EB Photometry

Photometry of Eclipsing Binaries

Most contributions of eclipsing binary observations by amateur astronomers have been times of minimum (ToMs) derived from photometric (visual, or instrumented)  time series data.  Usually only the ToMs are published -- often, the photometry does not get systematically archived.  This ignores longer term brightness variations that might be associated with mass loss, mass transfer, or other events, and does not systematically monitor for eclipse depth changes due to apsidal motion.  Also, because the photometry might only be available so long as the observer can be contacted, researchers are  unable to delve in to the reason for a discrepant (or interesting!) ToM.  Therefore, we urge that observers continue to report ToMs in whatever manner they choose (via a JAAVSO omnibus paper, their own paper in JAAVSO, or elsewhere), but that they also contribute the photometry to the AAVSO International Database (AID) for archiving.

Of course, the ideal is multi-band 'all sky' photometry, taken under 'photometric conditions', fully transformed to compensate for individual filter and instrument characteristics.  Few of us observe this way, and few of us have such good skies.  The most common way to observe EBs is differential photometry taken through a single filter.  That data should still be archived in the AAVSO International Database!  Even untransformed differential photometry, taken through a standard filter (typically V), has the potential to detect phenomena that are currently poorly studied.  If you are observing unfiltered, that data should also be archived in the AID.

Here are some of the possibilities for using this data:

  • Better understanding of the causes of scatter in times of minima, i.e. star spots distorting the shape of the in-eclipse light-curve.
  • Correction of erroneous ToMs caused by human or software error.
  • Search for correlation between out-of-eclipse brightness variations and period change events caused by mass transfer events or modulaton of the oblateness of the star by magnetic/convection changes (Applegate theory).
  • Search for eclipse depth variations caused by apsidal rotation of eccentric binary systems.
  • Search for other long term intrinsic variability of the components of the binary system.
  • Assessing the comparative accuracy of data from different observers and observing methods.

Finally, it is one of the basic principles of scientific research that one's data be available to other researchers.  Putting your photometry in to the  AAVSO International Database accomplishes that proactively and permanently.

Next:  recent observations.