ONCCXOOPT - Orion Nebula Cluster Chandra HRC Optical Sample
In the first of two companion papers on the Orion Nebula Cluster
(ONC), the authors presented their analysis of a 63 ks Chandra HRC-I
observation that yielded 742 X-ray detections within the 30' x 30' field of
view. To facilitate their interpretation of the X-ray image, they compiled a
multiwavelength catalog of nearly 2900 known objects in the region by
combining 17 different catalogs from the recent literature. They defined
two reference groups: an infrared sample, containing all objects
detected in the K band, and an optical sample comprising
low-extinction, well-characterized ONC members. They showed for both
samples that field object contamination is generally low. Their X-ray
sources are primarily low-mass ONC members. The detection rate for
optical sample stars increases monotonically with stellar mass from
zero at the brown dwarf limit to ~100% for the most massive stars but
shows a pronounced dip between 2 and 10 M_sun. They determined L_X and
L_X/L_bol or all stars in their optical sample and utilized this
information in their companion paper to study correlations between X-ray
activity and other stellar parameters.
In particular, the authors assembled an extensive catalog of known
X-ray/optical/IR and radio objects that fell within the HRC FOV. In addition
to their list of HRC sources and the Chandra source lists of Garmire et al.
(2000, CDS Cat. <J/AJ/120/1426>) and Schulz et al. (2001, CDS Cat.
<J/ApJ/549/441>), they considered 14 catalogs from recent publications,
producing a database of nearly 2900 distinct objects reported in at least one
of the studies considered. A full list of references is given in the first
column of Table 2 of the reference paper, along with a concise classification
of the work and the referenced table number(s) from the original work.
The authors' ONC optical sample is comprised of stars in the HRC FOV for which
they have a mass estimate, whose values of the visual absorption A_V are less
than 3.0, and which are either confirmed proper motion members or have unknown
proper motion (see Section 3.4.1 of the reference paper). For the 696 stars of
this optical sample, this HEASARC table (the full version of Table 4 of the
reference paper) lists sky position, mass, age, rotational period, Ca II line
equivalent width, HRC basal count rate (see Section 5 of the reference paper),
X-ray luminosity, and L_X/L_bol (see Sections 4 and 5 of the reference paper).
Chandra X-ray observation of the Orion Nebula Cluster.
I. Detection, identification, and determination of X-ray luminosities.
Flaccomio E., Damiani F., Micela G., Sciortino S., Harnden F.R.Jr,
Murray S.S., Wolk S.J.
<Astrophys. J. 582, 382 (2003)>
This table was created by the HEASARC in March 2007 based on the
CDS table J/ApJ/582/382, file table4.dat.
The table of Chandra HRC X-ray sources detected
in this observation (Table 1 of the reference paper) is available as the
HEASARC Browse table ONCCXOXRAY. The HEASARC has created links connecting
entries in the present table to those in this related table, based on
having a positional coincidence within 5 arcseconds. This compromise value may
be too large for positions near the center of the field (and hence produce
multiple matches) but too small for positions near the edge of the field (and
hence miss some matches): users can use the cross-correlation functionality in
Browse to vary the matching radius between the two tables.
A running number for the optical star in order of increasing
J2000.0 Right Ascension within the field. Note that this is not the same
as the source numbering scheme used for the X-ray sources.
The name of the star in the ONC Optical Sample using the '[FDM2003]
Opt' prefix recommended by the CDS Dictionary of Nomenclature of Celestial
Objects for these objects combined with the optical star source number.
The Right Ascension of the star in the selected equinox. This was given
in J2000.0 coordinates to a precision of 0.01 seconds of time in the original
The Declination of the star in the selected equinox. This was given in
J2000.0 coordinates to a precision of 0.01 arcseconds in the original table.
The Galactic Longitude of the star.
The Galactic Latitude of the star.
The stellar mass, in solar masses. See Section 3.3 of
the reference paper for details on how this was estimated.
The logarithm of the stellar age, in years. See Section 3.3
of the reference paper for details on how this was estimated.
The stellar rotation period, in days.See Table 2 and Section
3.3 of the reference paper for the sources of this information.
The optical star's Ca II 8542 Angstrom line equivalent
width, in Angstrom. See Table 2 of the reference paper for the source of this
This parameter is set to '<' if the corresponding HRC
count rate is an upper limit rather than a detection.
The basal HRC count rate, in ct/s, of the X-ray source with
which the optical star has been associated. Because the intensity of many of
the HRC sources varied during the observation, the authors did not use mean
count rates, but instead defined a basal count rate in order to remove the
effects of short-term (<~ 63 ks) variability. Their basal rate algorithm
searched for that count rate which was compatible with the largest possible
portion of the HRC light curve.
This parameter is set to '<' if the corresponding logarithm
of the X-ray luminosity is an upper limit rather than an actual value.
The logarithm of the stellar X-ray luminosity in the spectral band
between 0.1 and 4.0 keV, in erg/s, based on the basal X-ray count rate of the
source, an assumed distance to the ONC of 470 pc, and an HRC count rate to
X-ray flux conversion factor calculated as discussed in Section 5.1 of the
reference paper, i.e., assuming an isothermal (kT = 2.16 keV), optically thin
Raymond & Smith plasma, absorbed by a gas column density proportional to
the optical extinction: N_H = 2 x 10^21 x A_V.
This parameter is set to '<' if the corresponding
logarithm of the ratio of the X-ray to bolometric luminosity is an upper limit
rather than an actual value.
The logarithm of the stellar X-ray to bolometric luminosity
ratio, using the estimated X-ray luminosity as discussed above, and the
bolometric luminosity obtained from the source given in Table 2 of the
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