Lew's Telescope and CCD Camera Project

03 September 1999 Update

Is the Check Star Variable?

Light Curves obtained on the star GSC3132:1412

The following light curves consist of 50 point running averages for the star GSC3132:1412 which was used as a check star. Hans-Goran Lindberg notified me that it is a suspected variable, and it does show as "var" on the AAVSO chart for MV Lyr.

The data is not edited other than being grouped in points of 50 observations averaged. This process will result in a smooth curve.

The first curve is of the entire data set. If anything - it shows that the star is relatively constant over time. The magnitude scale for all charts is the same - the chart spans only 0.07 magnitude.

The data is presented on the same scale for each night in the rest of the curves. The window of time for each of the curves is 0.35 day (7.2 hours).

There is nothing set in concrete about these curves! Don't believe they represent an actual variation of brightness in the star! They are at best an indication of the variations in instrumental response over a night. The fact that many of them show a decrease in brightness of the star over the night (perhaps paralleling the outside temperature) makes one suspicious of the supposition that they could represent a variation in brightness of the star. Perhaps they represent differential extinction (doubtful - the stars are within 5 arc minutes and the airmass never exceeded 2) or some alignment or flexure as the telescope tracked over the sky. They are likely not due to positional variation on the CCD chip, as the guiding of the telescope is poor and the images are well distributed over the chip with more rapid frequency than the possible variation seen here. The raw data for the check star on two of the nights (JD 2451404 and JD ..405) is visible thru this link. Casual inspection of the data will show scatter much greater than the apparent variation here. On that chart, the scale is much greater than here.

Jerry Hudson of the UC Berkeley Astronomy Department has analyzed the data and seen no consistent periodicity of variation over the time scale here, although one night (JD 403) did show a strong peak at 13 cycles per day. It was not evident in other nights.

The reader is cautioned that this data represents nothing claimed as a stellar variation, however further data will be obtained!

There is a suggestion that there may be longer term variation shown in the daily averages - but the data may not be good enough to see what appears to be a slow decline in brightness: Don't believe all you see!!

Averaged daily measurements for the Check Star: GSC3132:1412. And there remains the further question, could the comparison star be varying (too?). It has not been suspected of being variable, while the check star has been so noted on the AAVSO chart.

More data will be posted as it is available!