Delving deeper into the world of photometry of variable stars, I decided to start building a light curve for a variable star in Gemini near the open cluster NGC2304, which I found in the same frame as my shot of a meteor trail I recently posted.  I used Muniwin to first find this star in the field and then to do the measurements of the star's magnitude.  I identified the star as ASASSN-V J065743.05+174345.8/SERIV 7 and gathered image data on three nights so far, 2-19-2022, 2-26-2022 and 3-1-2022.  All together, I acquired 107 three minute images.   The star has a period of 0.484715533 days, meaning the two stars complete an orbit around one another in this period of time.  To build a light curve, it is customary to "fold" the data into a single cycle.  In a single cycle the phase goes from 0 to 1, i.e., from beginning to end and the observations are reduced using the known  period to all be in the same cycle (this amounts to determining the days elapsed from the date and time of the very first observation to any given observation , dividing by the period and taking the decimal part of the answer as the phase).  To emphasize how amazing it is that such images and measurements can be obtained with back yard equipment, I deliberately left the arrow identifying the star pretty inconspicuous.  I hope you can see it!

The image posted here of the field is new and was compiled from the third set of observations.  Superimposed on the image of the field is the light curve I've obtained.  The points with the error bars are my data and the lighter blue points are drawn from the published light curve determined by the ASAS-SN (all sky automated survey supernovae) project run by the Ohio State University.  The agreement between the two curves is pretty good, although there is a bit of deviation at the beginning that deserves some investigation.  There are, of course, gaps in my data which I hope to fill in with more observations.  The problem is that Gemini is slipping to the west into my light polluted skies so I may get shut out for this year.

The variable star being studied here is an eclipsing binary of the Algol type, meaning a semi-detached pair of stars that obit one another along our line of sight.  The stars are quite close and mass exchange can occur as the system evolves.  When the cooler star passes in front of the hotter star, the brightness of the pair decreases the most, which is the primary eclipse and is the deeper dip in the plot.  Then when the hotter star passes in front of the cooler star, the brightness decreases less dramatically to produce the secondary eclipse.  In between eclipses, the brightness remains fairly constant.  Just for fun, I did a little calculating for the Algol system to see just how fast these close binary stars travel in their orbits.  To put what I found in perspective, note that the earth travels at about 67,000 miles per hour as it orbits the sun.  My calculations showed that the lower mass, cooler star in the Algol system travels at around 500,000 miles per hour!  Pretty zippy, indeed!