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