--- "G. G." <[EMAIL PROTECTED]> wrote: > While looking at the list of catalogs at Vizier site, I stumbled into > NOMAD catalog. It looks like the best catalog (currently) for > astrometric and photometric data.
It's the best for astrometric data, but read the description again- "astrometric" is listed before "photometric", so I'm not sure about the photometric data. There have been significant delays in finishing the UCAC catalog, which was intended as the "latest and greatest" in astrometric data, and my impression (having heard about Nomad in other places, such as MPML (asteroid astrometry mailing list)), is that Nomad was compiled to work around that delay, by combining the completed part of UCAC with the other previous "best astrometric" catologs. So I think the priority will be on astrometric data. I'd recommend checking some photometric reference sites on the web, such as AAVSO and "CALL" (Collaborative Asteroid Lightcurve List) <http://www.minorplanetobserver.com/astlc/default.htm> to see what photometric references they use. My impression from occasional asteroid lightcurve issues mentioned on MPML is that "high precision" photometric references are limited to small reference sets of stars (some star clusters have been used), but there may be a general all-sky catalog that's better than the rest for photometry. > Also, does anyone know how to download a catalog from Vizier site? I > looked and looked, but could not figure it out. You'll definitely be interested in this: <http://vizier.u-strasbg.fr/cats/II.htx> "CDS Catalogues. II. Photometric Data" The more obvious part of the Vizier website is set to allow downloading small parts of catalogs, and it's been awhile since I downloaded an entire catalog, but using the above link as a starting point, and for an example, I clicked the link for (II/272) Guide Star Photometric Catalog V2.4 (Bucciarelli+ 2001) (GSPC2.4,GSPC) which took me to <http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=II/272> Then clicking the "readme" in the green line near the top went to <http://vizier.u-strasbg.fr/viz-bin/Cat?II/272> The top line of the text says: Individual files can be fetched (via http) from "here". "Here" is a link going to <http://cdsarc.u-strasbg.fr/viz-bin/ftp-index?II/272> Browse the links there, it looks like the full catalog is at <http://cdsarc.u-strasbg.fr/ftp/cats/II/272/gspc24.dat.gz>, or in uncompressed form at <http://cdsarc.u-strasbg.fr/viz-bin/ftp-index?/ftp/cats/II/272/gspc24.dat> -John > By the way here is the description of NOMAD catalog: > > Description: > The Naval Observatory Merged Astrometric Dataset (NOMAD) > contains astrometric and photometric data for over 1 billion stars > derived from the Hipparcos (I/239), Tycho-2 (I/259), UCAC2 (I/289), > and USNO-B1.0 (I/284) catalogs for astrometry and optical hotometry, > supplemented by 2MASS (II/246) near-infrared photometry. For each > unique star the "best" astrometric and photometric data are chosen > from the source catalogs and merged into a single dataset. A sequence > of priorities is followed and NOMAD contains flags to identify the > source catalogs and gives cross-reference identifications. This > first release of NOMAD is not a compiled catalog; that is, if a star > is identified in more than 1 of the above mentioned catalogs, only > 1 catalog entry is chosen. > Thus the local and global systematic errors of the various > source catalogs will be present in this version of NOMAD. All source > catalogs astrometric data are on the International Celestial > Reference System within the limitations of the source catalogs. > > > --- In [email protected], John Mahony > <[EMAIL PROTECTED]> wrote: > > > > Unfortunately I know almost nothing about photometry. > > > > You can find just about any catalog on Vizier, and convert them for > CdC using > > CdC's catgen utility (see the "tools" section of the CdC download > page, at > > least for v2.x). > > > > -John ____________________________________________________________________________________ Choose the right car based on your needs. Check out Yahoo! Autos new Car Finder tool. http://autos.yahoo.com/carfinder/
