A compilation of catalogues for CCD calibrations This CDROM contains databases of stars for calibration of CCD frames. Star catalogs are placed in folders (usno, tyc, gsc, ...). Two types of catalogs are presents : astrometrics and photometrics. Astrometrics catalogs does not include stars for declinations lower than -42 degrees. Astrometric catalogs -------------------- The name of folders that contain astrometric catalogs can be found in the file astrom.txt tyc contains all stars of the tycho catalog. usno contains contains all stars, brighter than mag R 15.9, that are not in tyc gsc contains all stars of gsc that are not presents in the both previous catalogs. Each star is included in only one catalog. The format used to storage informations in the catalogs is based on a modified version of the USNO catalog. The following text is adapted from that of the USNO readme.use : 1) The coordinate system of the catalog is Right Ascension and South Polar Distance (SPD). This decision was based on compatibility with the ESA Hipparcos and Tycho mission and catalogs. In practice, SPD is far easier to manipulate than declination since it is positive definite. 2) The coordinates were converted to integers in the following manner. (RA in decimal hours)*15*3600*100, and ((DEC in decimal degrees)+90)*3600*100 Again, this choice agrees with Hipparcos/Tycho. 3) Coordinates are given in J2000 at the epoch of the original blue plate. Somewhere on this CD-ROM set is the catalog.tar file which contains a copy of the plate database. If it really makes a difference, please consult these files since they have been corrected for every known error. 4) The sky is partitioned into 24 zones of SPD, each of width 7.5 degrees. This is similar to the choice made by the Guide Star Catalog. Perhaps some software developed to search that catalog can be used for this catalog. 5) In each zone, the catalog is sorted by increasing value of RA. 6) Each of the 24 pieces of the catalog contains 2 files, and the naming convention is zonXXXX.YYY XXXX is 10 times the SPD (0, 75, 150, ... 1725) YYY = acc (ASCII accelerator file) = cat (binary catalog file) 7) Each catalog (.cat) file is a binary file containing 2 32-bit integers & 2 unsigned 8-bit integers for each entry. The FORTRAN dimension statement looks like (3,length). In a picture it looks like: | RA (1) | Dec(1) | Magb(1) | Magr(1) | RA (2) | Dec (2) | Magb (2) | ... As an illustration, the C-structure associated to the fields : typedef struct { unsigned long ra; unsigned long dec; unsigned char magb; unsigned char magr; } astrom ; 8) The byte order is LITTLE_ENDIAN, which is not the default for machines like Silicon Graphics but is the default of machines like DEC (or PCs). 9) Since the catalog files can be quite long, I have found it convenient to refer to the accelerator (.acc) file, and use a combination of lseek() and read() to access the catalog file. FORTRAN direct access I/O is terribly inefficient in that it does not easily handle making a big offset then doing small reads. 10) The accelerator file (.acc) contains the first index (1-based FORTRAN sense) for the first object every 15 minutes of RA and the number of objects in that chunk of RA. 11) The RA takes a full 32-bit integer as does the SPD. The third unsigned 8-bit integer has been packed according to the following format : BBB = 10 times the blue magnitude + 3. A star of magb=6 is stored as 90. In the case of gsc catalog, this fields contains the pseudo V mag read in the gsc. The forth unsigned 8-bit integer has been packed according to the following format: RRR = 10 times the red magnitude + 3. For usno catalog, northern plates are 103a-E emulsions and southern plates are IIIa-F emulsions. For tyc catalog, the original catalog give only B and V mag. In this field, the R mag was computed by the simple formula : R = V - (B-V). In the case of the gsc catalog, these fields contains the pseudo V mag read in the gsc. Note that the Loneos team suggests an empirical formula to compute an R mag from both B and V : " To get approximate V-R from B-V (for the range 0.3 < B-V < 0.9): V-R = 0.508(B-V) + 0.040. " Photometric catalogs -------------------- The name of folders that contain photometric catalogs can be found in the file photom.txt The format used to storage informations in the catalogs is based on a modified version of the USNO catalog. The following text is adapted from that of the USNO readme.use : 1) The coordinate system of the catalog is Right Ascension and South Polar Distance (SPD). This decision was based on compatibility with the ESA Hipparcos and Tycho mission and catalogs. In practice, SPD is far easier to manipulate than declination since it is positive definite. 2) The coordinates were converted to integers in the following manner. (RA in decimal hours)*15*3600*100, and ((DEC in decimal degrees)+90)*3600*100 Again, this choice agrees with Hipparcos/Tycho. 3) Coordinates are given in J2000 at the epoch of the original blue plate. Somewhere on this CD-ROM set is the catalog.tar file which contains a copy of the plate database. If it really makes a difference, please consult these files since they have been corrected for every known error. 4) The sky is partitioned into 24 zones of SPD, each of width 7.5 degrees. This is similar to the choice made by the Guide Star Catalog. Perhaps some software developed to search that catalog can be used for this catalog. 5) In each zone, the catalog is sorted by increasing value of RA. 6) Each of the 24 pieces of the catalog contains 2 files, and the naming convention is zonpXXXX.YYY XXXX is 10 times the SPD (0, 75, 150, ... 1725) YYY = acc (ASCII accelerator file) = cat (binary catalog file) 7) Each catalog (.cat) file is a binary file containing 2 32-bit integers & 8 signed 16-bit integers for each entry. The FORTRAN dimension statement looks like (3,length). In a picture it looks like: | RA (1) | Dec(1) | Magu(1) | ... | Magk(1) | RA (2) | Dec (2) | Magu (2) | ... As an illustration, the C-structure associated to the fields : typedef struct { unsigned long ra; unsigned long dec; short magu; short magb; short magv; short magr; short magi; short magj; short magh; short magk; } photom ; 8) The byte order is LITTLE_ENDIAN, which is not the default for machines like Silicon Graphics but is the default of machines like DEC (or PCs). 9) Since the catalog files can be quite long, I have found it convenient to refer to the accelerator (.acc) file, and use a combination of lseek() and read() to access the catalog file. FORTRAN direct access I/O is terribly inefficient in that it does not easily handle making a big offset then doing small reads. 10) The accelerator file (.acc) contains the first index (1-based FORTRAN sense) for the first object every 15 minutes of RA and the number of objects in that chunk of RA. 11) The RA takes a full 32-bit integer as does the SPD. The following fields are signed 16-bit integer and they has been packed according to be 1000 times the magnitude. R, and I magnitudes are given in the Cousin system. A value equal to -32.000 in a magnitude field means it is a blank field.