New Be phase at 28 Tauri ?

[Ernst Pollmann]

The present results have been presented to the 28-Tauri experts (R. Hirata, J. Katahira) at the Bisei-Observ. (Okayama, Japan) and leads to the following discussion:

Katahira:
For the observations with T < JD2454500, the H-alpha profiles are composed of two kinds of the emission components, i.e., the old disk component and the new disk one.

Pollmann:
You are right. Because of the two disk components, the spectra < JD2454500 are not comparable with those afterwards concerning the variability of the V/R ratio (see fig. spectra). Hence, a period analysis which included this time span can not be significant. My mistake...

Katahira:
Did you measure the radial velocities (RV) of the central dip of the Hα?

Pollmann:
I re-evaluated with the mirror method in spectra of Guarro, Houpert, Garrel, Pollmann, the Hα-absorption-core-RV of the same time span as the V/R-plot (see attachment). This evaluation leads to a RV-minimum at approx. JD 2455971-2455972.

Katahira:
The observed abnormal V/R-variation may correspond to a phenomenon around the minimum radial velocity epoch (near the periastron). Since the sudden abnormal V/R variation also suggests a deformation of the profile including the central dip, I would like to think it carefully. As the samples of the profile in the minimum radial velocity epoch, you can see those in fig. 6 of Nemravova et al. (2010). The abnormal V/R variation on a short time scale is not always occurred (or, not easily found) in the minimum radial velocity epoch.
If your group again shows a systematic variation of the Hα profile over the minimum radial velocity epoch, you can confirm a new aspect of the strucure of the growing disk. I am expecting such a finding.

Pollmann
The results in "Properties and nature of Be stars: Orbital and recent long-term variations of the Pleiades Be star Pleione = BU Tauri", http://jp.arxiv.org/abs/1003.5625, Authors: J. Nemravova et al. shows in fig. 5 and particularly in fig. 9 (see attachment), that the Halpha shell absorption core does reflect fairly well the orbital period (218 d) of the system (at least during the companion periastron passage).
In addition, with the orbital elements (solution 1) of this paper we should expect a periastron RV-minimum in approx. JD 2455571-2455573. Our measurements are fairly close to this date. Further, our RV-plot contains measurements in spectra of four observers with different spectrographs at different locations (Spain, France, Germany).
Jose Ribeiro did take part in the mentioned A&A paper, with spectra between 2454874 to 2454882. Perhaps he is able to say something to his RV measurements of the Hα absorption core, what might be helpful in this context.

[Ernst Pollmann]

The high observational density of Joan Guarro during the current visibility phase of 28 Tau, and our collaboration regarding the V/R and RV evaluation, did lead to the observation of a periastron passage, which is recognizably in both stellar parameters (see attachment).

The period of 218d and the phase zero at HJD 2440040.4 (Nemravova et al.) should let expect a periastron at HJD 2455954.

The RV curves of the Hα absorption core in Nemravova et al. (A&A, March 30, 2010) and Katahira et al. (PASJ, 48, 1996) are showing a comparable shape to our findings: a sharp decrease near to the periastron, followed with a slow increase afterwards.
However, how we have to understand the V/R minimum in this context, is not clear. There is nothing to find about it in literature.

Ernst Pollmann

[Ernst Pollmann]

The observation period of the star is terminated until the next visibility period. Here the last V/R and RV results.
Joan has done a great job.

Ernst Pollmann
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