Faint Cataclysmic Variable (CV) and Long Period Variable (LPV) CCD Project

By Gary Walker, Chairman, CCD Committee

The existing CCD program has yielded over 12 years of four-color photometry of the eight Hipparcos Long Period Variable Stars. Over 25,000 measurements have been contributed by members Ron Zissell, Tom Michalik, Don Pray, Priscilla Benson and Gary Walker. This program has given us a baseline of comparison, since each observer transformed his/her data so that the results were seamless with very low scatter and no biases between observers, even though five different sites, telescopes, CCD cameras, filters, and reduction software were used.

While four-color transformed photometry has indeed been a rewarding program, it has also been a very technically intense activity. At times, I had to remind myself that this was supposed to be fun. While four-color photometry will continue to be a part of the AAVSO program, we have added a program of 20 faint CV's and eight faint LPV's. These are all active in our visual programs, but they all go to 15th to 19th magnitude at minimum. Visual estimates are very difficult and sometimes impossible. This is why we want to monitor these stars using CCD cameras.

We have limited the program to CCD(V) estimates. This will allow observers who do not want to get involved with a complete set of filters and a filter wheel to simply use a single filter. In most cases, this filter can just screw into the camera nose. While unfiltered estimates may also be valuable, their high red sensitivity will make it impossible to combine with the visual data. Johnson-V CCD filters are available from Optec, & Murnaghan, as well as others. Make sure that you ask for properly red blocked filters suitable for use with a CCD.

Some photometry done in the past, be it PEP, Visual, or CCD is only as reliable as the comparison star magnitudes. In order to minimize errors arising from the use of different comparison stars, we are asking that you use the three comparison stars listed in the table below. The comparison stars are chosen, according to the following ground rules, to optimize the ease of getting good results. Rely on the two faint comps when the variable is near minimum; drop the faint comp star and use the bright one when the variable is in its brighter stage of the cycle.

Ground Rules Used to Pick the Comparison Stars

1. Choose comparison stars so that measurements are interpolated between a brighter and a fainter comp star. In some cases, this was not always possible and extrapolation will be required. It should not be necessary to extrapolate more than 2.5 magnitudes.
2. Use three comparison stars. For most faint monitoring, use the two fainter comparison stars.
3. Every attempt has been made to avoid comparison stars that are close to other stars that either contaminate the star measurement or the sky measurement.
4. When choosing program stars, those with bright nearby comparison stars have been avoided.
5. The middle comparison star was chosen to be used for any "after outburst" studies.
6. When two comparison stars have the same magnitude, the one closest in proximity to the variable is used. This was done to avoid confusion with the comparison stars.

The set of charts of faint cataclysmic and long period variables are available online or can be ordered (free of charge) from the AAVSO.

• Download the charts online. They can also be downloaded via ftp. Here is info on how to access the AAVSO ftp site.
• Use the feedback form to request copies to be postal mailed to you

Clear Skies,
Gary Walker
Chairman, CCD Committee

Data Format

The observations for the faint CV and LPV CCD(V) project should be submitted via WebObs, or your favorite submittal method. Remember to compute JD to three significant places, and magnitudes to one significant place.

CV & LPV Table