Information on Service '2Mass Query'

For a list of all services and tables belonging to this service's resource, see Information on resource 'The 2MASS point source catalog'

Overview

You can access this service using:

• form -- an interface for web browsers through an HTML form
• scs.xml -- a standard SCS interface as defined by the IVOA to access catalog-type data; SCS clients use http://dc.zah.uni-heidelberg.de/2mass/res/2mass/q/scs.xml? to access the service

VOResource XML (that's something exclusively for VO nerds)

Note b

Blend flag (upstream's bl_flg). This is a three character flag, one character per band [JHKs], that indicates the number of components that were fit simultaneously when estimating the brightness of a source:

"0"

Source is not detected, or is inconsistently deblended in that band.

"1"

One component was fit to the source in R_2 profile-fitting photometry (rd_flg="2"), or default magnitudes are from aperture photometry (rd_flg="1" or "4") or saturated star 1-d radial profile-fitting (rd_flg="3").

">1"

More than one component was fit simultaneously during R2 profile-fit photometry, where the value of the field is the number of components simultaneously fit. The maximum number of components is 7 in any band for the PSC, so this bflg is always a three character flag. Multi-component fitting occurs only for profile-fitting, and only when more than one detection is found within ~5". Single detections that are not well-fit by a single PSF are not split.

Note c

Contamination and confusion flag (upstream: cc_flg). This is a three character flag, one character per band [JHKs], that indicates that the photometry and/or position measurements of a source may be contaminated or biased due to proximity to an image artifact or nearby source of equal or greater brightness. The cflg in each band is set in hierarchical order according to the following table, in the event a source is affected by more than one artifact or condition:

"p"

Persistence. Source may be contaminated by a latent image left by a nearby bright star.

"c"

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"

Diffraction spike confusion. Source may be contaminated by a diffraction spike from a nearby star.

"s"

Electronic stripe. Source measurement may be contaminated by a stripe from a nearby bright star.

"b"

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"

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

Non-zero values the cflg in any band is an indicator that the measurements of that source may be contaminated.

Note p

pts_key is called cntr in the IRSA/GATOR version of 2MASS. This sequential number was defined when source records from final data processing were loaded into the Point Source Working Database.

Pts_key is incremented in order (or reverse order depending on the scan direction) of declination within a scan. For this reason, on average sources with close pts_key values are close to each other on the sky, except at Tile boundaries.

Pts_key ordering thus provides a useful mapping of the 2MASS release on storage media. PSC sources are cross-referenced in the XSC, Known Asteroid Detection List, Known Comet Detection List, and Planet and Planetary Satellite Detection List via the value of pts_key.

Note q

qflag is the photometric quality flag (upstream ph_qual). Three character flag, one character per band [JHKs], that provides a summary of the net quality of the default photometry in each band, as derived from the Read Flag (rflg), measurement uncertainties ([jhk]_cmsig), scan signal-to-noise ratios ([jhk]_snr), frame-detection statistics (ndet), and profile-fit reduced chi-squared values ([jhk]_psfchi). The value for qflag is set for a band according to the precedence of the table below. For example, a source that is tested and meets the conditions for category "X" is not tested for subsequent qualities.

"X"

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

"U"

Upper limit on magnitude. Source is not detected in this band (rflg="0"), or it is detected, but not resolved in a consistent fashion with other bands (rflg="6"). A value of qflag="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 rflg. When rflag="0", no flux has been detected. When rflg="6", flux has been detected at the location where the images were not deblended consistently in all three bands (JHKs).

"F"

This category includes rflg="1" or rflag="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"

This category includes detections where the goodness-of-fit quality of the profile-fit photometry was very poor (rflg=2 and [jhk]psf_chi>10.0), or detections where psf fit photometry did not converge and an aperture magnitude is reported (rflg=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 (rflg="1" or rflag="2").

"A"

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

"B"

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

"C"

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

"D"

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

Note r

rflg is upstream's Read flag (rd_flg). It is a three character flag, one character per band [JHKs], that indicates the origin of the default magnitudes and uncertainties in each band (j_m,h_m,k_m, j_cmsig, h_cmsig, k_cmsig). rflg values of "1", "2" or "3" generally indicate the best quality detections, photometry and astrometry (although other quality flags must be considered). Values of "0", "4", "6" and "9" in a band indicate either non-detections, or generally poor quality photometry and positions. The definitions of the rflg values are:

"0"

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"

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"

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"

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"

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"

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 rflg="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"

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.