(cba:news) new stars for mid-July

[Joe Patterson]

Dear CBAers,

We're finished now with V617 Sgr.  I completed the analysis, and it
really seems to be a virtual twin of T Pyx, with an identical light
curve and a similarly frantic rate of Porb increase.  The one thing it
lacks is nova eruptions... which means, in my opinion, keep sunglasses
handy.  Great to have some company in this truly tiny class of variable
stars.

We're also leaving HS1813+61.  I mentioned that before, but just to
stress it.

We can back off temporarily on V1432 Aql.  The main remaining issue is
counting cycles from year to year, and observations in mid-season (like
now) have relatively little leverage in proving that cycle count.  We'll
pick it back up in mid-September.

For PNV1915+07, the light curves continue to be fascinating, even as it
has declined to V~16.5.  So - keep on keepin' on.  ASASSN-13ax, the new
dwarf nova in Draco, is still at 15th mag and an excellent target.  I'm
torn about choosing between these targets - but so far, ASASSN-13ax has
been relatively neglected... so bear that in mind.

But there are three new stars in the midnight sky which should be
promoted to major-campaign status now.

1. V1101 Aql.  We've studied it just once, in 2004, when it showed a
rich power spectrum including a negative superhump.  It's around 14th
mag, so not a difficult target.  There's a neighbor star, but it's very
faint, so probably you're best off doing aperture photometry with a
large aperture (unless you're very adept with psf fitting).  We
definitely want LONG time series on this guy, because the expected
periods are somewhat long - and that means we really want a great spread
in longitude: I was hoping for Europe-Americas-AU/NZ.  With a dec of
+15, it's probably somewhat out of the Australites' comfort zone; but
try - a little bit of off-longitude data can really clobber those daily
aliases!

2. V1315 Aql.  Very similar comments.  Also 14th mag, also likely
negative superhumper, and with eclipses too.  Whichever of these you
choose, I recommend you stick with it, and stick with one comparison
star too; there's extra value when the data are repeatedly from the same 
observer, because it minimizes the problem of inter-telescope calibration.

3. An entirely new star, a 12th-mag guy which is a variable hard X-ray
source with a spectrum and Galactic latitude (30 degrees) which are
weird - and might be a bright CV in drag.  The J2000 position is 21h 24m 
12.44s +5d 2m 43.6s.  In Equuleus, where practically nothing lives.
This is probably not a known variable star, so it might be wise to use a 
V filter and pay attention to calibration.  See what you can learn about it!

Can I be so bold as to attach a wish list too?  Here are some
seasonally-appropriate stars which I would love to study, but I dunno if 
they are now magnitude-appropriate for the CBA.  (Remember, I live in 
New York, where we strain to see Albireo on the best of nights.)  Here 
they be: V4743 Sgr, V3890 Sgr, V4633 Sgr, V1494 Aql, V1500 Cyg, IM Nor. 
  How bright are these guys?  Each of them contains some fascinating 
physics, if they're bright enough for us to study.  Snapshots are fine!

Finally, it's just getting to be BW Scl season again - and we want to
see how the star has healed itself, or maybe not, from its recent
superoutburst.  In particular, we'd like to see whether the pulsations
have changed in frequency, amplitude, and coherence.  So this will be a
good southern target for the next couple of months.

joe p