[vsnet-alert 11461] Re: V713 Cep

[Denis Denisenko]

Hello all!

Gary Poyner wrote on Fri, 28 Aug 2009 10:18:01 +0100:

> V713 Cep (Antipin's Var75 Cep) is in or entering outburst...
>
> V713 Cep is also an eclipser, with a known P_orb 0.085853d
> and eclipse amplitude of ~2 mags.

I should remark this is definitely a typo caused by misunderstanding of 
my original message on the eclipses discovery back in August 2007.  The 
value quoted by Gary refers to DV UMa - not V713 Cep!  Read again 
[vsnet-alert 9516] at 
http://ooruri.kusastro.kyoto-u.ac.jp/pipermail/vsnet-alert/2007-August/001138.html 
and you will see what I mean.  Based on the data from the first two 
nights I wrote the following on 2007 Aug. 28 23:45:45 +0400:

"The preliminary value of period is 0.08542(2)d, the range of 
variability in V band is about 18.0-21.0:.
The eclipse ephemeris is as follows:
T = 2454338.371 + 0.08542 * E.
V713 Cep is very similar to UGSU-type star DV UMa (orbital period 
0.085853d)"

Thus, the quote above should actually read like this:

> V713 Cep is also an eclipser, with a known P_orb 0.08542d
> and eclipse amplitude of ~3 mags.

(Even 3.5, actually! - D.D.)

Later I have observed two more eclipses on the nights of 2007 Aug. 29 
and Sep. 3 which has improved the period value to P=0.085419(2)d.  Also 
note that the correct mid-eclipse time of the first epoch is 
T0=2454338.375(1).  By Sep. 09, 2009 (JD=2455083.5) star has made 8723 
revolutions.  Eclipse prediction using 0.085419(2) period value should 
be correct within +/-25 min (0.2P).  Actually it agrees with 
observations even better, within 5 minutes!

JD=2455073.400 eclipse observed by David Boyd and Ian Miller has E=8605 
which improves the orbital period value  to 0.0854184(2)d.

So, please use the following (geocentric!) light elements for V713 Cep 
eclipses:

T = 2454338.375 + 0.0854184 * E.

Also interesting is that the shape of the lightcurve is slightly 
changing with time.  Back in 2007, while at minimum, V713 was showing an 
apparent hump before the eclipse (phase 0.7-0.95), about 0.3m brighter 
than at 0.05-0.4.  Now, during the outburst, the light curve outside the 
eclipses is more or less symmetric after removing the fading trend.  

Best regards,

Den in Moscow

P.S. Sorry about the belated response!