28 Tau ARAS monitoring

Ernst Pollmann
Posts: 461
Joined: Mon Sep 26, 2011 7:16 pm

Re: 28 Tau ARAS monitoring

Post by Ernst Pollmann »

Dear Jon,
thanks for information of White´s photometric 2017 short-term observations (probably caused by pulsations).
Indeed it is great that TESS observations are planed in fall this year while the periastron passage at September 7th, whereby I hope that all the colleagues in the past will be again contribute with spectra to this campaign.

The accordance of your TESS Halpha observations 2018 - 2020 with our monitoring shown here (above) don´t surprises me. This typical behavior of the Halpha parameter EW, CA, V/R and RV have been observable during each periastron passage we monitored in the past
(see: IBVS Journal Vol.62, No.6239:
https://konkoly.hu/pub/ibvs/6201/6239.pdf
and been also confirmed by J. Katahira.

The exact coincidence of the CA maxima with the minima of V/R and RV and EW as a result of disk precession has never before been observed during the maximum shell phase in the years around 1980, or during the initial shell phase around August/October 1974. It is known that the precession of the disk depends on its size (radius) and its mass due to gravitational effects (Katz et al. 1982, Larwood et al. 1996, Lubow & Ogilvie 2001).

Independend of the disk precession, the individual changes of all this parameters results also from the truncated disk size during the periastron passages. In addition I think, particularly the rapid increase and decrease of the EW, is essential determined by the inclination angle in the observers view and hence of the central dip in Halpha during a periastron passage.

Ernst
Ernst Pollmann
Posts: 461
Joined: Mon Sep 26, 2011 7:16 pm

Re: 28 Tau ARAS monitoring

Post by Ernst Pollmann »

Dear colleagues,
today the periastron passage took place.
The Halpha central abbsorption (CA) seems to have achieved a maximum value, but further observations could show more about the behavior during the next days.
CA-timeseries.png
CA-timeseries.png (90.48 KiB) Viewed 13827 times
Please (if it possible) observe the star to get more data information.
For observers who wants to know more about shell lines in Be stars, see:
"Shell lines in disks around Be stars"; Hanuschik, A&A 295, 423-434, 1995.
Ernst Pollmann
Ernst Pollmann
Posts: 461
Joined: Mon Sep 26, 2011 7:16 pm

Re: 28 Tau ARAS monitoring

Post by Ernst Pollmann »

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)
Periodenanalyse CA und EW_20.2.21.png
Periodenanalyse CA und EW_20.2.21.png (473.37 KiB) Viewed 13751 times
Any comments?
Ernst Pollmann
Ernst Pollmann
Posts: 461
Joined: Mon Sep 26, 2011 7:16 pm

Re: 28 Tau ARAS monitoring

Post by Ernst Pollmann »

Thanks to the observers A. Stiewing, K. Alich, J. Martin and O. Thizy, it was possible, to cover with observations the for September 7th 2021 predicted periastron passage with the Halpha parameter EW, V/R, CA (central absorption, most typical) and RV.
But further observations would be helpful in order to determine the orbital period of 218 days as precisely as possible.
CA monitoring.png
CA monitoring.png (29.89 KiB) Viewed 12233 times
Ernst Pollmann
Ernst Pollmann
Posts: 461
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Re: 28 Tau ARAS monitoring

Post by Ernst Pollmann »

Dear colleagues,
our current monitoring of the Be star 28 Tau includes among others the observation of the depth of the central absorption (CA) in the Halpha emission (see attached Fig.). This CA reflects the disk inclination in the observers view.
The strong periodicity of the max. value of CA with its binary period of 218 days confirms each time the periastron passage of the compagnion star and hence the binary character of 28 Tau.
After the last periastron in our monitoring (JD 2459468) appears now an unexpected increase of CA, which feed the suspect, that there is a second companion star of the system.
Katahira, et al. (1996, PASJ, 48, 317), and Roberts et al. (The Astronomical Journal, 133, 2007 February) reports about signs of a possibility of a third body within their observations.
Possibly our unexpected observed increase of CA after the primary periastron might be in that sense an additional confirmation.
Please try to take spectra of 28 Tau as long as possible.
28tau_CA.png
Ernst Pollmann
Rainer Ehlert
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Joined: Thu Sep 29, 2011 9:36 pm

Re: 28 Tau ARAS monitoring

Post by Rainer Ehlert »

Hallo Ernst,

I just was able to shoot a series of 6 images with 300s exposure time.

LISA spectrograph @23µm slit on a TOA 130 with a 0.6X reducer.

Processed in PixInsight with Bias, Dark and Flat and then processed in RSpec.


Image
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°
Ernst Pollmann
Posts: 461
Joined: Mon Sep 26, 2011 7:16 pm

Re: 28 Tau ARAS monitoring

Post by Ernst Pollmann »

Hi Rainer.
unfortunately the spectral resolution is too low and hence the central absorption in Halpha not visible.

Ernst
Rainer Ehlert
Posts: 135
Joined: Thu Sep 29, 2011 9:36 pm

Re: 28 Tau ARAS monitoring

Post by Rainer Ehlert »

Ernst Pollmann wrote:Hi Rainer.
unfortunately the spectral resolution is too low and hence the central absorption in Halpha not visible.

Ernst

Hallo Ernst,

Thank you and understood :) but even so it was an interesting exercise.
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°
Ernst Pollmann
Posts: 461
Joined: Mon Sep 26, 2011 7:16 pm

Re: 28 Tau ARAS monitoring

Post by Ernst Pollmann »

Dear colleagues,
even when I communicated already some diagrams in terms of the time synchronous variability, here again as complementation and for clarification this kind of behavior of EW and CA (period = 280 d).
EW and CA have been detrended of the long-term trends of its original monitorings.
Ernst Pollmann
CA & EW detrended.png
Last edited by Ernst Pollmann on Fri Nov 04, 2022 5:57 pm, edited 1 time in total.
Ernst Pollmann
Posts: 461
Joined: Mon Sep 26, 2011 7:16 pm

Re: 28 Tau ARAS monitoring

Post by Ernst Pollmann »

Dear colleagues!
Pleione becomes more and more interesting.
Monitoring of the Halpha central absorption depth and EW provides the following information:
- the next periastron passage will take place at 20. November this year.
- at present the star is leaving the maximum shell phase
- approx. at autum 2023 it reaches the pure Be-phase.
- last Be-phase approx. 2001
Ernst Pollmann
CA versus EW.png
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