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
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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
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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
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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:
|
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. |