(cba:news) HZ Puppis and low-frequency signals

Joe Patterson jop at astro.columbia.edu
Sat Jan 18 09:31:45 EST 2014

Oh yes, I saw it, and was delighted to see that the aliasing situation 
was somewhat clarified.  Muchas gracias, Gordon!  But my experience with 
aliases is that they need to be absolutely shattered, not just resolved 
with good statistical confidence.  In some cases with CVs, the *fifth* 
best alias (from the published paper) turned out to be the correct 
choice.  In one, the author estimated the likelihood (of the choice that 
turned out to be correct) as <<0.001%.

I think there are two reasons for this:

(1) CV light curves are dominated by noise, not (usually) statistics. 
Humans just never appreciate noise.  Including this human - that's why I 
usually lose $$ at the race track.
(2) Orbital and precessional sidebands, periodic amplitude changes, and 
differential extinction.  All produce, or at least can produce, slow 
periodic wiggles in our light curves - on timescales not too different 
from the famous aliasing bugaboo (~1 c/d).

These worries are even greater when >95% of the data are from one site.
Many sites, many nights... that's the winning formula, because then the 
various non-statistical threats are not correlated.

To paraphrase Alexander Pope, in the world of low-frequency variations, 
a little noise is a dangerous thing.


On 1/18/2014 8:12 AM, Enrique de Miguel wrote:
> Joe,
> Just in case you missed it,  Gordon Myers uploaded a nice ~6h data set on HZ Pup on JD 671 which seemingly breaks the aliasing with the MDM data, favoring the 71.3 c/d peak (spin?) as well as the 66.6 c/d side band (spin-orb?). Obviously further series now will certainly help with the aliasing.
> Enrique
> On Jan 18, 2014, at 1:50 PM, Joe Patterson wrote:
>> Dear CBAers,
>> I'm still hoping for some off-longitude time series on HZ Pup, in the next few days.  We have two more nights at Kitt Peak, and probably will put it back on the menu since we haven't got data on it in a few days, and none from other longitudes.  The value would be greatly enhanced with some roughly contemporary data from other longitudes (and from the Americas too, since our observing window is brief and our long run of beautiful weather may end quickly).  If the periods are perfectly stable, the data need not be highly contemporary; but alias structure is much simpler when the data are close in time.
>> The Mon boys - V902 and V959 - also need help.  Both good CBA targets and equatorial, so everybody can see 'em.  Olde Whiteface is clearing out, and now would be a great time to observe them closely.
>> The Suzaku X-ray observation of V1159 Ori is now put off until late February, so we don't need more time-series data on it for a while. Snapshot V magnitudes would be nice though.
>> Finally, AQ Men.  I was delighted to see the recent response on this star from many of our southern stalwarts: Josch, Berto, Gordon, Bob Rea.  But for the next few days, maybe you could persuade your telescopes to slew over to HZ Puppis??
>> First time I ever said anything like that.
>> joe
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