh1       ?=99 Apparent hard-band (2-8keV) luminosity
                                 from XSPEC fit
  52- 57  F6.2  [10-7W] Lt1       ?=-99 Apparent full-band (0.5-8keV) luminosity
                                 from XSPEC fit
  59- 64  F6.2  keV     kT1       ?=-99 Plasma temperature inferred
                                 from XSPEC fit
  66- 71  F6.2  [cm-2]  NH1       ?=-99 Column density inferred
                                 from XSPEC fit
  73- 78  F6.2  [10-7W] Lhc1      ?=-99 Intrinsic hard-band (2-8keV) luminosity
                                 from XSPEC fit
  80- 85  F6.2  [10-7W] Ltc1      ?=-99 Intrinsic full-band (0.5-8keV) luminosity
                                 from XSPEC fit
  87- 92  F6.2  [cm-2]  NH2       ?=-99 H2 column density obtained from XPHOT
  94- 99  F6.2  [cm-2]  e_NH2     ?=-99 Error on NH2
 101-106  F6.2  [10-7W] Lhc2      ?=-99 Intrinsic hard-band (2-8keV) luminosity
                                 from XPHOT
 108-113  F6.2  [10-7W] e_Lhc2    ?=-99 Error on Lhc2
 115-120  F6.2  [10-7W] Ltc2      ?=-99 Intrinsic full-band (0.5-8keV) luminosity
                                 from XPHOT
 122-127  F6.2  [10-7W] e_Ltc2    ?=-99 Error on Ltc2


Global note:

Note (G1): Membership class as follows:
    W40-noKs = W40 stars without Ks-excess;
      W40-Ks = W40 stars with Ks-excess;
         W40 = W40 stars with no Ks-excess classification;
         FRG = foreground stars;
          EG = Extragalactic sources.


Nomenclature note:
    For tables 1, 2 and 4, sources are <[KGF2010] NNN> =
    <CXOW40 JHHMMSS.ss+DDMMSS.s> for Simbad.

History:
    From electronic version of the journal
(End)                 Greg Schwarz [AAS], Emmanuelle Perret [CDS]    13-Aug-2012