[vsnet-alert 2731] Re: EX Hya: Another brief brightening

["William S G Walker" <astroman@voyager.co.nz>]

Danie et al,

I'm always mystified by these so-called brief outbursts of EX Hydrae. Over
the years we've looked at the star for many hundreds of hours and haven't
seen one. But I notice that Brian Warner quotes them in his book reviewing
CVs. Are they real or just fortuitous observations of the spin hump maxima?

In the present case I note that there is an interesting coincidence of
times.
Predicted eclipse is at 1999 02 28.12844 and spin hump peak at 28.096. The
latter was running ~0.004 days late in mid-1998 so would be about 28.100.
The heliocentric correction is also +0.004 days so Danie's faint point at
28.119
becomes 28.123 and the bright point at 28.094 becomes 28.098. I think that
what has been observed is merely the different levels in one cycle. At
eclipse it can get as faint as 13.5. But eclipses coinciding with the spin
hump maximum are often hard to see.

In this case the eclipse was well out of phase with the spin hump maximum
so the amplitude is noticeable, even visually. I remember observing this
star in 1968 with Brian Marino and seeing similar results - since flare
stars were the 'thing' in those days we thought we had seen a flare.

Sorry there's nothing to contribute to the observations - there seem to
have been any number of interesting events - but this summer has been
unusually cloudy with a 30-50kph easterly for all but three days of
the two months since Xmas. Very unastronomical.

Regards,
Stan 
-------
> From: Danie Overbeek <Danie.Overbeek@mail.global.co.za>
> To: observations@aavso.com
> Cc: vsnet-alert@kusastro.kyoto-u.ac.jp; janhers@pixie.co.za

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