Monitoring Radial velocity of the HeI6678 line of zeta Tau

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Ernst Pollmann
Posts: 461
Joined: Mon Sep 26, 2011 7:16 pm

Monitoring Radial velocity of the HeI6678 line of zeta Tau

Post by Ernst Pollmann »

Dear colleagues,
I would like to come back again to the campaign "Long-term Radial velocity Monitoring of the HeI6678 line in zeta Tau":
There were certain investigations of Stan Stefl and his colleagues (ESO) until (approx.) 2008, which have been continued by me and later in collaboration with colleagues of the ARAS group (see attachment).
Stan found a period of 1503 days, our monitoring however leads to a period of 1216 days. Enough reasons to continue, particularly since the reason for this kind of variability is still unknown until now.
The attached upper plot shows our RV monitoring with the long-term variability component (the short-term variability comes from the 132 day orbital period).The middle plot shows the long-term component with a fitted period of 1216 days (PDM analysis of the data in the upper plot).The lower plot shows the investigation of Stan until 2008.
I found a first BeSS spectrum of Tim Lester (2015-09-15) as a start of the campaign for the next months until (approx.) March 2016. It would be great, if other zeta Tau interested observers would contribute with their spectra.

Ernst Pollmann
----------------------------------------------
International Working Group ASPA
Active Spectroscopy in Astronomy
http://www.astrospectroscopy.de
http://www.astronomie.de/astronomische- ... troskopie/
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zetatau_RV.png
zetatau_RV.png (133.33 KiB) Viewed 5262 times
Ernst Pollmann
Posts: 461
Joined: Mon Sep 26, 2011 7:16 pm

Re: Monitoring Radial velocity of the HeI6678 line of zeta T

Post by Ernst Pollmann »

Dear colleagues,
our long-term monitoring of the radial velocity (RV) of the HeI 6678 absorption line have been supplemented by data of my colleague Domagoj Ruzdjak of the University of Zagreb, Croatia, (Ruzdjak et al. 2009, A&A, 506, 1329).
With the longer investigation period of approx. 15 years (December 2000 to February 2016) we are able now to calculate a new long-term RV period.
Fig. above: the new long-term monitoring
Fig. middle: phase dispersed minimization analysis of the data
Fig. bottom: phase diagram of the found period of 1250 days.
The scatter is caused by the orbital 133 day RV period of the companion, and by very short-term RV variabilities with periods of approx. 0.4 days.
Comments are welcome!

Ernst Pollmann
----------------------------------------
International Working Group ASPA
Active Spectroscopy in Astronomy
http://www.astrospectroscopy.de
http://www.astronomie.de/astronomische- ... troskopie/
RV-Monitoring.png
RV-Monitoring.png (181.13 KiB) Viewed 5187 times
Ernst Pollmann
Posts: 461
Joined: Mon Sep 26, 2011 7:16 pm

Re: Monitoring Radial velocity of the HeI6678 line of zeta T

Post by Ernst Pollmann »

Addition of the report above:

The fact that ζ Tau has a binary companion in a 133 days orbit (Ruždjak et al. A&A 506, 1319–1333, 2009) probably means that any tilt of the Be star’s disk will be modulated by the tidal force of the binary companion. Approximately twice each orbit, a tilted disk will experience a tidal torque in the direction of coalignment with the orbital plane, and this results in a nodding motion that is seen, for example, in the precessing disk and jets of massive X-ray binary SS 433 (Collins & Scher 2002). For prograde precession, the nodding period is

Pn = 0.5 (Pp * Pb)/(Pp − Pb) = 0.5 (1250*133)/(1250-133) = 74.4 d

where Pp and Pb are the precessional and binary periods, respectively. The predicted nodding period, Pn = 74.4 d, is quite close to the observed V/R modulation period of 69.3±0.2 days discovered by Pollmann & Rivinius (2008, IBVS, 5813).During all intervals when the long-term RV and V/R changes were present, they always vary in phase.

At http://astrospectroscopy.de/media/files ... g_slow.AVI

you can see a film, which shows the nodding with Pp = 1429 d (constructed from G. H. Schaefer et al., The Astronnomical Journal, 140, 1838-1849, 2010).

Ernst Pollmann
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