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6.5 in 9.0 in -1.0 in [missing file: psfig.sty] AC 2000.2: The Astrographic Catalogue on <BR> The Hipparcos System 2016-07-26

AC 2000.2: The Astrographic Catalogue on
The Hipparcos System

Sean E. Urban, Thomas E. Corbin and Gary L. Wycoff
United States Naval Observatory, Washington, DC ∧ Erik Høg, Claus Fabricius, and Valeri Makarov
Copenhagen University Observatory, Denmark

Catalogue of Positions Derived from the Astrographic Catalogue Measures. Positions are on the Hipparcos System (HCRS, J2000.0) at the Mean Epochs of Observation.



1  Introduction

The AC 2000.2 is a revised version of the 1997 release of the AC 2000 (Urban et al. 1998). It was decided that the availability of an improved reference catalogue and the inclusion of the Tycho-2 photometry would be sufficient to warrant a complete re-reduction of the data and a new distribution of the catalogue.

The AC 2000.2 is a catalogue of positions and magnitudes of 4,621,751 stars covering the entire sky around the epoch of 1900. The data are derived from the images measured and published as part of the Astrographic Catalogue (AC). The positions are on the Hipparcos reference frame (ESA 1997), having originally been reduced plate-by-plate using an updated version of the Astrographic Catalog Reference Stars. Each of the 22 zones of the AC has been reduced independently, since telescopes, observing techniques and measurement methods varied. This document describes the history behind the Astrographic Catalogue, the reference catalogue used to transform the measurements to equatorial coordinates, the methodology employed in this transformation, the resulting catalogue and information about each participating observatory.

2  The Carte du Ciel

The Carte du Ciel was an international effort begun more than a century ago to determine positions better than 0.5 arcsec for all stars 11th magnitude and brighter using photographic plates and, using another set of plates, to publish charts representing the relative positions of all stars of 14th magnitude and brighter. The charts – generally called CdC – proved to be very expensive to photograph and reproduce, so many institutions did not complete this part of the work. However, the astrographic program designed to measure all stars to 11th magnitude was completed. Actually, the original goal of 11th magnitude was generally surpassed. In fact, some observatories routinely measured stars as faint as 13th magnitude. These plate measures, as well as the formulae used to transform them to equatorial coordinates, have been published in what is known as the Astrographic Catalogue (AC).

In total, 20 observatories from around the world participated in exposing and measuring the AC plates. Each was assigned a specific zone, between two parallels of declination, to photograph. In order to compensate for any plate defects, each area of the sky was to be photographed twice, using a two-fold, corner-to-center overlap pattern. This pattern was continued even at the zone boundaries; each observatory's plates would overlap with those of the observatories responsible for the adjacent zones. The participating observatories agreed to standardize the type of telescope, so each plate photographed had a similar scale of approximately 60 arcsec/mm. The measurable areas of the plates were 2 × 2 degrees, so the overlap pattern consisted of plates that were centered on every degree band in declination, but offset in right ascension by two degrees. The first plates in the even degree bands were centered at right ascension 0 hours 0 minutes; the first plates in the odd degree bands were centered with right ascension several minutes higher (corresponding to approximately one degree).

In addition to the overlap pattern and type of telescope, the observatories also agreed to expose a grid, called a réseau, on each plate. It was originally used to monitor emulsion shifts. After the shifts were demonstrated to be quite small, the practice of exposing a réseau on each plate was continued because it aided in the measuring of the star positions by letting the measurer refer each image position to the grid lines. Each réseau unit was approximately 5 mm. The réseau orientation defined the plate's x,y coordinate system.

All participating observatories (with the exception of Vatican) used one of two measuring methods, short-screw or eyepiece scale. In both methods, a set of spider wires was centered over an image, then the distance traveled by the slides carrying the spider wires was read. With the short-screw method, this distance was read off of the screws used to move the slides. Whereas for the eyepiece scale method, this distance was inferred by a scale in the focal plane of the microscope. In general, the eyepiece scale method was faster, but less precise.

Although telescope type, plate size, and use of a réseau were standardized, many other factors, such as reference catalogue used, reduction technique and printing formats were left up to the individual institutions.

3  Published Data

Most observatories published their results in several volumes, each of which consists of measures from plates centered on the same degree of declination. Generally, each line in the printed volumes contains data for one star, including the measured x,y value, a measure of brightness (magnitude or diameter), the plate number and a running number on the plate. Other data concerning epoch of exposure, hour angle at mid-exposure, air temperature, barometric pressure, réseau used, observer, measurer and measuring machine are usually provided by plate in separate tables. Additionally, provisional plate constants used to transform the x,y measures to standard coordinates are typically supplied.

The published data have been transferred to machine-readable form via double-entry (that is, typing each record twice to remove most keying mistakes) including errata found in the published volumes. An additional literature search has been conducted on all zones to increase the probability that all published errata not found with the original volumes have been corrected. Each page of each volume was searched for pertinent notes. If important notes were found, they were entered and the measures to which they refer were flagged. A summary of the data entry information can be found in Table tab:keypunch.

4  Compiling a New Reference Star Catalogue

The reference catalogue used throughout the individual plate reductions of the 1997 version of AC 2000 (hereafter referred to as AC 2000.1) was the Astrographic Catalog Reference Stars (ACRS; Corbin & Urban 1988, Corbin & Urban 1990, Corbin & Urban 1991). This was compiled on the system of the FK5 as realized by the International Reference Stars (IRS, Corbin 1991), and utilized the best data and reduction techniques available in the early 1990s.

Since its compilation, the FK5 has been superseded by the Hipparcos Catalogue. It was recognized that with the increased number of stars in the Hipparcos Catalogue over the FK5/IRS (~ 118,000 vs. ~ 40,000), the conversion of the catalogues making up the ACRS to the system of Hipparcos could be done more rigorously than the earlier conversions to the FK5 system. Since the systematic errors could be determined and removed more thoroughly, the final combined catalogue would be better. Additionally, the FK5/IRS data become very sparse fainter than magnitude 9.0, whereas Hipparcos contains over 35,000 stars listed as V=9.0 or fainter. This magnitude extension allows the removal of systematic errors in the fainter stars – something that was problematic for the original ACRS.

In addition to Hipparcos, several new catalogues unavailable at the time of compiling the original ACRS have been released. The most notable are the Tycho-1 Catalogue (ESA 1997), the Twin Astrograph Catalogue (TAC, Zacharias & Zacharias 1999), FOKAT (Polozhentsev et al. 1989), and a recompiled Second Cape Photographic Catalogue (CPC2, Zacharias et al. 1999).

Due to these improvements in astrometry, it was decided to compile a new reference catalogue. In this document, this new catalogue will be referred to as ACRS_1999. The ACRS_1999 is not being released as a separate catalogue because the data used in computing the astrometry were subsequently used in computing the proper motions of the Tycho-2 Catalogue (Høg et al. 2000). The ACRS_1999 can be thought of as a specialized subset of the data going into Tycho-2, which completely supersedes it.

4.1  Conversion of input catalogues to HCRS

The Hipparcos Catalogue (ESA 1997) plays a special part in the ACRS_1999. It is recognized as the optical realization of the International Celestial Reference Frame, ICRF (IAU 1999). The frame defined by the Hipparcos data is termed Hipparcos Celestial Reference Frame, HCRF (IAU 2001); the HCRF contains all Hipparcos stars with the exception of those believed to be multiple. These data – taken from the Hipparcos Catalogue – were used to convert all input catalogues to the HCRF by the method described below.

In total, 145 different observational catalogues (termed input catalogues in this document) were included specifically to strengthen the positions of the ACRS_1999 stars when brought to the epochs fo the AC plates. A list of these catalogues is found in Table tab:acrs. Each of the catalogues was converted to a standard format. Next, zero point corrections and elliptical aberration terms were applied, when necessary, to convert the positions to roughly coincide with the FK5 J2000.0 system. Following this, the Hipparcos stars contained in each catalogue were identified. Differences in right ascension and declination were computed for these stars following the application of the Hipparcos proper motions to bring the Hipparcos positions to the epochs of the input catalogue positions.

To remove the systematic differences between these input catalogs and Hipparcos, ``local'' mean differences between each catalogue and Hipparcos were made, and corrections to the input catalog positions based on those differences were applied. To compute these differences, for each star in the catalogue, nearby stars in common with Hipparcos were identified. In order to compute local systematic errors and not follow the random errors, a minimum number of stars in common to the input catalogue and Hipparcos had to be enforced. This minimum number was based on each input catalogue's random errors. For catalogues with large random errors, more Hipparcos stars were needed. The range in required Hipparcos stars was from 3 for the most accurate catalogues to 30 for the least accurate.

Additionally, since determining local systematics was the goal, only those stars in common with Hipparcos and close on the celestial sphere were used. For astrographs, typically the Hipparcos stars within two degrees of the star to be corrected were utilized. For transit circles, typically the Hipparcos stars within 30 minutes of time in right ascension and 5 degrees in declination were used. If the minimum number of stars discussed in the previous paragraph could not be met, the area could be expanded. How far this expansion was carried out was dependent on how quickly, spatially speaking, the systematic deviations from Hipparcos were changing. Catalogues whose density of Hipparcos stars was too low to adequately perform a local reduction were dropped from the input catalogue list.

Once nearby catalogue entries of Hipparcos stars were found for each input catalogue star, their positional differences with the Hipparcos data – that is, their residuals – were used to compute the local reduction to the Hipparcos system. Weights were assigned to each residual based on the distance to the star being corrected. To more heavily favor nearby Hipparcos stars, an elliptical, parabolic weighting method was used, as seen in the following equation.
  wi = 1 – \left[ \left( Dαi/ maxDα \right) 2+ \left( Dδi/ maxDδ \right) 2\right] (1)
The value of wi is the weight of the ith residual, Dαi and Dδi are the distances in right ascension and declination between the catalogue star whose correction is being computed and the ith Hipparcos star, and maxDα and maxDδ are the maximum distances whose weight is non-zero in right ascension and declination. Once weights to each nearby Hipparcos residual are computed, the weighted mean residual vector can be computed in the standard way. That is, for right ascension,
  Δ(α) = Σwi Δi(α)/Σwi (2)
where Δ(α) is the weighted mean vector in the right ascension direction, Δi(α) is the residual of the ith Hipparcos star. Similar formulation is used for the declination vector. A summation is used to get the mean residual vector, which is the systematic difference between the Hipparcos Catalogue and the input catalogue at that specific location. Hence, subtracting this vector from a star position will put it close to the HCRF.

The above technique describes correcting a catalogue for systematic differences with Hipparcos based on right ascension and declination. However, it is well known that other systematic deviations exist, most notably those based on magnitude and color. These, in turn, may have a positional dependency associated with them; so, corrections based on right ascension, declination, magnitude, color and all combinations of the four were computed and applied. This was done similarly to the technique just describe, however the definition of ``local'' was expanded to include those stars nearby not only in right ascension or declination, but also similar in magnitude or color. In order for a magnitude-dependent correction to be computed, typically only Hipparcos data from stars that were within 0.1 magnitudes of the input catalogue star were used. The same 0.1 magnitude difference in B-V was usually utilized in performing color corrections.

4.2  Computing catalogue weights

Once a catalogue was believed to be on the HCRS, individual star differences from Hipparcos were computed. (Note that the conversion to the HCRS utilized weighted mean differences using several stars, not individual differences.) These were used to compute the catalog standard error and weight utilizing the well-known formulae
  σα,δ = sqrt( Σ(xi)2– (Σxi)2/N/N) (3)
  Wα,δ = 1/σα,δ2 (4)
where σα,δ is the standard error per catalogue entry in right ascension and declination, xi are the individual differences between the stars in common between the input catalogue and Hipparcos in right ascension and declination, and N is the total number of stars in common between the two. The value Wα,δ is simply the computed weight of the catalogue in right ascension and declination. For some input catalogues, the number of observations per catalog entry given. In these cases, an error (hence weight) per observation could be computed. These catalogues have a ``Yes'' under the σ/sqrt(N) column of Table tab:acrs. For many catalogues, however, only a standard error (hence weight) per catalogue entry could be computed. These catalogues have a ``No'' under the σ/sqrt(N) column of Table tab:acrs.

This procedure was used for most catalogs; a few, however, had error estimates available for each star that closely coincided with the newly computed estimates. In these cases, the additional information in the form of published error estimates (hence weights) was used.

4.3  Computation of ACRS_1999 positions and motions

The reduced positions were grouped together by indivisual star. Mean positions, proper motions, and error estimates were computed following the method outlined by Corbin (1977), briefly described here.

4.3.1  ACRS_1999 mean positions

Computations are made using position unit vectors, defined by
  xi = cosδi ×cosαi (5)
  yi = cosδi ×sinαi (6)
  zi = sinδi (7)
Weighted mean (x,y,z) values, denoted as ({bar}x,{bar}y,{bar}z) and their associated epochs can be easily computed using the computed weights. Note that the weights wx, wy, and wz are equal to wα, wα, and wδ, respectively. From ({bar}x,{bar}y,{bar}z), a conversion back to mean right ascension and declination, ({bar}α, {bar}δ), is made using the formulae
  {bar}α = \left( {bar}y/{bar}x \right) (8)
  {bar}δ = \left( {bar}z/sqrt( 1 – {bar}z2) \right) (9)

4.3.2  ACRS_1999 proper motions

To compute proper motions, first the time derivatives of (x,y,z), denoted ({dot}x,{dot}y,{dot}z), are computed using
  {dot}x = Σxi ⋅wi ⋅τi/Στi2⋅wi (10)
with similar equations for {dot}y and {dot}z. The variable τi is the epoch difference between the ith catalogue position and the weighted mean epoch. Finally, proper motions in right ascension and declination, µα, µδ, are computed using
  µα= {dot}y {bar}x – {dot}x {bar}y /{bar}x2+ {bar}y2 (11)
  µδ= {dot}z/sqrt( (1–{bar}z2)) (12)

4.3.3  ACRS_1999 error estimates

The U.S. Naval Observatory typically computes standard error estimates based on the residuals of catalogue positions making up the mean position and proper motion. This has been termed the scatter method, because it is based on the scatter of the data around the computed value. The formulae used are detailed in Corbin (1977). For standard errors of the mean right ascension and declination, σ{bar}α, σ{bar}δ, we have
  σ{bar}α = \left[ Σ(Δyi {bar}x – Δxi {bar}y)2wi/(1–{bar}z2)(n–2)Σwi \right] 1/2 (13)
  σ{bar}δ = \left[ Σ(Δzi wi)/(1–{bar}z2)(n–2)Σwi \right] 1/2 (14)
where the values of Δxi, Δyi, Δzi are the residuals of the ith catalogue position from the computed (x,y,z) values at ith catalogue epoch. For the computation of the standard errors of µα and µδ we have
  σµα = \left[ Σ(Δyi {bar}x – Δxi {bar}y)2wi/(1–{bar}z2)(n–2)Σwi ⋅τi2 \right] 1/2 (15)
  σµδ = \left[ Σ(Δzi wi)/(1–{bar}z2)(n–2)Σwi ⋅τi2 \right] 1/2 (16)
where n is the number of catalogue positions used to compute {bar}α, {bar}δ,µα, and µδ. Even a cursory look at the above formulae will show that computation of the standard errors using this method cannot be made if there are only two catalogue positions used. In this case, the formulae
  σ{bar}α = \left[ 1/Σwi2 ∑wi2⋅σαi2 \right]1/2 (17)
  σµα = \left[ \left( 1/Στi2 \right)2 1/Σwi2 ∑wi2⋅σαi2⋅τi2 \right]1/2 (18)
were used. Similar formulae were used to compute position and proper motion errors in declination.

4.3.4  Refining the catalog

Since the purpose of compiling the ACRS_1999 was to provide a source of reference stars used to reduce the AC data on to the system defined by Hipparcos, it was decided to utilize the astrometry from the Hipparcos Catalogue for the ~30% of the stars in common. Hence the Hipparcos data were substituted for the compiled data. Hipparcos stars flagged with a G, V, or X in the Double and Multiple Flag field (H59) were removed from the ACRS_1999, as their astrometry is suspect. Additionally, stars marked in that same field with an O (orbit stars) were removed if the semi-major axis exceeded 100 mas. All stars marked as orbit stars in the Washington Double Star Catalog (WDS; Worley and Douglass 1996) were removed. Since measurements of blended images on the AC plates are often suspect, when an ACRS_1999 stars was found within 5 arcsec of another ACRS_1999 star, both were removed. Finally, all ACRS_1999 stars whose positional errors in either coordinate at epoch 1900 were computed to be at 450 mas or higher were removed.

4.3.5  ACRS_1999 characteristics

The ACRS_1999 contains 391,838 stars distributed over the entire sky, resulting in an average density of just under 10 stars per square degree. The magnitude distribution, using the Tycho-1 visual magnitude, can be seen in Fig fig:magdist.

The astrometric errors are magnitude dependent. Figures fig:poserr and fig:muerr – indicating positional errors at the ACRS mean epoch and proper motion at the same epoch, respectively – show this dependency. The wide range in positional errors, from near 1 mas for the brighter stars to over 30 mas for stars between magnitude 10 and 11, is due to the Hipparcos star distribution in the ACRS_1999. Positional errors in the Hipparcos Catalogue are generally 1 to 3 mas; for the best non-Hipparcos catalog, Tycho-1, the errors run from 10 to 50 mas. This is reflected in Fig. fig:poserr. For stars brighter than 8th magnitude, the primary source of astrometry is Hipparcos. Between 8 and 11, the ratio of Hipparcos to non-Hipparcos stars drops, and hence the errors increase. Beyond about magnitude 11, this ratio begins to increase, so the positional errors once again drop.

This same trend is reflected in the proper motion errors, seen in Fig. fig:muerr. The span in errors is less, however, since the Hipparcos values are generally between 1 and 3 mas/year whereas without Hipparcos, values of 2 to 5 mas/year are normal. No downturn of errors in the faintest stars is seen; this is where the Hipparcos proper motion errors are their highest.

magdist.psMagnitude distribution of the 371,838 ACRS_1999 stars is shown. Magnitude is from the Tycho-1 V (VT). The bar centered at magnitude 5.25 contains all stars brighter than 5.50. The one at 12.25 contains all stars at 12.00 and fainter. Positional errors of the ACRS_1999 stars by magnitude. The positional error is for the mean epoch of observation. Plotted are the averages of all stars taken within each magnitude range. Proper motion errors of the ACRS_1999 stars by magnitude. Plotted are the averages of all stars taken within each magnitude range.

Having the ACRS_1999, with a density providing an adequate number of reference stars on each AC plate (35 on average) and being on the Hipparcos system, allows one to continue the plate reduction process.

5  Preparing the Data for the Plate Reduction Software

It was necessary to prepare the data for the plate adjustment software. The preparation process consisted of three discrete tasks: matching the images with reference stars; matching images with those of the same star on another plate; and converting the data to a standard format. The last two steps were performed during the AC 2000.1 work. However, since they are an integral part of the reduction process, the descriptions are repeated here.

5.1  Matching images with the reference stars

Equatorial coordinates for all AC images were computed from the rectangular coordinates via the published plate constants. The ACRS_1999 data were then brought to the average epoch of each zone and transformed to the AC equinox, B1900.0. A positional match was then made between the AC and ACRS_1999. Checks were made to ensure that illegitimate matches had not taken place. An example of an illegitimate match is an ACRS_1999 star that matches with two separate AC images that are on the same plate. Also at this stage, all plates were checked to ensure that each contains an adequate number of identified reference stars. Fewer than expected matched reference stars on a plate may indicate problems with the published constants or plate centers. These plates were investigated, and the problems were corrected.

5.2  Matching images with those on other plates

The same equatorial coordinates computed in the previous step were used to identify images of the same stars that lie on different plates. Images within 2.0 arcsec of each other were generally identified as the same star at this stage. Illegitimate matches were investigated and treated appropriately. Each image was then assigned an internal star number that is unique for each star in the zone, regardless of the number of plates on which it appears. The data were verified to ensure that all images marked with an ACRS_1999 number have the same internal star number, and vice versa. No two images on one plate were allowed to have the same internal star number.

5.3  Converting data to a standard format

The data were combined in one, standard format file. This file contained all pertinent information about each plate and image. Plate information such as plate centers, sidereal time of exposure, meteorological data, measuring machine and measurer, réseau used, emulsion type, and epoch of exposure were included, if they were published. Data pertaining to each star, that is the x,y values, image diameter or magnitude, internal star number, and ACRS_1999 identifier, were included. A conversion from the published x,y units to units of millimeters, along with a translation of the coordinates to ensure that the origin is in the approximate plate center, was performed when necessary. The persons responsible for the zone preparations can be found in Table tab:people.

5.3.1  Conversion of the AC Magnitudes

The Astrographic Catalogue as originally published contains magnitude measures – usually in the form of image diameters and formula to convert them to stellar magnitudes. However these are non-uniform between zones, in part because of different techniques used by participating observatories. Many of the published magnitude measures are unreliable, especially for the faintest and brightest stars. Thus, it is desirable to transform them to a well-known – or often used – system, preferably to the same system as the reference catalogue, thus facilitating the removal of systematic errors that are a function of magnitude. The plates used were most sensitive in the blue spectral region, so a logical choice of systems was the Tycho-2 blue (BT). Tycho-2 contains about 2.5 million stars covering much of the AC magnitude range. The Tycho-2 photometry was made available for this in advance of publication.

Each zone was treated independently. Only stars identified in Tycho-2 as being single and with negligible variability were used for the calibration. Differences between AC and Tycho-2 BT magnitudes as a function of AC magnitude were computed. Polynomial expressions describing the results were computed via least-squares fitting. Some extrapolation of these polynomials was required because for most zones the magnitude limit is fainter in the AC than in Tycho-2. (Usually an extrapolation of less than 0.5 magnitude was used. Beyond that the corrections were held constant). For stars not used to compute the calibration – primarily non-Tycho-2 stars – the magnitudes found in the AC 2000.2 are based on the published diameters and the derived polynomial expressions. For stars in common with Tycho-2, the Tycho-2 BT magnitudes are given.

6  Preliminary Reductions and Investigation of Plate Models

The core of the plate reduction software was the same as that used in the reductions of the Cape Photographic Catalogue 2 data (Zacharias et al. 1992). For all zones, an eight-constant plate model, consisting of four orthogonal terms (a,b,c, and d), two non-orthogonal terms (e and f) and two tilt terms (p and q) was initially used, as shown in Eqs. eq:xmodel1 and eq:ymodel1 .
  ξ= ax + by + c + ex + fy + px2+ qxy (19)
  η= ay – bx + d – ey + fx + pxy + qy2 (20)
At this step, no corrections to the published x,y values were applied. Investigations of radial distortions, tangential distortions, magnitude equation, coma, periodic measuring errors and réseau-dependent systematic errors were investigated for each zone following the procedures outlined previously (Urban & Corbin 1996; Urban et al. 1996). Since an uncompensated systematic error may cause a star to be an outlier, only reference stars with residuals over five times the standard deviation of unit weight of the solution were removed while various plate models were investigated.

6.1  Corrections to the x,y values

Results of investigations of systematic errors may lead to applying a correction to the published star measures prior to final plate constant determinations. These are typically done on a zone-by-zone basis.

To investigate if radial distortion exists in the data, the reference star radial residuals were plotted against distance from the plate center. If a radial distortion was present, the corrections were described by a non-zero function. Additionally, the radial residuals were examined for magnitude, measurer and measuring machine dependence. A similar investigation was conducted looking for the existence of a tangential distortion, however none was found in any of the zones.

The presence of a magnitude equation, which is a systematic offset of stars based solely on their brightness, was investigated by plotting the reference stars' residuals with respect to the Tycho-2 BT magnitude. This was performed separately for both the x and y coordinates. The existence of a magnitude equation that is dependent on the x,y measures was also investigated. Additionally, magnitude equation varying with measurer and plate epoch was considered. Note that a magnitude equation outside the range of the reference stars is extremely difficult to find (Eichhorn 1974). It is possible to compensate for a magnitude equation in the magnitude range of the reference stars, but it is unwise to extrapolate those corrections to field stars that may be two or three magnitudes fainter.

The presence of coma, a change in scale based on magnitude, is uncovered in two ways. First, investigating the x,y-dependent magnitude equation will reveal coma if it exists within the range of the reference stars. Second, using fainter stars, a plot of the difference between the mean position (computed from overlapping plates) and an individual image position vs. plate coordinates of the individual position will, using data from hundreds of stars and different magnitude ranges, reveal the presence of coma. If coma was found, it was examined for variations with respect to plate epoch.

Errors caused by the measuring mechanism were investigated by analyzing the residuals of reference stars as a function of location on the x and y measuring apparatus (usually a screw or an eyepiece scale, see Section 2). The presence of an error with a period corresponding to the length of the measuring screw or eyepiece scale is quite likely caused by the machining of that part, but may also be a function of the measurer. In either event, these errors can be corrected.

Additionally, the presence of a remaining field distortion pattern can be examined by using plots similar to those produced while investigating coma. These patterns were investigated for dependence on magnitude, réseau, measuring machine and measurer.

Using the information from these investigations, a plate model was developed for each of the AC zones. Equations (eq:xprime) and (eq:yprime) show the corrected x,y values used in the final plate adjustments.
  x= x+RD + TD + ME x + MC x + S x mx + MA x + FDP x (21)
  y= y+RD + TD + ME y + MC y + S y my + MA y + FDP y (22)
In Eqs. (eq:xprime) and (eq:yprime), RD is the correction applied to compensate for radial distortion; TD is the correction to compensate for tangential distortion; ME and MC are corrections to compensate for magnitude equation and x,y-dependent magnitude equation; S is the correction for coma; MA corrects for measuring apparatus errors, and FDP compensates for any remaining field distortion pattern. The variable m is the computed magnitude. By substituting x, y for x,y in Eqs. eq:xmodel1 and eq:ymodel1, the 8 constants for each plate were computed. The significant systematic errors found and corrected in each zone are listed in Table tab:const.

7  Investigation of Discordant Data

Once a suitable plate model was determined, the computed positions were used to investigate problems such as mismatched images, blended images of multiple stars and typographical errors. Much of this work was performed during the AC 2000.1 reductions; the description is repeated here for completeness.

7.1  Incorrectly matched images from overlapping plates

Images may be incorrectly matched in a variety of ways. Images are originally matched in the way described in the subsection ``Matching images with those on other plates.'' Positions computed from the provisional plate constants can change significantly due to the new reductions. So, images earlier believed to be from two stars because their positions were dissimilar may now be recognized as coming only from one if their new positions are closer. To investigate this possibility, images closer together than a certain distance were investigated. The distance chosen depended on the range in plate epochs (since proper motion will then be a factor) as well as accuracy of the x,y measures. Images that fall outside the expected precision may be a result of a double star, poor measurements of the same star or good measurements of a star that has moved due to proper motion. Deciding which was the case was often difficult because no comparable catalogue with the epoch of the AC plates exists with which to check the stars in question. The Preliminary Version of the Third Catalogue of Nearby Stars (Gliese & Jahreiss 1991) aided in detecting high proper motion stars, but this catalogue, as its name states, contains only nearby stars. The Luyten's Two-Tenths Catalogue and its supplement (Luyten 1979, 1980; Luyten & Hughes 1980) has also been used in aiding in the identification of high proper motion stars, as was the Hipparcos Catalogue. The Washington Double Star catalogue (WDS; Worley & Douglass 1996), the internationally recognized source of visual double star data, was also used but is limited because of its incompleteness over the AC magnitude range and its occasional use of AC data. However, certain criteria were followed in deciding if two images were from the same or different stars. These criteria were zone specific, but for most zones images were identified as coming from the same star if an image was within 3.5 arcsec of a mean position and there was no indication of duplicity. Images from different stars, but incorrectly identified as coming from the same star, will result in a high standard deviation in right ascension or declination, σα or σδ. Stars with the largest σα and σδ were investigated for this possibility.

7.2  Duplicate entries

Virtually every zone has mistakenly printed some of its measures more than once. These were easily found since the data in question was either exactly the same as another record (in cases of true duplication) or the resulting star positions of two records were ridiculously close for the telescope scale and typical seeing. In general, images closer than 1.0 arcsec that appear on the same plate were suspected of being duplicate entries. In cases of this type, generally only one of the measures was kept.

7.3  Blended images

Images of double stars that are blended on one plate but discrete on another require special treatment. Two possible problems exist under these circumstances. First, if the blend is identified as one of the separate images, then the computed separation of the double star will be smaller than it is in actuality (since the blend will fall near the photocenter). Second, if the blend is not identified with either discrete image, then three sets of coordinates will be computed where only two stars exist.

Under the first scenario (a blend is matched with a discrete image), the data will consist of a multiple star system with at least one star having a large standard deviation of position, σα or σδ. To investigate this possibility, the area around each star was searched for the presence of another star. If a nearby star was found, then the data were examined for a blend if σα or σδ of either star exceeded a certain amount (usually 1.0 or 0.9 arcsec). Additionally, any two stars closer than about 3.0 arcsec, or any triple or quadruple systems, were examined.

Under the second scenario, (a blend is not identified with either of the discrete images), then a star system will appear to have one more member than it really has. To minimize this occurrence, an area with a radius of about 10 arcsec around each star was searched for the presence of two other stars. Additionally, an area with a radius of about 15.0 arcsec was searched for three other stars. If multiples were found, they were examined to ensure that images were identified correctly. In the situation described above, blends are discarded.

7.4  Large proper motion candidates

Due to the span of plate epochs, images from large proper motion stars may be displaced from one another by several arcsec and hence not be matched as coming from the same star. To minimize this occurrence, a search in the Luyten's Two-Tenths Catalogue and its supplement was made to identify high proper motion stars. An additional search for large proper stars in the Third Catalogue of Nearby Stars was also made. Stars in the final catalogue having large standard deviations of position are known high proper motion stars.

7.5  Typographical errors

A bright star may only appear to have one image if one of its records contains a typographical error. To find and correct this, all bright, single image stars were investigated. (The exact magnitude limit depends on the zone. Typically all stars down to 11.5 are investigated.)

The process involved generating positions for these images if one altered one of the digits of the printed x or y value, then performing a search within 2 arcsecs around these pseudo-positions. If another image was found at one of the locations, a typographical error may be present. For zones with x,y values published in millimeters, investigations down to the tenths position were made (0.1 mm ~ 6 arcsec). For those zones with x,y values published in réseau units, investigations down to the hudreths position were made (0.01 réseau unit ~ 3 arcsec). The Twin Astrograph Catalogue (TAC; Zacharias et al. 1996), was used to determine which of the two records, if either, should be changed for all zones north of, and including, Tacubaya. For the more southerly zones which are not covered by TAC, the Tycho Input Catalogue (Halbwachs et al. 1994) has been used. If a corresponding star was not found in the TAC or TIC, then a search in the the Digitized Sky Survey using the Skyview interface was made to determine which, if either, contains a typographical error.

To minimize the possibility of a printing error in the magnitude data, a standard deviation of the magnitude, σ mag, was generated from the computed magnitudes for every star appearing on more than one plate. The stars with the largest σ mag were investigated. Additionally, range checks were made on the original data as well as the final computed magnitudes to ensure that all values were reasonable.

7.6  Investigation of other potential problems

To investigate the possibility of a few plates being adjusted incorrectly due to such oddities as several poor reference stars on a plate or incorrectly removing accurate reference stars for poorer ones, the positions of the 500 stars with the largest σα and σδ were plotted for each zone. Additionally, the percentage of stars on each plate whose σα and σδ are in the highest 1% of that zone were computed. Plates that have more of these than expected were investigated.

Positions of all stars were plotted to ensure that the data contain no missing areas, such as a block of data having not been typed or accidentally discarded. Positions of stars having only one image, and positions of stars having multiple images, were plotted separately to investigate the possibility of missing plates.

To avoid the presence of non-stellar objects in the final catalogue, a search in the New General Catalogue of Nebulae and Clusters of Stars (NGC), the Index Catalogue (IC), and the Second Index Catalogue (Sinnot 1988) was made. The Digitized Sky Survey, using the Skyview interface, was used to graphically show potential NGC and IC objects present in the data. Those records found to be non-stellar NGC or IC objects have been discarded.

8  Final Plate Model and Weights

It was necessary to ensure that the plate models developed in each zone and the corrections applied to the data were still valid because they were originally developed on the data that included erroneous identifications and typographical errors. Once any needed revisions were made, plate weights were computed. For most of the AC zones, a plate's weight is the inverse of the variance of the positions of the stars which it contains, after removing the stars with the highest 1% σα and σδ. The removal of these stars prior to computing the plate weights reduced the possibility that a few, high proper motion stars adversely affected the weighting of an entire plate.

No grating was used in the AC program, so bright stars are over-exposed on the plates and should not be used in the final adjustment nor be included in the final catalog. All stars with mean computed magnitudes brighter than 4.0 have been removed prior to final plate adjustments. Also removed from determining the final plate parameters were reference stars with residuals larger than 3.0 times the standard deviation of unit weight of a plate solution. Once removed, the plate adjustment is performed again. These stars are included in the final catalog, but are treated as field stars.

9  Linking of Individual Zones

The Astrographic Catalogue was observed in discrete zones in the sky, and the reductions, by necessity, were made on individual zones. However it was desirable to link these together to make one, cohesive catalog. To do this, stars in common to adjacent zones were identified. Blended images, high proper motion stars, and typographical errors were investigated as described above. Each star was assigned a new internal star number. All images were combined to yield weighted mean right ascensions and declinations on the system defined by Hipparcos (HCRS) at the weighted mean epochs of observation.

9.1  AC 2000.2 plots

Figures fig:errra1 through fig:epoch1 clearly demonstrate the zonal dependence of the AC 2000.2. Figures fig:errra1 and fig:errdec1 show the average positional error for a single image with respect to location on the sky. Of course individual errors will vary, and many of the stars have more than one image. Figure fig:epoch1 provides information on the mean epochs of observation as function of location of the sky. The combination of the positional errors and epochs being a function of declination has consequences for any proper motions derived using the AC 2000.2 data. That is, the proper motion accuracies will also contain this dependence. This was true for the now superseded ACT Reference and Tycho Reference Catalogues, both of which utilized earlier reductions of the Astrographic Catalogue data. It is also true for the Tycho-2 Catalogue, but some of this zonal dependence was eliminated by the inclusion of additional astrometric catalogues. Figure fig:zones1 shows, on the same scale as Figs. fig:errra1 through fig:epoch1, the observatories responsible for photographing and measuring each area of the sky.

The average density of the AC 2000.2 is 112 stars per square degree; however, the sky is hardly uniform. The mean density as a function of sky position is shown in Fig. fig:dens1. The galactic plane is clearly visible, where some areas exceed 500 stars per square degree. On the other extreme, for large areas surrounding the galactic poles, the density drops by more than half of the average.

As a courtesy to the reader, Figs. fig:errra1 through fig:dens1 are provided on this CD-ROM in a larger format. They can be found on this directory in the files,,, and; each is in postscript format. Average error in right ascension of a single image as a function of sky coordinates. Each bin is approximately 9 square degrees. Average error in declination of a single image as a function of sky coordinates. Each bin is approximately 9 square degrees. Mean epochs of observation as a function of sky coordinates. Each bin is approximately 9 square degrees. Identification of observatories as a function of sky coordinates. Number of stars per square degree as a function of sky coordinates. Each bin is approximately 9 square degrees.

10  Cross-Referencing Information

The numbering between the AC 2000.1 and AC 2000.2 has been maintained. It should be noted, however, that there is not a strict one-to-one correspondence between the two versions; the main reason is that some images now known to be from high proper motions stars were not identified as such in AC 2000.1. Note that AC 2000.1 contains 4,621,836 whereas AC 2000.2 contains 4,621,751 stars. However, the numbering between the two remains consistent. In other words, the star numbered ``1'' in both versions refers to the same star.

In order to aid users and to facilitate other work utilizing the Astrographic Catalogue, most stars from the Hipparcos and Tycho-2 Catalogues have been identified. This cross-reference is not intended to be 100% complete; however, the vast majority of stars from these catalogues are identified.

11  Description of AC 2000.2

11..1  Right ascension

The mean right ascension for each star as computed from its weighted images, in units of hours, minutes and seconds of time, referred to the Hipparcos system (HCRS, J2000.0) at the weighted mean epoch of observation.

11..2  Declination

The mean declination for each star as computed from its weighted images, in units of degrees, minutes and seconds of arc, referred to the Hipparcos system (HCRS, J2000.0) at the weighted mean epoch of observation.

11..3  B-Magnitude

The magnitude is either taken directly from the Tycho-2 Catalogue or is an average of the computed magnitude based on the measured image diameters from the AC plates. To determine which is the case, one will need to check the V-Magnitude field. All stars with the V-magnitude field non-blank contain Tycho-2 photometry in both the B-Magnitude and V-magnitude fields. Stars with the V-magnitude field blank contain magnitudes based on the measured image diameters on the AC plates, which should roughly correspond to the Tycho-2 BT system. See the section ``Conversion of the AC Magnitudes'' for details.

11..4  Epoch

The mean epoch for each star as computed by its weighted images, in years.

11..5  Number of images used

The number of individual images used to compute position, magnitude (if from image diameters), epoch and standard deviation of position.

11..6  Standard deviation of weighted mean

The standard deviations of weighted means, σ\ and σ\ are computed for every star with more than one image. The formula used is:
  σ2x = x – x2/N– 1 (23)
  x = αi, δi (24)
  N≡N \left[ <w >2/<w2> \right] (25)
where w is the weight of an individual observation (generally the same for all stars on a plate).

11..7  AC 2000 number

This number is used in the reduction process to identify all images of the same star that may appear on different plates. This is generated at the U.S. Naval Observatory and added to the original x,y data. When the x,y data are released, these numbers can be used to link the data to the final catalog.

11..8  Hipparcos number

If a star has been identified as being in the Hipparcos Catalogue then the Hipparcos number is provided. This cross-referencing information is not 100% complete.

11..9  Tycho-2 number

If a star has been identified as being in the Tycho-2 Catalogue, then the Tycho-2 identifier is provided. Zeros have been inserted in blank fields. This cross-referencing information is not 100% complete.

11..10  V-Magnitude

The magnitude listed here is taken directly from the Tycho-2 Catalogue, otherwise it is blank. There are 20 cases where the Tycho-2 BT is given in the B-Magnitude column, but their is no corresponding Tycho-2 VT magnitude. For these stars, the V-Magnitude is set to .000 and a `3' is set in the Magnitude Flag field.

11..11  Magnitude Flag

This flag will give users caution regarding the photometry. A `1' is given if the star has a B magnitude fainter than 13.5 or a V magnitude from Tycho-2 VT fainter than 12.5. A `2' is given if the star was identified as a Tycho-2 star but the AC magnitude computed from the published diameters is given. This is done when the Tycho-2 BT magnitude is either not given or is listed as fainter than 14.00. No Tycho-2 VT magnitudes are given for these stars. In cases where both `1' and `2' are set, only `2' is given. A `3' is given if the star was identified as a Tycho-2 star, but there is no Tycho-2 VT magnitude. In these cases, the Tycho-2 VT magnitude is set to .000. There are 20 such instances. Only 1 star (AC 408635, Tycho-2 107200084801) should have a '3' flag in combination with another. For this star, the Tycho-2 BT is 13.51 and no Tycho-2 VT magnitude exists; the flag is set to `3'.

11..12  Verification Flag

A `1' in this field indicates the star has a single image and is not found in Hipparcos, Tycho-2, ACRS_1999 or the Hubble Guide Star Catalogue 1.2. These ``stars'' may not exist but instead may be the result of typographical errors, plate defects or other such blunders.

12  Participating Observatories

Work from the observatories that participated in the photographing and measuring of the Astrographic Catalogue data are summarized below. Some important characteristics of each zone can be found in Table tab:obschar1 and in Appendix A. The telescope characteristics agreed upon were a normal astrograph with an aperture of roughly 33 cm and a this instrument having a focal length of 3.43 m. This created a scale close to 60 arcsec/mm on the plates. All observatories, with the exception of Nizamiah, used this type of instrument.

12.1  The Royal Observatory at Greenwich

The Royal Observatory at Greenwich was an original participating institution in the Astrographic Catalogue project, sending representatives to the International Congress on Astronomical Photography held in Paris in 1887. This meeting outlined the plans for the Carte du Ciel project. Funding was provided shortly following this meeting. A telescope built by Sir Howard Grubb following the design agreed upon in Paris was delivered in May 1890. Greenwich centered its plates between +65 and +90 degrees, with five plates taken on the pole in different orientations. In total, 1153 plates were exposed and measured in this zone. Three exposures were made on each plate lasting six minutes, three minutes and 20 seconds. The telescope was moved 20 arcsec between the exposures, so the six and three minute exposures are offset from each other in declination, the six minute and 20 second exposure are offset in right ascension. The plate epochs span from 1892 to 1905.

After initially measuring some plates using micrometer screws, Professor H.H. Turner realized that a different measuring technique was required if the job were to be completed in a timely fashion. At his request, an eyepiece scale type measuring machine was built and greatly reduced the time to measure a plate. Many other observatories adopted this measuring procedure. Systematic measuring of the plates began in October 1894. A duplex micrometer, which is a measuring machine capable of measuring two plate simultaneously, was put into use in February 1895. This aided the identification of images of the same star but on different plates since it was possible to arrange the plates in the machine so that the same field of sky was coincident under the measuring apparatus. (Remember that each plate overlapped surrounding plates so that each area of sky appears on at least two plates.) All plates were measured in two orientations, with the plates being rotated 180 degrees between measurements. In all degree bands except the +65, +66, and +67 degree bands, the same measurer was used for both orientations. Both the six minute and three minute exposures were measured for all stars that appeared on the 20 second exposure. Details can be found in the introductions to the published volumes (Christy & Dyson 1904-1932).

12.2  The Vatican Observatory

The Vatican Observatory, located in Vatican City, was founded in 1888 while the Carte du Ciel program was in its infancy. Vatican staff members realized that participation in this program would immediately give their young observatory international recognition. Pope Leo XIII commissioned Father Francesco Denza and Father Giuseppe Lais to attend the Astrographic Congress and enroll the Vatican as one of the participating institutions.

After being accepted as a participant, the Vatican commissioned the Henry brothers of France to build the telescope and P. Gautier to build a machine to measure the stars on the plates. Father Denza describes the finished telescope: ``The instrument consists of two parallel telescopes: The photographic telescope with an aperture of 33 cm and a focal length of 3.43 m; and the finding telescope or collimator with 20 cm aperture and a focal length of 3.6 m. Both are housed in a metal tube with a rectangular cross section of 37 by 68 cm. Both objectives are fixed on the same block of bronze at one end of the tube and at the other end is the photographic plate holder and the eyepiece of the collimator. A thin metallic diaphragm separates the two telescopes. ...The photographic objective is a doublet of flint and crown and it is both achromatic and aplanic for the most intense chemical rays of the spectrum.'' (Denza 1891).

The telescope was installed in the Leonine Tower in 1891. This tower, located on the highest point of Vatican Hill, was originally constructed in 840 AD under Pope Leo IV as a defense against the Saracen invasions. It is about 20 meters above ground (about 100 meters above sea level) with walls about 4.5 meters in thickness.

The Vatican was assigned the strip of sky between +55 and +64 degrees on which to center the plates. In order to achieve the two-fold sky coverage 1040 plates would be needed. (Actually, 1046 plates were exposed and measured.) The job of photographing and developing the plates was carried out primarily by one person, Father Lais, who worked on this for over 25 years until the time of his death in 1921. Lais's aid, Carlo Diadori, completed the photographing in 1922. For the first several years that Father Lais was working at the telescope, no plates were being measured.

Father Johann Hagen, appointed director of the Observatory in 1906, was committed to seeing the project completed. He soon realized that the machine built by Gautier to measure the stars was too slow. After investigating different measuring techniques employed by other institutions, he decided on the use of an eyepiece grid. In the method used by Vatican, a 10 × 10 mm area of a plate, corresponding to 2 × 2 réseau intervals, was magnified in a microscope along with a grid which is segmented into 0.05 mm steps. The edge of the grid was aligned with the edge of the 2 × 2 réseau interval area. The location of a star within the magnified area was read from its apparent position on the grid. This method was indeed efficient, allowing the Vatican to be one of the first observatories to complete its assigned zone despite utilizing minimal manpower. However, the accuracy was not as high as can be obtained with the measuring techniques used at other participating institutions. Vatican was the only observatory in the Astrographic Catalogue program to use the eyepiece grid technique. Also during his trips to other observatories, Father Hagen saw extensive use of women in measuring the plates, freeing the full-time, male astronomers from this time-consuming, repetitive task. He brought in three nuns from the Instituto di Maria Bambina to measure the plates. These nuns worked from 1910 to 1921 and measured the vast majority of the Vatican data. The Oxford University Observatory agreed to compute the plate constants used to convert the rectangular measures to equatorial coordinates.

For additional information concerning the history of the Vatican Observatory and its personnel, see the book In the Service of Nine Popes (Maffeo 1991). Additional details regarding the Vatican's participation in the Astrographic Catalogue project can be found in the introductions to the data (Vatican 1914-1928), written in Italian.

12.3  The Catania Observatory

The Catania University Observatory, located in Catania, Sicily, centered its plates between +47 and +54 degrees. In total, 1010 plates were exposed and measured in this zone. The epochs span from 1894 to 1932, but over 95% were exposed prior to 1906. All the plates were measured using the short-screw method. Additional details can be found in the introductions to the published data (Catania 1907-1963).

12.4  The Helsingfors Observatory

The Helsingfors Observatory, located in Helsinki, Finland, centered its plates between +40 and +46 degrees. In total, 1008 plates were exposed and measured in this zone. The epochs span from 1892 to 1909, but over 94% were exposed prior to 1897. All the plates were measured using the short-screw method. One screw was used; the plates were rotated 90 degrees to measure both x and y coordinates. The plates measured early in the work had images from both the longest and middle exposures measured in one orientation. Later (after 1896), only the images from the longest exposure were measured, but the plates were rotated 180 degrees between measurements so these images were measured twice (this also helped remove any bias a measurer may have). Various aspects of the work are detailed in the introduction to Volume 1 (Helsingfors 1903-1937).

12.5  The Potsdam Observatory

In 1887, at the meeting of the International Congress which established the Astrographic Catalogue, the zone with plate centers from +39 to +32 degrees was assigned to the Potsdam Observatory, Germany. Potsdam began photographing the plates by 1893 and 1226 plates were exposed by the end of 1900. Each plate had two exposures of 5 minutes duration. Unfortunately, the measurements of the plates lagged behind the exposures. By the start of World War I only 406 plates were measured. Following the war, Potsdam announced it could no longer continue with the project, and a re-photographing of its zone was made by Oxford, Uccle, and Hyderabad. The remaining plates were never measured. An allied bomb during World War II destroyed virtually the entire set of plates (Dick 1988, 1990).

In total, 406 plates were measured and published as the Potsdam zone. These plate are scattered throughout the zone, so many are not overlapped by others. All were measured using one of two short-screw type measuring machines. The plates were measured in one direction only; the plates were not rotated. Various aspects of the work are detailed in the introductions of the printed volumes (Potsdam 1889-1915).

12.6  The Nizamiah Observatory, Hyderabad

In 1887, at the meeting of the International Congress which established the Astrographic Catalogue, the zone from –17 to –23 degrees was assigned to the Observatory of Santiago, Chile. By 1900, the work was still not progressing, so a proposal to establish an observatory in Montevideo, Uraguay was made. This, too, did not progress so Santiago asked to re-undertake the project. At the same time, the Nizamiah Observatory, located in Hyderabad, India, offered to work on this zone as well. So, in 1909 there were two observatories offering to work on the –17 to –23 zone. A resolution passed by the Congress in 1909 assigned the –17 to –20 zone to Hyderabad. After completing the photographing and measuring of these four bands in 1920, the International Astronomical Union recommended that Hyderabad continue photographing down to –23 degrees declination. This work was completed in 1928. This zone between –17 and –23 degrees is known as the Hyderabad South zone. Hyderabad also observed a section of the sky in the Northern hemisphere that Potsdam was originally assigned. This zone, between +36 and +39 degrees, is known as the Hyderabad North zone.

In total, 1260 plates were exposed and measured in the Hyderabad South zone. The epochs span from 1914 to 1928, with only a handful taken after 1923. For the Hyderabad North zone, 592 plates were exposed and measured. The epochs span from 1928 to 1937, with just a very few taken after 1934. The telescope used was not one of the Henrys' design, as all the other AC participation observatories used. Instead of a 33 cm, the Hyderabad instrument, built by Cooke and Sons of York, had an aperture of only 20 cm. Its objective was described as a ``patent photo-visual lens''. The smaller aperture meant longer exposures were required to achieve the desired magnitude limit set for the AC. The telescope's focal length was 133 inches. All the plates were measured using one of four eyepiece scale type measuring machines, all built by Cooke and Sons. Various aspects of the work are detailed in the introductions of the printed volumes (Edinburgh 1918-1930, London 1934-1946).

12.7  The Uccle Observatory

The Royal Observatory of Belgium, located in Uccle, was assigned the zone with plate centers running from +34 to +35 degrees. Although Uccle was not an original participating observatory in the AC project, it became one because the Potsdam Observatory, originally assigned to cover this area, was unable to fulfill its commitment. The telescope used was of similar design as the Henry brothers, but built by Gautier. In total, 320 plates were exposed between 1939 and 1950. The epochs of the plates are spread fairly uniformly, except for a lack of plates exposed between mid-1943 and mid-1945. The measurements took place at the Paris Observatory with the use of three short-screw measuring machines. The réseau used was one from the Toulouse Observatory. An introduction can be found in Volume 1 of the printed catalog (Paris 1960,1962).

12.8  The Oxford Observatory

The University Observatory at Oxford was originally assigned the zone +25 to +31 degrees on which to center the plates. This is known as the Oxford I zone. An additional zone with plates centered on +32 and +33 degrees declination was photographed at Oxford after Potsdam announced they would not be able to complete their assigned area (+32 to +39). This two degree band is referred to as the Oxford II zone.

The telescope used was the same design as the Henry brothers' instrument located in Paris. The Oxford lens was made by Sir Howard Grubb and attached to an existing Grubb 12 1/4 inch, which was utilized as a guiding instrument. All plates of the Oxford 1 zone were taken between mid-1892 and 1910, with over 80% exposed by the end of 1903. These plates were measured mostly by boys from the New College Choir School, and Mr. T. J. Moore, a gardener who was interested in astronomy. The measuring apparatus was designed with an eyepiece scale, similar to that employed by the Greenwich Observatory in their AC work, with the exception that only one plate was measured at a time whereas Greenwich measured two.

Mr. F.A. Bellamy of University Observatory at Oxford supervised much of the work in photographing the 320 plates required to complete the Oxford 2 zone. He employed the same techniques used in the Oxford 1 zone and used the same Grubb refractor operated 30 years earlier. Mr. Bellamy would have photographed the entire zone himself, however he died with 32 fields left unobserved. These 32 fields were exposed at the Royal Observatory at Greenwich by Mr. H.G.S. Barrett with the telescope used for the Greenwich Zone (+65 to +90). These last 32 plates were the only plates in the Astrographic Catalogue that did not have a réseau exposed on them, however they were measured with one clamped on the glass. All plates of the Oxford 2 zone were exposed between 1930 and 1936. (Actually there are two plates that appear to have typographical errors in their epochs. One is dated in 1918; the other in 1930, but 8 months prior to any other plate.) Mr. Barrett also supervised the measurement and reduction of these plates at Oxford, using the eyepiece scale technique. However World War II intervened preventing the determination of the plate constants for 92 of the fields. After the war, the constants for these remaining plates were determined under Dr. H. Kox at the Hamburg Observatory at Bergedorf. A detailed introduction covering the participation of the University Observatory at Oxford in the Astrographic Catalogue project can be found in Volume 1 of the Oxford I zone catalogue (Turner 1906-1911), as well as in the book The Great Star Map also by Turner. An introduction to the Oxford II zones can be found in Volume 1 of the Oxford II zone catalog (Paris 1953-1954).

12.9  The Paris Observatory

The Paris Observatory agreed to photograph the zone with plate centers between declinations +18 and +24 degrees. The telescope used was the original Henry brothers' instrument, after which all other AC telescopes were supposed to be patterned. In total, 1261 plates were photographed and measured. The measuring technique employed at Paris was the short-screw method, which was the most accurate utilized with the AC plates. The epoch range of the plates are from October 1891 through November 1927, however only 7 plates were exposed after 1907 and all but 100 were exposed prior to 1900. An introduction to the Paris Observatory's participation in the Astrographic Catalogue can be found in the introductions to the individual volumes (Paris 1902-1932).

12.10  The Bordeaux Observatory

The Bordeaux University Observatory, located in Floirac, France, was assigned the zone between +11 and +17 degrees declination on which to center its plates. The telescope used was a similar design to the Paris instrument and was built by the Henry brothers. In total, 1260 plates were exposed between 1893 and 1925, all but five being taken before 1913. The plates were measured at Bordeaux using the short-screw method. An introduction to the Bordeaux Observatory's participation in the Astrographic Catalogue project can be found in Volume 1 of the published data (Paris 1905-1934).

12.11  The Toulouse Observatory

The Toulouse University Observatory (France) agreed to participate in the Astrographic Catalogue project by taking plates centered between +5 and +11 degrees declination. In total, 1260 were exposed and measured. The epochs vary from 1893 to 1935, and were taken in three fairly distinct groupings. Most were exposed before the end of 1910. Another set is taken between 1918 and 1922. The last few plates are scattered between 1930 and 1935. All the plates were measured using a short-screw type measuring machine; however, not all plates were measured at Toulouse. Ninety plates were measured at the Bordeaux University Observatory and 36 were measured at the Paris Observatory. Various aspects of the work are detailed in the introductions of the printed volumes (Paris 1903-1948).

12.12  The Algiers Observatory

The Algiers Observatory was assigned the zone between –2 and +4 degrees on which to center its plates. All 1260 plates were exposed between 1891 and 1911. The plates were measured using the short-screw method. Details about the Algiers Observatory's participation in the Astrographic Catalogue project can be found in the introduction to the catalogues (Trépied 1903,Paris 1903-1924).

12.13  The San Fernando Observatory

The Naval Observatory of San Fernando (Spain) was assigned the area between –3 and –9 degrees declination on which to center its plates. The telescope used was built by Gautier, with the objective made by the Henry brothers. All of the 1260 plates were exposed between 1891 and 1917. Over 1000 were taken before 1899, then only a few per year until 1917. The plates were measured using a short screw micrometer. An introduction to San Fernando's participation in the Astrographic Catalogue project can be found in Volume 1 of the published data (San Fernando 1921-1929).

12.14  The Tacubaya Observatory

At the meeting of the International Congress which established the Astrographic Catalogue, the zone from –10 to –16 degrees was assigned to the National Astronomical Observatory of Tacubaya, located near Mexico City, Mexico. In total, 1260 plates were exposed and measured in the Tacubaya zone. (Actually, one of the plates had an incorrect and unknown plate center and has been discarded from the reductions, leaving a total of 1259 plates). All but five plates were exposed between 1900 and 1912. The five later plates were exposed between 1926 and 1938. All the plates were measured using the eyepiece scale method. An introduction to the history of the work can be found in Volume 1 part 1 of the –15 degree zone (Tacubaya, 1913-1962).

12.15  The Cordoba Observatory

At the 1887 Paris meeting, the zone from –24 to –31 degrees was assigned to the La Plata Astronomical Observatory. In 1900, the zone was re-assigned to Cordoba. The telescope was installed at the end of 1901. In 1908, Dr. Thome, the Director of Cordoba, died and Dr. Perrine was named new director. After some investigations, Perrine decided to re-observe all areas. He discovered that the telescope was out of focus and many of the plates were impaired, and that the plates were centered on apparent place coordinates, not at those defined at equinox 1900. Plates of this series were exposed starting in 1909 and finished by the end of 1913. These plates were measured between 1909 and 1920. In total, 1360 plates were exposed as part of the Astrographic Catalog.

The telescope used was one of the Henrys' design and build, following the standard with a 33 cm aperture and 3.47 m focal length. In the introduction written by Perrine, he states that the guiding is difficult because the guide scope has only a 19 cm aperture, as opposed to the more conventional 25 cm in use by most of the participating observatories. The mount was built by Gautier. Some plates showed a ``triangular distortion'' that was traced to a warp in the ring which held the lens in place. This ring was replaced in 1911. The lens, from August 9, 1910 until the end of the program, was stopped down to 11  inches. This, according to Perrine, greatly improved the image quality.

Virtually all plates were taken and developed by R. Winter or F.P. \linebreak Symonds. Four exposures on each plate were made; two long exposures of the same duration (both of 5 or 6 minutes) one medium exposure (of 60 to 90 seconds) and one short exposure (of 5 to 8 seconds). The telescope was moved in declination between exposures. In order to expedite the work, two measuring machines of the short-screw type were retro-fitted with eyepiece scales. As a result, 140 plates were measured using the short-screw method, the remaining 1220 plates were measured using the eyepiece scale method. In total, five different measuring machines were used, allowing each measurer to have his or her own machine. The réseaux used were supplied by Gautier and Prin; four were used throughout the work. Investigations of two of the réseaux were made in Paris and the deviations were found to be negligible; no corrections for the réseaux were applied to the measures. Only stars within one degree in right ascension and declination of the plate center were measured. All stars having three images were measured unless images ran together, which was the case of the brightest stars. Four measures were made on each star; a measure was made on both of the long exposures in both orientations of the plate. (Following an initial measurement of all stars, the plate was reversed 180 degrees and all stars re-measured.) In general, measures in the direct and reverse orientations of the plate were made on the same day by the same measurer. In total, 37 man-years went into measuring the plates. Various aspects of the work are detailed in the introduction of Volume 26 of the Observatory Results (Cordoba 1925-1934).

12.16  The Perth Observatory

At the International Congress which established the Astrographic Catalogue, the Observatory of Rio de Janeiro was assigned to photograph the area between –32 and –40 degrees declination. In 1900, the work at Rio had not progressed and so the Perth Observatory undertook the task. The telescope used was from Sir Howard Grubb, and was of similar design to other telescopes used for the AC work. Although observing was progressing, no resources were available to measure the plates. At this time, the Perth Observatory was primarily a meteorological station, and the meteorological work took precedence. This changed in 1908 when the Australian Federal Government established the Australian Weather Bureau. About this time, four women were hired as plate measurers. Professor Dyson of the Edinburgh Observatory offered assistance in the measuring. Perth accepted this offer and started sending those plates of the –40 degree zone. By 1915, the Edinburgh Observatory completed its commitment by measuring all of the plates centered on the –40, –39 and –38 degree band. This area is known as the Perth-Edinburgh AC zone. Observing continued at Perth until 1919, at which time all areas had been photographed. Personnel at Perth measured all plates between –37 and –32 degrees; this is known as the Perth zone. In total, 432 and 944 plates make up the Perth-Edinburgh and Perth zones, respectively.

All plates had three exposures taken, one of 4 minutes, 2 minutes and 13 seconds, or that of 6 minutes, 3 minutes or 20 seconds. The change in exposure times took place following a 1909 meeting of key personnel from different observatories participating in the AC. At that meeting, many people expressed concern about the uniformity of limiting magnitudes on different plates. Many of the Perth plates were re-examined and found to be unsatisfactory. The areas affected were re-observed and a method of ensuring more uniformity was developed.

In general, no guiding of the instrument other than the sidereal drive was made, as it was found unnecessary. All plates were the brand Ilford ``special rapid''. All were measured using an eyepiece scale machine, similar to the Oxford Observatory's. For all but 5 plates, the measurements done at Perth were made in two orientations of the plate by the same person; the plate being rotated 180 degrees between measurements. In total, 10 measurers were used at Perth. For the plates measured at Edinburgh, images were measured in two orientations of the plate, with the plate being rotated 180 degrees between measurements. For the direct orientation, the second exposure (either 2 or 3 minutes) was measured; the longest exposure was measured with the plate in reverse orientation. Quite often more than one measurer was used on each plate. Various aspects of the work can be found in the introduction to Volume 23 of the Perth-Edinburgh data (Perth 1922, Paris 1949-1952) and in Volumes 1 and 17 of the Perth data (Perth 1911-1921).

12.17  The Royal Observatory at the Cape of Good Hope

The Royal Observatory at the Cape of Good Hope, South Africa, took the zone between –41 and –51 on which to center its plates. In all, 1512 plates were exposed and measured. The epochs range from 1897 to 1912, with 97% of them being exposed prior to 1906. The telescope used was built by Sir Howard Grubb. Two machines were used to measure the plates, both were designed by David Gill and built by Repsold of Hamburg (Gill 1898). Both machines employed the short-screw measuring method and were of similar design. An introduction to the participation of the Royal Observatory at the Cape of Good Hope in the Astrographic Catalogue project can be found in Volume 1 of the published data (London 1913-1926) .

12.18  The Sydney Observatory

H.C. Russell, the Government Astronomer at Sydney, was in attendance at the 1887 meeting of the International Congress. He committed the Sydney Observatory to photograph the sky between declinations –52 and –64 degrees. The lens used for the project was built by Howard Grubb of Dublin, and it followed the general design established by the International Congress. The lens was delivered in December of 1890. Most of the telescope was built in Sydney. The observing program began in earnest in 1892. The telescope was moved twice in the course of the AC work; first from inside Sydney to Redhill (located about 12 miles from Sydney) in 1899, and then back to its original location in 1931. The observing was left unchanged until 1912, when W.E. Cooke took over the project. He was unsatisfied with the quality of many plates and eventually rejected and rephotographed many of the areas. Until this time, plates were being sent to Melbourne for measurement, but under Cooke the Sydney Observatory began to measure their own photographs. Prior to Cooke's arrival, plates were positioned so the center of the plate was in the sharpest focus (The astrograph used in photographing the plates did not have a flat field of focus, so some areas of the plate are in focus while others are not. This is true for all the telescopes used in the Astrographic Catalogue work). Cooke altered this and made the ring about 50 arcmin from the center the place with the sharpest focus. In 1926, Cooke retired and James Nagle took over. He altered the place of best focus in a ring about 40 arcmin from plate center. Nagle died in 1941, and H.W. Woods took over. Some plates were found unsatisfactory or missing. The remaining areas were photographed between 1944 and 1948. In total, 1400 plates were taken as part of the Astrographic Catalogue. All plates exposed between 1890 and 1930 were taken by James Short.

Plate measuring did not start for about six years after the first plates were taken. Evidently there was a suggestion about having all plates from all participating observatories sent to Paris for measurement. This plan was not ever put in place, but the Australians liked this idea so they decided that Melbourne would be used to measure both the Sydney and Melbourne plates. As mentioned above, this changed with Cooke's arrival and Sydney started measuring their own plates. There were four short-screw measuring machines used in Melbourne, and two eyepiece scale machines used at Sydney. From this point on, all stars were measured twice with the plates being rotated 180 degrees between measurements. Various aspects of the work are detailed in the introduction of Volume 53 of the data (Sydney 1925-1971).

12.19  The Melbourne Observatory

In 1887, following the meeting which established the Astrographic Catalogue, the British government agreed to have the Melbourne Observatory participate in the project. Melbourne was assigned the zone from –65 to –90 degrees. The telescope used was built by Howard Grubb of Dublin, and it followed the general design established by the International Congress. The telescope was delivered in December of 1890. The observing program started about one year later in January 1892 and continued until 1927 (Actually, one plate was exposed in 1940). Over 80% of the plates were exposed prior to 1898. In total, 1149 plates were taken as part of the Astrographic Catalogue. All plates had three exposures of 5 minutes, 2.5 minutes and 20 seconds duration, with the exception of the plates taken prior to February 26, 1892, whose exposures were slightly longer. The réseau was exposed on the plates shortly after the plates were removed from the telescope. In total, six different réseaux were used during the program; three were supplied by Gautier and three were made at Melbourne.

Plate measuring did not commence in earnest until November 1898, when six women were hired at Melbourne. Two measurers were used for each plate, one taking the northern half and one the southern. The plates were rotated 180 degrees and each half was remeasured by the same person. All reference stars on each plate were measured by both measurers. Four measuring machines were used throughout most of the work; all used short-screws for the star measurements. The Melbourne staff tried using an eyepiece scale measuring machine for the plates but found the measuring error too high.

Periodic and progressive screw errors were investigated. These were not applied, as they were found to be negligible by the Melbourne astronomers. (Investiations of the screw errors performed at the U.S. Naval Observatory as part of the AC 2000 work show this not to be true.) Investigations into errors of the réseaux were made and these corrections were applied to the data prior to publishing. Various aspects of the work are detailed in the introduction of Volume 1 of the data (Melbourne 1926-1929; Paris 1955-1958; Sydney 1963).

13  References

A  Notes on Participating Observatories Data Characteristics

Bytes Format Units Label Explanations
1- 2 I2 h RAh Right Ascension (hours) 4- 5 I2 min RAm Right Ascension (minutes) 7-12 F6.3 s RAs Right Ascension (seconds) 14 A1 — DE- Declination (sign) 15-16 I2 deg DEd Declination (degrees) 18-19 I2 arcmin DEm Declination (minutes) 21-25 F5.2 arcsec DEs Declination (seconds) 27-31 F5.2 mag B(mag) Magnitude - Tycho-2 BT if col 86-91 are non-blank; else from image diameters 33-40 F8.3 yr Ep Mean epoch of position 42-43 I2 — Num Number of images used 44-49 F6.3 arcsec e_RAs ?Standard deviation of mean, RA 50-55 F6.3 arcsec e_DEs ?Standard deviation of mean, Dec 57-64 I8 — AC2000 AC 2000 Number 66-71 I6 — HIPP ?Hipparcos Number 73-84 A12 — TYCHO-2 ?Tycho-2 ID 86-91 F6.3 mag V(mag) ?Magnitude - Tycho-2 VT else blank 92-92 I1 — MGFL ?Magnitude flag 93-93 I1 — VER ?Verification Flag
Byte-by-byte description of AC 2000.2 using format requested by the CDS.

Zone Country declination mearuring num of epoch or region of centers technique plates
Greenwich England +90 +65 scale 1153 1892 1905 Vatican Italy +64 +55 grid 1046 1895 1922 Catania Sicily +54 +47 screw 1010 1894 1932 Helsinki Finland +46 +40 screw 1008 1892 1910 Potsdam Germany +39 +32 screw 406 1893 1900 Hyderabad N India +39 +36 scale 592 1928 1938 Uccle Belgium +35 +34 screw 320 1939 1950 Oxford II England +33 +32 scale 320 1930 1936 Oxford I England +31 +25 scale 1188 1892 1910 Paris France +24 +18 screw 1261 1891 1927 Bordeaux France +17 +11 screw 1260 1893 1925 Toulouse France +11 +5 screw 1260 1893 1936 Algiers Algeria +4 –2 screw 1260 1891 1912 San Fernando Spain –3 –9 screw 1260 1891 1918 Tacubaya Mexico –10 –16 scale 1259 1900 1938 Hyderabad S India –17 –23 scale 1260 1914 1929 Cordoba Argentina –24 –31 both 1360 1909 1913 Perth Australia –32 –37 scale 944 1902 1919 Perth-Edinb. Australia –38 –40 scale 432 1903 1914 Cape S. Africa –41 –51 screw 1512 1897 1912 Sydney Australia –52 –64 both 1400 1892 1948 Melbourne Australia –65 –90 screw 1149 1892 1928
Characteristics of each observatory's plates

Zone stars images keyed and verified (thousand)(thousand)
Greenwich 179 322 USNO Vatican 256 480 CIDA, Venezuela (verified USNO) Catania 163 320 USNO Helsinki 159 284 USNO Potsdam 108 143 CIDA, Venezuela (verified USNO) Hyderabad N 149 242 USNO Uccle 117 159 USNO Oxford II 118 161 USNO Oxford I 277 471 Strasbourg Paris 254 436 Strasbourg Bordeaux 224 355 Strasbourg Toulouse 270 433 Strasbourg Algiers 200 330 Strasbourg San Fernando 226 346 USNO Tacubaya 312 518 USNO Hyderabad S 293 521 USNO Cordoba 309 467 Sternberg, Russia Perth 228 402 USNO Perth-Edinb. 139 202 USNO Cape 545 901 USNO Sydney 431 743 USNO Melbourne 218 392 Univ of Fla., USNO
Numbers of images in each zone and institutions aiding in keypunching the data, by zone

Zone prepared reduced
Greenwich Gary Wycoff, John Martin Sean Urban Vatican John Martin Sean Urban Catania John Martin, Gary Wycoff Sean Urban Helsinki Harry Crull, Edward Jackson, David Hall Sean Urban Potsdam Marion Zacharias Marion Zacharias Hyderabad N Edward Jackson Sean Urban Uccle Edward Jackson Sean Urban Oxford II John Martin Sean Urban Oxford I John Martin Sean Urban Paris Edward Jackson Sean Urban Bordeaux Edward Jackson Sean Urban Toulouse David Hall Sean Urban Algiers Edward Jackson Sean Urban San Fernando Gary Wycoff Sean Urban Tacubaya John Martin, Gary Wycoff Sean Urban Hyderabad S Edward Jackson, Sean Urban Sean Urban Cordoba Gary Wycoff Sean Urban Perth David Hall, Gary Wycoff, John Martin Marion Zacharias Perth-Edinb. David Hall, Gary Wycoff Sean Urban Cape Sean Urban Sean Urban Sydney David Hall, Gary Wycoff Sean Urban Melbourne Gary Wycoff Sean Urban
Personnel involved in USNO plate reductions

adjustment. Also includes single image precisions by zone.]Corrections applied to x,y data prior to final least squares adjustment. Also includes single image precisions by zone.

In the table, a ``Y'' indicates a correction was applied, an ``n'' indicates it was not. Values in parentheses indicates an additional dependence on those characteristics.

mg=magnitude, mr=measurer, mp=microscope, rs=reseau, ep=epoch,
x=x-coordinate, and y=y-coordinate.

Note that Ox II/Grn ``zone'' refers to the 32 plates observed at Greenwich for the Oxford II zone.

Zone radial dist Mag Eq. Coma Screw FDP \ ra \ dec
Greenwich Y(mg) Y n n n .29 .30 Vatican Y(mg) Y n Y(mr) Y(mp) .42 .44 Catania Y(mg) Y(x,y) n n Y(mg) .33 .30 Helsinki Y(mg) Y(x,y) Y Y(mr) Y .23 .22 Potsdam n Y(mr) Y n Y .26 .25 Hyder. N Y Y(x,y) Y n Y(mg) .33 .30 Uccle Y(mg,x,y) Y Y Y Y(mg) .33 .38 Oxford II n Y(x,y) n n Y .33 .32 Ox II/Grn Y Y n n n Oxford I n Y(x) n n Y .32 .31 Paris Y(mg) Y Y Y(mp) Y(rs) .21 .21 Bordeaux n Y(ep) n Y Y(rs) .22 .21 Toulouse Y(mg,mp) Y(y) n Y(mp) Y(rs) .29 .28 Algiers Y(mg) Y(y) n n n .19 .18 San Fer. Y(mg) Y Y n Y(mg) .32 .33 Tacubaya n Y(x) n n Y(mg) .25 .24 Hyder. S Y(mg) Y(x,y) Y n Y(mg,rs) .31 .32 Cordoba Y(mg) Y(x,y) n Y(mp) Y(mg) .32 .29 Perth Y Y Y n Y .29 .28 Per-Edin. Y(mg) Y(x,y) Y Y Y(mg) .29 .28 Cape n Y(x,y) Y(ep) Y(mp) Y(mg,rs) .28 .26 Sydney Y(mg) Y(mp,rs,x,y) n Y(mp) Y(mg,rs) .44 .40 Melbourne Y Y n Y(mp) Y(mg) .34 .32
Corrections applied to x,y data prior to final least squares

Catalogues used in the ACRS_1999 (units of mas)                                    

Name type σα σδ σ/ sqrt(N)
1ST CAPE FUND 1900 Transit Circle 589 564 Yes 2ND CAPE FUND 1900 Transit Circle 529 462 Yes 2ND MELBRN GC 1880 Transit Circle 1380 859 Yes 3RD MELB GC 1890 Transit Circle 1507 1117 Yes ABBADIA 00 –3/–9 Transit Circle 975 849 Yes ABBADIA 00 +16/+24 Transit Circle 988 810 Yes ABBADIA 00 –2/+4 Transit Circle 951 929 Yes AGK2 (BERGEDORF) Astrograph 205 198 No AGK2 (BONN) Astrograph 261 259 No AGK2a Transit Circle 165 217 No AGK3 Astrograph 204 191 No AGK3R Transit Circle 75 107 No ALBANY –2/+1 1900 Transit Circle 840 844 Yes ALBANY –20/–40 00 Transit Circle 836 1156 Yes ALBANY 10 Transit Circle 294 282 No ALGER AG 1900 Transit Circle 1156 958 Yes BERGEDORF I - 25 Transit Circle 432 540 Yes BERLIN 10 79/90 Transit Circle 504 617 Yes BERLIN 1920 Transit Circle 559 660 Yes BONN 00 +40/+50 Transit Circle 506 461 Yes BONN 20 Transit Circle 533 504 Yes BORD 00-II RE-OBN Transit Circle 397 377 Yes BORDEAUX II 1900 Transit Circle 1038 734 Yes BUCHAREST –11/+11 Transit Circle 381 493 Yes CAMC Series Transit Circle 176 237 Yes CAPE I - 50 Transit Circle 368 373 Yes CAPE II - 25 Transit Circle 468 453 Yes CAPE III - 25 Transit Circle 474 420 Yes CAPE –40/–52 1900 Transit Circle 743 671 Yes
Catalogues used in the ACRS_1999 (units of mas)

Catalogues used in the ACRS_1999 (units of mas), continued                       

Name type σα σδ σ/ sqrt(N)

CAPE 17 –30/–35 Astrograph 391 407 No CAPE 18 –35/–40 Astrograph 319 350 No CAPE 19 –52/–56 Astrograph 298 319 No CAPE 20 –56/–60 Astrograph 210 193 No CAPE 20 –60/–64 Astrograph 196 200 No CAPE 21 –64/–68 Astrograph 182 187 No CAPE 21 –68/–72 Astrograph 190 195 No CAPE 21 –72/–76 Astrograph 211 211 No CAPE 21 –76/–80 Astrograph 186 202 No CAPE 22 –80/–89 Astrograph 176 227 No CAPE G. C. (1900) Transit Circle 674 600 Yes CAPE I - 25 Transit Circle 469 459 Yes CAPE II - 50 Transit Circle 467 588 Yes CAPE ST 50 –30/–35 Transit Circle 742 668 Yes CAPE ST 50 –35/–40 Transit Circle 534 510 Yes CAPE ST 50 –52/–56 Transit Circle 722 608 Yes CAPE ST 50 –56/–60 Transit Circle 330 344 Yes CAPE ST 50 –60/–64 Transit Circle 302 336 Yes CAPE ST 50 –64/–68 Transit Circle 374 398 Yes CAPE ST 50 –68/–72 Transit Circle 376 380 Yes CAPE ST 50 –72/–76 Transit Circle 372 416 Yes CAPE ST 50 –76/–82 Transit Circle 328 370 Yes CAPE ST 50 –82/–90 Transit Circle 226 326 Yes CORDOBA 6429 ST 00 Transit Circle 722 715 Yes CORDOBA D 1950 Transit Circle 589 628 Yes CORDOBA E 1950 Transit Circle 618 952 Yes CPC2 Astrograph Ind. Ind. NA FAYET +5 TO +15 Transit Circle 559 607 Yes FAYET –5 TO +5 Transit Circle 165 240 No FOKAT Astrograph 220 238 Yes

Catalogues used in the ACRS_1999 (units of mas), continued

Catalogues used in the ACRS_1999 (units of mas), continued                       

Name type σα σδ σ/ sqrt(N)
GREENWICH 1910 Transit Circle 426 324 No GREENWICH 9Y2 Transit Circle 950 854 Yes GREENWICH I-50 Transit Circle 504 487 Yes GREENWICH II-25 Transit Circle 450 466 Yes HEIDELBERG ZOD 50 Transit Circle 375 453 Yes HIPPARCOS Satellite Ind. Ind. NA KONIGSBERG 25 Transit Circle 183 199 Yes KONIGSBERG 25-II Transit Circle 482 426 Yes KUSTNER - BONN 00 Transit Circle 368 332 No LA PLATA 3710 S 50 Transit Circle 712 658 Yes LA PLATA A 1925 Transit Circle 808 790 Yes LA PLATA B 1925 Transit Circle 811 679 Yes LA PLATA C 1925 Transit Circle 801 698 Yes LA PLATA D 1925 Transit Circle 1000 867 Yes LA PLATA E 1925 Transit Circle 911 857 Yes LA PLATA EROS 1930 Transit Circle 500 387 No LA PLATA F 1935 Transit Circle 485 518 Yes LA PLATA GC 1950 Transit Circle 564 585 Yes LEIDEN 25 XV/1 Transit Circle 460 576 Yes LEIDEN 25 XV/2 Transit Circle 458 664 Yes LEIDEN 25 XV/4 Transit Circle 2308 2069 Yes LICK 17 HARVD AG Transit Circle 246 345 No LICK 28 20/30 Transit Circle 222 202 No LICK ZODIACAL 1900 Transit Circle 424 335 Yes LUND 50 FAINT AG Transit Circle 710 749 Yes LUND AG 25 35/40 Transit Circle 661 696 Yes MADISON 1910 Transit Circle 444 468 Yes MUNICH A 1900 Transit Circle 681 749 Yes MUNICH B 1900 Transit Circle 730 680 Yes NICOLAEV –5/–20 50 Transit Circle 306 367 Yes NICE Transit Circle 111 148 No PARIS 1900 Transit Circle 1299 848 Yes
Catalogues used in the ACRS_1999 (units of mas), continued

Catalogues used in the ACRS_1999 (units of mas), continued                       

Name type σα σδ σ/ sqrt(N)
PARIS ASTR +17/+25 Astrograph 290 323 No PERTH 83 Transit Circle 211 405 Yes PERTH VOL 2 1900 Transit Circle 717 713 Yes PERTH VOL 3 1900 Transit Circle 899 974 Yes PERTH VOL 4 1900 Transit Circle 844 803 Yes PERTH VOL 5 1900 Transit Circle 909 798 Yes PERTH VOL 6 1900 Transit Circle 763 779 Yes PFKSZ 50 Transit Circle 59 62 No PULKOVA 1900 Transit Circle 1272 914 Yes PULKOVO 10 39/44 Transit Circle 300 288 No SAN LUIS 1910 Transit Circle 716 661 Yes SCHWACHER STERNE Transit Circle 108 148 No SRS Transit Circle 268 367 Yes STRASBOURG AG 1900 Transit Circle 1005 908 Yes SYDNEY 1499 IMD 25 Transit Circle 782 771 Yes SYDNEY –51/–63.5 Astrograph 84 80 No SYDNEY –48 TO –54 Astrograph 156 144 No TOULOUSE 00 III-B Transit Circle 462 380 No TOULOUSE III Transit Circle 684 572 Yes TOKYO PMC 86-89 Transit Circle 463 543 Yes TYCHO-1 Satellite Ind. Ind. NA USNO TAC Astrograph Ind. Ind. NA W1J00 Transit Circle 204 236 Yes W2J00 Transit Circle 274 319 Yes WASH 25 ZOD 6-IN Transit Circle 349 405 Yes WASH 33 –10/–20 33 Transit Circle 564 438 Yes WASHINGTON 00 9-IN Transit Circle 590 535 Yes WASHINGTON 20 Transit Circle 642 540 Yes WASHINGTON 250 Transit Circle 262 381 Yes WASHINGTON 350 Transit Circle 290 383 Yes WASHINGTON 40 9-IN Transit Circle 370 447 Yes WASHINGTON AG 1900 Transit Circle 1217 976 Yes WIEN AG 1900 Transit Circle 806 807 Yes
Catalogues used in the ACRS_1999 (units of mas), continued

Catalogues used in the ACRS_1999 (units of mas), continued                       

Name type σα σδ σ/ sqrt(N)
YALE v11 –10/–14 Astrograph 360 358 No YALE v12/1 –14/–18 Astrograph 316 264 No YALE v12/2 –18/–20 Astrograph 278 254 No YALE v13/1 –20/–22 Astrograph 285 251 No YALE v13/2 –27/–30 Astrograph 336 350 No YALE v14 –22/–27 Astrograph 305 277 No YALE v16 –6/–10 Astrograph 242 236 No YALE v17 –2 / –6 Astrograph 247 233 No YALE v18 +15 / +20 Astrograph 204 213 No YALE v19,22/2 +9/15 Astrograph 205 190 No YALE v20 +1 / +5 Astrograph 202 190 No YALE v21 +1 / –2 Astrograph 226 230 No YALE v22/1 +5 / +9 Astrograph 198 207 No YALE v24,25 +20/+30 Astrograph 187 153 No YALE v26/1 +85/+90 Astrograph 158 173 No YALE v26/2,27 50/60 Astrograph 118 135 No YALE v28 –30/–35 Astrograph 291 323 No YALE v29 –35/–40 Astrograph 278 288 No YALE v30 –40/–50 Astrograph 201 197 No YALE v31 –70/–90 Astrograph 193 219 No YALE v32 –60/–70 Astrograph 299 306 No
Catalogues used in the ACRS_1999 (units of mas), continued