M37CXO - M 37 Chandra X-Ray Point Source Catalog

Overview

Empirical calibrations of the stellar age-rotation-activity relation (ARAR) rely on observations of the co-eval populations of stars in open clusters. The authors used the Chandra X-ray Observatory to study M 37 (NGC 2099), a 500-Myr-old open cluster that has been extensively surveyed for rotation periods (P_rot). M 37 was observed almost continuously for five days, for a total of 440.5 ks, to measure stellar X-ray luminosities (L_X), a proxy for coronal activity, across a wide range of masses. The cluster's membership catalog was revisited to calculate updated membership probabilities from photometric data and each star's distance to the cluster center. The result is a comprehensive sample of 1699 M 37 members: 426 with P_rot, 278 with X-ray detections, and 76 with both. The authors calculate Rossby numbers, R_o= P_rot/tau , where tau is the convective turnover time, and ratios of the X-ray-to-bolometric luminosity, L_X/L_bol, to minimize mass dependencies in their characterization of the rotation-coronal activity relation at 500 Myr. They find that fast rotators, for which R_o < 0.09 +/- 0.01, show saturated levels of activity, with log(L_X/L_bol) = -3.06 +/- 0.04. For R_o >= 0.09 +/- 0.01, activity is unsaturated and follows a power law of the form R^beta_o , where beta = -2.03 (-0.14, +0.17). This is the largest sample available for analyzing the dependence of coronal emission on rotation for a single-aged population, covering stellar masses in the range 0.4 - 1.3 solar masses, P_rot in the range 0.4 - 12.8 days, and L_X in the range 10^28.4 - 10^30.5 erg s^-1. These results make M 37 a new benchmark open cluster for calibrating the ARAR at ages of ~ 500 Myr.

The central field of M 37 was observed five separate times between 2011 November 14 20:58 and 2011 November 1915:31 UTC for a total of 440.5 ks with the Advanced CCD Imaging Spectrometer (ACIS). The four ACIS-I chips and the ACIS-S3 chip were used in Very Faint telemetry mode to improve the screening of background events and thus increase the sensitivity of ACIS to faint sources. The exposure-weighted average aimpoint of the 16.9 x 16.9 arcmin² ACIS-I field of view is RA = 05^h 52^m 17.86^s,Dec = +32^o 33' 48.23" (J2000). The pitch angle for four observations was 103 degrees; due to scheduling constraints, it was 253 degrees for the fifth. Table 1 in the reference paper provides the basic information for the 5 Chandra observations and Figure 1 in that paper shows their footprints superimposed on a 40' x 40' i' image centered on M 37 obtained by Hartman et al. (2008, ApJ, 675, 1233, hereafter HA08) with the Megacam on the MMT telescope.

This HEASARC table contains all of the data from Table 3 of the reference paper, the M 37 Chandra catalog of 774 X-ray sources, and the data from Table 5, the catalog of optical objects, for those objects which have been identified as optical counterparts to the X-ray sources. It does not contain entries for those optical objects in Table 5 which lack X-ray counterparts.

Catalog Bibcode

2015ApJ...809..161N

References

Linking Stellar Coronal Activity and Rotation at 500 Myr: A Deep Chandra
Observation of M37

     Nunez A., Agueros M.A., Covey K.R., Hartman J.D., Kraus A.L.,
     Bowsher E.C., Douglas ST., Lopez-Morales M., Pooley D.A., Posselt B.,
     Saar S.H., West A.A.
    <Astrophysical J. 809, 161 (2015)>
    =2015ApJ...809..161N

Provenance

This online catalog was created by the HEASARC in December 2015 based on machine-readable versions of tables 3 and 5 from the paper which were obtained from the ApJ website.

Parameters

Source_Number
The X-ray catalog sequence number (XID), sorted by RA (J2000.0). Source designations with XID > 1000 are for sources in the ACIS-S3 chip.

Name
The IAU-style position-based source designation for the the Chandra X-ray source, viz., 'CXOU JHHMMSS.ss+DDMMSS.s'. Notice that the positional precision of these names is higher than those commonly used for Chandra sources.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 decimal degree coordinates to an accuracy of 10^-6 degrees (0.0036 arcseconds) in the original machine-readable table.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000.0 decimal degree coordinates to an accuracy of 10^-6 degrees (0.0036 arcseconds) in the original machine-readable table.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Error_Radius
The 80%-confidence level X-ray positional uncertainty, in arcseconds. See Section 2.2 of the reference paper for the details as to how this was estimated.

Off_Axis
The off-axis angle of the X-ray source, i.e., the distance to the average aimpoint of the Chandra observations, in arcminutes.

FB_Counts
The net (background-subtracted) source counts in the full (0.5-7 keV) band.

FB_Counts_Pos_Err
The 1-sigma upper error in the net (background-subtracted) source counts in the full (0.5-7 keV) band.

FB_Counts_Neg_Err
The 1-sigma lower error in the net (background-subtracted) source counts in the full (0.5-7 keV) band

SB_Counts
The net (background-subtracted) source counts in the soft (0.5-2 keV) band.

SB_Counts_Pos_Err
The 1-sigma upper error in the net (background-subtracted) source counts in the soft (0.5-2 keV) band.

SB_Counts_Neg_Err
The 1-sigma lower error in the net (background-subtracted) source counts in the soft (0.5-2 keV) band.

HB_Counts
The net (background-subtracted) source counts in the hard (2-7 keV) band.

HB_Counts_Pos_Err
The 1-sigma upper error in the net (background-subtracted) source counts in the hard (2-7 keV) band.

HB_Counts_Neg_Err
The 1-sigma lower error in the net (background-subtracted) source counts in the hard (2-7 keV) band.

FB_Flux
The absorbed energy flux of the Chandra source in the 0.5-7 keV band, in erg s^-1 cm^-2.

SB_Flux
The absorbed energy flux of the Chandra source in the 0.5-2 keV band, in erg s^-1 cm^-2.

HB_Flux
The absorbed energy flux of the Chandra source in the 2-7 keV band, in erg s^-1 cm^-2.

Median_Energy
The median photon energy, in keV, of the Chandra source, in the 0.5-7 keV band.

PSF_Fraction
The fraction of the PSF (at 1.497 keV) enclosed within the source extraction region. A PSF fraction significantly below 90% may indicate a source in a crowded region.

SB_Lx
The absorption-corrected X-ray luminosity in the 0.1-2.4 keV band, in erg s^-1. This is only given for sources with optical cluster member counterparts. It is calculated from the X-ray flux assuming a distance to the cluster of 1490 +/- 120 pc.

SB_Lx_Error
The standard deviation of the absorption-corrected X-ray luminosity in the 0.1-2.4 keV band, in erg s^-1. This is only given for sources with optical cluster member counterparts.

Prob_No_Source
The probability that the extracted X-ray counts are solely from the background, i.e., that there really is o source.

SNR
The photometric significance of the X-ray source, computed as the net counts divided by the upper error in the net counts.

Source_Anomaly_Flags
This parameter can contain flags indicating the presence of source anomalies, as follows:

        f: fractional time that source was on a detector is < 0.9;
        a: photometry and spectrum may contain > 10% afterglow events.

Ks_Var_Flag
The X-ray source variability characterization based on the K-S statistic (full band) from the single ObsID showing the most variability, coded as follows (no value is reported for sources with fewer than four net counts in the full band):

        a: no evidence for variability (0.05 <P_KS);
        b: possibly variable (0.005 < P_KS < 0.05);
        c: definitely variable (P_KS < 0.005).

Optical_ID
The identification of the optical match to the X-ray source. The authors' consolidated optical catalog is discussed in Section 3.2 of the reference paper. Identifications which are integers > 10,000 are from Hartman et al (2008, HA08), while others, e.g., vZ 439 (rendered as NGC 2099 439 in Simbad), are from the literature.

Optical_RA
The Right Ascension of the optical match in the selected equinox. This was given in J2000.0 decimal degree coordinates to an accuracy of 10^-8 degrees (0.000036 arcseconds) in the original machine-readable table (which is presumably not the actual precision of this coordinate).

Optical_Dec
The Declination of the optical match in the selected equinox. This was given in J2000.0 decimal degree coordinates to an accuracy of 10^-8 degrees (0.000036 arcseconds) in the original machine-readable table (which is presumably not the actual precision of this coordinate).

Optical_CXO_Offset
The offset between the X-ray source and optical counterpart positions, in arcseconds.

Xray_Notes
Additional notes on the X-ray source.

Gmag
The g magnitude of the optical counterpart to the X-ray source.

Gmag_Error
The standard deviation in the g magnitude of the optical counterpart to the X-ray source.

Rmag
The r magnitude of the optical counterpart to the X-ray source.

Rmag_Error
The standard deviation in the r magnitude of the optical counterpart to the X-ray source.

Imag
The i magnitude of the optical counterpart to the X-ray source.

Imag_Error
The standard deviation in the i magnitude of the optical counterpart to the X-ray source.

Rotation_Period
The rotation period of the optical counterpart to the X-ray source, in days.

Rotation_Period_Flag
This parameter can contain a flag giving information on the source and quality of the rotation period:

       0: non-clean HA09 period;
       1: clean HA09 period;
       2: ME08 period.

where HA09 = Hartman et al. (2009, ApJ, 691, 342), ME08 = Messina et al. (2008, A&A, 483, 253), and the significance of clean and non-clean periods is discussed in section 3.2 of the reference paper.

Prob_Single_Member
The probability P_s that the object is a single member of M 37.

Prob_Binary_Member
The probability P_b that the object is a likely binary member of M 37.

Prob_Member
The total probability P_mem = P_s + P_b that the object is a member of M 37. The authors considered stars with P_mem >= 0.2 to be candidate cluster members. The low P_mem threshold they used allows for a non-negligible number of contaminants into their cluster sample. However, since they expect most field stars to be much older and, thus, inactive or significantly fainter in X-rays, the contamination in their rotation-activity analysis of cluster stars should be minimal. The authors inspected objects with 0.1 <= P_mem < 0.2 that also have an X-ray counterpart with a hardness ratio (HR) <-0.3 (see Sections 4.3 and 4.4 of the reference paper) as these could potentially be stars that are younger than the average contaminating field star, and hence potential cluster members. They found 12 objects that met these criteria, and assigned them a P_mem value of 999. They thus use this P_mem value as a flag to highlight those stars that they consider to be cluster members based on these additional criteria

Stellar_Mass
The stellar mass of the optical object if a cluster member, derived as discussed in Section 4.1.1 of the reference paper, in solar masses.

Conv_Turnover_Time
The convective turnover time (tau) of the optical object if a cluster member, derived as discussed in Section 4.1.3 of the reference paper, in days.

Lbol
The bolometric luminosity of the optical object if a cluster member, derived as discussed in Section 4.1.2 of the reference paper, in erg s^-1.

Lbol_Error
The standard deviation of the bolometric luminosity, in erg s^-1.

Me08_ID
The identification number of the Messina et al. (2008, A&A, 483, 253 = ME08) optical match, if there is one. This is given for Hartman et al. (2008, ApJ, 675, 1233 = HA08) objects only.

Me08_RA
The Right Ascension of the Messina et al. (2008, A&A, 483, 253 = ME08) optical match in the selected equinox. This was given in J2000.0 decimal degree coordinates to an accuracy of 10^-8 degrees (0.000036 arcseconds) in the original machine-readable table (which is presumably not the actual precision of this coordinate). This is given for Hartman et al. (2008, ApJ, 675, 1233 = HA08) objects only.

Me08_Dec
The Declination of the Messina et al. (2008, A&A, 483, 253 = ME08) optical match in the selected equinox. This was given in J2000.0 decimal degree coordinates to an accuracy of 10^-8 degrees (0.000036 arcseconds) in the original machine-readable table (which is presumably not the actual precision of this coordinate). This is given for Hartman et al. (2008, ApJ, 675, 1233 = HA08) objects only.

Me08_Optical_Offset
The offset between the Hartman et al. (2008, ApJ, 675, 1233 = HA08) object and its Messina et al. (2008, A&A, 483, 253 = ME08) counterpart, in arcseconds.

Optical_Notes
Additional notes concerning the optical match.

Contact Person

Questions regarding the M37CXO database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:30:40 EDT