Center for Backyard Astrophysics   

CBA Network Photo
A global network of small telescopes dedicated to photometry of cataclysmic variables.

Since 1991 we have been engaged in long-term photometric studies of cataclysmic variables, mostly with CCD cameras mounted on small backyard telescopes. Cataclysmic variables are famous for their large quasi-periodic eruptions on timescales of weeks to years. Less well known, but equally fascinating, are their strictly periodic signals on short timescales (~10 minutes to ~4 days). These represent the spin of the white dwarf, the binary orbital period, "superhump" periods, and disk precession periods. They give excellent scientific return for monitoring closely over intervals of weeks to months, timescales which most traditional research programs cannot effectively study. As computers and imaging systems improve, it seems likely that networks on this type will bring a revolution to the science of variable stars, by tapping the energy and talents of backyard astronomers around the world.
Center for Backyard Astrophysics
CBA Utah's first contribution was June 21, 2001. It was a campaign to study V795 Her. A finder chart and a typical light curve are shown below. Since then, the following cataclysmic variables have been studied: ES Dra, WZ Sge, AO Psc, TT Ari, FS Aur, BK Lyn.
Each month new cataclysmic variables join the list for study as they become active. V795 Her Finder Photo
 
This image is of V795 Her, a cataclysmic variable of the DQ Hercules type. I have been monitoring this variable for six nights and have taken on average 460 images per night. This study is part of a Center for Backyard Astrophysics campaign directed by Dr. Joe Patterson of Columbia University, New York. Myself and others situated around the globe have been monitoring the behavior of this star system. Our data is sent to a common collection point and then analyzed for specific activity. This image is the first of the nights series that started on June 27, 2001. Overall 462 images were taken, each of 30 seconds duration with a cycle time of 50 seconds. The telescope is the Vermillion Cliffs Observatory 24" f/3.5 system with an ST-8e camera at prime focus.
This graph is the light curve for V795 Her and a check star. The measurement technique is to first dark subtract each image, flat field each image and then measure three stars in the field. The first star (V795HER) is the variable star. The second star is the comparison star and the third is a check star. The intensity of each star is measured and the background sky subtracted from them. Finally, the difference in magnitude between the variable and the comparison star is determined and the difference in magnitude between the check star and the comparison star is determined. A graph of these two differences forms the light curves. The upper curve (check-comp) is essentially flat verifying that the comparison star is not varying. The real science is the variable-comparison curve. This curve shows that V795 Her has a base period as well as a faster period superimposed on this base period. The base period is about 0.108 days and the faster period (called superhumps) shows the rotation of the accretion disk around the white dwarf star.