II. User's Guide to the 2MASS All-Sky Data Release

6. Ancillary Files

a. Scan Information Table Format

The following table contains brief descriptions of the parameters in the Scan Information Table, which provides basic data for each scan in the 2MASS All Sky Release. The table is organized according to the broad function and utility of the parameters: positional information, photometric information, source detection statistics, etc.

The columns in the following table are:

Column Name: The parameter name in the Scan Information Table. Click on this to go to the section of the Explanatory Supplement where the derivation and/or usage of that parameter is described in detail.

Format: The "C" format of the field in the Scan Information Table. Note that some fields contain null values that will require special handling when parsing the table drawn from either the IRSA/GATOR output or the ascii DVD or ftp versions.

Units: The units of the parameter. A value of "---" in this column means that the parameter is dimensionless.

nulls: A "yes" in this column means that this parameter can be null in the Scan Information Table. A "no" means that there will always be a value in this column in the Scan Information Table. Note that null values are represented differently in the IRSA/GATOR output and the ascii DVD or ftp versions.

Description: A brief description of the parameter and its values.

TABLE 1: Description of Fields in the Scan Information Table

Column Name Format Units nulls Description

Primary Information

scan_key/cntr %5d --- no The unique identification number for this scan. This column is called scan_key in the DVD and ftp versions of the Scan Information Table and cntr in the IRSA/GATOR version.

hemis %1s --- no Observatory from which data were obtained:

"n" = north = Mt. Hopkins

"s" = south = Cerro Tololo.

date %10s yyyy-mm-dd no The observation reference date for this scan expressed in ISO standard format. This is the UT date at sunrise for the night on which the scan was observed. Because it is possible for the UT date to change during a night of observations, the actual UT date for a source can differ from date by one day. Use the Julian Date (jdate) for a more accurate determination of the observation time of the scan.

scan %3d --- no Scan number (unique within date).

tile %6d --- no Tile identification number.

Positional Information

ra %10.6f deg no Right ascension of scan center for equinox J2000; this is computed from the interior corners ra_[1,2,3,4] and dec_[1,2,3,4] (see below).

dec/decl %10.6f deg no Declination of scan center for equinox J2000; this is computed from the interior corners ra_[1,2,3,4] and dec_[1,2,3,4] (see below). This column is called decl on the DVD versions of the Scan Information Table and dec in the IRSA/GATOR version.

glon %7.3f deg no Galactic longitude of scan center, as computed from ra and dec above. Galactic coordinates are derived by precessing reconstructed ra and dec to B1950, and performing rotational transformation into the l_II, b_II coordinate system.

glat %7.3f deg no Galactic latitude of scan center, as computed from ra and dec above. Galactic coordinates are derived by precessing reconstructed ra and dec to B1950, and performing rotational transformation into the l_II, b_II coordinate system.

ra_1 %10.6f deg no J2000 right ascension of the eastern corner at start of scan. This is the corner fully covered by all three bands.

dec_1 %10.6f deg no J2000 declination of the eastern corner at start of scan. This is the corner fully covered by all three bands.

ra_2 %10.6f deg no J2000 right ascension of the western corner at start of scan. This is the corner fully covered by all three bands.

dec_2 %10.6f deg no J2000 declination of the western corner at start of scan. This is the corner fully covered by all three bands.

ra_3 %10.6f deg no J2000 right ascension of the eastern corner at end of scan. This is the corner fully covered by all three bands.

dec_3 %10.6f deg no J2000 declination of the eastern corner at end of scan. This is the corner fully covered by all three bands.

ra_4 %10.6f deg no J2000 right ascension of the western corner at end of scan. This is the corner fully covered by all three bands.

dec_4 %10.6f deg no J2000 declination of the western corner at end of scan. This is the corner fully covered by all three bands.

General Information

sd %1s --- no Scanning direction:

"n" = north-going

"s" = south-going.

qual %2d --- no Quality score for scan:

"10" is highest grade

"0" is lowest.

hgl %1d --- no Special flag indicating whether or not this scan has a single-frame H-band or J-band electronic glitch:

"0" indicates no glitch

"1" indicates glitch.

cld %1d --- no Special flag indicating whether or not a cloud was found in the scan after comparison of its photometry to that of overlapping scans in the database:

"0" indicates no evidence for clouds

"1" indicates clouds.

xph %1d --- no Special flag indicating whether or not another photometric problem, not obviously cloud related, was found in the scan after comparing its photometry to that of overlapping scans:

"0" indicates no problem

"1" indicates compromised photometry.

anom %1d --- no Special flag indicating whether or not an unusual problem was found in the Atlas Images for this scan. Such problem include, but are not limited to, residual meteor trails, satellite trails, insect trails, and unusual reflections or glints from bright stars:

"0" indicates no such problem

"1" indicates an anomaly.

Time of Observation

ut %9.6f hr no Universal Time (UT) at beginning of scan.

jdate %12.4f day no Julian Date at beginning of scan.

Telescope and Instrument Fields

airm %4.2f --- no Airmass at beginning of scan.

zd %4.1f deg no Scan's distance from the zenith at beginning of scan.

ha %9.6f hr no Hour angle at beginning of scan.

rh %2d % no Relative humidity of telescope enclosure at beginning of scan.

air_temp %4.1f deg C no Air temperature at beginning of scan.

tel_temp %4.1f deg C no Telescope girdle temperature at beginning of scan. This temperature was used to adjust telescope focus to compensate for variations with temperature.

focus %5d --- no Focus setting of telescope at beginning of scan. This is a measure of the position of the focus mechanism, in units of 1.25 microns, relative to a reference position. This reference position changed each time the telescope was collimated.

hry %1d --- no Flag indicating the H-band array configuration for the camera:

"0" indicates the original configuration

"1" indicates the new (modified) configuration.

For the southern camera, the array configuration was never changed, so this flag is always "0". For the northern camera a new H-band array, first used on 13 Sep 1999 (UT), was installed in mid-survey. Before this date the flag is "0" and on or after this date it is "1".

c_strat %1d --- no Flag indicating the calibration strategy for this night's data:

"0" indicates original strategy in which two calibration fields were observed after every two-hour segment of regular survey scans

"1" indicates new strategy in which one calibration field was observed after every hour's segment of regular survey scans.

For data taken from the southern hemisphere, this flag is always "1". For data taken from the northern hemisphere this flag is set to "0" on dates before 11 Oct 1997 (UT), and to "1" for dates of 11 Oct 1997 (UT) or thereafter.

Photometric Information

j_zp_ap %7.4f mag no Photometric zero-point for J-band aperture photometry.

h_zp_ap %7.4f mag no Photometric zero-point for H-band aperture photometry.

k_zp_ap %7.4f mag no Photometric zero-point for K_s-band aperture photometry.

h_zperr_ap %6.4f mag no RMS-error of zero-point for H-band aperture photometry

k_zperr_ap %6.4f mag no RMS-error of zero-point for K_s-band aperture photometry

Source Detection Statistics

j_n_snr10 %6d --- no Number of point sources at J-band with SNR>10 (instrumental mag <=15.8)

h_n_snr10 %6d --- no Number of point sources at H-band with SNR>10 (instrumental mag <=15.1)

k_n_snr10 %6d --- no Number of point sources at K_s-band with SNR>10 (instrumental mag <=14.3)

n_ext %3d --- no Number of regular extended sources detected in scan.

Seeing Statistics

j_shape_avg %5.3f --- no J-band average seeing shape for scan. The seeing full-width at half maximum (in arcseconds) can be obtained from the approximate relation FWHM(arcseconds) = 3.13*(j_shape_avg) - 0.46.

h_shape_avg %5.3f --- no H-band average seeing shape for scan. The seeing full-width at half maximum (in arcseconds) can be obtained from the approximate relation FWHM(arcseconds) = 3.13*(h_shape_avg) - 0.46.

k_shape_avg %5.3f --- no K_s-band average seeing shape for scan. The seeing full-width at half maximum (in arcseconds) can be obtained from the approximate relation FWHM(arcseconds) = 3.13*(k_shape_avg) - 0.46.

j_shape_rms %5.3f --- no RMS-error of J-band average seeing shape.

h_shape_rms %5.3f --- no RMS-error of H-band average seeing shape.

k_shape_rms %5.3f --- no RMS-error of K_s-band average seeing shape.

j_2mrat %5.3f --- no J-band average 2nd image moment ratio.

h_2mrat %5.3f --- no H-band average 2nd image moment ratio.

k_2mrat %5.3f --- no K_s-band average 2nd image moment ratio.

Sensitivity Statistics

j_psp %6.3f --- no J-band photometric sensitivity paramater (PSP).

h_psp %6.3f --- no H-band photometric sensitivity parameter (PSP).

k_psp %6.3f --- no K_s-band photometric sensitivity parameter (PSP).

j_pts_noise %7.3f --- no The base-10 logarithm of the characteristic J-band point source scan noise, in units of log(mJy). This is the mode of the distribution of the noise-equivalent flux densities for all J-band R2-R1 detections in the scan. The noise-equivalent flux density for each detection is given by 1603x10³(mJy)*1.0857/sigma_m, where sigma_m is the photometric uncertainty, in magnitudes, before correction. 1603x10³ mJy was a preliminary estimate of the J-band flux-for-zero-magnitude, and it differs slightly from the final estimate of 1592x10³ mJy that is described in VI.4.a. To adjust the given value of j_pts_noise for the final calibration, subtract 0.0030.

h_pts_noise %7.3f --- no The base-10 logarithm of the characteristic H-band point source scan noise, in units of log(mJy). This is the mode of the distribution of the noise-equivalent flux densities for all H-band R2-R1 detections in the scan. The noise-equivalent flux density for each detection is given by 1075x10³(mJy)*1.0857/sigma_m, where sigma_m is the photometric uncertainty, in magnitudes, before correction. 1075x10³ mJy was a preliminary estimate of the H-band flux-for-zero-magnitude, and it differs slightly from the final estimate of 1024x10³ mJy that is described in VI.4.a. To adjust the given value of h_pts_noise for the final calibration, subtract 0.0211.

k_pts_noise %7.3f --- no The base-10 logarithm of the characteristic Ks-band point source scan noise, in units of log(mJy). This is the mode of the distribution of the noise-equivalent flux densities for all Ks-band R2-R1 detections in the scan. The noise-equivalent flux density for each detection is given by 698.1x10³(mJy)*1.0857/sigma_m, where sigma_m is the photometric uncertainty, in magnitudes, before correction. 698.1x10³ mJy was a preliminary estimate of the Ks-band flux-for-zero-magnitude, and it differs slightly from the final estimate of 666.8x10³ mJy that is described in VI.4.a. To adjust the given value of k_pts_noise for the final calibration, subtract 0.0199.

j_msnr10 %5.2f --- no The J-band magnitude at which SNR=10 is achieved for this scan, estimated using the photometric sensitivity parameter j_psp and zero point offset j_zp_ap. This estimate does not take into account the effect of confusion noise in high source density regions.

h_msnr10 %5.2f --- no The H-band magnitude at which SNR=10 is achieved for this scan, estimated using the photometric sensitivity parameter h_psp and zero point offset h_zp_ap. This estimate does not take into account the effect of confusion noise in high source density regions.

k_msnr10 %5.2f --- no The K_s-band magnitude at which SNR=10 is achieved for this scan, estimated using the photometric sensitivity parameter k_psp and zero point offset k_zp_ap. This estimate does not take into account the effect of confusion noise in high source density regions.

Information on Previous Releases

rel0 %1d --- no Flag indicating whether the scan is contained in the 2MASS Sampler Release.

"0" indicates non-inclusion in Sampler Release

"1" indicates inclusion in Sampler Release.

rel1 %1d --- no Flag indicating whether the scan is contained in the 2MASS First Incremental Data Release (IDR1).

"0" indicates non-inclusion in IDR1

"1" indicates inclusion in IDR1.

rel2 %1d --- no Flag indicating whether the scan is contained in the 2MASS Second Incremental Data Release (IDR2).

"0" indicates non-inclusion in IDR2

"1" indicates inclusion in IDR2.

TABLE 1: Description of Fields in the Scan Information Table
Column Name	Format	Units	nulls	Description
Primary Information
scan_key/cntr	%5d	---	no	The unique identification number for this scan. This column is called scan_key in the DVD and ftp versions of the Scan Information Table and cntr in the IRSA/GATOR version.
hemis	%1s	---	no	Observatory from which data were obtained: "n" = north = Mt. Hopkins "s" = south = Cerro Tololo.
date	%10s	yyyy-mm-dd	no	The observation reference date for this scan expressed in ISO standard format. This is the UT date at sunrise for the night on which the scan was observed. Because it is possible for the UT date to change during a night of observations, the actual UT date for a source can differ from date by one day. Use the Julian Date (jdate) for a more accurate determination of the observation time of the scan.
scan	%3d	---	no	Scan number (unique within date).
tile	%6d	---	no	Tile identification number.
Positional Information
ra	%10.6f	deg	no	Right ascension of scan center for equinox J2000; this is computed from the interior corners ra_[1,2,3,4] and dec_[1,2,3,4] (see below).
dec/decl	%10.6f	deg	no	Declination of scan center for equinox J2000; this is computed from the interior corners ra_[1,2,3,4] and dec_[1,2,3,4] (see below). This column is called decl on the DVD versions of the Scan Information Table and dec in the IRSA/GATOR version.
glon	%7.3f	deg	no	Galactic longitude of scan center, as computed from ra and dec above. Galactic coordinates are derived by precessing reconstructed ra and dec to B1950, and performing rotational transformation into the l_II, b_II coordinate system.
glat	%7.3f	deg	no	Galactic latitude of scan center, as computed from ra and dec above. Galactic coordinates are derived by precessing reconstructed ra and dec to B1950, and performing rotational transformation into the l_II, b_II coordinate system.
ra_1	%10.6f	deg	no	J2000 right ascension of the eastern corner at start of scan. This is the corner fully covered by all three bands.
dec_1	%10.6f	deg	no	J2000 declination of the eastern corner at start of scan. This is the corner fully covered by all three bands.
ra_2	%10.6f	deg	no	J2000 right ascension of the western corner at start of scan. This is the corner fully covered by all three bands.
dec_2	%10.6f	deg	no	J2000 declination of the western corner at start of scan. This is the corner fully covered by all three bands.
ra_3	%10.6f	deg	no	J2000 right ascension of the eastern corner at end of scan. This is the corner fully covered by all three bands.
dec_3	%10.6f	deg	no	J2000 declination of the eastern corner at end of scan. This is the corner fully covered by all three bands.
ra_4	%10.6f	deg	no	J2000 right ascension of the western corner at end of scan. This is the corner fully covered by all three bands.
dec_4	%10.6f	deg	no	J2000 declination of the western corner at end of scan. This is the corner fully covered by all three bands.
General Information
sd	%1s	---	no	Scanning direction: "n" = north-going "s" = south-going.
qual	%2d	---	no	Quality score for scan: "10" is highest grade "0" is lowest.
hgl	%1d	---	no	Special flag indicating whether or not this scan has a single-frame H-band or J-band electronic glitch: "0" indicates no glitch "1" indicates glitch.
cld	%1d	---	no	Special flag indicating whether or not a cloud was found in the scan after comparison of its photometry to that of overlapping scans in the database: "0" indicates no evidence for clouds "1" indicates clouds.
xph	%1d	---	no	Special flag indicating whether or not another photometric problem, not obviously cloud related, was found in the scan after comparing its photometry to that of overlapping scans: "0" indicates no problem "1" indicates compromised photometry.
anom	%1d	---	no	Special flag indicating whether or not an unusual problem was found in the Atlas Images for this scan. Such problem include, but are not limited to, residual meteor trails, satellite trails, insect trails, and unusual reflections or glints from bright stars: "0" indicates no such problem "1" indicates an anomaly.
Time of Observation
ut	%9.6f	hr	no	Universal Time (UT) at beginning of scan.
jdate	%12.4f	day	no	Julian Date at beginning of scan.
Telescope and Instrument Fields
airm	%4.2f	---	no	Airmass at beginning of scan.
zd	%4.1f	deg	no	Scan's distance from the zenith at beginning of scan.
ha	%9.6f	hr	no	Hour angle at beginning of scan.
rh	%2d	%	no	Relative humidity of telescope enclosure at beginning of scan.
air_temp	%4.1f	deg C	no	Air temperature at beginning of scan.
tel_temp	%4.1f	deg C	no	Telescope girdle temperature at beginning of scan. This temperature was used to adjust telescope focus to compensate for variations with temperature.
focus	%5d	---	no	Focus setting of telescope at beginning of scan. This is a measure of the position of the focus mechanism, in units of 1.25 microns, relative to a reference position. This reference position changed each time the telescope was collimated.
hry	%1d	---	no	Flag indicating the H-band array configuration for the camera: "0" indicates the original configuration "1" indicates the new (modified) configuration. For the southern camera, the array configuration was never changed, so this flag is always "0". For the northern camera a new H-band array, first used on 13 Sep 1999 (UT), was installed in mid-survey. Before this date the flag is "0" and on or after this date it is "1".
c_strat	%1d	---	no	Flag indicating the calibration strategy for this night's data: "0" indicates original strategy in which two calibration fields were observed after every two-hour segment of regular survey scans "1" indicates new strategy in which one calibration field was observed after every hour's segment of regular survey scans. For data taken from the southern hemisphere, this flag is always "1". For data taken from the northern hemisphere this flag is set to "0" on dates before 11 Oct 1997 (UT), and to "1" for dates of 11 Oct 1997 (UT) or thereafter.
Photometric Information
j_zp_ap	%7.4f	mag	no	Photometric zero-point for J-band aperture photometry.
h_zp_ap	%7.4f	mag	no	Photometric zero-point for H-band aperture photometry.
k_zp_ap	%7.4f	mag	no	Photometric zero-point for K_s-band aperture photometry.
h_zperr_ap	%6.4f	mag	no	RMS-error of zero-point for H-band aperture photometry
k_zperr_ap	%6.4f	mag	no	RMS-error of zero-point for K_s-band aperture photometry
Source Detection Statistics
j_n_snr10	%6d	---	no	Number of point sources at J-band with SNR>10 (instrumental mag <=15.8)
h_n_snr10	%6d	---	no	Number of point sources at H-band with SNR>10 (instrumental mag <=15.1)
k_n_snr10	%6d	---	no	Number of point sources at K_s-band with SNR>10 (instrumental mag <=14.3)
n_ext	%3d	---	no	Number of regular extended sources detected in scan.
Seeing Statistics
j_shape_avg	%5.3f	---	no	J-band average seeing shape for scan. The seeing full-width at half maximum (in arcseconds) can be obtained from the approximate relation FWHM(arcseconds) = 3.13(j_shape_avg) - 0.46*.
h_shape_avg	%5.3f	---	no	H-band average seeing shape for scan. The seeing full-width at half maximum (in arcseconds) can be obtained from the approximate relation FWHM(arcseconds) = 3.13(h_shape_avg) - 0.46*.
k_shape_avg	%5.3f	---	no	K_s-band average seeing shape for scan. The seeing full-width at half maximum (in arcseconds) can be obtained from the approximate relation FWHM(arcseconds) = 3.13(k_shape_avg) - 0.46*.
j_shape_rms	%5.3f	---	no	RMS-error of J-band average seeing shape.
h_shape_rms	%5.3f	---	no	RMS-error of H-band average seeing shape.
k_shape_rms	%5.3f	---	no	RMS-error of K_s-band average seeing shape.
j_2mrat	%5.3f	---	no	J-band average 2nd image moment ratio.
h_2mrat	%5.3f	---	no	H-band average 2nd image moment ratio.
k_2mrat	%5.3f	---	no	K_s-band average 2nd image moment ratio.
Sensitivity Statistics
j_psp	%6.3f	---	no	J-band photometric sensitivity paramater (PSP).
h_psp	%6.3f	---	no	H-band photometric sensitivity parameter (PSP).
k_psp	%6.3f	---	no	K_s-band photometric sensitivity parameter (PSP).
j_pts_noise	%7.3f	---	no	The base-10 logarithm of the characteristic J-band point source scan noise, in units of log(mJy). This is the mode of the distribution of the noise-equivalent flux densities for all J-band R2-R1 detections in the scan. The noise-equivalent flux density for each detection is given by 1603x10³(mJy)1.0857/sigma_m, where sigma_m is the photometric uncertainty, in magnitudes, before correction. 1603x10³ mJy was a preliminary estimate of the J-band flux-for-zero-magnitude, and it differs slightly from the final estimate of 1592x10³ mJy that is described in VI.4.a. To adjust the given value of j_pts_noise* for the final calibration, subtract 0.0030.
h_pts_noise	%7.3f	---	no	The base-10 logarithm of the characteristic H-band point source scan noise, in units of log(mJy). This is the mode of the distribution of the noise-equivalent flux densities for all H-band R2-R1 detections in the scan. The noise-equivalent flux density for each detection is given by 1075x10³(mJy)1.0857/sigma_m, where sigma_m is the photometric uncertainty, in magnitudes, before correction. 1075x10³ mJy was a preliminary estimate of the H-band flux-for-zero-magnitude, and it differs slightly from the final estimate of 1024x10³ mJy that is described in VI.4.a. To adjust the given value of h_pts_noise* for the final calibration, subtract 0.0211.
k_pts_noise	%7.3f	---	no	The base-10 logarithm of the characteristic Ks-band point source scan noise, in units of log(mJy). This is the mode of the distribution of the noise-equivalent flux densities for all Ks-band R2-R1 detections in the scan. The noise-equivalent flux density for each detection is given by 698.1x10³(mJy)1.0857/sigma_m, where sigma_m is the photometric uncertainty, in magnitudes, before correction. 698.1x10³ mJy was a preliminary estimate of the Ks-band flux-for-zero-magnitude, and it differs slightly from the final estimate of 666.8x10³ mJy that is described in VI.4.a. To adjust the given value of k_pts_noise* for the final calibration, subtract 0.0199.
j_msnr10	%5.2f	---	no	The J-band magnitude at which SNR=10 is achieved for this scan, estimated using the photometric sensitivity parameter j_psp and zero point offset j_zp_ap. This estimate does not take into account the effect of confusion noise in high source density regions.
h_msnr10	%5.2f	---	no	The H-band magnitude at which SNR=10 is achieved for this scan, estimated using the photometric sensitivity parameter h_psp and zero point offset h_zp_ap. This estimate does not take into account the effect of confusion noise in high source density regions.
k_msnr10	%5.2f	---	no	The K_s-band magnitude at which SNR=10 is achieved for this scan, estimated using the photometric sensitivity parameter k_psp and zero point offset k_zp_ap. This estimate does not take into account the effect of confusion noise in high source density regions.
Information on Previous Releases
rel0	%1d	---	no	Flag indicating whether the scan is contained in the 2MASS Sampler Release. "0" indicates non-inclusion in Sampler Release "1" indicates inclusion in Sampler Release.
rel1	%1d	---	no	Flag indicating whether the scan is contained in the 2MASS First Incremental Data Release (IDR1). "0" indicates non-inclusion in IDR1 "1" indicates inclusion in IDR1.
rel2	%1d	---	no	Flag indicating whether the scan is contained in the 2MASS Second Incremental Data Release (IDR2). "0" indicates non-inclusion in IDR2 "1" indicates inclusion in IDR2.

[Last Updated: 2003 Apr 18; Davy Kirkpatrick, Roc Cutri, Tracey Evans]