(cba:news) splicing CV light curves

Thu Aug 19 04:41:46 EDT 2021

Hi CBAers,

This is more along the lines of "chat"... but I see a particular night 
that illustrates the difficulties and successes of splicing data for 
multi-longitude light curves.

With filtered data, clear nights, and many well-placed longitudes, this 
is totally straightforward.  But such conditions never apply in the real 
world.

1. We're almost always stuck with unfiltered or wide-bandpass data, 
because our targets are just too faint for anything else.  This 
introduces differential extinction, which is why we avoid airmasses 
greater than 2.0.

2. Longitudes.  In the north, Europe-USA is sometimes easily spliced 
(long winter nights), and sometimes not (summer).  Quebec (Damien) and 
Chile (Josch) often help in the splice.  The south is more challenging, 
with wider oceans and fewer observers.

3. Since we are mainly period-mongerers, failing in the splice is 
usually no big deal.  It basically means that we're somewhat blind to 
small periodic signals in the range 0.5-2.0 days.  No problem outside 
that range, and not for large signals either.  Only in RARE cases do we 
miss the interesting physics we could learn from full-time, 
well-calibrated coverage (like a satellite - although they too have 
problems).

4. A recent night illustrates these matters.  I attach data on V1674 Her 
from three observers: Tonny (Spain), Damien (Quebec), and Joe U 
(Illinois).  If you plot them up with separate colors, you'll see that 
Tonny and Joe have only a small magnitude offset, and Damien's 
magnitudes are systematically ~0.06 mag fainter.  I go through this 
ritual for essentially every night and every star, applying additive 
offsets to get a consistent scale.  (Although for the fast periods which 
are our most common target, it doesn't really matter - I just "zero" 
every file.)

5. For V1674 Her, the 501-sec and 3.666 hr signals are obvious and 
seemingly dominant.  But there are small *slopes* in the nightly 
magnitudes that make me suspect some longer-period signal.  So some 
extra effort to obtain longer light curves might be nice - especially 
the Western USA (if you can see though the smoke!).

Finally, Hercules season is nearing an end, but Cygnus season is perfect 
(and long).  V1500 Cyg will be a great target throughout the next three 
months.  It's scarily faint (18.5-19), but the signals are very strong 
and slow (3-hour-ish).  Give it a try!

joe p
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