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Dear colleagues,
as complement to our publication in A&A 560, A30 (2013), we can notice today that a new V/R activity cycle has started (see attachment).
That means that the monitoring of the V/R ratio will be continued in order to confirm our found period of 84.2 day (+/- 2). Ernst Pollmann

Dear colleagues,
our current monitoring of the Halpha V/R shows a periodic behavior (period = 42d), that does not fit to the periodicity we observed from 10/2004 to 01/2020 (period = 84.2d).
The current period, the half of 84d, can´t be explain at present, which is why observations are very urgent.
It would be great, if interested obeserver could take at present spectra as much as possible.
Ernst Pollmann

Dear colleagues,
the V/R period of 42 days (instead of 84 d) is becoming increasingly clear. Here the current state of observation.
Ernst Pollmann

Hi Ernst,

Really interesting development. I know we emailed a bit about this, so hopefully you don't mind me posting here too.

Hydrodynamical models predict that binary-induced disk oscillations produce m = 2 density waves, illustrated in this plot:
Fig. from 2018ApJ...865...76C

In this case of m = 2 density waves, there are two 'arms' of overdense regions in the disk (and, between these, regions of underdensity). As we observe this pattern to evolve over the orbital period, we should see features that are double-waved at P_orb. Or, put another way, things like the V/R ratio have a dominant signal at half the orbital period. Fig. from 2018MNRAS.473.3039P

So, I believe that's what we're seeing with pi Aqr here- an m = 2 density wave with both arms of near-equal strength.

On the other hand, sometimes binary-induced density waves are still m = 2 (and two-armed), but one arm is much stronger than the other. When this happens, things like V/R have a dominant signal at the orbital period. This is what is seen, for example, in HD 55606: V/R ratios show a sinusoid at P_orb (so probably one of the two arms is much stronger).
Fig. from 2018ApJ...865...76C

For pi Aqr then, it seems like the density wave has evolved from having one dominant arm (when P_V/R = P_orb) to now having two arms of equal strength (where now P_V/R = 0.5 * P_orb). It is interesting to note that this transition seems to be happening as the disk is increasing in strength, as seen from the evolution of EW or E/C of Halpha. Also, at the same time, it seems as though a slower m = 1 oscillation is growing, seen in the relatively gradual increase of Ha V/R as plotted by Ernst above in the red circled region after JD = 2459000.

At any rate, I certainly agree this continues to be an interesting system to observe.

Dear Jon,
thank you for the graphically supported explanations, which illustrate the relationship between one-armed respectively two-armed density wave and Porb respectively Porb/2. I was not aware of your comprehensive publication on HD 55606 (Chojnowski et al. 2018).
Although in our investigations in A&A 560, A30 (2013) with the Doppler tomography we clearly determined the one-armed density wave in the attached figure, the more pressing question remains what triggered the development to m = 1. The still high Halpha EW can mean two things: higher disk mass and / or higher disk density. The latter would be more plausible because of the currently characteristics of two density waves (m = 2). The attached V / R period analysis clearly shows further the 42 day period and the question is how long it will last. Ernst Pollmann

Attached are my last 2 observations.

Any comments on the Astrophysics of this interesting change ?

Wishing you all a merry Christmas and a healthy new year.

Jack

Essex UK

Jack,
it seems that the V/R period has shortened from 42d to 24d.
The last two spectra of Al Stiewing and yours, let suggest this.
Concerning the physics behind I am in close contact with Anatoly Miroshnichenko.
He also took a lot of spectra of pi Aqr in December and we will exchange our results very soon.
We will inform as soon as possible. Ernst Pollmann

Hi Ernst,

Thanks for the update and for reminding me about that paper. I've been observing pi Aqr from about June - November 2020 with spectroscopy, but I've mostly waited on analyzing the data until space photometry from the BRITE satellites becomes available for pi Aqr over the same observing baseline, when I can then analyze the space phot. + spec. together.

I took a look at the NRES spectra that I collected over this period, and, similar to the observations you have presented in this thread, the most significant period is at 42.2 d. However there also seems to be:

1) variation in V/R ratios that isn't strictly periodic,
2) A much more slowly evolving pattern, since V/R is definitely > 1 between June - Nov.
3) An overall growing EW in Ha and Hb

Quite interesting to see the development of a 24d period. Is the amplitude of the 24d period similar to that of the 42d period?

Hi Jon,
first, thanks for sending the accepted gam Cas paper.
Here the data of analysis :

Period 42d:
P= 42.9d (+/- 0.73)
A= 0.0712 (+/- 0.014)
T0= 9070.4 (+/- 1.6)
RMS= 0.044

Period 24d:
P=24.7d (+/- 0.57)
A= 0.064 (+/- 0.004)
T0= 9170.1 (+/- 0.57)
RMS= 0.016

Best wishes,
Ernst

What is the change in period caused by ?

Jack

Essex UK