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. I was wondering if in the future
version of CDC an access to this catalog can be added in the "Online
resources".
Also, does anyone know how to download a catalog from Vizier site? I
looked and looked, but could not figure it out.
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
>
>
> --- "G. G." <[EMAIL PROTECTED]> wrote:
>
> > John,
> >
> > Thanks for responding.
> >
> > So, which catalogs (accessible through CDC) are photometric
catalogs?
> > Also, if none is, are there good photometric catalogs on-line?
> >
> > Thanks,
> > Gennady
> >
> > --- In [email protected], John Mahony
> > <jmmahony@> wrote:
> > >
> > > These were intended as astrometric catalogs, not photometric.
To
> > quote from
> > > "read.pht", the readme file on the USNO's website for the
> > photometric data in
> > > the USNO-A1.0 catalog:
> > >
> > > -----------------------------------------
> > > Summary:
> > >
> > > The photometric calibration of USNO-A1.0 is about as poor as
one
> > can
> > > have and still claim that the magnitudes mean something.
> > > .....
> > > --------------------------------------
> > >
> > > -John
> > >
> > >
> > >
> > > --- "G. G." <ggleyzer@> wrote:
> > >
> > > > Often, I use catalogs USNO-A and USNO-B to identify faint
stars.
> > > > However, on many occasions these catalogs do not agree.
Often,
> > the
> > > > difference is quite large (1+ magnitudes). Does anyone know
which
> > of
> > > > these catalogs is more accurate?
> > > >
> > > > Thanks,
> > > > Gennady
> > >
> > >
> > >
> > >
> > >
> >
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>
>
>
>
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