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ASCII source files

If you are lucky, your program stars are available in machine-readable form. If so, simply copy out the data for your program stars as fixed-format ASCII records, one star per record. It doesn't matter if the ASCII file contains extraneous data; they can be ignored in converting to MIDAS format. The command MAKE/STARTABLE helps you turn this flat ASCII file into a MIDAS table of program stars. It will first ask for the name you want to give your new program-star table. Then it checks to make sure you have the necessary information, such as the ASCII table of stellar data, and a format file.

It is important to make sure the star names in your source files match those in your data files. In building star files, keep in mind the need to have the same designations appear in the observational data. If your data-logging system makes you enter star names when they are observed, try to keep names short to avoid typing errors. That means using short, unique names in your program-star files, to match those that will appear in the data. If your data-logging system takes star names from files prepared in advance, try to adhere to the standard IAU name format (see the guidelines published in A&A ``Indexes 1990 and Thesaurus, Supplementary Issue, May, 1991'', pp. A11-A13; PASP 102, 1231-1233, 1990; and elsewhere).

If possible, use at least two names for each star, as recommended by the IAU. You can use two names in the star files, and just use one in data files; the reduction program is smart enough to match them up properly, or will ask for help if similar but not identical names occur. It is a good idea to separate aliases with an ``='' sign; just leave a space on either side of it, so the program doesn't take it as part of a name string. Ordinary spacing is allowed in names to make things readable: HR 8832, Chi Cygni, BD +4 4048, etc. Thus a name field might contain ``HD 24587 = CD -24 1945 = HR 1213''.

Although you can use any naming system you like for program stars, so long as the same name appears in star files and data files, a system of priorities is suggested for making up catalogs of standard stars. The basic principle is that small catalogs generally yield shorter names that are easier to use than do bigger catalogs. Generally, catalogs for brighter stars contain fewer entries; so the lists with the brightest limiting magnitude are preferred. Thus, common designations like Bayer letters and Flamsteed numbers are usually included for the brightest stars. The bright stars are also listed by HR number, and fainter ones by HD or DM number. Don't forget that there is considerable overlap among the BD, CD, and CPD; specify the catalog, not just a zone and number. The HST Guide Star Catalog is recommended for still fainter objects.

If the reduction program finds stars with different names but nearly identical positions, it will ask you if they are the same star. Be prepared to answer such questions, if you enter names inconsistently. Many users find that repeatedly answering such questions becomes tedious and irritating; you can avoid this problem by using identical name strings in both star files and data files.

Don't use names like STAR A and STAR B, as the matching algorithm will spot the common word STAR and ask if they are the same; instead, just use the letter. If it is necessary to intermix several similar names, try to make unique strings out of them. For example, if you are working on a group of clusters, and have local standards designated by the same letters in each, attach the letter to the field designation: M67_A, M67_B, etc.

Although it is not recommended, the CONVERT/PHOT command can extract apparent star positions from raw data files in ESO and Danish formats (see section 13.2.1). As intermediate output, this command will produce an ascii file that can be edited. Manual editing may be necessary if you do not use consistent naming conventions while observing.

Finally, don't try to create star files with incomplete data. Missing values cause problems when you try to reduce data. Be sure every entry is filled in correctly.

next up previous contents
Next: Format files Up: Star tables Previous: Star tables
Petra Nass