Summary of the 2mass -> DVO interpretations from the 2MASS Point Source Catalog

(update 2009/03/08 be EAM; originally based on 2008/03/10 emails from EAM to M. Liu)

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In the 2MASS PSC, all sources are described by the equivalent of a single database row, with separate fields in the row for J, H, and K specific measurements, and some fields common to all three filters. For example, the coordinates and observing time are all given as a single value for all three filters. In the conversion to the DVO representation, each measurement (JHK) of an object is converted to a separate DVO measurement entry. All 2MASS sources are guaranteed to have all three measurements instantiated, but in some cases the measurements may be upper limits (non-detections in those filters). Below, we list the relationship between the 2MASS information on the left side of the -> and the DVO measurement field on the right side.

  • ra, dec : recorded using the DVO standard of delta RA,DEC relative to the object's average RA,DEC location.
  • m -> mag
  • cmsig -> dM
  • msigcom -> dMcal (dMcal2 + dM2 = msigcom2)
  • stdap -> Map
  • snr : skipped
  • err_maj -> FWx (FWHM_MAJOR)
  • err_min -> FWy (FWHM_MINOR)
  • err_ang -> theta

  • x_scan -> Xccd

  • j_psfchi --> psfChisq for J-band measurement
  • h_psfchi --> psfChisq for H-band measurement
  • k_psfchi --> psfChisq for K-band measurement

  • jd -> time is set using the DVO representation of time (unsigned integer seconds, since 1970/01/01T00:00:00, ie UNIX Time)

The following 2MASS values are used to set bits in the phot_flags field:

  • ph_qual:

A = 0x0000.0001 Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with [jhk]_snr>10 AND [jhk]_cmsig<0.10857.

B = 0x0000.0002 Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with [jhk]_snr>7 AND [jhk]_cmsig<0.15510.

C = 0x0000.0004 Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with [jhk]_snr>5 AND [jhk]_cmsig<0.21714.

D = 0x0000.0008 Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with no [jhk]_snr or [jhk]_cmsig requirement.

E = 0x0000.0010 This category includes detections where the goodness-of-fit quality of the profile-fit photometry was very poor (rd_flg=2 and [jhk]psf_chi>10.0), or detections where psf fit photometry did not converge and an aperture magnitude is reported (rd_flg=4), or detections where the number of frames was too small in relation to the number of frames in which a detection was geometrically possible (rd_flg="1" or rd_flg="2").

F = 0x0000.0020 This category includes rd_flg="1" or rd_flg="3" sources where a reliable estimate of the photometric error, [jhk]_cmsig, could not be determined. The uncertainties reported for these sources in [jhk]_cmsig and [jhk]_msigcom are flags and have numeric values >8.0.

U = 0x0000.0040 Upper limit on magnitude. Source is not detected in this band (rd_flg="0"), or it is detected, but not resolved in a consistent fashion with other bands (rd_flg="6"). A value of ph_qual="U" does not necessarily mean that there is no flux detected in this band at the location. Whether or not flux has been detected can be determined from the value of rd_flg. When rd_flg="0", no flux has been detected. When rd_flg="6", flux has been detected at the location where the images were not deblended consistently in all three bands (JHKs).

X = 0x0000.0080 There is a detection at this location, but no valid brightness estimate can be extracted using any algorithm. rd_flg="9" and default magnitude is null.

  • rd_flag:

0 = 0x0000.0100 Source is not detected in this band. The default magnitude is the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The sky background is estimated in an annular region with inner radius of 14" and outer radius of 20".

1 = 0x0000.0200 The default magnitude is derived from aperture photometry measurements on the 51 ms "Read_1" exposures. The aperture radius is 4", with the sky background measured in an annulus with an inner radius of 14" and an outer radius of 20". Used for sources that saturate one or more of the 1.3s "Read_2" exposures, but are not saturated on at least one of the 51 ms "Read_1" frames.

2 = 0x0000.0400 The default magnitude is derived from a profile-fitting measurement made on the 1.3 sec "Read_2" exposures. The profile-fit magnitudes are normalized to curve-of-growth-corrected aperture magnitudes. This is the most common type in the PSC, and is used for sources that have no saturated pixels in any of the 1.3 sec exposures.

3 = 0x0000.0800 The default magnitude is derived from a 1-d radial profile fitting measurement made on the 51 ms "Read_1" exposures. Used for very bright sources that saturate all of the 51 ms "Read 1" exposures.

4 = 0x0000.1000 The default magnitude is derived from curve-of-growth-corrected 4" radius aperture photometry measurements on the 1.3 s "Read_2" exposures. This is used for sources that are not saturated in any of the Read_2 frames, but where the profile-fitting measurements fail to converge to a solution. These magnitudes are the same as the standard aperture magnitudes (j_m_stdap, h_m_stdap, k_m_stdap), but when they are the default magnitudes, it generally implies that they are low quality measurements.

6 = 0x0000.2000 The default magnitude is the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The sky background is estimated in an annular region with inner radius of 14" and outer radius of 20". This is used for pairs of sources which are detected and resolved in another band, but are detected and not resolved in this band. This differs from a rd_flg="0" because in this case there is a detection of the source in this band, but it is not consistently resolved across all bands.

9 = 0x0000.8000 The default magnitude is the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The sky background is estimated in an annular region with inner radius of 14" and outer radius of 20". This is used for sources that were nominally detected in this band, but which could not have a useful brightness measurement from either profile fitting or aperture photometry. This often occurs in highly confused regions, or very near Tile edges where a significant fraction of the measurement aperture of sky annulus falls off the focal plane.

  • cc_flag:

p = 0x0001.0000 Persistence. Source may be contaminated by a latent image left by a nearby bright star.

c = 0x0002.0000 Photometric Confusion. Source photometry is biased by a nearby star that has contaminated the background estimation. This is very common in high source density regions.

d = 0x0004.0000 Diffraction spike confusion. Source may be contaminated by a diffraction spike from a nearby star.

s = 0x0008.0000 Electronic stripe. Source measurement may be contaminated by a stripe from a nearby bright star.

b = 0x0010.0000 Bandmerge confusion. In the process of merging detections in the different bands for this source, there was more than one possible match between the different band components. This occurs in regions of very high source density, or when multiple sources were split in one band but not another.

0 = 0x0020.0000 Source is unaffected by known artifacts, or is not detected in the band.

  • bl_flag: (0 or 1 : not blended) a value of 1 -> 0x0010.0000; anything except 0 or 1 -> 0x0020.0000
  • gal_flag: (0 or 1 : not extended) a value of 1 -> 0x0040.0000; anything except 0 or 1 -> 0x0080.0000 (extNsigma is also set to 100)
  • mp_flag: a value of 1 -> 0x0100.0000; anything except 0 or 1 -> 0x0200.0000
  • dup_flag: a value of 1 -> 0x0400.0000; anything except 0 or 1 -> 0x0800.0000
  • use_flag: a value of 1 -> 0x1000.0000; no other values are allowed in the PSF

The following 2MASS values were used to set bits in the phot_flags field prior to the 32bit version (PS1_V1; 2009/03/08) :

  • ph_qual:

X = 0x0000 There is a detection at this location, but no valid brightness estimate can be extracted using any algorithm. rd_flg="9" and default magnitude is null.

U = 0x0001 Upper limit on magnitude. Source is not detected in this band (rd_flg="0"), or it is detected, but not resolved in a consistent fashion with other bands (rd_flg="6"). A value of ph_qual="U" does not necessarily mean that there is no flux detected in this band at the location. Whether or not flux has been detected can be determined from the value of rd_flg. When rd_flg="0", no flux has been detected. When rd_flg="6", flux has been detected at the location where the images were not deblended consistently in all three bands (JHKs).

F = 0x0002 This category includes rd_flg="1" or rd_flg="3" sources where a reliable estimate of the photometric error, [jhk]_cmsig, could not be determined. The uncertainties reported for these sources in [jhk]_cmsig and [jhk]_msigcom are flags and have numeric values >8.0.

E = 0x0003 This category includes detections where the goodness-of-fit quality of the profile-fit photometry was very poor (rd_flg=2 and [jhk]psf_chi>10.0), or detections where psf fit photometry did not converge and an aperture magnitude is reported (rd_flg=4), or detections where the number of frames was too small in relation to the number of frames in which a detection was geometrically possible (rd_flg="1" or rd_flg="2").

A = 0x0004 Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with [jhk]_snr>10 AND [jhk]_cmsig<0.10857.

B = 0x0005 Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with [jhk]_snr>7 AND [jhk]_cmsig<0.15510.

C = 0x0006 Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with [jhk]_snr>5 AND [jhk]_cmsig<0.21714.

D = 0x0007 Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with no [jhk]_snr or [jhk]_cmsig requirement.

  • rd_flag:

0 = 0x0000 Source is not detected in this band. The default magnitude is the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The sky background is estimated in an annular region with inner radius of 14" and outer radius of 20".

1 = 0x0010 The default magnitude is derived from aperture photometry measurements on the 51 ms "Read_1" exposures. The aperture radius is 4", with the sky background measured in an annulus with an inner radius of 14" and an outer radius of 20". Used for sources that saturate one or more of the 1.3s "Read_2" exposures, but are not saturated on at least one of the 51 ms "Read_1" frames.

2 = 0x0020 The default magnitude is derived from a profile-fitting measurement made on the 1.3 sec "Read_2" exposures. The profile-fit magnitudes are normalized to curve-of-growth-corrected aperture magnitudes. This is the most common type in the PSC, and is used for sources that have no saturated pixels in any of the 1.3 sec exposures.

3 = 0x0030 The default magnitude is derived from a 1-d radial profile fitting measurement made on the 51 ms "Read_1" exposures. Used for very bright sources that saturate all of the 51 ms "Read 1" exposures.

4 = 0x0040 The default magnitude is derived from curve-of-growth-corrected 4" radius aperture photometry measurements on the 1.3 s "Read_2" exposures. This is used for sources that are not saturated in any of the Read_2 frames, but where the profile-fitting measurements fail to converge to a solution. These magnitudes are the same as the standard aperture magnitudes (j_m_stdap, h_m_stdap, k_m_stdap), but when they are the default magnitudes, it generally implies that they are low quality measurements.

6 = 0x0050 The default magnitude is the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The sky background is estimated in an annular region with inner radius of 14" and outer radius of 20". This is used for pairs of sources which are detected and resolved in another band, but are detected and not resolved in this band. This differs from a rd_flg="0" because in this case there is a detection of the source in this band, but it is not consistently resolved across all bands.

9 = 0x0060 The default magnitude is the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The sky background is estimated in an annular region with inner radius of 14" and outer radius of 20". This is used for sources that were nominally detected in this band, but which could not have a useful brightness measurement from either profile fitting or aperture photometry. This often occurs in highly confused regions, or very near Tile edges where a significant fraction of the measurement aperture of sky annulus falls off the focal plane.

  • cc_flag:

p = 0x0000 Persistence. Source may be contaminated by a latent image left by a nearby bright star.

c = 0x0100 Photometric Confusion. Source photometry is biased by a nearby star that has contaminated the background estimation. This is very common in high source density regions.

d = 0x0200 Diffraction spike confusion. Source may be contaminated by a diffraction spike from a nearby star.

s = 0x0300 Electronic stripe. Source measurement may be contaminated by a stripe from a nearby bright star.

b = 0x0400 Bandmerge confusion. In the process of merging detections in the different bands for this source, there was more than one possible match between the different band components. This occurs in regions of very high source density, or when multiple sources were split in one band but not another.

0 = 0x0500 Source is unaffected by known artifacts, or is not detected in the band.

  • bl_flag: (0,1 : not blended) anything except 0 or 1 -> 0x0008
  • gal_flag: (0,1 : not extended) anything except 0 or 1 -> 0x0080
  • mp_flag: anything except 0 or 1 -> 0x0800
  • dup_flag: anything except 0 or 1 -> 0x1000
  • use_flag: anything except 0 or 1 -> 0x2000