28 Tau ARAS monitoring

Re: 28 Tau ARAS monitoring

Postby Ernst Pollmann » Fri Feb 02, 2018 3:12 pm

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
28tau_periastron.jpg (37.1 KiB) Viewed 1853 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).
28tau_halpha_ew.jpg

Ernst Pollmann
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Re: 28 Tau ARAS monitoring

Postby James Foster » Sat Feb 03, 2018 7:02 am

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
James R. Foster
Lhires III (2400/1800/600 ln/mm Grat) Spectroscope,
LISA IR/Visual Spectroscope (IR Configured Presently)
Alpy 600 with Guide/Calibration modules and Photometric slit
Star Analyzer 200
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Re: 28 Tau ARAS monitoring

Postby Ernst Pollmann » Wed Feb 07, 2018 4:54 pm

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/Precession-of-the-Disk-in-Plejone.pdf

Many thanks to all observers for the contribution of their spectra!!
Ernst Pollmann
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Re: 28 Tau ARAS monitoring

Postby Ernst Pollmann » Fri Mar 16, 2018 11:26 am

Dear colleagues,
related to the topic above the publication has been accepted at IBVS:
http://astrospectroscopy.de/media/files/Precession-of-the-Disk-in-Plejone.pdf

Ernst Pollmann
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Re: 28 Tau ARAS monitoring

Postby Ernst Pollmann » Sat Feb 16, 2019 8:27 am

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)
Flux_versus_Vmag.png

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.
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