Star catalogues update

Brian Skiff (bas@lowell.edu)

Some incremental progress is occurring in the "immense star catalogues" arena, so here is an update on what's become available. This follows on my long s.a.a. post about "new and upcoming star catalogues" that has been circulated here and in club newsletters around the planet.
 
USNO-A1.0
     First, given the continual, large circulation of new lurkers into the newsgroup, here is a brief recapitulation of the biggest of the star lists, USNO-A1.0. The catalogue was built by a group of folks at the U. S. Naval Observatory's Flagstaff Station, and contains nearly 500,000,000 detections of both stars and galaxies. It is a complete inventory of available Schmidt sky survey plates at two wavelengths (red and blue). The file comes to over 6 gigabytes, and in general is not available to amateurs, and cannot be used in commercial products. For most amateur use, however, this is not a hindrance, since usually you will be interested only in small areas at any one time.
     The Naval Observatory maintains a Web page for the catalogue and its derivatives at:

http://psyche.usno.navy.mil/pmm/
 
For producing lists of stars in small areas of the sky (say up to 10' square), it is quite easy simply to use one of three presently available search engines. These are located at the Strasbourg data center (Centre de Donnees astronomiques) in France, at the European Southern Observatory (ESO) in Germany, and at Lowell Observatory (ahem) at the following URLs:
 
CDS VizieR: http://vizier.u-strasbg.fr/cgi-bin/PMM-USNO-A1.0
 
ESO server: http://archive.eso.org/skycat/servers/usnoa
 
Lowell: http://asteroid.lowell.edu/cgi-bin/koehn/webnet
 
North Americans should use the Lowell site, since in general it will be faster than the European sites. All are similar in allowing you to enter a search center (equinox 2000 except at the CDS, where others are permitted), a field size, and some sort of magnitude limits. The CDS and Lowell servers are very flexible in allowing upper/lower magnitude and color limits, sorting by RA, radius, etc. Try them out to see which version you like best. (I happen to like the CDS version best, but given that the Lowell version resides on the other machine in my office, I always use the "in-house" version instead!)
 
ACT
     This past summer, the very precise Hipparcos and (less precise) Tycho star catalogues were released for general use. The Tycho catalogue contains somewhat over a million stars down to V mag. 10.5 to 11, with fairly good magnitudes and positions for each entry. However, because the time baseline of the measurements was rather short (only a few years), the proper motions of the stars are not very good, viz. about a factor of ten worse than the traditional astrometric catalogues such as the PPM.
     The U. S. Naval Observatory in Washington has combined a re-reduction of the old "Astrographic Catalogue" from the beginning of this century with Tycho to produce the "ACT Reference Catalogue". This provides greatly improved proper motions for 988,758 stars appearing in both catalogues. The files include the Tycho B and V photometry, identifications from the HD, BD, Cordoba, and Cape catalogues as well as Hipparcos numbers. The positions are for both epoch and equinox 2000. (The Hipparcos Tycho data, confusingly, are for epoch 1991.25 but equinox 2000). Details of the catalogue can be found at:
 
http://aries.usno.navy.mil/ad/act.html
 
This site includes a link to the Goddard data center, where the files can be retreived. The complete dataset weighs in at 50 megabytes, so plan carefully before you hit the "save as" button.
 
Astrographic Catalogue 2000
     The ACT page also includes a link to the original Astrographic Catalogue re-reductions, called "AC2000":
 
http://aries.usno.navy.mil/ad/ac.html
 
This re-reduction of the uncompleted survey by (mostly) European observatories contains precise positions and rough magnitudes for 4,600,000 stars as faint as mag. 13 (complete to around 12th). This dataset occupies half a gigabyte. The Web page includes some interesting historical information about the original 1900s-era project as well as details about the re-reduction using modern star catalogues as the reference frame.
 
Twin Astrograph Catalogue
     Still available at the USNO Web site is the "Twin Astrograph Catalogue" (TAC), which combines AC2000 with another new survey of northern stars done with a twin astrograph located in Washington DC. The on-line version includes 687,000 stars down to blue mag. 10.5-11 and north of -18 Dec. The star density is slightly higher than in the Tycho catalogue. The data can be retrieved in one-degree zones at: http://aries.usno.navy.mil/ad/tac.html
     Besides positions, the files contain fairly reliable B and V magni- tudes, and proper motions, along with Hipparcos and GSC identifications.
 
Spectral survey data
     Finally, I might mention the existence of a growing collection of lists containing positions and identifications for stars appearing in surveys to determine spectral types. These surveys were done mostly from the 1940s to the 1960s, and typically include stars down to blue mag. 12.5 in fields a few degrees on a side. I have begun to put these data into machine-readable form, collecting precise positions and identifications to go with them. _None_ of these data can be found at the data centers because the stars are identified for the most part only on charts appearing with the publications. Data for about 12,000 stars in eight fields (mostly in the northern Milky Way) are ready for public consumption at:
 
ftp://ftp.lowell.edu/pub/bas/starcats
 
I think these data will appeal mainly to producers of sky-chart software. For the regions involved, you can merge my lists with the GSC data (I give GSC names explicitly), so that the spectral and magnitude data can be shown for any particular entry. I would think this would be useful for both visual and CCD/photographers, since star colors (related to spectral type) are helpful, for instance, both in star-hopping to deep-sky objects and as an aid in identifying interesting objects appearing on images. I'm curious to know what observers and software-writers think about having this information available.
     All for now.
 
\Brian Skiff (bas@lowell.edu)