Column Descriptions for the 2MASS Second Incremental Release Point Source Catalog (PSC)

Column # Column Name Description Units Bytes Formata Nulls Allowed
1 ra  right ascension (J2000 decimal deg) deg 1-10 10.6f n
2 dec  declination (J2000 decimal deg) deg 12-21 10.6f n
3 err_maj  major axis of position error ellipse arcsec 23-26 4.2f y
4 err_min  minor axis of position error ellipse arcsec 28-31 4.2f y
5 err_ang  position angle of error ellipse major axis (E of N) deg 33-36 4hd y
6 designation  source designation formed from sexigesimal coordinates --- 39-52 14s n
  Notes for designation: This is the object sequence designation, or object "name" as specified by the IAU recommendations on source nomenclature. It is derived from the J2000 sexigesimal coordinates of the source and has the form HHMMSSS+/-DDMMSS, where HH are the hours of right ascension, MM the RA minutes and SSS are the deci-seconds of RA. DD are the degrees in declination, MM are DEC minutes and SS the declination seconds. Note that both the RA deci-seconds of time and DEC seconds of arc are truncated rather than rounded, per the IAU recommendation.
7 j_m  J selected "default" magnitude or 95% confidence upper limit mag 54-59 6.3f y
  Notes for j_m: This is the selected "default" magnitude for each band. For most srcs, the [jhk]_m values are the PSF fit mags for each band (rd_flg=2). If the source has a null PSF-fit magnitude but a valid std. aperture magnitude in a band, the [jhk]_m value for that band is the std. aperture magnitude (rd_flg=4). If the source is saturated in R2-R1 in a band, but not saturated in the R1 exposure, the default magnitude is the R1 aperture magnitude (rd_flg=1). If the source is saturated in even the R1 exposure (rd_flg=3) or if the source is a bright star placeholder (rd_flg=8), the default magnitude is given as -99.99. Finally, if a src is band-filled in a band, the value of [jhk]_m for that band is the band-fill 95%-confidence upper limit mag (rd_flg=0). This value is computed as follows:
    Lim95 = integrated flux + (2 * noise) 
where the noise in this case means the "local noise", computed as follows (using the DAOPHOT algorithm): 
    noise = sqrt(error1 + error2 + error3) 
where 
    error1 = variance in the local sky 
          = npix * skyvar 
    npix = number of pixels in the aperture 
    skyvar = the variance of the sky brightness 
    error2 = photon noise 
          = int. flux * Gain 
    error3 = (skyvar/nsky) * (npix ** 2) 
    nsky = number pixels in sky annulus 
    (skyvar/nsky) = square of the standard error of the mean sky brightness 
For the case in which the integrated flux is negative, the upper limit is 
    Lim95 = 2 * noise 
where 
    noise = sqrt(error1 + error3) 
8 j_msig  J "default" mag uncertainty mag 61-65 5.3f y
  Notes for j_msig: The mag sigma values corresponding to the selected "default" magnitude for each band are put in the [jhk]_msig fields. For non-detections (band-fills), the mag sigmas are null. An unphysically large magnitude sigma value (e.g. >0.36) indicates that the source was detected in that band, but either the brightness measurement encountered problems due to confusion or other contamination, or the detection is of very low confidence. Objects that are saturated in R1 in any band have magnitude sigmas of 9.999.
9 j_msigcom  J "total" mag uncertainty mag 67-71 5.3f y
  Notes for j_msigcom: The "combined" uncertainty in the quoted magnitude for each band that provides an estimate of all random errors that contribute to the photometric uncertainty. This uncertainty is the quadratic combination of the extraction uncertainites ([jhk]_msig), and the photometric zero point offset uncertainties from the night during which the source was observed ([jhk]_zperr from the "Scan Data" table), and the residual flat-fielding errors (estimated to be 0.005 mags for all bands). For R1 sources, the quadratic sum includes the RMS uncertainty in the normalization of the R1 photometry to the R2-R1 photometry ([jhk]_r1normrms from the "Scan Data" table).
10 h_m  H selected "default" magnitude or 95% confidence upper limit mag 73-78 6.3f y
  Notes for h_m: This is the selected "default" magnitude for each band. For most srcs, the [jhk]_m values are the PSF fit mags for each band (rd_flg=2). If the source has a null PSF-fit magnitude but a valid std. aperture magnitude in a band, the [jhk]_m value for that band is the std. aperture magnitude (rd_flg=4). If the source is saturated in R2-R1 in a band, but not saturated in the R1 exposure, the default magnitude is the R1 aperture magnitude (rd_flg=1). If the source is saturated in even the R1 exposure (rd_flg=3) or if the source is a bright star placeholder (rd_flg=8), the default magnitude is given as -99.99. Finally, if a src is band-filled in a band, the value of [jhk]_m for that band is the band-fill 95%-confidence upper limit mag (rd_flg=0). This value is computed as follows:
    Lim95 = integrated flux + (2 * noise) 
where the noise in this case means the "local noise", computed as follows (using the DAOPHOT algorithm): 
    noise = sqrt(error1 + error2 + error3) 
where 
    error1 = variance in the local sky 
          = npix * skyvar 
    npix = number of pixels in the aperture 
    skyvar = the variance of the sky brightness 
    error2 = photon noise 
          = int. flux * Gain 
    error3 = (skyvar/nsky) * (npix ** 2) 
    nsky = number pixels in sky annulus 
    (skyvar/nsky) = square of the standard error of the mean sky brightness 
For the case in which the integrated flux is negative, the upper limit is 
    Lim95 = 2 * noise 
where 
    noise = sqrt(error1 + error3) 
11 h_msig  H "default" mag uncertainty mag 80-84 5.3f y
  Notes for h_msig: The mag sigma values corresponding to the selected "default" magnitude for each band are put in the [jhk]_msig fields. For non-detections (band-fills), the mag sigmas are null. An unphysically large magnitude sigma value (e.g. >0.36) indicates that the source was detected in that band, but either the brightness measurement encountered problems due to confusion or other contamination, or the detection is of very low confidence. Objects that are saturated in R1 in any band have magnitude sigmas of 9.999.
12 h_msigcom  H "total" mag uncertainty mag 86-90 5.3f y
  Notes for h_msigcom: The "combined" uncertainty in the quoted magnitude for each band that provides an estimate of all random errors that contribute to the photometric uncertainty. This uncertainty is the quadratic combination of the extraction uncertainites ([jhk]_msig), and the photometric zero point offset uncertainties from the night during which the source was observed ([jhk]_zperr from the "Scan Data" table), and the residual flat-fielding errors (estimated to be 0.005 mags for all bands). For R1 sources, the quadratic sum includes the RMS uncertainty in the normalization of the R1 photometry to the R2-R1 photometry ([jhk]_r1normrms from the "Scan Data" table).
13 k_m  K selected "default" magnitude or 95% confidence upper limit mag 92-97 6.3f y
  Notes for k_m: This is the selected "default" magnitude for each band. For most srcs, the [jhk]_m values are the PSF fit mags for each band (rd_flg=2). If the source has a null PSF-fit magnitude but a valid std. aperture magnitude in a band, the [jhk]_m value for that band is the std. aperture magnitude (rd_flg=4). If the source is saturated in R2-R1 in a band, but not saturated in the R1 exposure, the default magnitude is the R1 aperture magnitude (rd_flg=1). If the source is saturated in even the R1 exposure (rd_flg=3) or if the source is a bright star placeholder (rd_flg=8), the default magnitude is given as -99.99. Finally, if a src is band-filled in a band, the value of [jhk]_m for that band is the band-fill 95%-confidence upper limit mag (rd_flg=0). This value is computed as follows:
    Lim95 = integrated flux + (2 * noise) 
where the noise in this case means the "local noise", computed as follows (using the DAOPHOT algorithm): 
    noise = sqrt(error1 + error2 + error3) 
where 
    error1 = variance in the local sky 
          = npix * skyvar 
    npix = number of pixels in the aperture 
    skyvar = the variance of the sky brightness 
    error2 = photon noise 
          = int. flux * Gain 
    error3 = (skyvar/nsky) * (npix ** 2) 
    nsky = number pixels in sky annulus 
    (skyvar/nsky) = square of the standard error of the mean sky brightness 
For the case in which the integrated flux is negative, the upper limit is 
    Lim95 = 2 * noise 
where 
    noise = sqrt(error1 + error3) 
14 k_msig  K "default" mag uncertainty mag 99-103 5.3f y
  Notes for k_msig: The mag sigma values corresponding to the selected "default" magnitude for each band are put in the [jhk]_msig fields. For non-detections (band-fills), the mag sigmas are null. An unphysically large magnitude sigma value (e.g. >0.36) indicates that the source was detected in that band, but either the brightness measurement encountered problems due to confusion or other contamination, or the detection is of very low confidence. Objects that are saturated in R1 in any band have magnitude sigmas of 9.999.
15 k_msigcom  K "total" mag uncertainty mag 105-109 5.3f y
  Notes for k_msigcom: The "combined" uncertainty in the quoted magnitude for each band that provides an estimate of all random errors that contribute to the photometric uncertainty. This uncertainty is the quadratic combination of the extraction uncertainites ([jhk]_msig), and the photometric zero point offset uncertainties from the night during which the source was observed ([jhk]_zperr from the "Scan Data" table), and the residual flat-fielding errors (estimated to be 0.005 mags for all bands). For R1 sources, the quadratic sum includes the RMS uncertainty in the normalization of the R1 photometry to the R2-R1 photometry ([jhk]_r1normrms from the "Scan Data" table).
16 rd_flg  source of JHK "default" mags (AKA "read flag") --- 111-113 3s y
  Notes for rd_flg: The read flag indicates the source of J,H,K "default" magnitudes as a 3-digit integer, where the 1st digit corresponds to the J band, the 2nd to the H band, and the 3rd to the Ks band. The values are as follows:
0: source is not detected in this band (is band-filled)
1: default mag is R1 aperture
2: default mag is R2-R1 profile-fit
3: default magnitude is -99.99. Source is saturated in R1.
4: default mag is R2-R1 standard aperture mag
8: default magnitude is -99.99. Source is "placeholder" for a very bright star heavily saturated in R1. Position information derived from Positions and Proper Motions Star Catalogue (Roser and Bastian, 1991).
17 bl_flg  indicates # JHK components fit to source (each digit=0|1|2) --- 115-118 4s y
  Notes for bl_flg: The "blend" flag indicates how many point source components were fit to each band's source during the profile fitting process. It is a 3-digit integer, where each digit can be 0, 1, or 2, and the 1st digit corresponds to the J band, the 2nd to the H band, and the 3rd to the Ks band.
18 cc_flg  indicates artifact contamination and/or confusion --- 120-123 4s y
  Notes for cc_flg: The contamination/confusion flag indicates whether the source's photometry and position may be affected by artifacts of nearby bright stars or by confusion with other nearby sources. The flag consists of a 3 character string, where the 1st character corresponds to the J band, the 2nd to the H band, and the 3rd to the Ks band. Sources are tested for contamination and/or confusion in the order given below, and once a flag is applied to the source, testing is stopped in that band. The flag values indicate the source may be:
U: unreliable source. Most likely a spurious detection of a meteor trail or a noise excursion.
N: photometric normalization problem due to the influence of a very bright star in the scan. Photometry in this band may be as much as 1 magnitude offset from the correct value.
P: affected by a nearby persistence artifact
D: affected by a nearby diffraction spike
S: affected by a horizontal "stripe" artifact (due to a bright star) at delta_y = 0, 256, -256 arcsec
R: affected by a nearby bright star reflection artifact
C: affected by confusion with another nearby source
B: affected by confusion in bandmerging
0: default value -- not contaminated or not detected in the band
19 extd_flg  indicates src associated with or contaminated by an ext. src --- 125-128 4hd y
  Notes for extd_flg: The "extended" flag is set to 0 if the point source is not associated with an extended source, 1 if it is identically associated with an object in the extended source catalog (e.g. the nucleus of a galaxy), or 2 if it is simply contaminated by an extended source (e.g. a star superimposed on the disk of a galaxy).
20 mp_flg  source is positionally associated with an asteroid or comet --- 130-130 1hd n
  Notes for mp_flg: This object is positionally associated with the location of a known minor planet or comet at the time of the 2MASS observation. See the table of known asteroid and comet detections for this data release for more information.
21 id_opt  associated optical source catalog ID (closest match) --- 132-135 4s y
  Notes for id_opt: The catalog ID and other association parameters are given for the closest optical match found within 5 arcsec. The ID consists of a single-letter abbreviation for the catalog (e.g., 'T' for Tycho, 'U' for USNO-A).
22 b_m_opt  catalog blue mag of associated optical source mag 137-141 5.2f y
23 r_m_opt  catalog red mag of associated optical source mag 143-147 5.2f y
24 dist_opt  distance in arcsec relative to associated optical source arcsec 149-153 5.2f y
25 phi_opt  position angle relative to optical source (E of N) deg 155-158 4hd y
26 nopt_mchs  number of optical sources within 5 arcsec of 2MASS src --- 160-163 4hd y
27 date  observation date --- 165-170 6s y
28 hemis  hemisphere (N/S) of observation --- 175-175 1s y
29 scan  scan number (unique within date) --- 177-180 4hd y
30 id  source ID number (unique within scan) --- 182-187 6d y
31 glon  galactic longitude (decimal deg) deg 189-198 10.6f n
32 glat  galactic latitude (decimal deg) deg 200-209 10.6f n
33 j_psfchi  J band reduced chi-squared value of fit --- 211-216 6.2f y
34 h_psfchi  H band reduced chi-squared value of fit --- 218-223 6.2f y
35 k_psfchi  K band reduced chi-squared value of fit --- 225-230 6.2f y
36 j_m_stdap  J standard aperture magnitude or BF aperture-photometry mag mag 232-237 6.3f y
  Notes for j_m_stdap: If a src is not detected in a band (band-filled), this field in that band contains the band-filled aperture-photometry mag. It is calculated by measuring the brightness within an 8" diameter aperture at the position of the source on the Atlas Image. 
    BFMag = ZERO_CAL - 2.5 log10(flux) 
where ZERO_CAL is the zero calibration magnitude. Note that this field may have to represent a negative flux; in such a case, the value is 
    BFMag = 99.0 - [ZERO_CAL - 2.5 log10(|flux|)] 
This encoding requires fluxes close to zero to be clipped. The clipping distance is set to 0.01 DN above zero for positive fluxes and below zero for negative fluxes. For example, the positive flux 0.0005 DN would be clipped at 0.01 DN and encoded as 
    BFMag = ZERO_CAL - 2.5 log10(0.01) 
         = 24.93 (for ZERO_CAL = 19.93) 
For a negative flux of -0.0005 DN, the clipping would yield -0.01 DN, and the encoding would be 
    BFMag = 99.0 - [ZERO_CAL - 2.5 log10(0.01)] 
         = 74.07 (for ZERO_CAL = 19.93) 
BFMags near 50 cannot occur, so 50 marks the boundary between positive and negative flux encoding.
37 j_msig_stdap  J standard ap. mag/BF ap.-photometry mag uncertainty mag 239-243 5.3f y
38 h_m_stdap  H standard aperture magnitude or BF aperture-photometry mag mag 245-250 6.3f y
  Notes for h_m_stdap: If a src is not detected in a band (band-filled), this field in that band contains the band-filled aperture-photometry mag. It is calculated by measuring the brightness within an 8" diameter aperture at the position of the source on the Atlas Image. 
    BFMag = ZERO_CAL - 2.5 log10(flux) 
where ZERO_CAL is the zero calibration magnitude. Note that this field may have to represent a negative flux; in such a case, the value is 
    BFMag = 99.0 - [ZERO_CAL - 2.5 log10(|flux|)] 
This encoding requires fluxes close to zero to be clipped. The clipping distance is set to 0.01 DN above zero for positive fluxes and below zero for negative fluxes. For example, the positive flux 0.0005 DN would be clipped at 0.01 DN and encoded as 
    BFMag = ZERO_CAL - 2.5 log10(0.01) 
         = 24.93 (for ZERO_CAL = 19.93) 
For a negative flux of -0.0005 DN, the clipping would yield -0.01 DN, and the encoding would be 
    BFMag = 99.0 - [ZERO_CAL - 2.5 log10(0.01)] 
         = 74.07 (for ZERO_CAL = 19.93) 
BFMags near 50 cannot occur, so 50 marks the boundary between positive and negative flux encoding.
39 h_msig_stdap  H standard ap. mag/BF ap.-photometry mag uncertainty mag 252-256 5.3f y
40 k_m_stdap  K standard aperture magnitude or BF aperture-photometry mag mag 258-263 6.3f y
  Notes for k_m_stdap: If a src is not detected in a band (band-filled), this field in that band contains the band-filled aperture-photometry mag. It is calculated by measuring the brightness within an 8" diameter aperture at the position of the source on the Atlas Image. 
    BFMag = ZERO_CAL - 2.5 log10(flux) 
where ZERO_CAL is the zero calibration magnitude. Note that this field may have to represent a negative flux; in such a case, the value is 
    BFMag = 99.0 - [ZERO_CAL - 2.5 log10(|flux|)] 
This encoding requires fluxes close to zero to be clipped. The clipping distance is set to 0.01 DN above zero for positive fluxes and below zero for negative fluxes. For example, the positive flux 0.0005 DN would be clipped at 0.01 DN and encoded as 
    BFMag = ZERO_CAL - 2.5 log10(0.01) 
         = 24.93 (for ZERO_CAL = 19.93) 
For a negative flux of -0.0005 DN, the clipping would yield -0.01 DN, and the encoding would be 
    BFMag = 99.0 - [ZERO_CAL - 2.5 log10(0.01)] 
         = 74.07 (for ZERO_CAL = 19.93) 
BFMags near 50 cannot occur, so 50 marks the boundary between positive and negative flux encoding.
41 k_msig_stdap  K standard ap. mag/BF ap.-photometry mag uncertainty mag 265-269 5.3f y
42 ndet_flg  number of >3-sig. ap. mag measurements, # possible (jjhhkk) --- 271-276 6s y
  Notes for ndet_flg: This flag consists of 6 single-digit numbers, two digits per band in the order JJHHKK. The 1st digit for each band indicates the number of frames with >3-sigma aperture mag measurements, and the 2nd digit indicates the number of frames in which aperture measurements were possible. (This flag is AKA the N-out-of-M statistic).
43 j_h  default J-H mag color mag 278-284 7.3f y
  Notes for j_h: For bands with source detections and non-negative fluxes, the [jhk]_m default mag values are used to calculate the mag colors J-H,...R-K,...etc. If one or both of the bands used in the calculation is not-detected, no color is calculated.
44 h_k  default H-K mag color mag 286-292 7.3f y
  Notes for h_k: For bands with source detections and non-negative fluxes, the [jhk]_m default mag values are used to calculate the mag colors J-H,...R-K,...etc. If one or both of the bands used in the calculation is not-detected, no color is calculated.
45 j_k  default J-K mag color mag 294-300 7.3f y
  Notes for j_k: For bands with source detections and non-negative fluxes, the [jhk]_m default mag values are used to calculate the mag colors J-H,...R-K,...etc. If one or both of the bands used in the calculation is not-detected, no color is calculated.
aThese are C format statements, which do not include blanks that separate fields and which are set to the maximum possible number of characters in each string. Fields that have values much less than the maximum possible number may have additional leading blanks. For example, 10° < ra < 100° will have a format 9.6f. A caveat is that fields that are allowed to contain "null," as indicated in the final column of this table, must be read in as strings, checked for null, and then converted to the appropriate type.