Call for monitoring Be stars in the TESS sectors

Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Sat Oct 24, 2020 3:43 pm

Hi all,

In about one month from now, TESS will begin to observe sector 32 (2020-Nov-19 to 2020-Dec-17), followed by sector 33 (2020-Dec-17 to 2021-Jan-13). The next three months are probably the most exciting time to observe Be stars along with TESS. Even though there are very few Be stars being observed between now and Nov. 19, we can start to observe stars that will be visited by TESS in sectors 32 and 33 to build up more of a spectroscopic baseline. That way, when TESS is observing them, it will be easier for us to tell if the star is building up or dissipating a disk.

Importantly, the best TESS targets for the next three months are visible from both hemispheres! I've been updating the TESS Be target list and observing schedule (https://docs.google.com/spreadsheets/d/1dQUAzUpqNojht747Cbo5TuAFNsFtvodU46BSZGiOAfE/edit?usp=sharing) with notes and a priority scheme, and applying for telescope time and coordinating observations for many of these targets. Any observations of these targets will be useful for forthcoming studies where we analyze the spec. + phot. data together to better understand the relationships between the star and the disk. Higher SNR observations are best, since we may be looking for small changes in emission over just a few days. But, I think even lower SNR observations can be useful to keep track of longer term changes (i.e. has the disk grown or changed between now and the end of the TESS light curve?).

For example, here's a plot of TESS data from last year for one of these stars- OT_Gem = TIC 14498757. These sharp brightening events are almost definitely related to very quick mass ejection episodes, and it would be great to see how the emission lines respond. If anyone is curious to see more of these TESS light curves, I can make a folder with most of them for the stars in the spreadsheet available.
Attachments
TESS_lc.png
OT_Gem_TESS_yr1
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Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Sun Nov 15, 2020 7:56 pm

Hi everyone,

I've been continuing to observe the stars that are emphasized in the spreadsheet linked to in the previous post. Here's just a few examples of some of my current favorites that are showing interesting variability now. TESS is observing sector 32 on Nov. 19, so especially for some of these stars (25 Ori, 228 Eri, Lam Eri) I'll be attempting to ramp up observations as much as possible in the hopes of capturing some interesting behavior with spec. + TESS. Of course, any additional observations of these targets will be greatly appreciated, as I've been having bad luck with weather and hardware problems. Also, any observations now and over the next month of stars in TESS sector 33 are also good to provide context for the TESS observations.

25 Ori is my highest priority at the moment. Observations of sufficient SNR to capture the profile of He 6678 are especially exciting, as this line (and TESS phot.) is very sensitive to the timing of mass ejection events.

25_Ori_plot_2.png
25 Ori DAO
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lam_Eri_plot_2.png
Lam Eri DAO
lam_Eri_plot_2.png (100.53 KiB) Viewed 2883 times


OT_Gem_plot_2.png
OT Gem DAO
OT_Gem_plot_2.png (95.63 KiB) Viewed 2883 times


alpha$_01.png
228 Eri
alpha$_01.png (55.53 KiB) Viewed 2883 times
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Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Thu Nov 19, 2020 2:35 pm

Hi all,

A spectrum I got of 25 Ori last night continues to show interesting variability. The 'spike' in last night's spectrum in absorption on the blue side of the line is real (we see this feature also in other He lines from the same spectrum, so it's not simply an artifact in He 6678). TESS just started observing this star today (or maybe yesterday), so I will be continuing to get as many observations as possible with my current spectroscopic observing campaigns, and this will definitely be a good star to monitor for the next month+. The second observation in this plot, with the fainter blue line, is probably a case of bad continuum normalization, but I haven't checked closely yet.


He_6678_Nov19.png
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Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Sat Nov 21, 2020 4:26 pm

lam Eri might be starting to build a disk as of last night or two nights ago, so this is another interesting one to monitor (it's disk having recently dissipated). The possible growing emission feature is subtle, but appears in roughly the same spot in Halpha and Hbeta (on the blue side of the line only). I'll continue to get spectra of this one too.


Ha.png
lam_Eri_Ha


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

Postby J Labadie Bartz » Sun Nov 22, 2020 2:59 am

25 Ori is definitely showing some interesting variability right now. Three spectra taken tonight (from the same instrument, spaced by about 1-2 hrs) even have strongly variable features with respect to each other, especially in He 6678, and the Ha and Hb emission features (relative to the continuum) are variable, which altogether is suggestive of some active mass ejection (and also continuum level variability, and, of course, pulsational variability as already seen by TESS + BRITE in years past).

He6.png


Hb3.png
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Ha3.png
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Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Mon Nov 23, 2020 12:55 am

Quick update on Lam Eri. I no longer think this system is beginning to grow a disk. A relatively higher quality spectrum from tonight does not show any enhancement in emission features. Still unclear to me what the nature of the variability is in the Ha and Hb spectra that are attached. Could be related to pulsation, I guess. There is also the chance that this is a more complex system, as the TESS data show evidence of a (near-)contact EB with a period of ~0.7 days (this pair would not include the Be star, but are perhaps altogether part of a triple system).

Hb_today.png


Ha_today.png


On the other hand, 25 Ori continues to show dramatic variability over just the past few nights, and on even shorter timescales (and it is currently being observed from space by TESS). Main points:
- the rapid (over just 24 hrs) decrease in Halpha and Hbeta relative to the continuum, and the fact that both are already at relatively strong levels of emission very likely means that it is the continuum level itself that is rapidly increasing (rather than a big decrease in line emission strength).
- There are some strong changes in He 6678, suggesting a high level of activity in the inner disk.

I'm continuing to monitor 25 Ori over the next month, but of course the more the merrier! Halpha observations are valuable since it is clearly variable on short timescales, and so are (high-SNR) observations of Helium lines and the bluer hydrogen lines.

He_today_25_Ori.png
25_Ori_He


Hb_today_25_Ori.png
25_Ori_Hb


Ha_today_25_Ori.png
25_Ori_Ha
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Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Wed Dec 09, 2020 8:15 pm

25 Ori is still looking interesting. A few spectra from NRES over a 24 hr period even show significant variation, and TESS is continuing to observe this star until Dec 17- any spectra of Halpha or He 6678 in particular have value. Other stars in the spreadsheet at the top of this page, especially the ones marked in green for sectors 33 and 34 are also good to observe, but at a lower cadence than 25 Ori.

If anyone is observing these targets, please let me know so that we can better coordinate things, especially over the next few months where there are good TESS targets visible from the northern hemisphere. I've found it useful to monitor observations in nearly real time to adjust the priority and cadence based on new info (i.e. if we start seeing a new disk being built, then more focus should go to that system).

25Ori_He6678_1day_a.png
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Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Fri Dec 18, 2020 1:03 am

Looks like Lam Eri was growing a disk after all! A spectrum from just a few minutes ago shows clear evidence of disk growth. However, today (or sometime within the last 24 hrs) TESS moved to the next field and is no longer observing Lam Eri, so at least for me it is not a very high priority target. Still, I think it is valuable to get spectra at a low cadence in Halpha to monitor the behavior of the emission features over the next few weeks/months. Once the TESS data become available we can see what was happening photometrically before/during this mass ejection event.

smoothed_b_Halpha_01.png
Lam_Eri_Ha_new_disk
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Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Tue Jan 05, 2021 11:46 pm

Hi all,

Just a short and quick update. I'm now processing the TESS data from last year (TESS yr 2; July 2019 - July 2020), and including the relevant BeSS/ARAS spectra whenever possible. Presently I'm focusing on 'flicker' stars, or stars that experience short-lived (~days) mass ejection.

This plot for QR Vul shows one example where you see the flicker in the light curve + spectra over the same time span. A nice thing about this one is that it starts being roughly disk-less (at the very beginning of the TESS LC), and then it is easy to see the Halpha emission and TESS brightening from the newly ejected material. The higher priority stars in the spreadsheet here (https://docs.google.com/spreadsheets/d/ ... edit#gid=0) are likely to show similar behavior.

I hope to use the QR Vul example in a paper I'm currently drafting. There are definitely many other good targets where mass ejection is captured in both TESS + spectra from the past ~1-2 years. Once the paper is more matured, I'll contact people who have contributed spectra to the project about being included.

QR_Vul_LC_and_line-profiles_stacked_01.png
QR_Vul_flicker


Happy (retrospective) Holidays and New Year!

And thanks to Olivier Thizy, Etienne Bertrand, Erik Bryssinck, Umberto Sollecchia, Valerie Desnoux, Franck Houpert, and Christian Buil whose spectra are in the above plot!
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Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Tue Jun 22, 2021 3:56 am

Hi everyone,

TESS is returning to the northern hemisphere in a few days (June 24 2021) where the satellite will continue to observe large parts of the northern sky for the next 15 months.

Here is a spreadsheet that lists the classical Be stars that will be observed photometrically by TESS: https://docs.google.com/spreadsheets/d/1L19I6ouR7H2uM8fi5O9tRlcF3e3I2Mbp20csDygYfLc/edit?usp=sharing

The spreadsheet is organized by TESS sector, where the dates for each sector are listed in the "README" tab on the bottom. The first sector is sector 40 (2021-Jun-24 to 2021-Jul-23). I've marked the brighter stars since these are easiest to observe from the ground, and have typed out notes for some of the stars that I have been observing recently, plus others based on spectra on the BeSS website or with interesting features from earlier TESS observations.

The main goal here is to acquire relevant time-series spectra before and during the TESS observations so that the spectra and photometry can be interpreted together. Different stars have different observing needs. For example, HD_175863 will be observed in 11 of the next 15 TESS sectors, so low cadence observations of Halpha can show how the disk changes in strength over several months to see if any particular activity captured by TESS (e.g. higher amplitude stellar pulsation) corresponds to disk build-up. Other stars, like 12_Vul, warrant higher cadence observations (every 1 - 3 days) because earlier TESS data shows photometric evidence for short-lived mass ejection events (lasting only for a few days), and spectroscopic monitoring can help to tell us details about the mass ejection timing, how much material is ejected, and how symmetric (or not) the ejected mass is.

There are lots of good targets in the coming months for spectroscopic observations. I'm monitoring many of these stars with my own observing programs, and will continue to update the table with notes based on these observations. But, there are too many stars for any one observer, so a group effort to observe many of these systems simultaneous with the TESS will build up a really nice dataset that can (and will) be used for studying the properties and variability of the Be stars.

For anyone who is interested in this, if you'd like to be able to edit the spreadsheet that is linked above, let me know and I can provide access so that you can add your own observing notes for any targets that you visit. Also I will continue to update the spreadsheet as I analyze newer spec. observations and older TESS photometry for these stars.

Just to finish with a more concrete example and a plot...

For 12_Vul, the TESS photometry clearly shows pulsational variability (the more rapid changes in brightness), but also brightening events that happen when the star ejects mass. There are spectra on BeSS taken ~20 days before TESS observed 12 Vul, and also ~3 days after TESS finished observing. These spectra show an increase in emission, meaning that the disk has more material after the end of the TESS obs. compared to 20 days before the TESS observations. With higher cadence spectra, we could better see exactly when the disk starts to build up and when it dissipates and see how the emission lines compare to the brightness changes. Then, using models that describe Be star disk build-up and dissipation, we can fit the models to the photometry + Halpha line to estimate the amount of material that was ejected in each of the short outburst events.

LC_and_line-profiles_04.png
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