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28 Tauri seems to go from the Be-shell phase into the normal Be-Phase (see comparison of spectra of Guarro/February/2012 to Pollmann/September 2011).
The shell phase differs to the normal Be phase in a larger thickness of the disk, which leads to deeper absorption lines under the stellar continuum. For 28 Tau the following cycles of activities can be differentiated:

Be-phase 1887-1904
B-phase 1904-1938
Shell-phase 1938-1955
Be-phase 1955-1972
Shell-phase 1972-1989
Be-phase 1989-2005
Shell-phase 2005-2012
Be-phase 2012- ?

The star does have gone through three developments within the last century. It would be interesting to monitor the brightness in V and B (possibly through Sebastian Otero, Argentina). But also the spectroscopic monitoring should be continued, to confirm the change of phase (or not).

Ernst Pollmann
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Active Spectroscopy in Astronomy
http://www.astrospectroscopy.de

Dear Ernst,
As you know, the comparison between two profiles is resolution dependant. R5000 for Joan and R11000 for yours. There is an eshell spectra R10000 from Stephane Charbonnel available for 2012 Jan, 16. I made a new comparison of your 2009 profile (orange) with Stephane one (violet) and it seems there is no odds variations of profile, specially in the absorption part. It need a Ew evalauation cause it is not resolution dependant.

Thierry

Dear Thierry,
in general you are right.
Also I do know the link between spectral resolution and profil resolution.

But in this case, the spectra series of Joan Guarro, started with 2012/01/24 to 2012/02/12 (see attachment), does show impressively, the continuous decrease of the absorption core. With the same spectral resolution R = 5000 !!!
So, this fact seems to be a fairly good indicator for a phase change.

On the other hand we can not exclude completely the possibility, that such a type of changes may be caused by changes of the disk position angle at the sky (W. Hummel, 1998 A&A...330...243H; Hirata, ASPC..361..267H).
Before this background it make sense, to continue spectroscopic monitoring.

Best wishes,
Ernst

A brand new spectrum of Thierry Garrel of 2012/02/29 with a deeper absorption, compared with the Jan./Feb. series of Joan Guarro (see attachment), lets doubts arise, whether a phase change has really begun (as I did assume). It seems, there is another reason, which causes the strong change of the intensity of the absorption core.

Interesting in this context is also the change of the V/R-ratio from V>R to V<R at 2012/02/10.
R. Hirata did observe in 2006 a change of the polarisation angle of 60° > 130°, connected with edge on > pole one in Halpha. I suggest, to take up contact to him, in order to introduce and discuss our observation results. Because of the two disks in this system it's difficult to understand what really happend.

Ernst Pollmann
----------------------------------------
Active Spectroscopy in Astronomy
http://www.astrospectroscopy.de
http://www.astronomie.de/astronomische- ... troskopie/

It is obvious, as you noted, in Joan Guarro spectra that there is an evolution of the absorption part and of the V/R ratio. But comparison with a higher resolution spectra, here mine is R10000 is not possible cause of the absorption part is more resolved, so it is deeper than in R5000 spectra.
Conclusion: only Ew analysis may indicate something but would it be delicate to do cause of the V/R ratio variation ?
Conclusion 2: It is the time for many observers to take high/intermediate resolution spectra of 28 Tau and have a greater population of spectra. This system is very interesting
Thanks Ernst for your effort aimed to a better knowing of this system and to bring us such relative facts.

Thierry

I did send R. Hirata (one of the experts of 28 Tau) our observation results.
Perhaps he is able to explain, what causes did lead to this change of the absorption intensity within a relatively short term phase.

The last transition to the Be-phase took place approx. 1989 (~ JD 2447000). This has been accompanied in fact with a increase of the Halpha-EW (see the attached plot). But as we can see in this plot, it's not so clear, in which phase of the EW development we are, at present.

The V/R ratio doesn't show significant characteristics. Only a very slow tendency to a higher value. Also a period analysis didn't provide periodic.
But the time span is possibly to short, in order to recognize clear characteristics.

Ernst

hello
I don't know if it can help. I just realize that i have acquired one spectra of Pleine at 2012-02-01. It's a "low" resolution spectra: 1200. LISA 19 micron slit.
Files are available here. http://perso.crans.org/~lemoult/spectro ... /vrac.html Regards
Thierry Lemoult

Hi Thierry (L.),
thanks a lot for your nice spectrum, but this level of spectral resolution seems to be too low, for using in this context.
Nevertheless, I evaluated the Halpha EW: = -8.3 Angstr. Compared with the current level of about 11 Angstr., I would say this is too low.
I wonder about this, because the rule says, that EW evaluation is independently of instrumental influences. However the V/R ratio (=1.007) does fit well.

Ernst

New EW and V/R data in spectra of Th. Garrel and F. Houpert have been transfered into the corresponding monitorings (see attachment).
The sudden interest and the contributions with spectra at this star is really great.
Thus I did try once more with the extended new V/R data a AVE period analysis (see attachment).
But again: the result didn't show significant periodic.

Ernst

I did try to find periodic components in the data set with the phase dispersion minimization procedure (PDM). PDM is part of the program AVE (Analisis de Variabilidad Estelar).
The PDM technique is a fast and accurate method of determining periodic components of data sets with erratic time intervals, poor coverage, non-sine-wave curve shape, and/or large noise components.
With largest caution (!!), a possible periodicity is suggested:
Period = 408 d
To = 2453984

It should be our job now, to observe the star as much as possible in order to confirm this result (or not).

Ernst