Call for monitoring Be stars in the TESS sectors

Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Mon Nov 11, 2019 9:09 pm

Hi all,

I should have mentioned this sooner, but the spreadsheet (https://docs.google.com/spreadsheets/d/ ... sp=sharing) has been updated with regards to stars being observed in this current, and also the next, TESS sector. In particular I am focusing on two targets right now: V801_cas and CT_cam. Like before, I am trying to get as many NRES spectra as possible for these two right now. Over the next few nights I hope to have enough data that I can choose to focus on just one of these (probably V801 Cas, since it is brighter and more active; but CT Cam is just as interesting). Any spectra of these two stars in particular will be greatly appreciated.

Here is an incomplete and short list of some of the highest priority targets right now:

# ID, Tess_mag, Spectral_type, RA, DEC
CT_Cam 7.05 B2Vne 54.5043 55.17084
V801_Cas 6.08 B1Ve 47.22574 62.38456
CR_Cam 7.47 B2Ve 52.16344 62.49296
V818_Cas 7.77 B2Vne 357.47124 62.21413
BD+61_39 8.585 B0.5IV 5.072612 62.463852
V780_Cas 7.64 B1Vpe 30.65169 59.68809
BD+56_534 8.93 B2IIIe 34.86046 57.0784
HD_237056 8.04 B0.5Vpe 45.65787 57.61279
BD+45_681 7.886 B5V 44.314165 46.019957

All of the observations so far, especially for V357 Lac, look great (and obviously V442 And). Soon I will work on combining the many NRES + BeSS spectra for this star in anticipation of the TESS data becoming available (rough estimate of 1 - 1.5 months).
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Re: Call for monitoring Be stars in the TESS sectors

Postby Robin Leadbeater » Fri Nov 15, 2019 8:35 pm

Hi Jon,

BD+45_681 7.886 B5V 44.314165 46.019957 is not listed in BeSS. It has a clear Be disc signature though. I will upload my spectra of this star to the BAA database instead
https://britastro.org/specdb/

Cheers
Robin

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Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Tue Nov 26, 2019 4:05 pm

Hi all,

Here's an update on one of the Be stars that was being intensely monitored recently- V357 Lac. The first month of TESS data is now available (from TESS sector 16; 2019-Sep-11 to 2019-Oct-07), and there will be one more month of data coming out still from sector 17. Lots of spectra were taken simultaneously with these two sectors.

The attached plots show information from the TESS light curve and the spectra. There's a lot going on in this plot, so here is a description of each panel:

1st panel: Lomb-Scargle periodogram (y-axis log scale). This is basically the Fourier Transform of the TESS light curve. The most relevant features are that there are two frequency groups near 1.2 and 2.4 c/d. This means that sinusoidal signals with these frequencies exist in the data.

2nd: Wavelet plot. This shows how the frequencies from the top plot change over time. The two frequency groups are variable in their power. This is also clear just by looking at the TESS data.

3rd: 2-min cadence TESS light curve (black). Red: low-frequency signals showing the slower variation. The colored vertical lines are epochs of spectroscopic observations that have been submitted to BeSS.

4th: same TESS LC, but with the red curve subtracted (makes it easier to see the higher frequency signals and their changes).

5th: Halpha EW. Larger number -> more Halpha emission (relative to the continuum).

7th, 8th: ignore. These should be the peak separation and V/R values for Halpha, but they aren't being calculated correctly by my code yet.

Then the rest are some spectroscopic features when available. All the BeSS spectra cover Halpha. The big Halpha panel has time increasing upwards, with spacing scaled to the time between observations. There isn't much change in the profile of the Halpha line, but it clearly starts to decrease in strength in the first half of the dataset, then increases again. This effect is actually not caused by the Halpha emission line changing. Rather, it is the underlying continuum that is increasing, while the line emission remains relatively steady (could be increasing actually, but more work needs to be done to attempt to measure this properly).


diagnostic_plot_99.png



This plot shows the TESS data that I extracted from the pixels and calibrated myself. This was done because the default TESS data reduction pipeline removes long term trends in the data, because this makes it easier to find exoplanets and do things like asteroseismology. But with Be stars, we're also interested in the long-term trends. The important point of this plot is that the continuum brightness increases significantly (10-15% !), and then starts to decrease again during the first month of TESS observations. I think the red points are more reliable, but I'm still working on this part. There is a complicated convolution of astrophysical signals and instrumental signals that are difficult to disentangle properly.

LC_plot_sector_16.png



Bottom line: This project seems to be going really well- excellent work! V357 Lac shows very interesting signals in its light curve, and the longer term trend is almost certainly associated with mass ejection on short timescales. The simultaneous spectra provide essential complementary information. Once the next sector of TESS Data for this star is available then a more quantitative analysis of the spectra will begin. Although the NRES telescopes had hardware problems for the first month for this star, I was able to get many spectra during the second month, which will combine nicely with the spectra submitted to BeSS. As far as I know, a dataset like this that captures mass loss on short timescales in Be stars has never existed before.

Finally, there is an almost overwhelming amount of data between all of your spectra and the TESS data. If there are any objects you are interested in checking up on (TESS data available up until Oct. 07 so far), let me know and I can send along data and plots from TESS.

-Jon

p.s. the text at the top of the big plot is wrong. This is V357 Lac, B1:V:nnep.
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Re: Call for monitoring Be stars in the TESS sectors

Postby J Labadie Bartz » Mon Jun 01, 2020 2:42 pm

Hi everyone,

I hope you are all healthy and doing well these days. I apologize for the extended silence on my part in regards to this project. After TESS stopped observing most Be stars a few months ago I have been focusing on obtaining and analyzing the available data from the first year of the TESS mission, so I haven't had much time to focus on this spectroscopic observing aspect of the project (which is okay, since TESS really hasn't been observing Be stars for the past many months).

Anyway, time to ramp this back up! The final month of the TESS survey of the northern (ecliptic) hemisphere is almost here, and during it many Be stars will be observed.

TESS Sector 26: 2020-Jun-08 to 2020-Jul-04. I've updated the spreadsheet (https://docs.google.com/spreadsheets/d/ ... sp=sharing) to highlight the stars that TESS is observing in this time span, with priorities in the left-most column for the best targets. As a reminder, you are free to edit the spreadsheet with any notes or comments (in the 'observing notes' column) and/or to indicate if you made an observation on some night (in the 'observed' column). There is no clear favorite star, so the best observing strategy is a spectrum every few days for the stars with a priority number, but if you notice anything interesting this strategy can change to focus on the interesting target.

A related topic: There is another space photometry mission, BRITE, that observes Be stars. BRITE is different from TESS, in that BRITE is less precise (but still excellent quality) but BRITE also has much longer observing baselines. There is a very nice Be star, Pi Aqr, that BRITE is observing from May 30 - Nov 30 2020. This is an exciting opportunity for a number of reasons.
- Pi Aqr is a known Be + hot subdwarf (sdO) binary, where we know that the hot subdwarf star donated mass and angular momentum to the Be star, spinning it up.
- It is located at +01 degrees, making it accessible from both hemispheres, and it is bright at V = 4.6.
- It is known to be rather active and variable.
- At my university (University of Sao Paulo), we will attempt a 2-3 week polarimetric observing campaign, which is a technique that is very sensitive to the inner disk, which will allow us to measure any changes to the inner disk with excellent precision.
- It is likely that we will also have some time on a 4-m telescope to get very high quality spectra, possibly at the end of June.
- This star is the main focus of the PhD thesis of a graduate student here at the University of Sao Paulo, and she will use the space photometry + polarimetry + spectroscopy to model the inner disk as mass from the star is being ejected which is an exciting topic because no one knows how mass is ejected, and the dynamics of the ejected gas contains important clues about its ejection. Also, she is working on models of the Be + disk + subdwarf system to see how the disk behaves in the presence of a binary companion, which is also an important development in Be star science.

So, any and all spectra taken of Pi Aqr between now and Nov. 30 would be of great help to this project! I will be using ~all of my remaining NRES telescope time on this target, but I must concentrate the time only in the last 2 weeks of June, to coincide with the spectra from the 4-m telescope. If you are interested in helping with the Pi Aqr project by obtaining spectra, please let me know! Of course we want to use telescope time most efficiently, so it will be helpful to have an idea of who can be working on this. For example, it is much better to have three observations with one taken each night, instead of three observations in the same night.

We can use spectra of any resolution with a minimum S/N of 50. Low resolution and or low S/N can be used for a qualitative analysis of the line profile variations, that are quite useful to us. On the other hand, a more quantitative analysis of key features, such as peak separation and V/R variations, is also planned, and for those a minimum resolution of R ~ 10000 and S/N >~ 100 are necessary. If you have an echelle spectrograph, please consider a high (>100) S/N, as echelle spectra will cover some key spectral features that are often quite weak in emission.

In short: all spectra with S/N > 50 and any resolution are welcome, but higher resolution spectra should have higher S/N so that their full potential can be used.

Soon I will post an update about how we have been combining your spectra with the recent TESS observations to learn some interesting things, but first I wanted to post the above time-sensitive information and requests.

Looking forward to being more active on here and in touch with you all again!

Best regards,
-Jon
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Re: Call for monitoring Be stars in the TESS sectors

Postby Ernst Pollmann » Thu Jun 04, 2020 7:57 am

Hi Jon,
here my monitoring of the star as collaboration with different ARAS observers.

Monitoring the Hα equivalent width (EW) and V/R of π Aqr

Hα equivalent width


As discussed in Bjorkman et al. (2002, ApJ, 573, 812), π Aqr’s previous disk likely developed in the early 1950s and persisted until December 1994. Analysis of spectroscopic data obtained after 1996, when the star was in a diskless “normal B star” phase, revealed it star has a close binary companion with a circular orbit and period of 84.1 days.

Fig. 1 indicates that the likely beginning of the disk transformation to its minimum state of pure absorption could be observed on 1995 July 15 (JD 2449914; EW = 1.1 Å). The temporal evolution of the Hα EW of π Aqr provides clear evidence of a disk-loss event from July 1995 until November 2003 (JD 2452945).

The timescale for π Aqr’s disk-loss episode (~3055 days) corresponds to 36 complete orbits of its binary companion which suggests that the companion´s orbital motion was not responsible for triggering the disk-loss episode. After the start of its minimum pure absorption state, π Aqr’s Hα EW remained until June 2004 (approx. JD 2453181). It's a nice coincidence that the ARAS EW monitoring began when π Aqr was building a new disk. As in Fig. 1, this process is going on very steeply since August 2014 (approx. JD 2456875).

Hα V/R
The recent increase of the Hα EW needs a close attention, because it might be the beginning of a large disk development, such as that in the 1950's. The fact that nothing has changed to the V/R variations yet (Fig. 2) is probably due to a slow disk re-structuring process. As more matter is added to the disk, its density structure will probably change and the density enhancement, which is moving with the period of 84.2 d (Fig. 3) in phase with the secondary companion now (Zharikov et al. 2013, A&A, 560, A30), may be modified.

What we see is that Be stars with small disks that result in a weak line emission (such that in π Aqr between 2001 and 2005) may show phase-locked V/R variations (Hα-V/R period analysis of the binary π Aqr, Pollmann, IBVS No. 6023, 2012). Be stars with larger disks (or with disks that contain more mass) and a stronger line emission show much larger periods of the V/R variations that do not match the orbital periods (examples are γ Cas, ζ Tau, 48 Lib). It is unknown what happens when a Be star disk gets larger and exhibits a stronger line emission. We suggest that the phase-locked V/R variations will not be observed anymore, but rather larger period V/R variations may develop.

However, when and whether such a transition occurs is unknown as well. If π Aqr is indeed going to increase its disk mass, then it is the right target to start getting answers to the above questions. Perhaps, there are already some data on stars that show such a transition between different periods, but π Aqr is in transition right now and a dense monitoring is very valuable.
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