Appendix B
HST File Names

This appendix describes the syntax of HST data file names, which encode a large amount of information about the files themselves. Datasets retrieved from the Archive as described in Chapter 1 consist of multiple files in FITS format, each with a name that looks like this:

ipppssoot_sfx.fits 

• Rootname: The first part of the file name (ipppssoot) is the rootname of the dataset to which the file belongs. All files belonging to a given dataset share the same rootname.
• Suffix: The three-character second part of the name (sfx) is called the suffix, and it indicates the type of data the file contains.
• Format: The identifier .fits indicates that this file is in FITS format. For example, an FOC data file named x3l80101t_d0f.fits is a FITS file belong to the dataset with rootname x3l80101t, and its suffix d0f indicates that it contains raw science data.

  In order to use IRAF/STSDAS tasks to work with data from instruments other than NICMOS and STIS, you will want to convert these FITS files into GEIS format. See page 2-11 for instructions on how to convert FITS files to GEIS files using strfits. Like FITS files, the names of GEIS files also derive from a file's rootname and suffix, and they look like this:

ipppssoot.sfx 

The identifier referred to here as a "suffix" has often been called an "extension" in the past. However, the individual pieces of FITS files are also known as "extensions" (see "Working with FITS Image Extensions" on page 2-4). For clarity, this handbook will use the term "extension" when refering to a component of a FITS file and the term "suffix" when referring to the three character identifier in a filename.

IPPPSSOOT Root File Names

Character	Meaning
I	Instrument used, will be one of: E - Engineering data F - Fine Guidance Sensors N - Near Infrared Camera and Multi-Object Spectrograph O - Space Telescope Imaging Spectrograph S - Engineering subset data T - Guide star position data U - Wide Field/Planetary Camera-2 V - High Speed Photometer W - Wide Field/Planetary Camera X - Faint Object Camera Y - Faint Object Spectrograph Z -Goddard High Resolution Spectrograph
PPP	Program ID; can be any combination of letters or numbers (46,656 combinations possible). There is a unique association between program ID and proposal ID.
SS	Observation set ID; any combination of letters or numbers (1,296 possible combinations).
OO	Observation ID; any combination of letters or numbers (1,296 possible combinations).
T	Source of transmission or association product number M - Merged real time and tape recorded N - Retransmitted merged real time and tape recorded O - Retransmitted real time (letter `O') P - Retransmitted tape recorded R - Real time (not recorded) T - Tape recorded 0 - Primary association product (number zero) 1-8 - NICMOS background association product

Suffixes of Files Common to all Instruments

OMS Files

http://www.stsci.edu/ftp/instrument_news/Observatory/

obslog/OL_1.html

OCX Files

After early February 1995, OCX files were produced only when an observation was used to locate the target for an Interactive Target Acquisition. At this time, mission and spacecraft information were moved to the PDQ reports and the Observation Logs (OMS jitter image and jitter table).

Trailer Files

When you search the Archive with StarView for observations involving associations of exposures, your search will identify the final association product. The rootnames of association products always end in zero (see Table B.1 above.) If you request both Calibrated and Uncalibrated data from the Archive, you will receive both the association product and the exposures that went into making it. The corresponding association table, located in the file with suffix asn and the same rootname as the association product, lists the exposures belonging to the association. You can read this file using the STSDAS tprint or tread tasks (see "Tables" on page 3-2). The exposure IDs in the association table share the same ipppss sequence as the association rootname, followed by a base 36 number nn (n = 0-9,A-Z) that uniquely identifies each exposure, and a character t that denotes the data transmission mode (see Table B.1).

In practice, STIS and NICMOS store the exposures belonging to associations differently. The exposures belonging to a STIS association all reside in the same file, while the exposures belonging to a NICMOS association reside in separate datasets. See the relevant Data Structures chapters for more details.

Information on the exposures belonging to an association is also available through StarView (see Chapter 1). From the <Welcome> Screen, click on [HST Instrument Searches] to get the <HST Instruments> screen, and then click on the [Associations] button for the instrument of interest. You can then search for the various exposures belonging to an association by entering the rootname of the association in the Association ID field and clicking on [Begin Search] . An Association Results Screen will display the results of the search, which you can step though using the [Step Forward] button. Figure B.1 below gives an example of a NICMOS Association Results Screen. Note the differences between the association rootname and coordinates and those of the individual exposure.

Figure B.1: Association Results Screen from StarView