The Minor Planet Observer
and
Palmer Divide Observatory

2007 Shoemaker Grant Recipient

AAVSO Batch Processing

The above screen shot was created in Canopus after analyzing images in PhotoRed using the new AAVSO batch processing and reduction methods. The two sessions matched perfectly and did not require any zero-point changes.

AAVSO Reporting

"I am VERY impressed! This AAVSO routine is just the ticket for fast reduction of the eclipsing binary work and will be a great boon to all variable observers." – E.W., KS

In January 2008, the AAVSO implemented a new reporting format for CCD observations. PhotoRed has been modified to meet the requirements of the new method and to better conform to the approach used by most AAVSO observers. However, the new format does introduce some new ways of looking at old concepts, particularly when talking about ensemble photometry, so you need to keep an open mind and not assume what has been is what is.

In the simplest approach, it is not required that you get transforms or determine nightly extinction values. In this case, the data would be reported as NOT TRANSFORMED. If, however, you determine or know the color index values of the comps and targets and have found the basic transforms for your system, then you can include these corrections in the data and would report the data as TRANSFORMED. With only a little time and care, reporting transformed values can significantly improve the accuracy of your work, so you should consider finding the transforms for your system.

Ä       The QuickMags routines and data table formerly used for AAVSO observations are no longer used. At this time, there is no routine to convert the QuickMags data to the new AAVSO tables and probably won’t be. The data storage requirements to comply with the new AAVSO standards are substantially different. The old QuickMag tables do not include a significant portion of the required data.

(Download Users Guide PDF with AAVSO Batch Processing tutorial for a detailed look at the procedures in action)

The AAVSO Format – Beware the Check Star

The full AAVSO format document is available on the AAVSO web site. In short, here are some highlights and how PhotoRed works within the new guidelines.

1. Ensemble photometry is allowed. To do so requires that there be a “check” star whose magnitude is presumably known. The definition of a check star for this purpose differs from the old one for a check star.

Before, and under the new format when not claiming ENSEMBLE photometry, the check star magnitude was subtracted from the comparison star magnitude for each observation. The trend of those values should have been a straight line, indicating that neither star was variable.

The definition of a check star when doing ensemble photometry is that it is “second target” but of known and constant magnitude. It is treated like the target in that the one or more comparison stars are used to find a reduced magnitude for the check star for each observation. This reduced magnitude is reported along with the reduced magnitude of the target.

In a perfect world, the values for the check star would be identical for each observation and would exactly match the true magnitude of the star. Since this will not likely be true, the difference between the reduced magnitude for the check star and its accepted (catalog magnitude) can be computed and that difference applied to the target’s reduced magnitude to get its “true” magnitude.

Ä       PhotoRed always uses ENSEMBLE photometry, even if using one comparison and one “check” star. This is not a user-settable option. Therefore, you must always have at least one comp, one and only one check star, and one and only one target in each Batch Reference File (see below).

2. The AAVSO format is a character-delimited file, i.e., each line in the simple text file is an observation with the “fields” being separated by one of three characters. PhotoRed always uses the comma as the delimiter. This is not a user-settable option.

3. The application of transforms is allowed. This is a user-settable option available at the time you measure the images.

4. The format allows for DIFFERENTIAL (offsets from the comp magnitude) or ABSOLUTE (reduced to "true" magnitude). The AAVSO strongly encourages ABSOLUTE. PhotoRed forces that method. This is not a user-settable optinon.