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) |
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| 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) |
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| 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) |
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| 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). |
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| 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 |
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| 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. |
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| 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. |
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| 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. |
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| 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. | ||||||