[vsnet-alert 9784] Z And outburst?

[Taichi Kato]

  According to Eddy Muyllaert, the symbiotic variable Z And
has brightened.  This may be another ongoing outburst.

  YYYYMMDD(UT) mag  observer
  20071210.783 110 (Georg Comello)
  20071210.881 106 (Franck Gobet)
  20071210.951 106 (Gary Poyner)
  20071211.854 108 (Franck Gobet)
  20071211.897 110 (Erwin van Ballegoij)
  20071211.930 106 (Gary Poyner)
  20071212.860 107 (Franck Gobet)
  20071214.935 110 (Franck Gobet)
  20071215.981 106V (Eienne Morelle)
  20071216.587 106 (Yutaka Maeda)
  20071216.853 109 (Eddy Muyllaert)
  20071216.856 109 (Franck Gobet)
  20071216.890 105 (Gary Poyner)
  20071216.938 110 (Erwin van Ballegoij)
  20071217.740 110 (Georg Comello)
  20071217.858 106V (Eienne Morelle)
  20071217.861 109 (Franck Gobet)
  20071217.885 110 (Erwin van Ballegoij)
  20071218.573 105 (Hiroyuki Someya)
  20071218.865 109 (Franck Gobet)
  20071222.754 108 (Eddy Muyllaert)
  20071222.839 108 (Gary Poyner)
  20071222.850 111 (Erwin van Ballegoij)
  20071226.578 104 (Yutaka Maeda)
  20071229.743  99 (Eddy Muyllaert)

  Z And has undergone outbursts quasi-periodically in the
recent years:

  Approximate dates of maxima:

  JD-2400000
  50597
  51793 (1196)
  52565:  770:
  53205   640:
  53880:  675:

  ~580 d has passed since the last outburst maximum.

  The mean period between these maxima is ~661 d, which is
substantially shorter than the proposed orbital period
(759 d, Formiggini and Leibowitz 1994, they also reported
a period of 656 d; Mikolajewska and Kenyon 1996).

  Sokoloski et al. (ApJ 636, 1002) interpreted Z And outbursts
as a combination of disk-instability phenomenon and nuclear
burning.  They referred the ~700 d period (same phenomenon
as above) to as a rebrightening (triggered by disk instability?).
If the present brightening indeed leads to another outburst,
the supposed 650-700 d period seems to be further supported.
The rise is faster than decline in all cases, suggesting that
some sort of explosion/instability was taking place.
Multicolor photometry and multiwavelength observations
as in Sokoloski et al. would be encouraged.

  By the way, there is a novel interpretation of multiperiods
in symbiotic stars.  see
http://arxiv.org/abs/0712.2120