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ACRS: Help

ACRS - Astrographic Catalog of Reference Stars


Overview

For a number of years there has been a great demand for a high-density catalog of accurate stellar positions and proper motions that maintains a consistent system of reference over the entire sky. The Smithsonian Astrophysical Observatory Star Catalog (SAO; SAO Staff 1966) has partially met those requirements, but its positions brought to current epochs now contain errors on the order of 1 second of arc, plus the proper motions in the SAO differ systematically with one another depending on their source catalogs.

With the completion of the Second Cape Photographic Catalogue (CPC2; de Vegt et al. 1989), a photographic survey comparable in density to the AGK3 (Dieckvoss 1975) was finally available for the southern hemisphere. These two catalogs were used as a base and matched against the AGK2 (Schorr & Kohlschuetter 1951-58), Yale photographic zones (Yale Trans., Vols. 11-32), First Cape Photographic Catalogue (CPC1; Jackson & Stoy 1954, 55, 58; Stoy 1966), Sydney Southern Star Catalogue (King & Lomb 1983), Sydney Zone Catalogue -48 to -54 degrees (Eichhorn et al. 1983), 124 meridian circle catalogs, and catalogs of recent epochs, such as the Carlsberg Meridian Catalogue, La Palma (CAMC), USNO Zodiacal Zone Catalog (Douglass & Harrington 1990), and the Perth 83 Catalogue (Harwood [1990]) to obtain as many input positions as possible. All positions were then reduced to the system of the FK4 (Fricke & Kopff 1963) using a combination of the FK4, the FK4 Supplement as improved by H. Schwan of the Astronomisches Rechen-Institut in Heidelberg, and the International Reference Stars (IRS; Corbin 1991), then combined with the CPC2 and AGK3. The total number of input positions from which the ACRS was formed is 1,643,783.

The original catalog is divided into two parts. Part 1 contains the stars having better observational histories and, therefore, more reliable positions and proper motions. This part constitutes 78 percent of the catalog; the mean errors of the proper motions are +/-0.47 arcsec per century and +/-0.46 arcsec per century in right ascension and declination, respectively. The stars in Part 2 have poor observational histories and consist mostly of objects for which only two catalog positions in one or both coordinates were available for computing the proper motions. Where accuracy is the primary consideration, only the stars in Part 1 should be used, while if the highest possible density is desired, the two parts should be combined.

The ACRS was compiled at the U. S. Naval Observatory with the intention that it be used for new reductions of the Astrographic Catalogue (AC) plates. These plates are small in area (2 x 2 deg) and the IRS is not dense enough. Whereas the ACRS was compiled using the same techniques developed to produce the IRS, it became clear as the work progressed that the ACRS would have applications far beyond its original purpose. With accurate positions and proper motions rigorously reduced to both the FK4 and FK5 (Fricke et al. 1988) systems, it does more than simply replace the SAO. Rather, it provides the uniform system of reference stars that has been needed for many years by those who require densities greater than the IRS and with high accuracy over a wide range of epochs. It is intended that, as additional observations become available, stars will be migrated from Part 2 to Part 1, with the hope that eventually the ACRS will be complete in one part. Additional details concerning the compilation and properties of the ACRS can be found in Corbin & Urban (1989) except that the star counts and errors given here supersede the ones given in 1989.


Catalog Bibcode

<I/171/acrs*.dat>

References

Corbin, T.E., & Urban, S. E. 1991, Astrographic Catalogue Reference Stars
	(Washington, U.S. Naval Observatory)

Provenance

The HEASARC revised this database table in August, 2005, in order to add Galactic coordinates.

Parameters

Name
Source designation. Depending on position of source, it could be the BD, the CD or the CPD designations. Stars which are not in any of these catalogs have all been disgnated NN (for no name). For stars like these, refer to the parameter ACRS ID for the preferred designation (i.e., the ACRS name).

Vmag
Magnitudes are photographic and come from the AGK3 in the north, and the CPC2 in the south.

RA
The Right Ascension of the object in the selected equinox.

Dec
The Declination of the object in the selected equinox.

LII
The Galactic Longitude of the object.

BII
The Galactic Latitude of the object.

RA_J2000
The Right Ascension of the object, in sexagesimal format, as given in the original catalog, in J2000 coordinates.

Dec_J2000
The Declination of the object, in sexagesimal format, as given in the original catalog, in J2000 coordinates.

RA_B1950
The Right Ascension of the object, in sexagesimal format, as found in the original data, in B1950 coordinates.

Dec_B1950
The Declination of the object, in sexagesimal format, as found in the original data, in B1950 coordinates.

Catalog_Part
The catalog part can be either 1 or 2, as discussed in the overview. Stars in Part 1 of the catalog have the most reliable positions and proper motions.

Mean_Error_RA
The mean error in the Right Ascension of the position at the original epoch, in seconds of time.

Mean_Error_Dec
The mean error in the Declination of the position at the original epoch, in arcseconds.

Cent_PM_RA_B1950
The centennial proper motion in Right Ascension, B1950 system, in seconds of time per century.

Cent_PM_Dec_B1950
The centennial proper motion in Declination, B1950 system, in seconds of time per century.

Error_Cent_PM_RA
The mean error in the proper motion in Right Ascension, in seconds of time per century. These proper motion errors were derived from the dispersion of the catalog positions used to determine the proper motion.

Error_Cent_PM_Dec
The mean error in the proper motion in Declination, in arcseconds per century. These proper motion errors were derived from the dispersion of the catalog positions used to determine the proper motion.

Original_Epoch_RA
The original epoch of the Right Ascension and the Right Ascension proper motion. The original epoch parameters refer to the mean epoch of the mean position from the respective proper motion solution.

Original_Epoch_Dec
The original epoch of the Declination and the Declination proper motion. The original epoch parameters refer to the mean epoch of the mean position from the respective proper motion solution.

Number_Positions_RA
The number of Right Ascension positions used to determine the proper motion and mean position of this coordinate.

Number_Positions_Dec
The number of Declination positions used to determine the proper motion and mean position of this coordinate.

RA_Weight
The sum of the weights of the catalogs used to determine the Right Ascension.

Dec_Weight
The sum of the weights of the catalogs used to determine the Declination.

ACRS_ID
An identifier for each star based upon the recommended IAU nomenclature (per PASP, 102, 1444, 1990). A `J` inside the name indicates that the following coordinates found in the name are in the Julian reference system and are for the year 2000.0, the standard equinox designated for Julian system coordinates.

ACRS_Number
A sequential number beginning with 1 for part 1, and with 500001 for Part 2. These numbers will not remain ordered as stars migrate.

BD_Number
Bonner Durchmusterung number.

CD_Number
Cordoba Durchmusterung number.

CPD_Number
Cape Photographic Durchmusterung number.

AGK3_Number
Identifier from the AGK3 Catalog.

CPC2_Number
Identifier from the Second Cape Photographic Catalogue.

Cent_PM_RA_J2000
The centennial proper motion in the Right Ascension coordinate (J2000.0), in seconds of time per century.

Cent_PM_Dec_J2000
The centennial proper motion in the Declination coordinate (J2000.0), in arcseconds per century.

Delta_Orig_Epoch_RA
The original epoch for the source minus J2000 for the Right Ascension coordinate, in centuries. Thus, if the original epoch of the RA for a source were 1945.000, this parameter would have a value of -0.550.

Delta_Orig_Epoch_Dec
The original epoch for the source minus J2000 for the Declination coordinate, in centuries. Thus, if the original epoch of the Declination for a source were 1945.000, this parameter would have a value of -0.550.


Contact Person

Questions regarding the ACRS database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk
 
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