VV Cep up-to-date

The current state of the ARAS campaign observation results seems to explain the periodic time behavior of the equivalent width EW and the flux of the Hα emission components V&R as it is shown in Fig. 1 & 2.

Fig. 1: Periodic time behavior (Period = 42 d) of the component V(top) & R(bottom) EW left, Flux right

Fig. 2: Phase diagrams of the 42 day period of V(top) &R(bottom) EW left, Flux right

According the EW & Flux periodicity of V & R in Fig. 1 & 2 we have of course to expect a corresponding periodicity of the flux ratio of V/R. Fig. 3 shows the PDM period analysis of the V/R ratio of the data in Fig. 1. Fig. 4 shows the corresponding phase diagram.

 Fig. 3: PDM analysis of the ratio V/R (data of Fig. 1)

Fig.4: V/R Phase diagram of the found period of 42 days in Fig. 3

Based on these results, a new geometric structure of the emission sources has been developed in collaboration with Phil Bennett. A draft of this scenario is shown in Fig. 5 and as animation below.

Fig. 5: New geometric structure of VV Cep

Fig. 6: Precessing emission lobes on the rotational axis of the disk

A precessing disk rotation axis as it is shown in Fig. 6 with a period of 42 days, would inevitably have to result in a simultaneous variation of radial velocity of the V(max) flux. Precise radial velocity (RV) measurements of the Hα V component, based on LHIRES III spectra have been performed by the ARAS observers (Schwarz, Kalbermatten, Bryssinck, Foster, Bertrand, Sawicki, Martin, Stiewing, Pollmann).

Fig. 7 shows the PDM period analysis of RV measurements from 220 spectra from January 2018 to June 2019 with a period 0f 50.9 days and seems to confirm the periodic precession movement of the B star disk rotational axis.

             Fig. 7: PDM period analysis of the radial velocity monitoring of the V emission component;                       Period = 50.9 days

Fig. 8 shows the phase diagram of the found period.

Fig. 8: Phase diagram of the 50.9 d RV period of the V emission component

Because of the small average RV amplitude of approx. (+/-) 1.7 km/s, this is not as simple as it seems. In spite of the high accuracy in wavelength calibration (order 10^-3 to 10^-4 Å) by using the new program SpectroCalc (developed by M. Schwarz, Austria), the error in RV is in the range of (+/-) 3 km/s in one observation night. All spectra have been calibrated with metal lines of the M star around Hα:

FeI 6546.245
TiI 6556.066
CaI 6572.781
FeI 6593.878

This method of calibration led to a radial velocity relative to the M star without any contribution of the system velocity. But the period of approx. 51 days still is unclear at this time, compared to the 42 days found in analysis of the precession period of the disk rotational axis. 


Movie of the precession of the disk axis

Ernst Pollmann, 2019-07-14