1 Page 1 - - *********************************************************** * * * * * The 90 000 Stars Supplement * * * * to the * * * * PPM Star Catalogue * * * * * *********************************************************** - - - - S. Roeser and U. Bastian 0 Astronomisches Rechen-Institut, Heidelberg - A. Kuzmin 0 Sternberg Astronomical Institute, Moscow - - - - 0 Heidelberg, December 1993 1 Page 2 - - *********************************************************** * * * * * Introduction to the 90 000 Stars Supplement * * * * * *********************************************************** - - 0 Preface ======= 0 The idea of this introduction to the 90 000 Stars Supplement is to deliver a short explanation together with the catalogue itself. It briefly describes the catalogue and its format, with heavy reference to the introductions to PPM North and PPM South. The 90 000 Stars Supplement is also described in a paper by Roeser, Bastian and Kuzmin in Astron. Astrophys. Suppl., 1994. - - 0 Contents ======== - 1. Scope of the 90 000 Stars Supplement 2. Construction 3. Properties 4. Practical usage 5. Availability 6. Format of the machine-readable version 0 Table 1 References Acknowledgements 1 Page 3 - 1. Scope of the 90 000 Stars Supplement ======================================= 0 Since its appearance in 1966 the SAO Catalogue (SAO, 1966) has been the primary source for stellar positions and proper motions. Typical values for the rms errors are 1 arcsec in the positions at epoch 1990, and 1.5 arcsec/century in the proper motions. The corresponding figures for the AGK3 (Heckmann et al., 1975) on the northern hemisphere are 0.45 arcsec and 0.9 arcsec/century. Common to both catalogues is the fact that proper motions are derived from two observational epochs only. Both catalogues are nominally on the B1950 / FK4 coordinate system. 0 The PPM Star Catalogue (R|ser and Bastian, 1991, Bastian et al., 1993; for a short description see R|ser and Bastian, 1993) effectively replaced these catalogues by providing more precise astrometric data for more stars on the J2000 / FK5 coordinate system. Compared to the SAO Catalogue the improvement in precision is about a factor of 3 on the northern and a factor of 6 to 10 on the southern hemisphere. In addition, the number of stars is increased by about 50 percent. Typical values for the rms errors on the northern hemisphere are 0.27 arcsec in the positions at epoch 1990, and 0.42 arcsec/century in the proper motions. On the southern hemisphere PPM is much better, the corresponding figures being 0.11 arcsec and 0.30 arcsec/century. 0 The improvement over the SAO Catalogue was made possible by the advent of new big catalogues of position measurements and by the inclusion of the century-old Astrographic Catalogue (AC) into the derivation of proper motions (for a description of AC see Eichhorn, 1974). But even PPM does not fully exploit the treasure of photographic position measurements available in the astronomical literature of the last 100 years. 0 The Astrographic Catalogue contains roughly four million stars that are not included in PPM. For most of them no precise modern-epoch position measurements exist. Thus it is not yet possible to derive proper motions with PPM quality for all AC stars. But among the 4 million there is a subset of some 100 000 CPC-2 stars (see below) that are not included in PPM. These stars constitute the 90 000 Stars Supplement to PPM. 1 Page 4 - 2. Construction =============== 0 The CPC-2 gives 276 000 high-quality photographic star positions on the southern hemisphere. The plates were taken around 1966 in South Africa and were measured in Great Britain. The resulting positions were published recently (Zacharias et al., 1992). 172 000 CPC-2 positions were already used in the construction of PPM. The remaining 100 000 were not used because no precise later-epoch observations were available and because the PPM concept aimed at having more than two epochs per star. 0 The 90 000 Stars Supplement provides J2000 positions and proper motions for the majority of these remaining 100 000 stars. It was constructed in essentially the same way as PPM, but with only CPC-2 and AC as observation catalogues. The former was used as published, since it is on the system of FK5. The latter (AC) was used in the fully reduced form that was produced for the PPM project. 0 A provisional star list for the Supplement was set up by cross-identifying CPC-2 with PPM and retaining only the non-identified stars. It contained 102 681 stars. This list was then automatically cross-identified with AC. In cases of doubt the GSC, NLTT and the Cape Photographic Durchmusterung were used to verify the identity. If doubts still remained or if the individual AC measurements were grossly discordant, the star was deleted from the list. Also deleted were all stars having only one AC counterpart (the missing of the second one making the star dubious), and of course those 4147 objects having no AC counterpart at all. 0 Proper motions were thus derived from three or four positions for a vast majority of the remaining stars: one from CPC-2 (each CPC-2 position in fact is the mean of four independent plate measurements) and two or three from the overlapping plates of AC. Only a few thousand stars have more than 4 positions. The details of the catalogue construction process are largely identical to those of PPM South. 0 The resulting star catalogue contains 89 676 stars. Besides the astrometric parameters the 90 000 Stars Supplement provides magnitudes, spectral types (if available) and cross-identifications to other star catalogues (Bonner Durchmusterung, Cordoba Durchmusterung, Henry Draper Catalogue). 1 Page 5 - 3. Properties of the 90 000 Stars Supplement ============================================ - A rough summary of the astrometric precision is given in Table 1, below, along with comparison data for the main parts of PPM. The numbers in the table are mean values. The numbers for individual objects vary. The Supplement stars are in fact divided in two well-separated groups. The division is caused by two major classes of precision of the CPC-2 positions. The division is obvious in the precision of the present-day positions, but less so in proper motions, since there is a large variation of epochs and mean errors in the AC positions. 0 The positions and proper motions provided by the 90 000 Stars Supplement are less precise than those in the southern part of PPM, but they are more precise than those of PPM north. Thus the already existing imbalance between the two hemispheres (see Table 1) is further increased. - - 4. Practical usage ================== 0 The practical usage of the 90 000 Stars Supplement is perfectly the same as for the main parts of PPM. Explanations are given in the Introductions to PPM North and PPM South. - - 5. Availability =============== - Magnetic tapes containing PPM and its 90 000 Stars Supplement can be obtained from the astronomical data centres, e.g. the Centre de Donnees Astronomique de Strasbourg (CDS), Strasbourg, France and the Astronomical Data Centre at Goddard Space Flight Centre, Greenbelt, USA. There will be no printed version of the 90 000 Stars Supplement, but inclusion into the various forthcoming "astronomical catalogues sampler" CD-ROMs is aimed at. 1 Page 6 - 6. Format of the machine-readable version ========================================= 0 The machine-readable version of the 90 000 Stars Supplement to PPM contains 2 physical files. They are perfectly analogous to Files 1 and 2 of the machine-readable version of PPM South. Thus the description need not be repeated here. 0 Table 1: Error budget of PPM and the 90 000 Stars Supplement ============================================================ 0 The table gives some information on the accuracy of PPM and the 90 000 Stars Supplement. The individual columns of the table contain, in turn, the declination zone, the total number of stars and average values for a number of characteristic quantities: star density (stars per square degree), number of source positions used for each star, mean epochs for right ascension and declination, mean errors of the proper motions (in arcsec/century) and mean errors of the 1990 positions (in arcsec). 0 The last two lines give rough statistics of the SAO Catalogue for comparison. - decl. no.of star no. mean ep. mean err. mean err. (deg.) stars dens. obs. 1900+ prop. mot. pos. 1990 - PPM, north 0 +90..-2.5 181731 8.7 6.2 31.5 30.7 0.43 0.42 0.27 0.27 0 PPM, south 0 -2.5..-90 197179 10.3 6.1 61.8 61.6 0.30 0.30 0.11 0.11 0 90 000 Supp. 0 +1.5..-90 89676 4.4 3.4 55.4 54.8 0.46 0.44 0.19 0.18 - SAOC, north 0 +90..-2.5 133000 6.4 2.0 30 30 1.5 1.5 0.9 0.9 0 SAOC, south 0 -2.5..-90 126000 6.3 2.0 30 30 1.5 1.5 1.2 1.2 1 Page 7 - References. =========== 0 Bastian, U., R|ser, S., et al., 1993, PPM Star Catalogue, Vols. III and IV, positions and proper motions of 197179 stars south of -2.5 degrees declination. Astronomisches Rechen- Institut, Heidelberg. Spektrum Akademischer Verlag, Heidelberg, Berlin, New York, 1993. 0 Eichhorn, H., 1974, Astronomy of Star Positions, Frederick Ungar Publ. Co., New York. 0 Heckmann, O., Dieckvoss, W., Kox, H., G}nther, A., Brosterhus, E., 1975, AGK3. Star catalogue of positions and proper motions north of -2.5 declination. Hamburg-Bergedorf 1975. 0 R|ser, S., Bastian, U., 1991, PPM Star Catalogue, Vols. I and II, positions and proper motions of 181731 stars north of -2.5 degrees declination. Astronomisches Rechen-Institut, Heidelberg. Spektrum Akademischer Verlag, Heidelberg, Berlin, New York, 1991. 0 R|ser, S., Bastian, U., 1993, The final PPM Star Catalogue for both hemispheres, Bull. Inform. CDS, 42, 11. 0 R|ser, S., Bastian, U., Kuzmin, A., 1994, PPM Star Catalogue: The 90 000 Stars Supplement, Astron. Astrophys. Suppl., in press. 0 SAO, Staff of, 1966, Star Catalogue. Positions and proper motions of 258997 stars for epoch and equinox of 1950.0. Publ. Smithsonian Inst. of Washington,D.C., No. 4562. 0 Zacharias, N., de Vegt, C., Nicholson, W., Penston, M., 1992, CPC-2 - the Second Cape Photographic Catalogue. A&A 254, 394. 1 Page 8 - Acknowledgements ================ 0 This work was made possible by the key-punching of the Astrographic Catalogue, performed by many patient and careful workers at Moscow, supervised by V.V. Nesterov. Financial support was provided by Deutsche Forschungsgemeinschaft and the Russian Academy of Sciences.