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                 *            Introduction to PPM              *
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-          Contents
           ========
-           1. Scope of PPM                                            1
0           2. Construction of PPM                                     2
0           3. Properties of PPM                                       6
0           4. Practical Usage of PPM                                  9
0           5. List of Critical Comments on Individual Stars          10
0           6. List of Remarks on Individual Stars                    12
0           7. Short Explanation of the Magnetic Tape Version of PPM  21
0           8. Short Explanation of the Printed Catalogue             24
0              References                                             26
0              Acknowledgments                                        27



           Preface
           =======
0          The idea of this Introduction to PPM is to deliver a short
           explanation together with the catalogue itself. It should not be
           understood as a detailed description of the work performed in the
           construction of PPM. This will be given in a forthcoming paper
           (Bastian and Roeser 1990).

                                             S. Roeser and U. Bastian
                                             Astronomisches Rechen-Institut
                                             Heidelberg, June 1989
1
           (Introduction to PPM)                                      Page 1
-
           1. Scope of PPM
           ===============
0          PPM gives positions and proper motions of 181731 stars north of
           -2.5 degrees declination. Its main purpose is to provide a
           convenient, dense and accurate net of astrometric reference stars
           on the northern celestial hemisphere. This net is designed to
           represent as closely as possible the new IAU (1976) coordinate
           system on the sky, as defined by the FK5 star catalogue (Fricke
           et al., 1988).  In other words, it is a representation of the FK5
           system at higher star densities and fainter magnitudes.
0          Two older catalogues of similar character have served the same
           purpose in the past decades: AGK3 and the SAO Catalog.  There
           are three major reasons to replace these now:
0          1) SAOC and AGK3 are representations of the now obsolete FK4
           system of positions and proper motions.  Astronomers should have
           direct access to the FK5 system.
0          2) The accuracy of positions and proper motions in AGK3 and SAOC
           is no longer satisfactory. Astronomers should have a more
           accurate tool.  Over more than a century astrometrists have
           accumulated a vast treasure of measured star positions. The fact
           that much of this treasure is now available in machine-readable
           form and the power of present-day computers make it easy to
           analyse and combine this quantity of data.
0          3) Proper motions in AGK3 and SAOC were derived from only two
           separate source positions per star. This lack of redundancy leads
           to a large number of coarse errors in those catalogues.  With
           more than two measurements per star such errors can be largely
           avoided.  In this way astronomers now get a more reliable
           astrometric tool.
0          For purely practical reasons PPM presently covers only the
           northern celestial hemisphere plus the strip between the equator
           and -2.5 degrees declination.  For the time being, a southern
           hemisphere portion of the SAO Catalogue, transformed to the
           system of FK5 (J2000), is appended to the magnetic tape version
           of PPM. In this way the magnetic tape users are provided with a
           star catalogue on the system of FK5 (J2000) on the southern
           hemisphere also.
0          An extension of PPM to the south pole is obviously necessary. It
           has to be provided in the near future.
1
           (Introduction to PPM)                                      Page 2
-
           2. Construction of PPM
           ======================
-          In principle, the construction of PPM proceeded in the same way
           as for other astrometric compilation catalogues in the past: For
           each star, a mean position and a proper motion are derived from a
           number of measured positions (found in published source
           catalogues) by a least-squares adjustment.  In detail, however,
           quite a number of new methods and concepts were used which
           greatly reduced the effort for this undertaking.  PPM was
           constructed in several steps, each of which will now be explained
           very briefly.
-          Step 1: Compilation of the star list.
0          The star list for PPM was constructed starting from the magnetic
           tape version of AGK3, which contains 181581 stars.  All FK5 stars
           (Basic FK5 plus Bright Extension) north of -2.5 degrees
           declination were added, if not already included.  In the course
           of the work six AGK3 stars had to be deleted (because they are
           non-existent) and five close companions to AGK3 stars were added.
           This gave the final list of 181731 stars.
-          Step 2: Identification of stars in the source catalogues
0          The complete list of source catalogues is given in Chapter 3,
           below, along with an explanation of their abbreviations, with
           bibliographic references and some statistics.
0          The stars in each of the source catalogues were identified with
           the objects of the star list.  This was done in a fully automatic
           process.  Problem cases recognized in this process were
           investigated manually to detect typing errors in the source
           catalogues, to correctly identify double star components, to
           avoid the effects of grossly incorrect positions in the star list
           etc.
0          Prior to the identification of Astrographic Catalogue data (given
           as x,y plate coordinates originally) a rough plate reduction was
           performed, using published approximate plate constants.
-          Step 3: Construction of a preliminary system of positions and
                   proper motions.
0          A preliminary system of positions and proper motions is necessary
           to eliminate systematic deviations between the individual source
           catalogues. For this purpose we used AGK3, but with its positions
           and proper motions corrected to the system of NIRS (Corbin,
           1978), the latter being regarded as a representation of the FK4
           system. This correction was done using the systematic differences
           between AGK3 and NIRS given by Schwan (1985).
-          Step 4: Reduction of source catalogues to the preliminary system
0          Zonal systematic deviations as well as magnitude- and colour-de-
           pendent systematic deviations between each of the source
1
           (Introduction to PPM)                                      Page 3
-
           catalogues and the preliminary system were determined and
           eliminated.
           For Astrographic Catalogue zones we performed second-order plate
           reductions, using the preliminary system as reference. The
           resulting star positions were further corrected for magnitude-
           and colour-dependent deviations and for effects of higher-order
           distortion ("coma").
-          Step 5: Determination of weights for the source positions
0          In a least-squares adjustment weights have to be assigned to the
           individual measurements, according to their mean errors.
           Magnitude-dependent mean errors of the positions were determined
           for each source catalogue. For Astrographic Catalogue zones this
           was achieved by investigating the differences between positions
           of the same star measured on different (overlapping) plates.  For
           Yale and AGK1 zone catalogues the differences between the source
           positions and a preliminary version of PPM (Roeser and Bastian,
           1988) were investigated.  For the Carlsberg Meridian Circle
           catalogues (CMC 1985-1988) the differences from FK4 were
           investigated by R. Bien (1988).  For AGK3R the mean errors given
           by Eichhorn (1974) were used.
-          Step 6: Least-squares adjustment
0          A standard weighted least-squares adjustment of the mean
           positions and proper motions was performed for each star -
           separately for right ascensions and declinations. Automatic tests
           for unduly large scatter among the measurements (based on the
           chi-square sum) and automatic elimination of obvious outliers
           (based on appropriately normalized individual residues) were
           implemented. All stars having bad chi-square sums beyond a
           certain significance limit, but still not showing obvious
           outliers, were marked as "problem cases" (see flag 'P' in column
           19.1 of the printed catalogue). This occurred in about 950 cases.
-          Step 7: Manual treatment of difficult cases
0          The automatic outlier elimination deleted about 5500 measured
           coordinates (out of more than 2 million).  Tight restrictions,
           however, were imposed on this automatic process in order to avoid
           spuriously "good" results. This created about 800 "difficult
           cases" that were treated manually. A majority of these turned out
           to be coarse errors in AGK3, the rest were caused by errors in
           other source catalogues, mixed-up double star components etc.
           For about 180 objects no satisfactory solution could be found.
           These were added to the "problem cases" of step 6, giving a total
           of 1120 PPM stars with flag 'P'.
0          Another group of stars was subject to manual checks: Those AGK3
           stars not found in any source catalogue except AGK2 and AGK3
           (about 60 cases). We checked these for coarse errors of AGK3 by
           locating the stars on Palomar Sky Survey prints - with a
           precision of a few arcsec. In most cases they were found at the
           predicted positions. Nine cases were indeed caused by errors in
           both AGK2 and AGK3. We kept the data for these nine objects, but
           marked them as severe problem cases (see flag 'C' in column 19.1
           of the printed catalogue).
1
           (Introduction to PPM)                                      Page 4
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-          Step 8: Transformation from the preliminary to the final system
0          The positions and proper motions derived thus far were transformed
           from the preliminary system (described above) to the new IAU
           (1976) coordinate system, as defined by FK5. This step had two
           major parts: First, a transformation from the preliminary system
           to a presumably better representation of the FK4 system was
           performed.  Then a standard transformation from the FK4 system
           (B1950) to the FK5 system (J2000).
0          The first part became necessary because of the discovery of two
           sorts of systematic deviations between the preliminary system and
           the FK4 system:
            - Uncorrected atmospheric dispersion in the original AGK2 and
           AGK3 positions had caused a strong colour-dependent and
           declination-dependent systematic error.  This was corrected.  No
           other colour or magnitude equations were applied to the
           preliminary system. In other words: The colour and magnitude
           system of PPM is identical to that of AGK3 (except for the
           dispersion effect, of course).
            - In the course of the work we found indications for zonal
           errors of our preliminary proper-motion system. Therefore we did
           not keep this for the final system of PPM. Instead we constructed
           a new system of positions and proper motions from the systems
           of AGK3R (unchanged) and the CMC catalogues (after transformation
           to the FK4 system).
0          The transition from FK4 system to FK5 system followed exactly the
           same procedure as was used in the construction of FK5 (Fricke, et
           al. 1988).
0          More details on the construction and properties of the system of
           PPM will be given by Roeser (1989).
-          Step 9: Introduction of FK5 data for FK5 stars
0          For the stars contained in FK5 Part I (the Basic Fundamental
           Stars) and in FK5 Part II (the Bright Extension Stars), PPM gives
           the original FK5 data. These were introduced by simply copying
           them from the machine-readable version of FK5.
-          Step 10: Provision of cross-references and auxiliary data
0          In addition to the astrometric data PPM gives cross-references to
           other star catalogues, magnitudes, spectral types and a number of
           flags for each star.
0          Much manual labour went into the provision of cross-references.
           They were determined by different methods, ranging from direct
           cross-identification (based on positions only) to simply copying
           historic work done by others (in the cases of catalogues having
           low positional accuracy such as DM and HD).  Cross-references are
           given explicitly for four catalogues: Bonner Durchmusterung
           (abbreviated DM), SAO Catalog, Henry Draper Catalogue (HD) and
           AGK3. Three more cross-references are given implicitly by flags
           (see columns 19 of the printed catalogue):
           Flag 'F' in column 19.4 denotes the stars contained in FK5 (Parts
           I and II).
1
           (Introduction to PPM)                                      Page 5
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           Flag 'H' in column 19.3 indicates stars that are contained in
           AGK3R and/or one of the CMC catalogues.
           The double star flag 'D' (column 19.2) was created by
           cross-referencing PPM with the Catalogue of Components of Double
           and Multiple Stars (Dommanget 1988).
0          The magnitudes and spectral types were copied either from AGK3 or
           from FK5 (see Chapter 8 for details).
0          Various sorts of auxiliary information are given in the List of
           Critical Comments and in the List of Remarks (Chapters 5 and 6),
           and indicated by the 'C' and 'R' flags.
1
           (Introduction to PPM)                                      Page 6
-
           3. Properties of PPM
           ====================
-
0          Random Errors
+          _____________
-          The table below shows a summary of the error budget of PPM.  Each
           line of the table gives the following data for the particular set
           of stars indicated:  The number of stars in the set, the average
           number of source positions per star, the average of the mean
           epochs (for right ascension and declination), the average of the
           mean errors of proper motion (for right ascension and
           declination) and the average of the mean errors of position at
           epoch 1990 (again for right ascension and declination). Units are
           seconds of arc and seconds of arc per century, respectively.  At
           the bottom of the table the corresponding values for AGK3 and
           SAOC are given for comparison (a more complete comparison of PPM
           with SAOC, AGK3 and the - future - HIPPARCOS catalogue is given
           by Roeser and Bastian 1989, Fig. 3).
-                        Table 1: Error budget of PPM
-          set of stars   No.     No.   mean epochs   mean err.   mean err.
                          stars   obs.                prop. mot.  pos. 1990
0          PPM, all stars 181731  6.2  1931.5 1930.7  0.43 0.42   0.27 0.27
           PPM, HPS stars  31841  7.8  1950.3 1948.0  0.24 0.25   0.12 0.12
           PPM, FK5 stars   1365  ---  1954.2 1945.2  0.08 0.10   0.04 0.05
0          AGK3           181581  2.0  1945   1945    0.95 0.95   0.45 0.45
           SAOC, north    133000  2.0  1930   1930    1.5  1.5    0.9  0.9
0          Three subsets of PPM are shown in the table: The first line
           refers to the entire catalogue, the last line to the 1365 FK5
           stars and the second line to the High-Precision Subset (HPS) of
           PPM. This subset will be briefly discussed now.
0          PPM essentially was constructed by combining AGK3 with
           early-epoch catalogues. So the mean epochs of PPM are quite early
           and the present-day accuracy is dominated by the accuracy of the
           proper motions. Therefore it would be highly desirable to have a
           repetition of AGK3 at present epoch.  This not being available,
           we decided to introduce the Carlsberg Meridian Circle (CMC)
           catalogues, nos. 1 to 4 (CMC 1985 -1988).  In addition, we
           introduced AGK3R because of its higher accuracy compared to AGK3.
           The High-Precision Subset of PPM is defined as the set of PPM
           stars for which either CMC or AGK3R observations are available.
           Its superior precision in present-day positions is mainly due to
           the fine work done at the Carlsberg Meridian Circle.
0          Note that (on average) more than 6 measured positions are
           available per star.  This redundancy allowed us to discover (and
           avoid) a large number of coarse errors in the source catalogues.
           It ensures that PPM contains very few coarse errors. For 1064 PPM
           stars the redundancy was not sufficient to resolve discrepancies
           between the source positions. They carry the 'P' flag mentioned
           above.
1
           (Introduction to PPM)                                      Page 7

-
           Source Catalogues
+          _________________
0          More than 1.1 million source positions (i.e. right ascensions and
           declinations) were used for the construction of PPM.  The
           following table lists the various groups of source catalogues
           used and the total number of positions derived from each group.
           More information on the catalogues as well as bibliographic
           references are given in the book by Eichhorn (1974), except for
           the CMC catalogues.
-                   Table 2: Source Catalogues
-               Astrographic Catalogue zones   466 278
                AGK3                           181 581
                AGK2                           181 581
                AGK1                           141 146
                Yale zone catalogues            80 574
                Gyllenberg, 1926                11 498
                Prager, 1923                     8 602
0               CMC 1, 2, 3, 4                  25 656
                AGK3R                           20 581
0               Total                        1 117 497
-
           Systematic Errors
+          _________________
0          We did our very best to ensure that PPM is on the system of FK5.
           Such a goal, however, can be reached to a certain accuracy only.
           We estimate that the residual systematic deviations between PPM
           and the FK5 system have a typical size of 0.05 arcsec for the
           positions at mean epoch and of 0.2 arcsec per century for the
           proper motions.
0          These numbers do not hold, however, for a few special groups of
           objects: The very blue stars (spectral types B2 and earlier), the
           very faint stars (fainter than about 12 in photographic
           magnitude) and the very bright stars (brighter than about 7, but
           not in HPS or FK5). Because these groups are very small by number
           it was neither possible to check our preliminary system to the
           desired accuracy, nor could we correct the individual source
           catalogues to this system with the desired accuracy. So we just
           do not know anything about possible systematic errors for these
           small groups.
0          Another possible systematic error stands out clearly from our
           data, but still cannot be removed. It is a magnitude equation in
           right ascension, affecting stars fainter than about 10.5 mag
           (photographic). It shows up as a systematic difference between
           PPM and the CMC catalogues (remember that, by definition, the
           magnitude dependence of the proper-motion system of PPM is that
           of AGK3. The CMC catalogues were transformed to that system
           before inclusion into PPM). It has a mean value of about 0.08
1
           (Introduction to PPM)                                      Page 8
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           arcsec for stars between 10.6 and 11.0 mag, and 0.15 arcsec for
           stars fainter than 11.0 mag. The cause of this systematic
           difference cannot be identified with existing astrometric data.
           Therefore, it cannot be removed in a reasonable way.  More details
           will be given by Roeser (1989).
1
           Some Statistics
+          _______________
0          PPM contains 131502 SAOC stars, which corresponds to almost 99
           percent of all SAOC stars in the celestial region covered by PPM.
           It contains 85357 HD stars, corresponding to about 70 percent of
           all HD stars in the region.  There are 16031 double star flags
           ('D'), 1120 problem cases ('P' flags), 22 critical comments ('C'
           flags) and 228 less important remarks ('R' flags). The 'R' flags
           refer to peculiar DM designations and variable-star designations
           mostly.
1
           (Introduction to PPM)                                      Page 9
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           4. Practical Usage of PPM
           =========================
0          PPM gives positions for a standard epoch (J2000) and a standard
           coordinate system (mean equator and equinox for J2000 in the new
           IAU (1976) system of astronomical constants).
0          To apply PPM as astrometric reference at a different
           observational epoch, but still in the J2000 coordinate system,
           proper motions must be taken into account.  For most purposes a
           simple linear formula (position difference equals epoch
           difference times proper motion) is sufficient. But note that this
           procedure will give inaccurate results close to the pole.  Better
           formulae are given, e.g., by Murray (1983) and in the introduction
           to FK5.
0          To apply PPM as astrometric reference for a different equator and
           equinox, but still in the IAU (1976) system of astronomical
           constants, precession has to be taken into account. The relevant
           formulae and numerical values are given, e.g., by Lieske (1979) and
           in the introduction to FK5.
0          Note that simply precessing from J2000 to B1950 will still not
           give results in the old (FK4) astronomical coordinate system.
           This differs from the new IAU (1976) system by a correction to
           the precessional constant, a correction to the position of the
           vernal equinox, by the treatment of elliptical aberration and by
           complicated zonal corrections.  All this adds up to several
           tenths of an arcsec in position and a few tenths of an arcsec per
           century in proper motion.
0          Application of proper motion and precession still gives mean
           positions. In order to derive apparent positions for PPM objects
           one also has to apply nutation, aberration, stellar parallax, and
           relativistic light-bending (see e.g. Murray, 1983).
           For most practical uses of PPM these effects can be ignored. But
           PPM contains a small number of stars with fairly large paral-
           laxes. They are not indicated in the catalogue.
0          For each star PPM gives mean errors for right ascension and
           declination at their respective mean epochs T. Standard error
           propagation calculus can be used to calculate the mean error of a
           PPM position for an epoch t different from the mean epoch:
           Denoting the mean error of one coordinate at mean epoch by E(T),
           the mean error of proper motion by E(PM), the mean error of
           position at epoch t is given by
0                     2            2            2            2
                  E(t)    =    E(T)    +   E(PM)    *   (T-t)
0          Using more PPM stars in an application will usually give better
           results because of the partial cancellation of the purely
           accidental errors of the PPM data.  However, this improvement
           will never get beyond the systematic errors of PPM, as discussed
           in the previous chapter.
0          Applications demanding utmost accuracy rather than high star
           density should use HPS stars only.
1
           (Introduction to PPM)                                     Page 10
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           5. List of Critical Comments on Individual Stars
           ================================================
0          The following list gives, for each star included: The PPM number,
           the AGK3 number (if any) and a critical comment.  Any positions
           given in the comment refer to equinox J2000.0.
0          All stars included in this list carry the 'C' flag.
0           20679 +66 0812 :
            Planetary nebula NGC 6543
0           42555 +45 0003 :
            An orbital double star. There is also +45 0002 in
            AGK2, but not in AGK3. A difficult problem, which
            cannot be solved at the moment.
0           43225 +40 0059 :
            BD +40 147. Centre of M32 according to SIMBAD(CDS).
0           43228 +40 0060 :
            BD +40 148. Centre of M31 according to SIMBAD(CDS).
0           50954 +41 0889 :
            FK5 339. This is an orbital double star. FK5 data
            are given referring to centre of gravity.
0           56062 +43 1399 :
            Globular cluster NGC 6341 = M92
0           72938 +31 0789 :
            FK5 287. This is an orbital double star. FK5 data
            are given referring to centre of gravity.
0           76814 +38 1224 :
            Companion to FK5 485. AGK2 and AGK3 are wrong. In our
            opinion GC gives the correct position and proper
            motion. Difficult case in photographic astrometry.
            PPM position and proper motion is derived from the
            the GC mean position and one CMC observation.
0           86045 +38 2138 :
            see 86047 and 86049.
0           86047          :
            FK5 793. The centre of gravity of 61 Cyg. Data copied from
            FK5. See also 86049.
0           86049 +38 2136 :
            86045 and 86049 are the components of 61 Cyg.
            see also 86047. Both stars are of poor quality in
            PPM, because positions and proper motions are derived
            neglecting the large parallax of these stars.
0           112552 +21 2332 :
            Inspection on POSS shows: This star does not exist.
            The companion AGK3 +21 2333 is a double star with
            approximate separation 15 arcsec.
            AGK3 data are copied. Do not use them.
1
           (Introduction to PPM)                                     Page 11
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            150880 +5 0838  :
            Inspection on POSS shows: Both AGK2 and AGK3 are wrong.
            Positions and proper motions are derived from two AC
            measurements. There is another star at position:
             6 37 17.19 +5 7 57.6, Epoch 1915.0.
0           150973 +08 0809 :
            This is NGC 2261
0           151210 +2 0793  :
            Inspection on POSS shows: Both AGK2 and AGK3 are wrong.
            There is a star in the AC at position:
             6 46 27.50 +2 9 42.8, Epoch 1910.0
            AGK3 data are copied. Do not use them.
0           151371 +3 0869  :
            Inspection on POSS shows: Both AGK2 and AGK3 are wrong.
            This star is n o t  BD +3 1431. The position of
            BD +3 1431 is  6 50 54.36 +3 27 23.9, Epoch 1910.2.
            AGK3 data are copied. Do not use them.
0           152571 +8  973  :
            Inspection on POSS shows: Both AGK2 and AGK3 are wrong.
            Positions and proper motions are derived from two AC
            measurements.
            AGK3 claims that AGK3 +8 973 is BD +8 1757, but according
            to the coordinates given in the Bonner Durchmusterung the
            the BD star is about 4 arcmin south and at the same R.A. as
            given in AGK2/3. This star is in AC at position:
             7 24 20.78 +8 19 15.9, Epoch 1920.12. This is the BD star.
            The declination difference suggests an error in the AGK2/3
            measurements of 2 mm.
0           153068 +05 1072 :
            FK5 291. This is an orbital double star. FK5 data
            are given referring to centre of gravity. This
            star is omitted in the printed version of AGK3.
0           159607 +2 1655  :
            Inspection on POSS shows: Both AGK2 and AGK3 are wrong.
            There is a star in AC at position:
            13 15 56.82 +2 40 39.4, Epoch 1910.4.
            AGK3 data are copied. Do not use them.
0           165440 +9 2185  :
            Inspection on POSS shows: Both AGK2 and AGK3 are wrong.
            Positions and proper motions are derived from two AC
            measurements. It is a companion to AGK3 +9 2184.
0           166000 +2 2269  :
            Inspection on POSS shows: Both AGK2 and AGK3 are wrong.
            There is a star in the Astrographic Catalogue (AC) at
            position: 18 30 53.79 +2 5 27.6, Epoch 1910.0
            AGK3 data are copied. Do not use them.
0           168632 +4 2602  :
            Inspection on POSS shows: Both AGK2 and AGK3 are wrong.
            Positions and proper motions are derived from the
            measurements in AC and by Lopez (1987).
1
           (Introduction to PPM)                                     Page 12
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           6. List of Remarks on Individual Stars
           ======================================
0          The following list gives, for each star included: The PPM number,
           the AGK3 number (if any) and a remark.  In contrast to the
           Critical Comments these remarks are not of direct relevance to
           astrometry. Most remarks refer to peculiar DM designations and to
           variable-star designations.  Any positions given in the comment
           refer to equinox J2000.0.
0          All stars included in this list carry the 'R' flag.
-              736 +85 0058    BD +85 0059 austr
0              737 +85 0059    BD +85 0059 bor
0             4213 +85 0399    BD +84 0540 bor
0             5978 +70 0252    BD +70 0353 bor
0             5979 +70 0253    BD +70 0353 austr
0             6564 +73 0195    BD +73 0362 bor
0             6565 +73 0194    BD +73 0362 austr
0             8570 +71 0401    BD +71 0677 bor
0             8571 +71 0402    BD +71 0677 austr
0            10800 +76 0836    BD +75 0780 austr
0            10801 +76 0837    BD +75 0780 bor
0            11191 +70 0777    BD +70 1233 austr
0            11426 +78 0551    BD +77 0879 austr
0            11427 +78 0551a   BD +77 0879 bor
0            12044 +62 0026    BD +62 0029 austr
0            13092 +61 0153    BD +60 0272 bor(AGK2)
0            13093 +61 0154    BD +60 0272 austr(AGK2)
0            14737 +64 0258    BD +63 0489s1
0            14738 +64 0259    BD +63 0489s2
0            16337 +65 0408    BD +65 0592 bor
0            19128 +61 0873    BD +61 1454 bor
0            19129 +61 0872    BD +61 1454 austr
0            19225 +67 0640    BD +67 0857 austr
0            19226 +67 0639    BD +67 0857 bor
1
           (Introduction to PPM)                                     Page 13
-
             22874 +60 1381    BD +60 2239 bor
0            22875 +60 1382    BD +60 2239 austr
0            22923 +65 1105    BD +64 1552s1
0            24229 +64 1186    BD +64 1764 austr
0            24230 +64 1187    BD +64 1764 bor
0            24348 +68 1014    BD +68 1366 austr
0            24349 +68 1013    BD +68 1366 bor
0            24660 +62 1473    BD +61 2506 bor
0            24661 +62 1474    BD +61 2506 austr
0            25060 +51 0012 SS Cas. On one AC plate it has a companion (also
                            variable? ) at position  0 9 36.63 +51 33 58.2 .
0            25788 +56 0096    BD +55 0191D
0            25791 +56 0097    BD +55 0191ABC
0            26075 +50 0132    BD +50 0228Aa according to AGK2
0            27500 +54 0285    BD +53 0509 austr
0            27501 +54 0286    BD +53 0509 bor
0            28515 +55 0346    BD +54 0684s2
0            29017 +57 0457 This AGK2 star was omitted in the printed
                            version of AGK3.
0            29111 +50 0459    BD +50 0985 bor
0            29236 +52 0443    BD +52 0848 bor
0            29237 +52 0444    BD +52 0848 austr
0            30659 +58 0568 This star is wrongly identified in AGK3 to be
                            BD +58 961a. The correct identification is
                            +58 961. The star is HD 237537 and has
                            spectral type K2 according to HD.
                            Consequently, spectral type M9, given in AGK3, is
                            wrong. This spectrum belongs to BD+58 961a =
                            HD 47929, a star not contained in PPM.
0            36165 +59 1134    BD +59 1842 bor
0            36166 +59 1133    BD +59 1842 austr
0            36357 +50 1269    BD +50 2520 austr
0            36358 +50 1268    BD +50 2520 bor
0            37314 +53 1220    BD +53 2228 bor
0            37315 +53 1221    BD +53 2228 austr
1
           (Introduction to PPM)                                     Page 14
-
0            37610 +52 1296    BD +51 2645p2
0            37611 +52 1297    BD +51 2645p1
0            37667 +51 1344    BD +51 2661 bor
0            37668 +51 1345    BD +51 2661 austr
0            38331 +51 1432    BD +51 2821p2
0            38332 +51 1433    BD +51 2821p1
0            38663 +52 1418    BD +51 2898 bor
0            38664 +52 1417    BD +51 2898 austr
0            41324 +57 1624    BD +57 2657 austr
0            41350 +52 1707    BD +52 3341 bor
0            41950 +55 1690    BD +55 2981s1
0            42988 +48 0047    BD +48 0141 bor
0            42989 +48 0048    BD +48 0141 austr
0            43816 +40 0119    BD +40 0260a seq
0            44379 +43 0208    BD +43 0356 bor
0            44469 +47 0208    BD +47 0508s1
0            45477 +46 0288    BD +46 0633p1
0            45582 +44 0291    BD +44 0589 bor
0            45583 +44 0292    BD +44 0589 austr
0            47415 +44 0472    BD +44 1036p1
0            48885 +44 0639    BD +44 1402 austr
0            48886 +44 0640    BD +44 1402 bor
0            50828 +49 0822    BD +50 1575 bor
0            50829 +49 0821    BD +50 1575 austr
0            55572 +48 1261    BD +48 2421a prec
0            55574 +48 1263    BD +48 2421a seq
0            58003 +49 1511    BD +49 2959b seq
0            58005 +44 1577    BD +44 3078 bor
0            58006 +44 1578    BD +44 3078 austr
0            58174 +44 1594    BD +44 3107s1
1
           (Introduction to PPM)                                     Page 15
-
             58554 +39 1976    BD +39 3832 bor
0            58555 +39 1975    BD +39 3832 austr
0            58885 +44 1669    BD +44 3261p1
0            58886 +44 1670    BD +44 3261p2
0            59824 +43 1820    UW Cyg
0            63398 +44 2119 This AGK2 star was omitted in the printed
                            version of AGK3.
0            63400 +44 2118 CMC has observed AGK2 +44 2119.
                            +44 2119 = BD +43 4305 = LHS 3853 = EV Lac.
                            It is a flare star and astrom. binary,
                            P=28y, a= 0.04".
0            64939 +39 2543    BD +38 5114 bor
0            64941 +39 2544    BD +38 5114 austr
0            66259 +35 0130    BD +35 0266 austr
0            66260 +35 0129    BD +35 0266 bor
0            67031 +33 0203    BD +32 0390 austr
0            67032 +33 0204    BD +32 0390 bor
0            67168 +37 0259    BD +36 0453AB
0            67839 +34 0295    BD +33 528B in AGK3
0            68514 +35 0353    R Per
0            68820 +34 0408    BD +34 0744 bor, but austr according to AGK2
0            69837 +38 0522    BD +38 1001s1
0            76100 +36 1089    BD +37 2218 bor
0            76101 +36 1090    BD +37 2218 austr
0            78728 +36 1364    BD +36 2626CD
0            82523 +34 1814    BD +34 3463 austr
0            82668 +35 1753    BD +34 3494s1
0            83206 +35 1822    BD +35 3703AB
0            83207 +35 1823    BD +35 3703s1
0            83534 +39 2011    BD +39 3910s1
0            83538 +39 2012    BD +39 3910s2
0            83664 +32 1842 A faint double star not measured in AC.
0            83719 +37 1855    BD +37 3651 bor
1
           (Introduction to PPM)                                     Page 16
-
0            83720 +37 1856    BD +37 3651 austr
0            85463 +30 2192    BD +29 4160 austr
0            87076 +34 2235    BD +33 4359 austr
0            87077 +34 2236    BD +33 4359 bor
0            87448 +30 2471    BD +30 4617 bor
0            87449 +30 2472    BD +30 4617 austr
0            87475 +31 2276    BD +30 4622 austr
0            87962 +39 2417    BD +38 4808 austr
0            87963 +39 2418    BD +38 4808 bor
0            88329 +32 2277    BD +32 4546 bor
0            88330 +32 2276    BD +32 4546 austr
0            91866 +28 0295    BD +28 0448 bor
0            91867 +28 0294    BD +28 0448 austr
0            91890 +26 0264    BD +26 0443 austr
0            91891 +26 0265    BD +26 0443 bor
0            92457 +24 0288    BD +23 0449 austr
0            92458 +24 0287    BD +23 0449 bor
0            92765 +25 0331    BD +25 0593 austr
0            92766 +25 0332    BD +25 0593 bor
0            94304 +20 0496    BD +19 0905 bor
0            94305 +20 0497    BD +19 0905 austr
0            94779 +28 0546    BD +28 0868 austr
0            95670 +27 0624    BD +27 1035 austr
0            96431 +27 0713    BD +27 1206 austr
0            96432 +27 0712    BD +27 1206 bor
0            96463 +23 0713    BD +23 1477 austr
0            96464 +23 0712    BD +23 1477 bor
0            97653 +22 0897    BD +23 1744 austr
0            97654 +22 0898    BD +23 1744 bor
0            97837 +28 0827    BD +28 1440 bor
1
           (Introduction to PPM)                                     Page 17
-
             97991 +28 0845    BD +28 1474 austr
0            99247 +26 0987    BD +26 1885 bor
0            99248 +26 0988    BD +26 1885 austr
0            99374 +28 0979    BD +28 1707 austr
0            99455 +24 1065    BD +24 2067 bor
0           100883 +27 1117 Double star in AGK2: +27 1117 and +27 1118.
                            The AGK3 measurement refers to the centre and
                            was not used for PPM.
0           100884 +27 1118 This AGK2 star was omitted in the printed
                            version of AGK3.
0           101958 +24 1314    BD +25 2518 bor
0           101975 +21 1297    BD +21 2429 bor
0           102684 +23 1318    BD +23 2584 bor
0           102685 +23 1319    BD +23 2584 austr
0           104347 +25 1597    BD +25 2973 bor
0           104348 +25 1598    BD +25 2973 austr
0           105039 +25 1673    BD +25 3108 bor
0           105040 +25 1674    BD +25 3108 austr
0           105654 +21 1678    BD +21 3063 bor
0           106982 +25 1901    BD +25 3473 austr
0           106983 +25 1902    BD +25 3473 bor
0           109767 +21 2053    BD +21 3927 bor
0           110507 +21 2112    BD +21 4073s1
0           110508 +21 2113    BD +21 4073s2
0           111510 +20 2287    In printed AGK2/3 BD +19 4464p1
0           111960 +20 2329    BD +19 4525 austr
0           112396 +20 2371    BD +20 4822 bor
0           112397 +20 2372    BD +20 4822 austr
0           113400 +28 2523    BD +27 4131 austr
0           114011 +28 2614    BD +28 4282 bor
0           114012 +28 2615    BD +28 4282 austr
0           115008 +27 2697    BD +26 4540 austr
1
           (Introduction to PPM)                                     Page 18
-
            115977 +22 2581    BD +21 4999 bor
0           116009 +24 2583    BD +23 4830p2
0           116010 +24 2584    BD +23 4830p1
0           126928 +10 1274    BD +10 2072p1
0           126930 +10 1275    BD +10 2072p2
0           129303 +10 1567    BD +10 2466p1
0           129304 +10 1568    BD +10 2466p2
0           133569 +12 1829    BD +12 3253s1
0           133571 +12 1830    BD +12 3253s2
0           134095 +19 1680    RY Her
0           134248 +11 1993a This star is a close companion to 134249. In
                            AGK3 this pair had only one entry (centre of
                            light?). It is unclear which of the companions
                            is HD 165475.
0           134249 +11 1993 This star is a close companion to 134248. In
                            AGK3 this pair had only one entry (centre of
                            light?). It is unclear which of the companions
                            is HD 165475, but from a remark in GC it is
                            clear that 44864 = SAO 103373 = GC 24655
0           134415 +10 2192    BD +10 3434s1
0           134416 +10 2193    BD +10 3434s2
0           136159 +19 1867 This AGK2 star was omitted in the printed
                            version of AGK3.
0           136160 +19 1866 Double star in AGK2: +19 1866 and +19 1867.
                            The AGK3 measurement refers to +19 1867 and not
                            to +19 1866.
0           148223 +05 0540    BD +05 0776p1
0           148226 +05 0541    BD +05 0776p2
0           149628 +05 0689    BD +05 1043p1
0           149631 +05 0690    BD +05 1043p2
0           150058  +1 0662 This AGK2 star was omitted in the printed
                            version of AGK3.
0           151093 +05 0860    BD +05 1373p1
0           151095 +05 0861    BD +05 1373p2
0           151096 +05 0862    BD +05 1373s1
0           151097 +05 0863    BD +05 1373s2
1
           (Introduction to PPM)                                     Page 19
-
            151581 +03 0887    BD +03 1471p1
0           151582 +03 0888    BD +03 1471p2
0           151709 +00 0825    BD +01 1635p1
0           152202 +03 0956    BD +03 1609p1
0           152207 +03 0957    BD +03 1609p2
0           152338 +04 0950    BD +04 1652p1
0           152339 +04 0951    BD +04 1652p2
0           152441 +03 0987    BD +03 1651s1
0           152442 +03 0988    BD +03 1651s2
0           154155 +02 1086    BD +02 1916s1
0           154161 +02 1089    BD +02 1916s2
0           159258 +07 1684    BD +08 2654s1
0           159259 +07 1685    BD +08 2654s2
0           159970 +07 1756    BD +08 2747s1
0           159973 +07 1757    BD +08 2747s2
0           161865 +05 2052    BD +05 3070s1
0           161866 +05 2053    BD +05 3070s2
0           163056 +06 1957    BD +06 3288p1
0           163059 +06 1958    BD +06 3288p2
0           164086 +08 2122    BD +08 3427s2
0           165886 +07 2419    possibly BD +7 3700
0           167690 +06 2469    BD +06 4103s1
0           167691 +06 2470    BD +06 4103s2
0           168472 +08 2604    BD +08 4190p1
0           168475 +08 2605    BD +08 4190p2
0           168783 +08 2638    BD +08 4237s1
0           168787 +08 2639    BD +08 4237s2
0           169828 +09 2732    BD +09 4492p1
0           169830 +09 2733    BD +09 4492p2
0           171945 +07 3164    BD +06 4855s1
0           171946 +07 3165    BD +06 4855s2
1
           (Introduction to PPM)                                     Page 20
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0           173580 +6 3146  Inspection on POSS shows: Both AGK2 and AGK3
                            are correct. This star is not measured in AC,
                            but there is a star in AC nearby at position:
                            22 56 41.10 +6 36 36.4, Epoch 1918.77.
                            On POSS the AC star has a faint companion.
0           173772 +06 3158    BD +05 5135p2
0           173773 +06 3157    BD +05 5135p1
1
           (Introduction to PPM)                                     Page 21
-
           7. Short Explanation of the Magnetic Tape Version of PPM
           ========================================================
-          The PPM magnetic tape contains 5 physical files.  The records
           within each file have constant length.  They are grouped into
           physical blocks of various constant lengths depending on how
           the tape has been prepared.
0          The five files are:
0           - File 1: The text of this Introduction to PPM, in exactly
                      the same format as the printed Introduction.
            - File 2: The catalogue as an easily readable table, very
                      similar to the format of the printed catalogue.
            - File 3: The catalogue in the format in which the preliminary
                      version of PPM was delivered in 1988.
            - File 4: The southern part of the SAO Catalogue, in the same
                      format as file 2.
            - File 5: The southern part of the SAO Catalogue, in the same
                      format as file 3.
0          The remainder of this chapter gives very short descriptions of
           these five files. It describes only the formats of the files. The
           precise meaning of the individual data items is not described
           here, but in the Explanation of the Printed Catalogue (Chapter 8,
           below). In the present chapter the individual data items are
           denoted by mnemonic abbreviations which are the keys to the
           explanations in Chapter 8.
0          The tables defining the individual files give the following
           information for each data item:
            - name of the item (mnemonic)
            - position of the item within each record (first and last byte)
            - FORTRAN format
            - physical unit, if any
            - maybe a remark
0          In addition there is information on record length etc. at the top
           of each table.
-          File 1: The Introduction to PPM
+          _______________________________
0          This is a text file, given in exactly the same format as the
           printed Introduction to PPM. Record length is 80 bytes, but only
           76 bytes are actually used (the remaining being always blank).
           This file can be used to produce printed versions of the
           Introduction to PPM on any printer able to interpret the paper
           feed characters '1' (form feed), ' ' (single line feed), '0'
           (double line feed), '-' (triple line feed) and '+' (no line
           feed).  Page headings, page numbering etc. appear as in the
           printed Introduction.  Just submit the file to your printer. The
           printed pages contain 66 lines at maximum.
1
           (Introduction to PPM)                                     Page 22
-
           File 2: The PPM catalogue as an easily readable table
+          _____________________________________________________
0          This is the main file giving the catalogue proper. Record length
           is 133 bytes. The format is very similar to that of the printed
           catalogue. You can use this file to produce a rough printed
           version of PPM by just submitting it to a printer capable of
           printing 133 characters per line.  No page headings, form feed
           characters etc. are included, of course.
0           PPM     2 -   7   I6
            DM     10 -  18   A9
            Mag    20 -  23   F4.1
            Sp     25 -  26   A2
            R.A.   28 -  39   F2.0,1X,F2.0,1X,F6.3  hours, minutes, seconds
            Sign   42 -  42   A1  Sign of declination ('+' or '-').
            Dec.   43 -  53   F2.0,1X,F2.0,1X,F5.2  degrees, arcmin, arcsec
            PMA    56 -  62   F7.4       sec/year
            PMD    64 -  69   F6.3       arcsec/year
            N      71 -  72   I2
            SA     74 -  75   F2.0       0.01 arcsec
            SD     77 -  78   F2.0       0.01 arcsec
            SPMA   80 -  83   F4.1       0.001 arcsec/year
            SPMD   85 -  88   F4.1       0.001 arcsec/year
            EPA    90 -  94   F5.2       years since 1900.0
            EPD    96 - 100   F5.2       years since 1900.0
            SAO   102 - 107   I6
            HD    109 - 114   I6
            AGK3  117 - 125   A9
            Notes 127 - 131   5A1
0          Be careful not to miss the sign of the declination (byte 42)
           while transforming this formatted file into a numeric file on
           your computer.
-          File 3: The PPM catalogue in the format of the preliminary PPM
+          ______________________________________________________________
0          File 3 again contains the catalogue proper. It was added to the
           PPM tape just for the convenience of those users that received
           the preliminary PPM on tape. To transfer File 3 from the tape to
           their home computer they can use exactly the same reading routine
           as for the preliminary PPM.  The only difference is in bytes 2 to
           10, which now contain the PPM number, but contained the AGK3
           number in the preliminary PPM.
0          Note that some information contained in File 2 is missing.  On
           the other hand, File 3 gives a version of PPM for equinox and
           epoch B1950.0, FK4 system (see items RA50, Dec50, PMA50 and PMD50
           in the table below).
0          Record length is 138 bytes.
0                   2 -   4   A3    3 characters 'PPM'
            PPM     5 -  10   I6
            Mag    11 -  16   F6.1
            Sp     19 -  20   A2
            Note   22 -  22   A1    Problem flag. May be blank, 'P' or 'C'.
                                    For further explanations see column
                                    19.1 of the printed catalogue.
            RA50   24 -  38   D15.8   radians
                                      Right ascension for equinox and
                                      epoch B1950, FK4 system
1
           (Introduction to PPM)                                     Page 23
-
            Dec50  40 -  54   D15.8   radians
                                      Declination for equinox and epoch
                                      B1950, FK4 system
            PMA50  56 -  67   D12.5   radians/tropical century
                                      Proper motion in R.A. for equinox and
                                      epoch B1950, FK4 system
            PMD50  69 -  80   D12.5   radians/tropical century
                                      Proper motion in Dec. for equinox and
                                      epoch B1950, FK4 system
            R.A.   82 -  96   D15.8   radians
                                      Right ascension for equinox and
                                      epoch J2000, FK5 system
            Dec.   98 - 112   D15.8   radians
                                      Declination for equinox and
                                      epoch J2000, FK5 system
            PMA   114 - 125   D12.5   radians/julian century
                                      Proper motion in R.A. for equinox
                                      and epoch J2000, FK5 system
            PMD   127 - 138   D12.5   radians/julian century
                                      Proper motion in Dec. for equinox
                                      and epoch J2000, FK5 system
-
           File 4: Southern part of SAO Catalog in the format of File 2
+          ____________________________________________________________
0          We are well aware of the fact that any user of an astrometric
           catalogue such as PPM needs the entire sky.  File 4 is intended
           to provisionally satisfy this need because a southern hemisphere
           extension of PPM is not yet available.
0          The file contains a J2000 version of the southern portion of the
           SAO Catalog. This portion was selected from the original SAO
           Catalog in such a way that there is neither a gap nor an
           overlap with PPM on the sky.  The machine-readable version of the
           SAO Catalogue provided by Roman and Warren (1984) was used for
           this purpose.  The SAO coordinates and proper motions were
           transformed to the equinox and epoch J2000 (FK5 system) in the
           standard way.
0          Basically, the format of File 4 is the same as that of File 2.
           But the following data items are always blank: PPM, N, SA, SD,
           EPA, EPD, AGK3, and all Notes except the last one.  The last of
           the five Notes, corresponding to column 19.5 of the printed
           catalogue, is always set to 'S'.
-
           File 5: Southern part of SAO Catalog in the format of File 3
+          ____________________________________________________________
0          File 5 provides the same subset of the SAO Catalog as File 4,
           but in a different format.  The format of File 5 is the same as
           that of File 3, except for the first two data items. Bytes 2 to 4
           contain the 3 characters 'SAO' instead of 'PPM' and bytes 5 to 10
           contain the SAO number instead of the PPM number.
1
           (Introduction to PPM)                                     Page 24
-
           8. Short Explanation of the Printed Catalogue
           =============================================
0          The stars are arranged in bands of 10 degrees width in decli-
           nation.  Within each of these bands they are ordered according to
           right ascension. This arrangement was also used in the SAO
           Catalog.
0          Column 1, PPM     Serial no. of the star in PPM.
0          Column 2, DM      Designation of the star in the Bonner
                             Durchmusterung. Doubtful identifications
                             are omitted (blank). The character 'x' denotes
                             peculiar DM suffixes, which are given in the
                             List of Remarks on Individual Stars.
0          Column 3, Mag     Photographic magnitude, copied from AGK3.
                             Visual magnitude for FK5 stars, copied from FK5
0          Column 4, Sp      Spectral type, copied from AGK3; for FK5 stars
                             copied from FK5.
0          Column 5, R.A.    Right Ascension for the equinox and epoch
                             J2000.0, on the system of FK5, given in
                             hours, minutes and seconds of time.
                             For FK5 stars original FK5 data are given.
0          Column 6, Dec.    Declination for the equinox and epoch
                             J2000.0, on the system of FK5, given in
                             degrees, minutes and seconds of arc.
                             For FK5 stars original FK5 data are given.
0          Column 7, PMA     Proper Motion in Right Ascension for epoch
                             and equinox J2000.0, on the system of FK5,
                             given in seconds of time per Julian year.
                             For FK5 stars rounded FK5 data are given.
0          Column 8, PMD     Proper Motion in Declination for epoch and
                             equinox J2000.0, on the system of FK5,
                             given in seconds of arc per Julian year.
                             For FK5 stars rounded FK5 data are given.
0          Column 9, N       Number of individual published positions
                             used for the derivation of the position
                             and proper motion given (cols. 5 to 8).
                             For FK5 stars N is set to zero.
0          Column 10, SA     Mean error of right ascension at the mean
                             epoch of right ascension, multiplied by the
                             cosine of declination, given in units of
                             0.01 seconds of arc.
                             For FK5 stars rounded FK5 data are given.
0          Column 11, SD     Mean error of declination at the mean
                             epoch of declination, given in units of
                             0.01 seconds of arc.
                             For FK5 stars rounded FK5 data are given.
0          Column 12, SPMA   Mean error of proper motion in right ascension,
                             multiplied by the cosine of declination,
                             given in milliseconds of arc per Julian year.
                             For FK5 stars rounded FK5 data are given.
1
           (Introduction to PPM)                                     Page 25
-
0          Column 13, SPMD   Mean error of proper motion in declination,
                             given in milliseconds of arc per Julian year.
                             For FK5 stars rounded FK5 data are given.
0          Column 14, EPA    Weighted mean epoch of the individual published
                             positions used for the derivation of right
                             ascension and proper motion (cols. 5 and 7),
                             given in years since 1900.0.
                             For FK5 stars original FK5 data are given.
0          Column 15, EPD    Weighted mean epoch of the individual published
                             positions used for the derivation of decli-
                             nation and proper motion (cols. 6 and 8),
                             given in years since 1900.0.
                             For FK5 stars original FK5 data are given.
0          Column 16, SAO    Designation of the star in the SAO Catalog.
                             Doubtful identifications are omitted.
0          Column 17, HD     Designation of the star in the Henry Draper
                             Catalogue.
                             Doubtful identifications are omitted.
0          Column 18, AGK3   Designation of the star in AGK3.
                             Doubtful identifications are omitted.
0          Column 19, Notes  A number of notes on the individual stars are
                             given in these columns. Notes P, C and D mark
                             objects that should preferably not be used as
                             astrometric reference stars.
0              Column 19.1   P    problem case, preferably not to be used as
                                  astrometric reference star.
               Column 19.1   C    a critical remark on this object is given
                                  in the List of Critical Remarks, it
                                  should not be used as astrometric refe-
                                  rence star.
               Column 19.2   D    double star, preferably not to be used as
                                  astrometric reference star.
               Column 19.3   H    member of the High-Precision Subset (HPS)
                                  of PPM.
               Column 19.4   F    member of FK5, high precision stars,
                                  mostly very bright stars.
               Column 19.5   R    a remark on this star is given in the
                                  List of Remarks on Individual Stars.
1
           (Introduction to PPM)                                     Page 26
0
           References
           ==========
0          Bastian, U., Roeser, S. (1990): in preparation.
0          Bien, R. (1988): private communication.
0          CMC (1985-1988): Carlsberg Meridian Catalogue La Palma,
                  Numbers 1 to 4. Copenhagen University Observatory,
                  Royal Greenwich Observatory and Real Instituto y
                  Observatorio de la Armada, San Fernando.
0          Corbin, T. (1978): The proper motions of the AGK3R and SRS
                  stars. IAU Colloquium No. 48, Eds. F.V Prochazka and
                  R.H. Tucker, 515.
0          Dommanget, J. (1988): in HIPPARCOS, Scientific Aspects of
                  the Input Catalogue Production II, Proceedings of a
                  Colloquium held at Sitges, Spain, 1988,
                  eds. J. Torra and C. Turon, page 191.
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1
           (Introduction to PPM)                                     Page 27
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           Acknowledgments
           ================
0          Generations of careful and patient observers and plate measurers
           have laid the base for the present work. Compared to their labour
           all other efforts that went into the preparation of PPM - inclu-
           ding our own - are small.
0          We gratefully acknowledge the help of Hamburger Sternwarte (C. de
           Vegt and H. M. Steinbach) and of Observatoire de Strasbourg
           (D. Egret and A. Fresneau) in providing the raw Astrographic
           Catalogue on punched cards. Several tons of cards were moved with
           the help of many hands in Strasbourg.  Also we thank T. Corbin of
           US Naval Observatory for providing a magnetic tape containing
           part of the Strasbourg punched data already.
0          Heidelberger Druckmaschinen AG is gratefully acknowledged for
           technical help in the reading of the punched cards.
0          We thank the CMC group at La Palma for giving the CMC 4 catalogue
           to us prior to publication.
0          Last but not least we have to thank many people at our institute,
           especially E. Roehl and E. Mueller for careful checks and
           completion of the Astrographic Catalogue data, M. Erbach, M.
           Fleischer and T. Lederle for much valuable information on source
           catalogues, H. Schwan for many fruitful discussions and for his
           data on systematic differences between several catalogues, R.
           Bien for the determination of weights for the CMC catalogues and
           H. Bernstein for advice on mathematical statistics. Finally we
           want to thank R. Wielen, director of ARI, for giving us the
           opportunity to do this work.
