Changes in Comparison Star Sequences in VSD/VSP

There are some changes to the sequences plotted in charts in VSP versus the original AAVSO charts. The following are the four main reasons for the changes, in order of likeliness:

1. A missing comparison star is suspected of being a variable star.

This is a bug in the database. Comparison stars that are also NSV stars were omitted from the initial population of the VSP database. This is a high priority to be fixed and should be resolved soon.

2. A new comparison star is from overlapping AAVSO charts.

One of the beauties of VSP is its ability to customize the field of view being plotted. This means observers are no longer restricted to the A,B,C,D, etc. fixed scale of charts. The center of the field can also be customized, such as to fall between two variables. But this also means that stars from different sequences can appear on the same chart.

Below are links to three AAVSO charts annotated to illustrate this overlapping issue:

1. This is the AAVSO b-scale chart for V Vul. Note the star circled in red has no comp star value.
2. This is the AAVSO d-scale chart for a nearby star, BV Vul. Note the star circles on that chart does have a comp star value (89).
3. This is the b-scale chart for V Vul plotted with VSP. Note the 89 star that was on the BV Vul chart, is now on the V Vul chart. This is because that same part of the sky can be seen on both charts.

The second phase of VSD development involves the reconciliation of the sequences with each other and with other available photometry. That will be a time intensive and challenging process. Until then, go ahead and use the new comp stars you see on the field. As always, report the chart ID with your observation.

3. A changed comparison star has different values on different AAVSO charts.

This is related to #2 above. However, in some cases the problem is that the same comparison star exists on two charts - but with a different magnitude! This is a bad situation that can only be corrected via the reconciliation process mentioned above. Until then, just use the value you see printed on the VSP chart.

4. A human error.

A.k.a. Murphy's Law. Each sequence was entered by a member of the Comparison Star Database Working Group and then verified by another member. As a result, data fidelity is pretty good. But with over 72,000 stars there is bound to be errors that slipped through. The challenge is to determine what is a real human error and what is an error related to the above problems #2 or #3. If you think you found a real human error, e-mail it to vspcharts -att_ aavso.org. Tell us the chart ID of the VSP chart where you found the error, a description of the error itself and whether you checked to see if that star exists on any other charts (i.e. you made sure it isn't due to error #2 or #3). Those that were checked will receive a higher priority than those that weren't, but we'll keep all reports. Once the reconciliation process is completed, we'll go through the reports and fix the human errors.