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[vsnet-alert 4142] Re: EX Hya brighert? (Pearce)



Greetings,

After running on Tau 3 until it set I turned the CCD camera onto EX Hydrae
about 1145UT on Feb 7. The star appeared its normal brightness. 

Visual observers often seem unaware that this star is subject to both
eclipses at about 98 minute intervals and white dwarf spin period
fluctuations with a period of 67 minutes. The amplitude of the latter is
usually between 0.3 and 0.7 magnitudes but I have seen it larger on a few
occasions. On one occasion in 1968 it was almost flarelike. 

The eclipses are difficult to see at times and the interaction between
these and the spin humps, with variations in the mass flow rate, causes the
brightness of EX Hydrae to be very erratic in quiescence. Outbursts are
rare and very important! If you see the star brighter than V = 12 tell the
world.

Regards,
Stan



----------
> From: Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>
> To: vsnet-alert@kusastro.kyoto-u.ac.jp
> Subject: [vsnet-alert 4133] EX Hya brighert? (Pearce)
> Date: Sunday, February 06, 2000 9:52 PM
> 
> EX Hya brighert? (Pearce)
> 
> From: "Andrew Pearce" <arpearce@ozemail.com.au>
> Subject: EX Hya
> Date: Mon, 7 Feb 2000 07:32:43 +0800
> 
> This may be another short period variation at minimum, however I have
observed a
> brightening of EX Hya as detailed below:
> 
> Feb 5.806UT  13.1
> Feb 6.757UT  12.6
> 
> The observation on Feb 6th was made at 0210 hrs local time. 
Unfortunately it
> clouded over shortly thereafter and I couldn't make any further
observations
> despite there being another 2 hours of dark time.
> 
> Observations for the 30 days preceding Feb 5th show the star to have
remained at
> a relatively constant brightness around mag 13.1-13.2.  Certainly no 0.5
mag
> increase as is the case now.
> 
> Hopefully I'll make further observations tonight.
> 
> Regards
> Andrew Pearce (PEX)
> 
> ---
> 
> HYAEX 20000205.806 131 PEA
> HYAEX 20000206.757 126 PEA
> 

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