Interactive 2MASS Image Service Help

The Interactive 2MASS Image Service provides fast interactive viewing and retrieval of a single 2MASS Image set. The service allows both Atlas and Quicklook image sets to be retrieved - each "Quicklook" image corresponds to a 2MASS Atlas Image that has been lossy-compressed with hcompress, using scale = 4.0 and quant = 1.0 parameters. The Quicklook Images delivered by this service are restored from the lossy-compressed files in FITS format with full WCS information contained in the image headers. These images are suitable for position measurements, finding charts and visual inspection of the near-infrared sky.

There are three image retrieval modes provided by the Interactive Service:

  1. Retrieve Image by Position or Object Name
  2. Retrieve Image by coadd_key
  3. Retrieve Image by Date, Hemisphere, Scan, and Image number

Each mode is described in more detail below.

Finally, note that interactive query results contain a concise data tag which can be used to re-run a query. Publishing data tags in journal articles provides readers with the means to locate and access the data the article is based on. See these instructions for further details.

CAUTION:

Always use 2MASS Atlas Images for photometric measurements -
2MASS Quicklook Images are restored from lossy-compressed files.

Retrieve Images by Position or Object Name

Description

This retrieval mode first finds all of the 2MASS Image sets I1, I2, ... , In which contain the specified position or object P. Out of the image sets found, the "best" one is selected and returned (Quicklook image sets are also decompressed). The selection algorithm operates as follows :

  1. For each image set Ij, 1 <= j <= n containing P, the minimum distance dj between P and the 4 edges of Ij is computed.
  2. The image Ik with the largest minimum distance (dk >= dj for 1 <= j <= n) is selected.

The algorithm effectively returns the most centered image set relative to P.

If you wish to select image set(s) covering a position according to your own criteria, you can obtain a listing of all the image sets covering a position or object using the 2MASS Image Inventory Service.

Query Inputs
Coordinates or Object Name

This input field must contain either a sky coordinate or an object name resolveable via IRSA, NED, or SIMBAD (2MASS object names are resolved by IRSA, all other names are resolved via NED/ SIMBAD). This coordinate or object name corresponds to the position to be searched for 2MASS Image sets.

If the input field contains a string which can be interpreted as a coordinate representation, it is used as such: both decimal degree and sexagesimal notations are supported. If not, the string is sent first to IRSA, then to NED, and finally to SIMBAD to attempt name resolution. The range of acceptable name formats is set by those projects.

Examples :

  • m83
  • NGC 7479
  • 2MASXJ23045666+1219223
  • 17h 44m 34s -27d 59m 13s Equatorial J2000
  • 23h04m56.63s 12d19m22.7s Equ J2000
  • 17h44m34s -27d59m13s
  • 00h42m44.3s +41d16m08s b1950
  • 00:42:44.3 -41:16:08
  • 00 42 44.3 -41 16 08 b1983
  • 004244.3 -411608
  • 17h -27d Equ J2000
  • 17h -27d
  • 34.5565 54.2321 gal
  • 34. 54. ecl
Subimage Size

This optional input field allows the retrieved 2MASS Image set to be subsetted before being made available for download. This restricts data retrieval to an area of interest in the full 2MASS Image set.

If you wish to subset the retrieved image set, use this input field to specify the desired width/height (in arcseconds) of the subimage. Whenever possible, the subimage will be centered on the retrieval position or object P. This is impossible if P lies too close to an edge of the full 2MASS Image set.

Leaving this field blank (or specifying a subimage size of 0) will cause the entire 2MASS Image set (512 X 1024 pixels, 8.5 X 16 arcmin) for P to be returned.

The minimum allowed width is 10.0 arcseconds, and the maximum is 1024.0 arcseconds. Positive values which do not fall into this range will automatically be clamped to lie in [10.0, 1024.0].

Date

This input field is used to optionally specify the observation date of the desired image set. All image sets with an observation date not matching the given one will be removed from the list of 2MASS Image sets covering P prior to "best" image set selection.

The date format used is strict: you must specify exactly 6 numeric characters corresponding to a date in yymmdd format (yy: last 2 digits of the observation year, mm: integer month, dd: integer day).

Examples :

  • August 4, 1997 : 970804
  • August 4, 2000 : 000804
  • August 4, 2001 : 010804
  • January 4, 2001 : 010104
  • February 4, 2001 : 010204
  • February 5, 2001 : 010205

Although the 2MASS Image Service verifies the date format before it attempts to find the desired image set, the service will not check to see if there were any 2MASS observations on the specified date. If you enter a date on which no data was taken (or an erroneous scan or image number), the service will simply notify you that it was unable to find any image sets matching your retrieval criteria.

Hemisphere

This input field is used to optionally specify the observatory hemisphere of the desired image set. All image sets with an observatory hemisphere not matching the given one will be removed from the list of 2MASS Image sets covering P prior to "best" image set selection.

The observatory hemisphere of a 2MASS Image is the hemisphere of the 2MASS observatory where the image was taken. There are only two possible values: north (Mt. Hopkins), and south (Cerro Tololo).

Scan

This input field is used to optionally specify the nightly scan number of the desired image set. All image sets with a scan number not matching the specified one will be removed from the list of 2MASS Image sets covering P prior to "best" image selection.

The value of this input field must be an integer between 1 and 999 (inclusive).

Image

This input field is used to optionally specify the image number of the desired image set. All image sets with an image number not matching the given one will be removed from the list of 2MASS Image sets covering P prior to "best" image set selection.

The value of this input field must be a positive integer.

coadd_key

This input field is used to optionally specify the coadd_key value of the desired image set. Note that if coadd_key is specified, then the values of the Date, Hemisphere Scan, and Image inputs are ignored. All image sets with a coadd_key not matching the specified one will be removed from the list of 2MASS Image sets covering P prior to "best" image set selection.

The value of this input field must be a positive integer.

Band

This option allows you to choose the 2MASS band(s) for which images are returned.

  • J: Selecting this option will cause only the J-band image to be returned.
  • H: Selecting this option will cause only the H-band image to be returned.
  • Ks: Selecting this option will cause only the Ks-band image to be returned.
  • All: Selecting this option will cause images for all three bands to be returned.

CAUTION:

Always use 2MASS Atlas Images for photometric measurements -
2MASS Quicklook Images are restored from lossy-compressed files.

Retrieve Image by coadd_key

Description

This retrieval mode finds and returns the 2MASS Image set with the specified coadd_key value. A coadd_key is a unique identification number for a record in the Atlas Image Data Table, and corresponds to a 2MASS Atlas Image. Each source in the 2MASS All-Sky Point and Extended Source Catalogs (accessible via Gator) is tagged with a coadd_key referencing the Atlas Image the source was extracted from. The value of this key is stored in the coadd_key column of the catalogs.

If you wish to retrieve image sets for a list of coadd_key values, use the 2MASS Batch Image Service.

Query Inputs
coadd_key

This input field must contain the coadd_key value of the desired image set.

Band

This option allows you to choose the 2MASS band(s) for which images are returned.

  • J: Selecting this option will cause only the J-band image to be returned.
  • H: Selecting this option will cause only the H-band image to be returned.
  • Ks: Selecting this option will cause only the Ks-band image to be returned.
  • All: Selecting this option will cause images for all three bands to be returned.

CAUTION:

Always use 2MASS Atlas Images for photometric measurements -
2MASS Quicklook Images are restored from lossy-compressed files.

Retrieve Image by Date Hemisphere Scan and Image number

Description

This retrieval mode finds and returns the 2MASS Image set with observation date, observatory hemisphere, scan number, and image number identical to the given values.

If you wish to retrieve all the 2MASS Image sets for a given observation date, observatory hemisphere, and scan number, use the 2MASS Batch Image Service.

Query Inputs
Date

This input field must contain the observation date for the desired image set. The date format used is strict: you must specify exactly 6 numeric characters corresponding to a date in yymmdd format (yy: last 2 digits of the observation year, mm: integer month, dd: integer day).

Examples :

  • August 4, 1997 : 970804
  • August 4, 2000 : 000804
  • August 4, 2001 : 010804
  • January 4, 2001 : 010104
  • February 4, 2001 : 010204
  • February 5, 2001 : 010205

Although the 2MASS Image Service verifies the date format before it attempts to find the desired image set, the service will not check to see if there were any 2MASS observations on the specified date. If you enter a date on which no data was taken (or an erroneous scan or image number), the service will simply notify you that it was unable to find any image sets matching your retrieval criteria.

Hemisphere

The hemisphere of the 2MASS observatory where the desired image set was taken. There are only two possible values: north (Mt. Hopkins), and south (Cerro Tololo).

Scan

The nightly scan number of the desired image set. The value must be an integer between 1 and 999 (inclusive).

Image

The image number of the desired image set. The value must be a positive integer.

Band

This option allows you to choose the 2MASS band(s) for which images are returned.

  • J: Selecting this option will cause only the J-band image to be returned.
  • H: Selecting this option will cause only the H-band image to be returned.
  • Ks: Selecting this option will cause only the Ks-band image to be returned.
  • All: Selecting this option will cause images for all three bands to be returned.

CAUTION:

Always use 2MASS Atlas Images for photometric measurements -
2MASS Quicklook Images are restored from lossy-compressed files.