* * * * * Comparison stars for Guide8.0 users * * * * *
Over the last year or so I have been busy collecting good quality photometric data of stars - with
emphasis on the magnitude 10-15 range - that could be incorporated in Guide8.0 with the principle
aim to have good comparison stars as close to a faint comet as possible.
Below you find a number of files that I feel may be useful for other observers as well.
A brief explanation on how to install and (de)activate the data can be found here.

Arne Henden's photometry.
Over the years Arne Henden has compiled a large collection of photometric fields north of
declination -30o. Especially for comet observers (but others may find it useful as well) I have made
a selection of stars down to magnitude 15.5 that meet a number of criteria. They must have been
measured at least twice, have B-V between 0.00 and 1.00, and have an error <0.10 magnitude.
A zipfile containing the prn-file with the star selection, and a matching tdf-file can be
downloaded here. Date of last update: September 23, 2005

In addition I have prepared 3 supplementary files:
 * The first supplement contains stars down to magnitude 15.5 with B-V between 0.00 and 1.00, but
that have only been measured once. It should be used with some care, because lack of a second (and
third ect..) measurement precluded the detection of obvious variable stars.
It can be downloaded here. Date of last update: September 23, 2005
 * The second supplement is an extension to the main file with (slightly) red stars having B-V
between 1.01 and 1.50.
It can be downloaded here. Date of last update: September 23, 2005
 * The third supplement is an extension to the main file with stars fainter than magnitude 15.5.
It can be downloaded here. Date of last update: September 23, 2005

In Guide8.0 the stars from the different sets are clearly distinguished by their own colour.
The stars from the main catalog have their magnitude added in green. The 'faint' stars are shown
in pale green, the reddish stars in red, and the stars with only a single measurement in orange.

The ICQ-code for this reference is HN.
The original files, with photometry often down to magnitude 20+, can be downloaded from Arne Henden's ftp-site.

Brian Skiff's LONEOS file.
Brian Skiff has compiled a large 'all sky' file with high quality data from the literature.
I have made a special selection for comet observers with stars down to magnitude 16.0 and B-V
between 0.00 and 1.00. A zipfile containing the prn-file with stellar data, and a matching tdf-file
can be downloaded here. Date of last update: December 27, 2004

In Guide8.0 the stars from the special selection have their magnitude labelled in yellow.
The ICQ-code for this reference is SK.
Brian Skiff's complete LONEOS file can be downloaded here.

Landolt photometry.
Between 1982 and 1993 Landolt published photometry for a large number of stars, mainly along the
equator. A zipfile containing the prn-file with stellar data, and a matching tdf-file can be
downloaded here. Date of last update: March 9, 2004

In Guide8.0 the stars from this file have their magnitude labelled in pale blue.
The ICQ-code for this reference is L.

TASS photometry.
Data obtained between 1996 and 1998 with the TASS Mark III survey have been collected in the tenxcat
catalog. This survey covered a wide strip along the equator, roughly covering declination +2 to -4
degrees. From this we have made a special selection that had to meet the following requirements:
only stars with a V-magnitude in the range 10.0-14.0, at least 5 measurements both in V and I with
a standard deviation <0.20, and V-I<1.2 are included.
TASS gives only measurements in V, I and sometimes R. V-I is similar to, or slightly larger than B-V
as a first approximation (for stars with B-V ~1.0), so V-I<1.2 was choosen as a suitable limit to
eliminate most red stars. Stars fainter than magnitude 13 may still have rather large errors and
should only be used with extreme care, even in this special selection.
A zipfile containing the dat-file with stellar data, and a matching tdf-file can be downloaded
here. Date of last update: March 9, 2004

In Guide8.0 the stars from this file have their magnitude labelled in purple.
Sofar no ICQ-code has been assigned to this reference.
The original catalog with TASS data can be acccessed here.