VX Fornax

On the 14th of September 2009 I visually detected an outburst of the now WZ Sge- type dwarf nova VX For at a visual magnitude of 13.0. The first-ever outburst detection in 19 years!

CCD Image of VX For in Outburst

VX For was discovered by William Liller, of Vina del Mar, Chile on October 25th, 1990 at photographic magnitude 12.5. This was a very faint system normally at 20th magnitude that suddenly brightened by 7 or 8 magnitudes in the visual. The outburst lasted more than 10 days. VX For was listed as a likely candidate for a WZ Sge-type dwarf nova (Kato et al. 2001a).

Joe Patterson, of the Center for Backyard Astrophysics recalls the 1990 event.

[Wow, I’ve lived to see the day!
This star zoomed to 12.6 from about 20.5 in 1990, and stayed bright for
many weeks (declining at ~0.1 mag/day).  The spectra made it pretty
clear it was an erupting dwarf nova, and even in 1990 it seemed very,
very likely that the star would flash superhumps.  But I studied it for
7 straight nights at Cerro Tololo, and found only small and apparently
aperiodic wiggles in the light curve.  Basically a very high-quality
nothing.  Then my run ended… and I’ve always wondered what this star is.

Now it’s 2009, and we know a lot more about the WZ Sge syndrome among
dwarf novae.  The most extreme of these stars generally take quite a
long time to sprout actual superhumps; WZ Sge itself takes 10 days. So
that’s a pretty good conjecture – that it’s quite extreme even among the
WZ Sge class… and that had I taken over that 0.9 m telescope and
refused to leave, I would eventually have seen those telltale superhumps.
We don’t yet know much about this eruption, but if it’s a super (odds
are decent), then this is the glamor object of the year for dwarf novae.]

Light curve of the September 2009 outburst of VX For from my visual observations. Several re-brightening detections were also observed.


New WZ Sge-type Dwarf Nova.

Ordinary superhumps were observed soon after this outburst detection which suggested an SU UMa-type superoutburst. It was later found that the start of the outburst was missed, and VX For also underwent five rebrightenings! VX For is now classified as a WZ-Sge type dwarf nova.

VX For received a lot of attention worldwide from CCD observers, which is shown in this light curve from the AAVSO database. CCD observations in green. Black dots are visual observations.

Back to light curves

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