(cba:news) stars of mid-april

Joe Patterson jop at astro.columbia.edu
Mon Apr 17 07:16:25 EDT 2000


Dear CBAers,

     The pendulum swings south again.  Two important dwarf novae in
eruption (likely supermax) now.

     V551 Sgr has been bright for about a week now, observed by Stubbings
and (I think) Pearce.  At 18h-34d, it's perhaps a bit too early for long
observing runs, but at this writing there is nothing known at all about
its orbital or superhump periods.  It appears to be a bona fide SU UMa 
star, and is said to be a WZ Sge type (very rare eruptions).  That makes
it nutritious food for the CBA.  (Unfortunately in this biz, you usually
can't afford to wait till you're hungry again, nor for the food to appear
just at scheduled mealtimes.  Not even as good as being a predator.)  So
let's see what V551 Sgr is going to tell us.  If an ambitious Arizonan 
could supplement our NZ/AU efforts, then we could break the daily alias
in spite of the somewhat unfavorable sky position.  Probably only another
4-7 days of being bright.

     Likewise for V2051 Oph, only this guy at 1708-25 is better placed
for everyone.  Plus, it eclipses.  We've covered two previous supermaxima,     
but rather poorly.  This one can be done by some northerners (Arizonans,
anyway).  If we could get coverage anywhere near what we (mostly Kiwis)
got for OY Car, that would be superb.  Plus, who knows, maybe some
springboks will wander into a telescope dome at Sutherland and complete
the global circuit.  I think it'll stay bright for 7-10 more days.

     The X-ray transient in UMa.  The amplitude has declined to about 0.04
mag, but continues to track the 0.17 d period previously found by Lew Cook.     
No period change yet (18 days).  Dave Harvey coming back on line has
rescued us, as his superior observing conditions at Tucson have enabled us
to get down deeper into the grass.  (He lives next to a shopping center, 
but it's Arizona!).  Space observations of this object continue, and so
should we - I just wanted to urge the Europeans not to give up, the signal
is really there but just looks pathetic.  

     So this week's winners are V2051 Oph or V551 Sgr in the south, and 
XTE1118 and/or V2051 Oph in the north.  For the smaller scopes unable to     
get faint or south enough, I recommend CR Boo, which we still want to
cover with great assiduity once these erupters settle down.

     By the way the DV UMa paper is nearing completion.  Anyone with unsent
data, send it in!


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