Sequence Selection and Revision Guidelines
The guidelines used to select these sequences were established by the International Chart Working Group in July 2002. It is important to emphasize that these are guidelines, not absolute rules.
Each sequence is considered on a case by case basis.
- Utilize photometry that is accurate to at least 0.05 only.
0.05 being the standard for a visual chart; 0.02 the standard for a CCD chart.
- CCD charts should be linked to the complete sequence information via the web.
- Utilize comparisons of known color only. (B-V, or its equivalent in the sequence color index)
- Choose comp stars that range between 0.3<B-V<1.0 , (or its equivalent
in the sequence color index), with a conscious effort to limit the range to ~0.7.
- Steps between comp stars should be between 0.3 and 0.5 throughout the
range of the variable.
- No redundant or duplicate values.
- Exclude close doubles as comp stars.
- Identify close companions to the variable as comp stars (if possible), to
aid in identification.
- Choose comp stars as close to the variable as possible. As a general rule,
the fainter the comp star the closer to the variable.
- Avoid large spatial distances between comps in the same magnitude range.
- For visual charts, take position angle effect into account. Endeavor to
pick comps along a line running E and W of the variable if there is a
- Tycho-2 data can be used to 10.5V. However, each star must be weighed on its own
merits for errors.
- Avoid high proper motion stars.
- When no better alternatives exist, micro-variables with an amplitude of 0.03V or less are acceptable to use for visual sequences, but should be called out as variables in the photometry tables for CCD work.
When revising existing sequences there are additional guidelines.
- Utilize as many of the comparisons from previous versions of the sequence as are appropriate.
- Eliminate redundancies and duplications
- Eliminate red stars
- Eliminate variables
- Eliminate close doubles