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II/241           2MASS Catalog Incremental Data Release   (IPAC/UMass, 2000)

The Two Micron All Sky Survey, 2nd Incremental Data Release Skrutskie M.F., Schneider S.E., Stiening R., Strom S.E., Weinberg M.D., Beichman C., Chester T., Cutri R., Lonsdale C., Elias J., Elston R., Capps R., Carpenter J., Huchra J., Liebert J., Monet D., Price S., Seitzer P. <Proc. Workshop "The Impact of Large Scale Near-IR Sky Surveys", 25 (1997)>
ADC_Keywords: Infrared sources ; Photometry, infrared ; Surveys Description: The Two Micron All Sky Survey (2MASS) project is designed to close the gap between our current technical capability and our knowledge of the near-infrared sky. In addition to providing a context for the interpretation of results obtained at infrared and other wavelengths, 2MASS will provide direct answers to immediate questions on the large-scale structure of the Milky Way and the Local Universe. To achieve these goals, 2MASS is uniformly scanning the entire sky in three near-infrared bands to detect and characterize point sources brighter than about 1 mJy in each band, with signal-to-noise ratio (SNR) greater than 10, using a pixel size of 2.0". This will achieve an 80,000-fold improvement in sensitivity relative to earlier surveys. 2MASS uses two new, highly-automated 1.3-m telescopes, one at Mt. Hopkins, AZ, and one at CTIO, Chile. Each telescope is equipped with a three-channel camera, each channel consisting of a 256x256 array of HgCdTe detectors, capable of observing the sky simultaneously at J (1.25 µm), H (1.65 µm), and Ks (2.17 µm), to a 3σ limiting sensivity of 17.1, 16.4 and 1.3mag in thge three bands. The 2MASS arrays image the sky while the telescopes scan smoothly in declination at a rate of ∼1' per second. The 2MASS data "tiles" are 6° long in the declination direction and one camera frame (8.5') wide. The camera field-of-view shifts by ∼1/6 of a frame in declination from frame-to-frame. The camera images each point on the sky six times for a total integration time of 7.8 s, with sub-pixel "dithering", which improves the ultimate spatial resolution of the final Atlas Images. The University of Massachusetts (UMass) is responsible for the overall management of the project, and for developing the infrared cameras and on-site computing systems at both facilities. The Infrared Processing and Analysis Center (IPAC) is responsible for all data processing through the Production Pipeline, and construction and distribution of the data products. The 2MASS project involves the participation of members of the Science Team from several different institutions. The 2MASS project is funding by the National Aeronautics and Space Administration (NASA) and the National Science Foundation (NSF). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file out.sam 292 1000 2MASS Point Source Catalogue, sample output, incremental data release 2 (March 2000).
See also: http://www.ipac.caltech.edu/2mass/ : 2MASS documentation Nomenclature Notes: As specified by the IAU recommendations on source nomenclature, the object designation is derived from the J2000 sexagesimal 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. It was discovered that about 100,000 objects have non-unique source designations; a column f_Name was added to flag those objects which name appears more than once in the survey. Byte-by-byte Description of file: out.sam
Bytes Format Units Label Explanations
1- 10 F10.6 deg RAdeg Right ascension (J2000) 12- 21 F10.6 deg DEdeg Declination (J2000) 23- 26 F4.2 arcsec MajAxis ? Major axis of position error ellipse 28- 31 F4.2 arcsec MinAxis ? Minor axis of position error ellipse 34- 36 I3 deg Theta [0,180]? Position angle of error ellipse major axis (E of N) 38 A1 --- f_Name [* ] A '*' flags a non-unique source designation 39- 52 A14 --- Name Source designation -------------------------------------------------------------------------------- 54- 60 F7.3 mag Jmag ?=-99.999 J selected "default" magnitude (1) 62- 66 F5.3 mag eJmagd ? J "default" magnitude uncertainty (2) 68- 72 F5.3 mag e_Jmag ? J "total" magnitude uncertainty (3) 74- 80 F7.3 mag Hmag ?=-99.999 H selected "default" magnitude (1) 82- 86 F5.3 mag eHmagd ? H "default" magnitude uncertainty (2) 88- 92 F5.3 mag e_Hmag ? H "total" magnitude uncertainty (3) 94-100 F7.3 mag Kmag ?=-99.999 K selected "default" magnitude (1) 102-106 F5.3 mag eKmagd ? Ks "default" magnitude uncertainty (2) 108-112 F5.3 mag e_Kmag ? Ks "total" magnitude uncertainty (3) -------------------------------------------------------------------------------- 114-116 A3 --- rd_flg [012348] Source of JHK "default" mag (4) 119-121 A3 --- bl_flg [012] JHK components fit to source (5) 124-126 A3 --- cc_flg [UNPCDSRGB0] Artifact contamin./confusion (6) 131 I1 --- extd_flg [0,2]? Extended source contamination (7) 133 I1 --- mp_flg [0,1]? Association with asteroid or comet (8) -------------------------------------------------------------------------------- 138 A1 --- Id_opt [UT] Associated optical source (9) 140-144 F5.2 mag Bmag ? Blue mag of associated optical source 146-150 F5.2 mag Rmag ? Red mag of associated optical source 153-156 F4.2 arcsec Dist_opt ? Distance to associated optical source 159-161 I3 deg PAopt [0,360]? position angle to optical source 165-166 I2 --- Nopt_mchs ? Number of optical sources within 5 arcsec -------------------------------------------------------------------------------- 169-178 A10 --- Date Observation date (MM/DD/YYYY) 183 A1 --- Hemis [ns] Hemisphere of observation 186-188 I3 --- Scan ? Scan number (within date) 190-195 I6 --- Id Source id number (within scan) 197-206 F10.6 deg GLON Galactic longitude 208-217 F10.6 deg GLAT Galactic latitude 219-224 F6.2 --- Jpsfchi ? J band reduced chi2 value of fit 226-231 F6.2 --- Hpsfchi ? H band reduced chi2 value of fit 233-238 F6.2 --- Kpsfchi ? K band reduced chi2 value of fit -------------------------------------------------------------------------------- 240-246 F7.3 mag Jm_stdap ? J standard or BF aperture magnitude (10) 248-253 F6.3 mag eJmstdap ? error on Jmstdap 255-261 F7.3 mag Hm_stdap ? H standard or BF aperture magnitude (10) 263-268 F6.3 mag eHmstdap ? error on Hmstdap 270-276 F7.3 mag Km_stdap ? K standard or BF aperture magnitude (10) 278-283 F6.3 mag eKmstdap ? error on Kmstdap -------------------------------------------------------------------------------- 287-292 A6 --- Ndet_flg [0-9 ] Number of aperture measurements (jjhhkk) (11)
Note (1): This is the selected "default" magnitude for each band (centered at J: 1.25, H: 1.65 and Ks: 2.17µm). For most sources, 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 -99.999. Finally, if a source 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) Note (2): 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. Note (3): 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). Note (4): 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 -99.999. Source is saturated in R1. 4: default mag is R2-R1 standard aperture mag 8: default magnitude is -99.999. 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, See Catalogues I/146, I/193, I/208). Note (5): 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: source not detected in band, 1: single profile fit to isolated source, or 2: multiple sources detected abd fit simultaneously The 1st digit corresponds to the J band, the 2nd to the H band, and the 3rd to the Ks band. Note (6): 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) 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 Note (7): 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). Note (8): 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 more information. Note (9): 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: 'T' for Tycho-ACT (see Cat. I/246) 'U' for USNO-A (see Cat. I/252>) Note (10): If a source 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. Note (11): 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).
Important Notice: Please include the following in any published material that makes use of the 2MASS data products: "This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by the National Aeronautics and Space Administration and the National Science Foundation." History: History: * 07-Sep-2000: first version of 2nd Incremental Data Release * 19-Mar-2001: added f_Name column which flags non-unique source names.
(End) Sebastien Derriere, Francois Ochsenbein [CDS] 07-Sep-2000
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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