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Gamma Persei eclipse 2019

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Gamma Persei eclipse 2019

Gamma Persei is a long term eclipsing binary. The first ever eclipse minimum of Gamma Per was observed in September 1990, about which, some scientific publications have been written. The following eclipse was expected to be in April 2005, but no definite expected window was described anywhere. From late March to end of April 2005, I did observe the star and took a few digital images of the sky around it as well. In only one of these observations, I observed Gamma Per to be slightly fainter than normal; mag. +3.1 instead of +2.9, which has on 18th April 2005. I have no other observations of mine, nor found many other observation from others around the expected minimum of 2005, so I cannot be sure if my 18th April 2005 observation is indeed reliable.

The minimum could be around 21st November 2019, if the period given as 5330 days in some sources is correct. Or, it could be as much as a month later if the period is longer, as it is written as 5346 or 5350 days in other sources. In AAVSO, the period is given as 5346 days, which puts the next eclipse around 25th December 2019:

Because of this uncertainty in the period of Gamma Per, it is certainly a good idea to monitor the star for its upcoming minimum from 1st November 2019 on.

One last interesting possibility is, Gamma Per and Zeta Aur, another long term eclipsing binary, may be at their respective minimums. The next minimum of Zeta Aur is expected to be around 14th November 2019. surprise

BGW's picture
thank you

Thank you for the "heads up" about these eclipses.  Maybe I'll get out my eps Aur equipment...

Gary Billings

sah's picture
Zeta Aur

I have observed three eclipses of Zeta Aur in the past decade. The system consists of a B7 type star being eclipsed by a type K4 super giant. Because of this, the eclipse is about 0.5 mag deep in B and much less in V and R. It is almost undetectable in I. I do not have U band capability but the eclipse is quite deep in that band. Because the K star is about 40 times larger than the B star, the partial phases of the eclipse are very short (only a couple of days). I expect the descending leg of the eclipse to occur from Oct 24 to 27 and the ascending leg Dec 1 to 4. The total phase of the eclipse will last the entire month of Nov.


HQA's picture
gamma per

I was contacted in July by Brian Mason (USNO), Elizabeth Griffin and others, who had observed gam Per during the 1990 eclipse,  about photometric monitoring of the upcoming eclipse.  I suggested that they contact HQ to set up a campaign.  Tom Calderwood has contacted a few PEP folks to begin monitoring.

Because of this contact from some old friends (I've been in astronomy too long!), BSM_NH2 has been monitoring gam Per since July 24 at SU/B/V/SR/I.  It is a tough target in that there are no bright comparison stars nearby.  There are some useable comps, if you offset the field so that gam Per is near one edge.  Of course, they have no multifilter calibration, so I've been working on that as well.  The 1990 photometry used tau Per as the main comparison star - a long period EB, but currently constant (as it was in 1990).

Therefore, I set up BSM_NH2 to take lots of short exposures, with the plan to stack and use these fainter comps.  Currently, this means:

3x60sec SU

10x3sec B

20x2sec V

20x1.5sec SR

20x1.5sec I

The 1270 images collected so far sounds like a lot, but really only amounts to 17 visits to the field.

The reason I bring this up is that I'm collecting the data, but have't have time to analyze it.  If anyone (like Gary) is interested in helping, I can get the images shared via VPHOT or put on ftp.  In the near future, I'm hoping to be able to do real-time stacking with MaximDL at the telescope, so that the image quantity will be drastically reduced.  I just need more time to test software!


BGW's picture
Great to hear gam Per is

Great to hear gam Per is being monitored.  Thanks for suggesting I might like to process the data:  I would like to, but I really REALLY shouldn't take on another project right now.  I have vast amounts of my own data that hasn't been reported or published yet...

Gary Billings

HQA's picture
zet aur

zet Aur is another good target for the BSM telescopes.  Note that we do have an SU filter and so can do U-band photometry of the system.  The last BSM data was taken in 2015 of this system.  If you are interested in following it, submit a propsal at

This system is pretty easy, with eta Aur nearby for a good comparison star.



tcalderw's picture
PEP plans (UBV)

For PEP observers, my plan is that we use tau Per as comparison and theta Per as check (I'll update the AAVSO list of PEP stars).  Here is a paper with data from the last eclipse:

As you can see, U band was poorly sampled.  If you, or someone you know, has an SSP5 please contact me so we can talk about U band work.  I presently have two U band observers lined up but would like more.

I can use advice about second-order extinction (hint, hint, Arne)




Sebastian Otero
Sebastian Otero's picture
tau Per as another EA/GS

It is useful to note that tau Per is another EA/GS binary with a period of 1515.61 d. but the next eclipse won't happen until March 2022.
It is not an official comparison star for this reason. Range is V= 3.93 - 4.09.


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