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Sequence Selection and Revision Guidelines

Please Note: SeqPlot is a tool designed for use by the Sequence Team to create comparison star sequences for use in AAVSO Charts. For consistency sake, all variable star data submitted to the AAVSO database should be based on comparison star sequences chosen by this experienced team of volunteers. If you need a sequence or a revision to a sequence for a star, please follow the instructions given here to make your request and you will receive a response from the Team in a very timely manner. If you have specific needs for your sequence please communicate them to the Sequence Team.

Before creating a sequence please check for currently available comparison stars by creating a finder Chart and photometry table in VSP using the coordinates of your target star with the desired range of magnitudes, filters and covering a sufficiently large field of view to include off-center positioning of your target star. Use existing comparison stars whenever appropriate. To avoid potential confusion between comp stars with identical chart labels, use AUIDs from the CCD table, rather than chart labels, to identify comp stars.

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.

1) 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.

2) CCD charts should be linked to the complete sequence information via the web.

3) Utilize comparisons of known color only. (B-V, or its equivalent in the sequence color index).

4) 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.

5) Steps between comp stars should be between 0.3 and 0.5 throughout the range of the variable.

6) No redundant or duplicate values.

7) Exclude close doubles as comp stars.

8) Identify close companions to the variable as comp stars (if possible), to aid in identification.

9) Choose comp stars as close to the variable as possible. As a general rule, the fainter the comp star the closer to the variable.

10) Avoid large spatial distances between comps in the same magnitude range.

11) 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 choice.

12) Tycho-2 data is not recommended but can be used to 10.5V if absolutely necessary. However, each star must be weighed on its own merits for errors.

13) Avoid high proper motion stars.

14) 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

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484