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Re: (cba:news) (cba:chat) Maxie update (Joe Patterson) [2018-10-10T13:39:03Z]

Hi HB,
Well, we should have a conversation about that some time!. The issue is finding a period which "satisfactorily" describes the wiggles in the light curve.  For ~90 days, it was obvious... because the data spanned an average of ~16 hours out of 24, and the amplitude was huge (averaging ~0.35 mag). But there were still *some* ambiguities, for two reasons:
(1) The period wasn't quite constant, and there's no (divine) guidance as to how to describe this - only one physical process with a nonzero and variable dP/dt, or one with a nonzero dP/dt which morphed into a different process with a constant P (orbit?).
(2) At low frequency (~1.4 cycles/day), there is always a concern about noise: the effects arising  from splicing data from many telescopes, differential extinction arising from high airmass (we encouraged LONG runs, and couldn't have succeeded without them), our "Asia gap"... , or nonrepeating peaks in the power spectrum in the vicinity of P_sh (CVs are notoriously erratic and powerful at low frequency). Only the latter is technically "noise" - but they're all hazards!
CVs at quiescence are often much easier to analyze, because the dominant signal is usually pure orbit.  Next year! The star doesn't seem to be in any hurry to calm down.
Your data is really good!  I hope you can keep going for the few weeks left in the season. 

joe
BTW when I say "snapshot magnitudes", I really mean "short time series".  The star's flickering is still (and probably will remain) too high to trust one snapshot magnitude. 




On 10/10/2018 7:23 AM, Heinz-Bernd Eggenstein wrote:

Hi!

Not sure I understand this correctly: Would you see immediately from your data processing if a given ephemeris would be correct (e.g. because your tomography suddenly gives a consistent "picture" which would not likely happen from just "luck")? If so, would there be a way to "just" use massive computing power to guess the right period? (Thinking computing clusters or even volunteer distributed computing...). Just curious (as this is basically what I do for a living :-) :  looking for pulsars in radio, gamma and gravitational wave data to detect objects by "guessing the right parameters" and then testing the hypotheses against the data).

Cheers
HB

-----------------------------------------------------------------
Heinz-Bernd Eggenstein, Scientific Software Engineer
Max Planck Institute for Gravitational Physics
Callinstrasse 38
D-30167 Hannover,  Germany
Tel.: +49-511-762-17153 (Room 036)

-----"cba-chat" <cba-chat-bounces@xxxxxxxxxxx> wrote: -----
To: cba-chat@xxxxxxxxxxx
From: David Buckley
Sent by: "cba-chat"
Date: 10/09/2018 11:00PM
Subject: Re: (cba:chat) (cba:news) Maxie update

Hi Joe,

We've been observing it here in SA of and on since May with both 1-m and
10-m (SALT), mostly ~200 msec to look for QPOs (seen earlier in the
o/b). We've also gotten a fair bit of spectroscopy (1.9-m + SALT) and
have been playing around with trailed spectra and Doppler tomography (of
HeII and H-beta). Some results seem to indicate that there might be a
stream, but its position is not right, so not sure what the correct T_0
to use is for this. If its not strictly orbital, then this is a problem,
of course, for tomography.   So apart from the strong presumed SH
period, has anything else popped out in terms of periods which we might
use to phase the velocities?

Cheers,

David.


On 2018/10/09 10:39 PM, Joe Patterson wrote:

Hi CBAers,

As many of you know, Maxie has been plummeting in brightness at around
0.08 mag/day in recent days.  It almost got to V=15.0 a few days ago,
but now seems to have rebounded by ~0.7 mag - quite a big jump if it's
actually true.

In addition, the 0.7 d periodic signal continues.  No proof that it's
the residue of the once-proud superhump, but that's a good possibility.
Twilight has greatly shortened the runs, but it's still (barely)
possible to see that periodic signal.  So the star is good for another
week - V filter only, and no need for good time resolution.  After
that, snapshot V magnitudes will be fine.

joe p

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