Call for monitoring Be stars in the TESS sectors

Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Sun Jun 21, 2020 8:22 pm

Hi Ernst,

Ernst Pollmann wrote:unfortunately, most of the Echelle spectra in BeSS only show the area around HeI6678 very incompletely, so that they can often not be used.
That is unfortunate, although I had pointed this out once, but nothing has changed.
t


Thanks for pointing this out- I'd have to agree based on looking through a few. I'll pass along this word of caution to the PhD student (Amanda Rubio) who will be doing much of the analysis, but I hope/expect lots of the BeSS data to still be useful.

Something I should have noticed sooner when I remarked on the He 6678 line from 2006 vs. measurements from the past month is the quantifiable difference in peak separation. In Sept. 2006 the V and R peaks of He 6678 are separated by roughly 600 km/s and have the ~same intensity, but now the peaks are separated by about 450 km/s (and have much different intensities). At first glance this suggests a few things:

- In 2006, the He 6678 emitting region has roughly cylindrical symmetry (otherwise the V and R peaks would be different strengths), or, if there is asymmetry, the spectrum was taken at a time when the blue- and red-moving regions of the disk are near equal in strength. Probably this can be determined by looking at some of the other spectra nearby in time.

- In 2006, since the peaks have a wide separation, the gas emitting this line is moving relatively fast, i.e. it is very close to the star where orbital velocity is high.

- Now, there is clear asymmetry in the He emission peaks. The typical picture of the disk in binary systems like this is a spiral density wave, which manifests nicely in the plot you showed of the V/R ratio of Halpha phased to the orbital period. Since the He emission originates in the inner disk close to the star, perhaps this asymmetry can give us an idea of how tightly wound this spiral wave is. On the other hand, I haven't seen obvious asymmetries in some other metal lines, which form further out than He emission, but still very much interior to Halpha, so the asymmetric He emission could mean something else entirely. Time will tell as more of the orbit is covered and the peaks continue to shift.

- Now, the peak separation in He emission is lower by about 150 km/s compared to 2006, suggesting lower velocity of the emitting gas, meaning there is less hot He-emitting gas very close to the star. Also, I can't tell if this is just an optical illusion, but the emission peaks now look more narrow, suggesting a lower velocity dispersion = the gas is in a more narrow 'ring' than it was in 2006. This could mean a lower rate of mass ejection from the star compared to 2006.

- The continuum flux from the star + disk now is almost certainly higher than it was in 2006 (based on your plot of Halpha EW vs. time; probably a few tenths of a magnitude), which should act to suppress the apparent strength of emission features seen recently, but this shouldn't have any impact on their location, shape, and relative strengths.

- With how much material is in the disk, there ought to be an accretion disk as material flows from the Be disk to the binary companion. I wonder if this is something that can be detected? Seems difficult.

Just out of curiosity, have you measured the Halpha peak separation to see how that changes over the orbit? Some other similar systems I'm aware of have the peak separation follow a sinusoid at half the orbital period due to the density structure of the disk. At some point this will be done with the NRES spectra, which I think will be a useful quantity for Amanda's models of the disk, but so far I haven't done any sort of quantitative measurements.
J Labadie Bartz
 
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Re: Call for monitoring Be stars in the TESS sectors

Postby Ernst Pollmann » Mon Jun 22, 2020 4:53 pm

Hi Jon,
thanks for your considerations, I fully agree.
The HeI6678 line seems to be an appopriate indicator for studying the disk development and dynamic during a very early state close to the surface of the primary.
In that sense I just drawed for this line profile during 2005-2006 the attached velocity behavior which shows the drastic velocity decrease if developed Helium gas is transfered in to a ring with increasing distance from the photosphere.

Best wishes,
Ernst
piaqr_HeI6678_2005-2006.png
piaqr_HeI6678_2005-2006.png (43.02 KiB) Viewed 724 times
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Re: Call for monitoring Be stars in the TESS sectors

Postby Benjamin Mauclaire » Mon Jun 22, 2020 8:56 pm

Hi Ernst,

I hope you're going fine.
Why are you talking about a ring?
In such system without any intense magnetic field it would be a disk rather than a ring.

Cheers,

Benji
Spcaudace spectroscopy software: saving you hundred hours of frustration.
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Re: Call for monitoring Be stars in the TESS sectors

Postby Ernst Pollmann » Tue Jun 23, 2020 1:09 pm

Hi Benji,
I used the term "ring" in the same context as Jon did in his message above (6th paragraph).

Best wishes,
Ernst
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