Browse
this table...

NGC6357OID - NGC 6357/Pismis 24 Chandra Point Source Optical/IR Identifications Catalog

HEASARC
Archive

Overview

Circumstellar disks are expected to evolve quickly in massive young clusters harboring many OB-type stars. Two processes have been proposed to drive the disk evolution in such cruel environments: (1) gravitational interaction between circumstellar disks and nearby passing stars (stellar encounters), and (2) photoevaporation by UV photons from massive stars. The relative importance of both mechanisms is not well understood. Studies of massive young star clusters can provide observational constraints on the processes of driving disk evolution.

The authors investigate the properties of young stars and their disks in the NGC 6357 complex, concentrating on the most massive star cluster within the complex: Pismis 24. They use infrared data from the 2MASS and Spitzer GLIMPSE surveys, complemented with their own deep Spitzer imaging of the central regions of Pismis 24, in combination with X-ray data to search for young stellar objects (YSOs) in the NGC 6357 complex. The infrared data constrain the disk presence and are complemented by optical photometric and spectroscopic observations, obtained with VLT/VIMOS, that constrain the properties of the central stars. For those stars with reliable spectral types, they combine spectra and photometry to estimate the masses and ages. For cluster members without reliable spectral types, they obtain the mass and age probability distributions from R and I-band photometry, assuming these stars have the same extinction distribution as those in the "spectroscopic" sample. The authors compare the disk properties in the Pismis 24 cluster with those in other clusters/star-forming regions employing infrared color-color diagrams.

The authors discover two new young clusters in the NGC 6357 complex. They give a revised distance estimate for Pismis 24 of 1.7 +/- 0.2 kpc. They also find that the massive star Pis 24-18 is a binary system, with the secondary being the main X-ray source of the pair. The authors provide photometry in 9 bands between 0.55 and 8 micron (um) for the members of the Pismis 24 cluster. They derive the cluster mass function and find that up to the completeness limit at low masses it agrees well with the initial mass function of the Trapezium cluster. They derive a median age of 1 Myr for the Pismis 24 cluster members.

The R-band observations were performed on 2008 April 1 and 6, and the I-band observations were done on 2008 May 1, both using the VIMOS instrument on the VLT. The near-IR photometry in the J, H and Ks bands were taken from the 2MASS. The mid-IR photometry at 3.6, 4.5, 5.8 and 8.0 um were obtained withe the Spitzer IRAC camera, both from the GLIMPSE I survey and from deep observations of the central Pismis 24 region carried out by the authors on 2006 September 29. The X-ray observations were made by the Chandra ACIS-I instrument and previously published by Wang et al. (2007, ApJS, 168, 100: the HEASARC NGC6357CXO table). The X-ray sources were matched to sources detected in the VIMOS R and I bands based on positional coincidence, using a 1.5 arcseconds tolerance. The accuracy of the optical and X-ray positions was 0.6 and 1.0 arcseconds, respectively. Given the high space density of sources in the central regions of Pismis 24, there may be a substantial number (up to 1/6 of the sources) of "false positives", according to the authors.

This table contains the list of 643 optical/IR counterparts to the Chandra X-ray sources found by Wang et al. (2007) which were identified by the present authors: for 136 of the 779 X-ray sources, no counterparts were found.


Catalog Bibcode

2012A&A...539A.119F

References

Star formation and disk properties in Pismis 24.
    Fang M., van Boekel R., King R.R., Henning T., Bouwman J., Doi Y.,
    Okamato Y.K., Roccatagliata V., Sicilia-Aguilar A.
    <Astron. Astrophys. 539, A119 (2012)>
    =2012A&A...539A.119F        (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in March 2012 based on CDS Catalog J/A+A/539/A119 files table1.dat and table3.dat.

Parameters

Source_Number
A unique identificaton number for the optical/IR counterpart to the X-ray source, in order of increasing J2000.0 Right Ascension.

Name
The name of the optical/IR counterpart to the X-ray source, based on the '[FVK2012]' prefix (for Fang, van Boekel, King 2012) and the source number, e.g., '[FVK2012] 643'. This was created by the HEASARC in anticipation of its adoption by the CDS Dictionary of Nomenclature of Celestial Objects.

Wtf07_Source_Number
The Wang et al. (2007, ApJS, 168, 100, HEASARC NGC6357CXO table) X-ray source identification number, in order of increasing J2000.0 Right Ascension. Note that only 643 of the 779 X-ray sources have optical/IR counterparts listed in the present table.

Offset
The angular separation between the X-ray source and the optical/IR counterpart match, in arcseconds.

RA
The Right Ascension of the optical/infrared counterpart to the Chandra X-ray source in the selected equinox. This was given in J2000 coordinates to an accuracy of 0.01 seconds of time in the original table.

Dec
The Declination of the optical/infrared counterpart to the Chandra X-ray source in the selected equinox. This was given in J2000 coordinates to an accuracy of 0.1 arcseconds in the original table.

LII
The Galactic Longitude of the optical/infrared counterpart to the Chandra X-ray source.

BII
The Galactic Latitude of the optical/infrared counterpart to the Chandra X-ray source.

Rmag
The VIMOS R magnitude of the optical/infrared counterpart to the Chandra X-ray source.

Rmag_Error
The rms uncertainty in the VIMOS R magnitude of the optical/infrared counterpart to the Chandra X-ray source.

Imag
The VIMOS I magnitude of the optical/infrared counterpart to the Chandra X-ray source.

Imag_Error
The rms uncertainty in the VIMOS I magnitude of the optical/infrared counterpart to the Chandra X-ray source.

Jmag
The 2MASS J magnitude of the optical/infrared counterpart to the Chandra X-ray source. The typical 3-sigma limit for the 2MASS survey is 17.1 in the J band.

Jmag_Error
The rms uncertainty in the 2MASS J magnitude of the optical/infrared counterpart to the Chandra X-ray source.

Hmag
The 2MASS H magnitude of the optical/infrared counterpart to the Chandra X-ray source. The typical 3-sigma limit for the 2MASS survey is 16.4 in the H band.

Hmag_Error
The rms uncertainty in the 2MASS H magnitude of the optical/infrared counterpart to the Chandra X-ray source.

Ks_Mag
The 2MASS Ks magnitude of the optical/infrared counterpart to the Chandra X-ray source. The typical 3-sigma limit for the 2MASS survey is 15.3 in the Ks band.

Ks_Mag_Error
The rms uncertainty in the 2MASS Ks magnitude of the optical/infrared counterpart to the Chandra X-ray source.

IRAC_3p6_um_Mag
The IRAC 3.6um magnitude of the optical/infrared counterpart to the Chandra X-ray source. See Sections 2.1.2 and 2.1.3 of the reference paper for information on the limiting magnitudes for the IRAC observations.

IRAC_3p6_um_Mag_Error
The rms uncertainty in the IRAC 3.6um magnitude of the optical/infrared counterpart to the Chandra X-ray source.

IRAC_4p5_um_Mag
THe IRAC 4.5um magnitude of the optical/infrared counterpart to the Chandra X-ray source. See Sections 2.1.2 and 2.1.3 of the reference paper for information on the limiting magnitudes for the IRAC observations.

IRAC_4p5_um_Mag_Error
The rms uncertainty in the IRAC 4.5um magnitude of the optical/infrared counterpart to the Chandra X-ray source.

IRAC_5p8_um_Mag
The IRAC 5.8um magnitude of the optical/infrared counterpart to the Chandra X-ray source. See Sections 2.1.2 and 2.1.3 of the reference paper for information on the limiting magnitudes for the IRAC observations.

IRAC_5p8_um_Mag_Error
The rms uncertainty in the IRAC 5.8um magnitude of the optical/infrared counterpart to the Chandra X-ray source.

IRAC_8p0_um_Mag
The IRAC 8.0um magnitude of the optical/infrared counterpart to the Chandra X-ray source. See Sections 2.1.2 and 2.1.3 of the reference paper for information on the limiting magnitudes for the IRAC observations.

IRAC_8p0_um_Mag_Error
The rms uncertainty in the IRAC 8.0um magnitude of the optical/infrared counterpart to the Chandra X-ray source.

Spect_Type
The spectral type of the optical/infrared counterpart to the Chandra X-ray source estimated from VIMOS spectroscopic observations of the Pismis 24 cluster made by the authors using the IDL "Hammer" package.

Vmag_Extinction
The V-band extinction, in magnitudes, by which the best-fit "Hammer" spectral template was reddened using a standard ISM extinction law in order to fit the observed spectrum of the optical/infrared counterpart to the Chandra X-ray source.

Stellar_Mass
The mass of the optical/infrared counterpart to the Chandra X-ray source, in solar masses. This was estimated for spectroscopic members of Pismis 24 from the dereddened R vs. (R-I) color-magnitude diagram by comparison with the theoretical pre-main-sequence evolutionary tracks of Dotter et al. (2008, ApJS, 178, 89).

Stellar_Age
The age of the optical/infrared counterpart to the Chandra X-ray source, in miilions of years (Myr). This was estimated for spectroscopic members of Pismis 24 from the dereddened R vs. (R-I) color-magnitude diagram by comparison with the theoretical pre-main-sequence evolutionary tracks of Dotter et al. (2008, ApJS, 178, 89).

Class
The HEASARC Browse object classification of the optical/infrared counterpart to the Chandra X-ray source, based on the spect_type parameter value.


Contact Person

Questions regarding the NGC6357OID database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 28-Aug-2012