2MASS Image Metadata Table Help

Both the 2MASS Image Inventory Service and the 2MASS Batch Image Service return meta-data tables for the 2MASS Images they find and retrieve. Meta-data tables are generated in three different formats :

HTML format

The HTML version of an image meta-data table is formatted for convenient on-line viewing of image meta-data. This table includes links so that users can view and download individual FITS images.

VO table file format

This XML image meta-data table is provided to support NVO applications, and conforms to the Simple Image Access standard. These tables contain detailed documentation which is not reproduced here.

IPAC ASCII table file format

The ASCII version of an image meta-data table can be used as an input to the 2MASS Batch Image Service.

This help page provides a guide to the contents of the ASCII and HTML 2MASS Image Meta-Data Tables. Each row in a meta-data table describes a different 2MASS FITS image.

2MASS Image Metadata Table Columns

download For the IPAC ASCII format, this column contains a URL allowing the described FITS image to be downloaded directly. The HTML format also contains a URL allowing the described image to be viewed using the Interactive 2MASS Image Service.
id An identifier for each FITS Image found or retrieved.
scntr This column will contain null values unless the meta-data table is the result of a query involving a list of constraints (positions, coadd_keys, or DHSs). When non-null, the value of this column is an integer identifier for the search constraint the FITS Image was found/retrieved for.
name The original file name of the FITS image or H-compressed FITS image.
type The type of the image, which is either 'Q' (for 2MASS Quicklook Images), or 'A' (for 2MASS Atlas Images).
dataset The data set the image was retrieved from. There are 5 possible values:
  • "asky" indicates the image is a 2MASS All-Sky Survey Image
  • "askyw" indicates the image is a 2MASS All-Sky Working Survey Image (these are a superset of the All-Sky Survey Images)
  • "6x" indicates the image is a 2MASS 6X Survey Image
  • "6xw" indicates the image is a 2MASS 6X Working Survey Image (these are a superset of the 6X Survey Images)
  • "cal" indicates the image is a 2MASS Calibration Survey Image
xdate The reference date of the FITS image, in yymmdd format (yy: last 2 digits of the observation year, mm: integer month, dd: integer day). This can differ by one day from the actual UT observation date.

Note: date is frequently a database manager reserved word, so the column name xdate is used instead.

hem The hemisphere of the 2MASS observatory where the FITS image was taken. There are only two possible values: 'n' = north (Mt. Hopkins), and 's' = south (Cerro Tololo).
scan The nightly scan number of the FITS image.
image The image number of the FITS image.
band The 2MASS band of the FITS image. There are only three possible values: 'J' = J band image, 'H' = H band image, and 'K' = Ks band image.
crval1 The equatorial J2000 right ascension (RA) of the FITS image reference location (in degrees).
crval2 The equatorial J2000 declination (Dec) of the FITS image reference location (in degrees).
crpix1 The x coordinate of the FITS image reference location (in pixels).
crpix2 The y coordinate of the FITS image reference location (in pixels).
nl The height of the image (in pixels).
ns The width of the image (in pixels).
ut_date UT Date when the FITS image was taken, in yymmdd format (yy: last 2 digits of the observation year, mm: integer month, dd: integer day).
coadd_key The coadd_key value of the FITS image. This is a unique identifier for the observation date, observatory hemisphere, nightly scan number, and image number of the FITS image. Each source in the 2MASS All-Sky Point and Extended Source Catalogs (accessible via Gator) is tagged with a coadd_key value identifying the 2MASS Image set it was extracted from.
seesh Seeing Full Width Half Maximum (in arcseconds)
magzp Photometric zero-point magnitude of the FITS image.
msnr10 Approximate SNR=10 magnitude of the FITS image.
cdelt1 The width of a pixel (in degrees)
cdelt2 The height of a pixel (in degrees)
ctype1 Coordinate system and projection of the FITS image x-axis.
ctype2 Coordinate system and projection of the FITS image y-axis.
crota2 The angle of rotation between the FITS image y-axis and North (in degrees)
bin Spatial index value of the FITS image reference location.
search_ra This column will only appear if the meta-data table is the result of a query involving a list of positions. The column value corresponds to the right ascension (equatorial J2000 degrees) of the position the image was found/retrieved for.
search_dec This column will only appear if the meta-data table is the result of a query involving a list of positions. The column value corresponds to the declination (equatorial J2000 degrees) of the position the image was found/retrieved for.
sub_size This column will only appear if the meta-data table is the result of a query involving a list of positions. The column value corresponds to the requested subimage size (in arcseconds) for the position the image was found/retrieved for.