[vsnet-alert 610] (fwd) hooray, a little class gets a new member (EG Cnc)

[Taichi Kato <tkato>]

(vsnet-obs 4501 in original)



                EG CANCRI, A SHINY NEW WZ SAGITTAE STAR

     We have obtained time-series photometry of EG Cnc on each night
(December 1-5) since Schmeer's exciting recovery of the star after its
19-year slumber.  We used data from four stations of the Center for
Backyard Astrophysics (CBA), and added brief coverage from the Cerro
Tololo 1-m telescope.  The star continues a linear decline at
0.12 mag/night, and was at V=12.83 on December 5.3 UT.  During December
1-3, the star showed a periodic modulation at 0.0572+-0.0002 d, with
ever-decreasing amplitude (averaging .03 mag peak-to-trough).  On
December 4-5, the signal weakened further and disappeared into the
noise.

     This is reminiscent of AL Com, which had a large outburst in April
1995 after a 20-year quiescence.  AL Com showed an "outburst orbital
hump" exactly at Porb for the first 5 days, then lost periodic signals
for 4 days until the main superhumps (at Porb + 1.1%) appeared suddenly
and with large amplitude on day 10.  Those superhumps rumbled through
the light curve for at least another month.

     It's still too early to know how extensive the resemblance is.
But so far, the outburst of EG Cnc is distinctive for the *smallness*
of the photometric waves, and for their rapid disappearance even while
the star remains bright.  It's tempting to guess that the 82.4 min
waves reported here (and by Matsumoto in vsnet-alert 607) aren't the
real superhumps, but some sort of "warm-up" for the real thing which is
still a few days away.  They're really just not sufficiently "super":
quite small, and no provable displacement of period from Porb since the
latter is completely unknown.

     I would bet dollars to doughnuts (American phrase; translates well
enough, I guess, since dollars are a strong currency) that EG Cnc will
grow strong genuine superhumps within a few days.  This would offer a
great chance to watch the growth of superhumps in real time, which is
very rarely possible since there is seldom much warning for these
things.  At magnitude 12.8 and decently placed in the night sky, the
star could provide a historic opportunity for learning the timescale of
superhump growth, an important subject poorly constrained by
observation or theory.

     So shrug off that morning frost and get thee to a telescope!  And
we would be absolutely delighted to hear from observers who manage to
obtain any time-series photometry.


Joe Patterson, Jonathan Kemp           David Harvey
CBA-New York                           CBA-Tucson

Tonny Vanmunster      David Skillman      Seiichiro Kiyota
CBA-Belgium           CBA-Maryland        CBA-Tsukuba

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