(cba:news) stars for the solstice

Joe Patterson jop at astro.columbia.edu
Sun Jun 8 08:24:00 EDT 2014


Hi CBAers,

Getting back in the saddle here after three weeks gobbled up by 
end-of-school-year, observing run, AAS meeting, even a Camp Uraniborg 
40th year reunion.  And one more meeting (SAS/AAVSO/CBA) coming up in a 
few days - where many of us (15?) will get together in California.  Just 
to get you thinking in advance... an issue I'd like to clarify there is: 
how to make our data available to others in a convenient and transparent 
way.  David Boyd's paper on V1432 Aql, to be given at the SAS, has made 
me want to pull the trigger on this *now*.  It's as good a paper as I 
could have done, or better - but it took a few rounds of correspondence 
and some persistence to shake the data loose from us.  We have to set up 
an easier access - including, I think, access by people we don't already 
know.  The AAVSO is the natural channel for this.  To be discussed!

STARS FOR THE SEASON.

STARS TO RETIRE: HS1813+6122, HP Lib, V1084 Her.  We have enough!  Also 
AM CVn and T Pyx; effectively, the Sun has already retired them - but 
just to make it official for these old friends of ours.  GW Lib and V355 
UMa also should retire, victims of sunlight and neglect.  NR TrA also in 
this category, because the coverage (mainly from Berto, Gordon, Bob Rea, 
and Simon Lowther) has been so good.

DQ HER STARS.  Some quite nice targets of this type, and easy to observe 
since they're bright (mostly 13.5-15.5) and don't *require*, though they 
*like*, long runs.  V1223 Sgr, IGR J17303-0601 and DQ Her itself are 
very good targets - and others, seasonally appropriate, from Koji 
Mukai's intermediate-polar webpage:

http://asd.gsfc.nasa.gov/Koji.Mukai/iphome/iphome.html

NY Lup, V2306 Cyg, RX J2133+51, and V2069 Cyg all need work.  I list all 
these in order of what I'd judge as decreasing priority (i.e. V1223 Sgr 
as highest priority) - but the stars occasionally flash unexpected 
phenomena (low states, period changes) which make any assessment of 
priority very rough.

SUPERSOFT BINARIES, or kissin' cousins.  Those are: V Sge, V617 Sgr, and 
WX Cen.  We need to study the orbital light curves; but after you get a 
few orbits, and for sure a few eclipses, you can move on.  The main 
interest here is study how this (the eclipse time, and orbital light 
curve generally) changes over the years.  The orbital periods appear to 
change rapidly - and there is still no understanding of *why*.

RECENT CLASSICAL NOVAE.  You bet!  My #1 fascination in recent years - I 
guess since BK Lyn amazed us by announcing itself as a 2000 year old 
nova.  It'd be wonderful to know how the orbital light curves of novae 
change with the years after outburst - when the hot white dwarf should 
be cooling down from a half million K.  Nobody knows the rate of this 
cooling, but I believe we can find out by tracing the evolution of the 
orbital light curves.  For this purpose, there are now some great novae 
available in the sky: V1974 Cyg, V1494 Aql, V1500 Cyg, V4743 Sgr, and 
V339 Del lead the cavalcade.  I'm also pow'f'l curious about V630 Sgr (N 
Sgr 1936), but I imagine it's too faint for CBA scopes.

WEIRD STARS. The best for last.  V418 Serpentis!  As many of you know, 
we've mostly steered away from dwarf novae in recent years; there are so 
many of them, and we've observed >100 of them in their outbursts (so, as 
a class, their novelty is declining).  But some stars are just too weird 
to resist.  V418 Ser might be such a star; its 64 minute period is too 
short for a hydrogen-rich star, and too long for a helium-rich dwarf 
nova - or at least will require some tinkering with the theory for such 
things.  (The reason is that there's a P-root-rho relation for the 
lobe-filling secondaries, and the densities appropriate to helium and 
hydrogen should be quite distinct.)  The star is now at ~17th mag, but 
try to follow it as far as possible into the muck.  The usual time 
series, as long as possible.

BRIGHT AND/OR EASY STARS.  Some readers of these pages have small 
scopes, or have just recently started time-series photometry. 
Relatively bright or "easy" (large-amplitude periodic signal) stars 
might then be the most suitable.  V339 Del, V Sge, V1223 Sgr, and FO Aqr 
are good choices.

SAME COMPARISON STAR!  Just a reminder to keep the same comparison star. 
  It's helpful when everyone uses the same comp star, but not 
super-important.  What matters most is that you choose one and stick 
with it.

Many stars in this note.  But as usual, fidelity to one star tends to be 
a winning strategy, except possibly for the DQ Hers.  This means that 
cba-chat communications about your chosen targets are very useful - 
because very long time series (possible only for distant telescopes) are 
absolutely optimum for period-finding on this rotating planet of ours. 
For most targets, the rewards diminish after 3-4 weeks; I'll try to 
improve my promptness in demoting stars, but you might want to adopt 
that timescale as a sort of default value.

I've learned a lot from the recent cba-chat flurry triggered by Tonny 
Vanmunster.  Thanks for sending all that stuff... and anything you can 
do to lure Tonny back from his exoplanet interlude would be great for 
the CBA!

joe p
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