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.
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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
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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
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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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Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Sat Sep 19, 2020 8:21 pm

Hi everyone,

While TESS is continuing to observe the southern ecliptic for the next ~9 months, there are some upcoming opportunities for both hemispheres that I am starting to plan for. These targets are just starting to be visible at the very end of the night, and will be observed by TESS in November/December/January. These are all bright, and I am working with the LCO network and some other proposals to establish a spectroscopic baseline prior to TESS, so that we have some context by the time TESS observers. Any observations of these targets submitted to BeSS over the next few months will likewise be of value.

25 Ori is perhaps the most interesting of these targets. Years of BRITE observations, and 1 month of TESS, show clear frequency groups, and also short-lived outbursts that may repeat. I obtained about 200 spectra of 25 Ori during BRITE observations a few months ago, and found that some of the photometric frequencies also exist in spectroscopy, but only at certain times (i.e. some spectroscopic frequencies are only strong during mass-loss episodes), while others have constant amplitudes.

HD 44783 06:31:09.56 +11:15:04.96 V=6.1 | B2Vnne TESS s33. A spectrum from last night shows this as a shell star with a symmetric Halpha profile, with E/C~2.
HD 43285 06:15:40.12 +06:03:58.21 V=6.3 | B5IVe TESS s33
V715 Mon 06:49:03.66 +01:00:07.45 V=6.1 | B3IIIe TESS s33
HD 44783 06:24:02.28 +08:53:06.05 V=6.2 | B9IIIe TESS s33
25 Ori 05:24:44.83 +01:50:47.20 V=4.9 | B1Ve TESS s33 **Most interesting**
ome Ori 05:39:11.15 +04:07:17.28 V=4.6 | B3Ve TESS s33
2 Ori 04:50:36.72 +08:54:00.65 V=4.3 | A1Vne TESS s32. Currently has a weak disk signature in Halpha, double-peaked and symmetric, but well within the absorption line.
OT Gem 07:24:27.65 +15:31:01.92 V=6.4 | B2Ve TESS s33

TESS Sector 32 = 2020-Nov-19 to 2020-Dec-17
TESS Sector 33 = 2020-Dec-17 to 2021-Jan-13

And,
Pi Aqr 22:25:16.623 +01:22:38.63 V=4.6 | B1IVe BRITE
- Pi Aqr is currently being observed by the BRITE satellite from May 30 - Nov 30, 2020. Observations in Halpha and/or He6678 are especially useful, as myself and many others are observing this target in spectroscopy and polarimetry during the BRITE observations. Over the past ~120 days, the emission in all lines has remained strong, including in He 6678. There are also signs of rapid variability in the polarization color on timescales of hours. While preliminary, this all suggests that mass-loss is ongoing, feeding the disk against the forces that would otherwise act to dissipate it.

For fun, I re-reduced the TESS data for a nice target that was observed by nine observers (Charbonnel, Buil, Berardi, Lester, MAETZ, Leadbeater, Bryssinck, GARDE, and HOUPERT) plus a few NRES observations from myself over the TESS baseline. I think this is an excellent example of a short outburst seen in phot. + spec. that really highlights the power of this observing network.

I have not yet caught up to the BeSS observations from the past year taken for TESS targets, but as soon as I start working on a paper for these I'll be in touch.

LC_and_line-profiles_01.png
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Re: Call for monitoring Be stars in the TESS sectors

Postby Olivier GARDE » Sun Sep 20, 2020 9:13 am

Hi Jon,

Thanks for your message. I will take spectra of Tess sector as soon as possible, but the weather in France still remain bad during one week...
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Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Tue Sep 22, 2020 4:58 pm

Great, thanks Olivier. I too have been having bad luck with weather. I am working this week on putting together a spreadsheet for the next year or so of TESS observations, similar to the one in an earlier reply in this thread for TESS year 2. It takes some time, because the sky is big and the TESS sectors shift from year-to-year, so I can't simply copy things over.

I just remembered another really cool target that will also be observed in TESS sector 33 (2020-Dec-17 to 2021-Jan-13):
HD 55606 07 13 34.100 -02 04 39.0999 V=9.

I don't think this one is in BeSS yet. This is a Be + sdO binary (Porb = 93.8 d) that is observed nearly edge-on and has some really interesting features (info in this paper if you're interested, https://ui.adsabs.harvard.edu/abs/2018ApJ...865...76C/). For one, in that 2018 paper observations show a clear accretion disk around the secondary. There are also dramatic shell profiles at certain phases in the orbit, which may indicate either disk warping, or structure in the z-direction in the disk, phase-locked to the binary orbit.

Although kind of faint, I'm trying to get spectra of this star over the next few months so that when TESS observes it we know things like if the disk is growing/stable/shrinking, if there are shell profiles during the TESS obs., if there's any sign of an accretion disk around the secondary, and any asymmetry in the Be disk. There are some unusual features in the TESS data from year 1, but are hard to interpret since the status of the disk at that time was unknown. Right now HD 55606 is barely high enough in the sky for maybe 1-2 hours at the very end of the night, but it will continue to become more visible over the next few months.
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