28 Tau ARAS monitoring

[Ernst Pollmann]

Dear colleagues,
here I want to show once more in detail the 28 Tau periastron observation of several members of the ARAS group.
The evaluation of V/R and RV allows very precisely the time determination of the periastron passage. This result shows impressively the advantage of campaign observations within a community.

28tau_periastron.jpg (37.1 KiB) Viewed 23110 times

It shows also very clear the process of disk deformation at the V/R change during the minimum of the radial velocity, a phenomenon that could be observed for a first time since August 2011 (approx. JD 2455800), when the mass of the disk reached the minimum.
This disk minimum is reflected in our monitoring of the Halpha EW (see the following monitoring).

Ernst Pollmann

[James Foster]

To: Ernst,

Great feedback on the 28 Tau Campaign. I just emailed you 23 more spectra of 28 Tau to use. I'll upload these into the BeSS database and
process 2 more I did when learning the LhiresIII / Isis in Oct17. Cheers!

James

[Ernst Pollmann]

Dear colleagues,
The total monitoring of the Halpha profile of 28 Tau since October 2004 enables to investigate aspects of the precession of the disk.
Despite the intention to publish this investigation at IBVS, I want to inform here the involved observers about the results. The pre-publication is to find at:
http://astrospectroscopy.de/media/files ... lejone.pdf

Many thanks to all observers for the contribution of their spectra!!
Ernst Pollmann

[Ernst Pollmann]

Dear colleagues,
related to the topic above the publication has been accepted at IBVS:
http://astrospectroscopy.de/media/files ... lejone.pdf

Ernst Pollmann

[Ernst Pollmann]

Dear colleagues!
Investigations by astronomers of the University "Western Ontario" (Canada) on the topic "Equivalent width of Be star disks and V-brightness" and related modelling efforts are the reason for our measurements on the same topic.
The attached diagram shows in our study the relationship between the Halpha line flux and the V-brightness of 28 Tau. Therein, the line flux is derived from the Halpha equivalent width (see definition on the ordinate; EW measured from spectra of ARAS observers; Vmag measured by W. Vollmann, Vienna).
It seems that in the Be-Shell phase, the steepness of the line is less than in the Be phase (see straight line equations).
What are the reasons?
I mean, the deeper central absorption dip (CA) in the Halpha emission and hence the corresponding lower line flux leads to a less steepness during the Be shell phase. In our monitoring, we also observe a CA variability that changes in the cycle of periastron passages with a period of 218 days (http://ibvs.konkoly.hu/pub/ibvs/6201/6239.pdf)

A possible cause for this could be a libration of the disk rotation axis. It will be interesting to see how, in the future, this correlation changes from the Be-Shell phase to the Be-phase. Thanks to all the ARAS observers for their spectra which enables to study that phenomenon.
Ernst Pollmann

[Ernst Pollmann]

Dear colleagues,
the next periastron passage of 28 Tau will take place on 9th of April. I know it´s a bit critically to take spectra because of the low heigth and darkness, but it would be great, if someone would be able to try it.
If yes, then we might be able to complete sucessful our monitoring with this event in terms of radial velocity, V/R and CA (central absorption core).

Ernst Pollmann

[Ernst Pollmann]

Dear colleagues,
thanks to tireless observations by A. Stiewing, J. Martin, J. Guarro and M. Leonardi, the periastron passage on April 9th 2019, has been captured by measurements of the parameter CA (central absorption depth of Halpha), the ratio V/R and the radial velocity RV.

Even if the passage because of the visibility conditions was not captured for 100%, the orbital period of the companion of that Be binary system have been confirmed with 218.176 days. See also:
http://ibvs.konkoly.hu/pub/ibvs/6201/6239.pdf

Obviously the parameter CA seems to be particularly useful for such a studies (at least at Pleione). The next periastron passage will take place on November 19th 2019.

The attached Fig. a shows the time series of CA, Fig. b shows the phase diagram of the period analysis, Fig. c shows the ratio V/R and Fig. c shows the radial velocity RV.

summery.png (418.42 KiB) Viewed 20873 times

Ernst Pollmann

[Ernst Pollmann]

Further spectra of Al Stiewing (Arizona), which were the last possible in this visibility period, precises the orbital period (see phase plot).
Great engagement of Al, thank you so much.

summery_24.4.19.png (473.02 KiB) Viewed 20732 times

Ernst Pollmann

[Ernst Pollmann]

Dear colleagues,
around November the 13th this year we have to expect again the next periastron passage of BU Tau (Pleione). In terms of our long-term monitoring (see the previous postings here) of the Halpha radial velocity, V/R and CA (central absorption) it would be great, if Be star interested observer could contribute with their spectra to the observation of this passage.
The following link lead to an IBVS paper which describes what happens with the mentioned parameter above during a periastron passage.

https://astrospectroscopy.de/Projects;f ... ?id=342150.

Ernst Pollmann

[James Foster]

To: Ernst,

Here is one I did of 28 Tau last month while using the LhiresIII for the 1st time at Mt. Pinos, CA (2500 meters elevation):

I'll start doing this once a week until a few weeks after peristron passage.

James