(cba:news) ER UMa shows the way...

Joe Patterson jop at astro.columbia.edu
Mon Feb 7 09:50:36 EST 2011

But what way that is, quien sabe?

A sudden spell of great Mediterranean weather has struck, and Enrique's 
data shows that ER UMa, in its present quiescence, is flashing very 
strong negative superhumps.  This discovery cries out for follow-up, and 
in particular much closer study of the ER UMa class.  The only real 
precedent is V503 Cyg, which could be considered a borderline ER UMa 
star, and which showed a very strong negative superhump persisting for 
months (Harvey et al. 1995 or thereabouts).  But there are other clues 
hanging around which suggest this could be a property of the class - or, 
more specifically, could be a signature of an underlying correlate: high 
accretion rate at quiescence.  That would embrace such stars as V592 
Cas, BK Lyn, and V1974 Cyg into the club - all with short Porb, all 
mysteriously bright at "quiescence", and all with negative superhumps. 
Adding a second mystery doesn't explain the first... but it does suggest 
an organizing principle for a research program.


1. Let's keep following ER UMa until it scrapes the trees on your 
northwest horizon.  Keep cba-chat humming to keep track of who plans to 
do what, but don't shy away from some redundancy (which really helps 
with calibration).

2. Let's put YZ Cnc on the program.  A bright borderline ER UMa star 
which CBA has never done.  Especially in quiescence, but maybe all the time.

3. Let's put BK Lyn on the program.  We have some great data in the bank 
- but the superhump is so strong and apparently permanent that *this* is 
the star to test for really long-term stability (months to years).

4. Let's put AH Men back on the program.  Same comments as BK Lyn. 
Still decently seasonal due to the outrageous declination (-81 deg).

Other matters.

That same spell of great Mediterranean (or European anyway) weather gave 
us great runs on V1212 Tauri from Enrique and Etienne Morelle, and this 
puts the star to bed for the year - and maybe forever.  Very nice 
positive (apsidal) superhump.  Bob Rea's amazing sentry work has also 
rung down the curtain on T Pyx.  The season had just started, but the 
photometric wave agrees *exactly* with the long-term ephemeris - so that 
one's a proverbial wrap.  Finally, Enrique has obtain a few eclipses of 
UMa 6, which tweaks the ephemeris and ends the season for that star also.

Fot those wishing to read about the theory of negative superhumps, look 
up Matt Wood's papers on ADS.  They're nicely written and let the reader 
into the subject with great mathematical gentleness.  Michele Montgomery 
has also written some excellent papers, but she doesn't show much 
mathematical mercy.  The proper word might be STORY, though, rather than 
theory; the observational basis for the whole subject is still pretty slim!

Finally, it would be good to get some late-season data on V1062 Tau. 
Runs early and late in the season are the key to defining the period 
sufficiently accurately to bridge the yearly gaps.  Any old joe 
astronomer can observe stars transiting at local midnight - time-series 
2-3 months out of season really do the heavy lifting for our ephemeris 


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