Tue, 10/27/2020 - 09:29
Dear colleagues,
don´t forget to observe the next periastron passage on February 1th 2021!!
This time there are very good opportunities to observe totally the rise and the descent of the parameters EW, V/R, RV and CA.
Ernst Pollmann
Ernst,
While I do not yet have spectroscopy capability, I've begun observing 28 TAU in B, V and I. My 1st upload was today, I expect a couple sets per week through February, but can continue longer. I am using the BSM network for images.
Peter
Dear colleagues!
As is known, the variable angles of inclination of Be star disks manifest themselves in the observer's line of sight as variable depths of the central absorption depression (CA) of the Halpha emission (Hanuschik, A&A 295, 1995;
http://articles.adsabs.harvard.edu/pdf/ ... .295..423H
A variable depth of the central depression in the Halpha emission thus also leads to a reciprocal variability of the equivalent width EW.
In simple words:
at a small angle of inclination (pole on) maximum emission can be observed (central absorption small, CA value F/Fc = large);
at a large angle of inclination (edge on), lower emissions can be observed (central absorption deep, CA value F/Fc = small).
The change in the inclination angle of the disk is mainly caused in the periastron by the (unobservable) secondary star [for its possible nature see: RevMexAA (Serie de Conferencias), 5, 114-116, 1996].
This geometrical regularity can be observed very well in the phase of the periastron passages of the companion star in the Be binary star 28 Tau (Pollmann, IBVS Vol. 62, No. 6239; https://konkoly.hu/pub/ibvs/6201/6239.pdf)
The last period determinations based on radial velocity measurements (P = 218.058 d) date back to 2010 (Nemravova et al.
https://www.aanda.org/articles/aa/pdf/2 ... 885-09.pdf)
The very sharp peaks of the EW and CA changes at 10 periastron passages meanwhile suggest that these should also be used (perhaps preferably) for the future monitoring of the orbital period of the companion star.
The orbital periods presented here:
EW (periastron) = 218.119d (± 0.049)
CA (periastron) = 217.883d (± 0.084)
/sites/default/files/users/user63093/Periodenanalyse%20CA%20und%20EW_20.2.21.png
Comments are welcome.
Ernst Pollmann