Saving files to tape

 At the end of your run, and probably following each night of observations, you will want to backup your data to an exabyte (8 mm) tape. This can be done in one of three ways: The slowest, obsolete method is to translate the FIGARO files to FITS format using the snvfits program or the allsnv script, and then backup the files directly to the exabyte drive on the Microvax:

This method is no longer recommended, as it uses the VMS backup command to create a backup saveset on the exabyte tape. Since most observers return to their home institutions and reduce their data on Unix machines, such tapes will have to be read using a non-standard Unix utility, such as vmsbackup.

A better method is to copy the translated FITS files to one of the Unix workstations, using the ftp command, and then save the files to the exabyte drive on the Unix machine, using the tar command:

Both of the above methods involve translating the FIGARO files to FITS on the realtively slow VMS observing computer. The current preferred method of saving one's data is to instead transfer the raw FIGARO files to the Unix machine and translate them to FITS format there, using the fig2fits program:

Although this translation runs much faster on the Unix machines, note that the default fig2fits program (/usr/local/bin/fig2fits) will not create the ETALONZ header keyword correctly. In the case of observing frames taken with the FPSEQ Fabry-Perot command, the ETALONZ keyword is placed in the raw data files correctly. However, if the observing frame was taken using SNAP or any other method other than FPSEQ, the Z position of the etalon is recorded in the standard NIGHT header keyword. The snvfits and allsnv programs on the Microvax are aware of this distinction and create FITS files with the correct value for the ETALONZ keyword in all cases. There is a modified version of the fig2fits program on the Unix machines (/home/user/Zodiac/bin/fig2fits), which can be used to create FITS files with correct ETALONZ fields. You may want to edit the file /home/user/Zodiac/bin/fits_head with correct fields for other FITS header keywords.

Finally, note that the exabyte drives currently on the Unix machines are not capable of writing tapes in low-density (2.3 Gigabyte) mode. This includes tapes that have already been written in low-density mode; such tapes cannot be overwritten. Therefore, be sure to bring high-density tapes, or, better yet, new tapes for archiving your data.

Each dome also has CD/RW drives for recording data on CD-ROMs. This is an excellent solution and very appropriate for Fabry-Perot observing, where the volume of data per night is usually less than the size of a single CD-ROM (650 MB). Instructions on using the CD/RW drives are available at the observatory and on the web.