(cba:news) (cba:chat) BK Lyn mag 14.2... also DI UMa, RZ LMi, and IX Dra

Joe Patterson jop at astro.columbia.edu
Thu Mar 29 04:15:18 EDT 2012


Hi Joe,

Yes, that's very likely it - it's right on schedule.  Also, 14.0 is 
about right for a super.

But all that is based on this year.  Seems to be a bona fide dwarf nova 
this year - but it has been a novalike variable for 20 years, and we've 
been very persistent at looking too.  In fact, my guess is that it has 
been a novalike variable for 2000 years... or more precisely, between 
1904 and 1910 years (there's a good chance it was a classical nova in 
101 AD).  Nova->novalike->dwarf nova: the decathlete of eruptive variables.

Those of you observing this star have probably gotten used to those 
beautiful huge waves in the star at V~16 - the negative superhumps. 
They're nearly gone at V=14.  How come?  Supposedly, CVs should *grow* 
superhumps in superoutbursts, not suppress them.

Au contraire, sort of. *Negative* superhumps (by definition P<Porb) seem 
to be completely indifferent to outbursts.  They shine with an 
amplitude which is constant in ENERGY UNITS, not in magnitude units. 
That wave is still there with the same amplitude in energy units, but is 
slightly swamped by the 6x increase in unmodulated light.

That's not the whole story, but it explains the great diminution of the 
periodic signal.  In addition, BK Lyn does, like all the other 
short-period dwarf novae, grow positive superhumps in superoutburst. 
That'll be there too.  But just to make our life a bit harder, the P+ 
and P- signals are fiendishly separated by about 0.98+-0.01 
cycles/day... so there's an illusion of aliasing in the power spectrum. 
  And in addition, the beating of these signals of similar amplitude 
means that at unlucky longitudes, the two can cancel. (Our 
multi-longitude data sorts all this out just fine, but single-site data 
is bedevilled by that awkwardness.)

I speculate that all the ER UMa stars do something similar to this.  ER 
UMa itself definitely does.  It did last year, and Enrique's analysis 
(to be presented at Big Bear) will show that in spades this year.  And 
V503 Cygni definitely does (old CBA paper by Harvey et al.)  We'd love 
to cover the other members: in this season, that means DI UMa and RZ LMi 
- and IX Dra, if you're partial to the far north. These stars are a 
little fainter than ER & BK... but I think most people can do 'em: the 
effects in ER/BK/V503 are really quite large.

And to make room for these targets, let's end the season on BH Lyn and 
LN UMa; we have enough data on these stars.

But keep up the pressure on CR Boo!  At a dec of +8, it seems to be 
nobody's favorite; no one can get long runs.  But with enough global 
cooperation, we can overcome this.

BTW, thanks for that handy tool for listing targets.  I earnestly 
promise to use it more!  Once I get caught up with work, hahaha.

Mariners 3, A's 1.  Ichiro rules.  Play Ball!

joe


On 3/28/2012 10:35 PM, Joe Ulowetz wrote:
> Would this be considered a super outburst? It's brighter than I've seen it
> before.
>
> -Joe U.
>
>
>
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