| Description: A 9-character identifier used to specify data products, or sometimes sets of associated data products, in MAST (the Mikulski Archive for Space Telescopes). In HST data files, this is the value of FITS keyword ROOTNAME. The name ASN_ID, for "association identifier" is also sometimes used. Values are always converted to lower case, if necessary. In MAST, you can find these products by entering this ID into the search box on this page: archive.stsci.edu/cgi-bin/dataset_lookup/ The nine characters can generally be interpreted as follows: - the first letter indicates the instrument, 'u' for WFPC2, 'j', for ACS, etc.; - the next three characters are unique to each HST program; - the next two characters indicate the HST visit within the program; - two characters generally increment for successive observations during the visit, using "base 36" where the characters used are digits 0-9 plus letters a-z; - the last character indicates a transmission method, and is generally not important for scientific purposes. However, if it is a digit, this indicates that this particular file is the result of merging two or more other HST observations from this visit. |