QX Cas

As you know, NGC 7790 is one of the standard transformation fields.  One of the reasons I started observing this field many decades ago is because there are a number of variable stars in or near the cluster.  My three favorite ones were the three cepheid variables: CEa, CEb and CF Cas.  CEa/b are a neat pair, separated by only 2.7 arcsec.  All three have 5-day periods, highlighting their common origin.  If you observe this cluster, you should submit data on CF Cas and keep its light curve current.  CEab is a nice pair to use for determining seeing, but I don't recommend submitting data on either star unless you have excellent seeing and can split the pair cleanly.  I do have a nice set of CEab photometry, where I've psf-fit the stars, in case someone wants to write a paper about these stars.

However, there is another neat variable only a few arcmin SE of the cluster center: the tenth-magnitude QX Cas.  This is a possible triple system, with the inner pair an eccentric eclipsing B1V binary with 6.0047d period, and a third star that precesses the line of nodes.  This means that it was an eclipsing system in ~1950-1980, but since then has NOT been eclipsing. Kjurkchiva et al. (2007) presented a spectroscopic orbit with e=0.22.

QX Cas has the rare distinction of being a star that has quit varying.  Moffett and Barnes (1983) indicated that the amplitude of the eclipse was less than Sandage found a couple of decades earlier, and soon thereafter, observers reported no variation at all.  Bonaro et al. (2009) presented a paper at an AAS meeting that highlighted this.  I know of no recent paper, and the few data points in the AID do not show any variability.

I've been observing QX Cas off and on for decades, waiting for it to resume its eclipses.  I was thinking that it would be a neat project for the CCD observers to obtain as complete a light curve as possible before it vanishes this season, and then build a similar light curve once per year for a while to see what happens.  As an incentive, you get to observe NGC7790 and obtain your transformation coefficients.  As a further incentive, I'll be happy to inspect the photometry submitted to the AAVSO/AID and give suggestions for improving your observational techniques (hence the posting to the Photometry Forum).  As with the campaign for BL Boo, you will have to suffer public comments, as I want everyone to learn from these observing campaigns.

QX Cas is a nice early evening object for the next month or two for northern observers.  Submit some data!  Especially those of you not in North America should contribute, as the 6.00day period will make obtaining a complete orbital coverage difficult!  If you have observations of NGC7790 taken over the last few years for determining your transformation coefficients, you should inspect them to see if QX Cas is visible, and submit its measures as long as it is not saturated.

Arne