spectro-aras.com

Quick update on 12 Vul. TESS is observing this Be star from July 23 until Aug. 20. I got a spectrum a few minutes ago (JD = 2459437.2) that shows Halpha at clearly higher emission levels compared to 3 days ago, so it is currently in the process of building up a disk (or at least recently ejected material is evolving). I see that Olivier Thizy has a nice series of spectra that go at least until the end of July on BeSS, which generally show that the disk had been dissipating. Anyway, this continues to be a good target to observe for at least the next 10 days. I'll continue to get one spectrum every one or two nights, and any additional spectra will be great in filling in the time coverage. I expect that we'll see some clear evidence of the mass ejection events in the TESS data too, once that becomes available.

While I'm at it...

The bright Be star and member of the Pleiades, Merope (= 23 Tau), might be a nice target to monitor closely. In the below plot made from ~25 years of BeSS spectra, you can see that the emission level has been fading since ~1995. I observed Merope a few days ago and the Halpha double peaks are clearly above the continuum level, so it seems like the disk is once again building up. TESS will be observing this star for three consecutive sectors, from 2021-Aug-20 to 2021-Nov-06. If the disk continues to build during this time, then we have a good opportunity to compare the properties of the TESS light curve to the Kepler light curve, which was taken a few years ago (i.e. when the disk was dissipating).

Small update: 12 Vul is definitely ejecting material now. Comparing a spectrum from today (the reddest line w/ strongest emission) vs. yesterday, Halpha emission has clearly increased, and the red/blue asymmetry is varying (the ejected material so far is not azimuthally symmetric). I have some more observations scheduled later today (~7 hrs after the time of this post), but any additional Halpha observations are certainly welcome as they should help to resolve the rapidly-changing V/R emission levels as material orbits the star on hours to ~1d timescales. Should aim for high SNR since we are looking for small changes over short timescales.

It's been a while since my last update, but TESS is currently observing Be stars in the northern hemisphere. I've compiled a target list, sorted according to when TESS is observing various fields in this 'cycle 5'

https://docs.google.com/spreadsheets/d/ ... sp=sharing

Right now TESS is in 'sector 58', so highlighted in green are all the stars being observed right now (in column P = 'c5'). See the README tab on the bottom of the spreadsheet to match TESS sectors to calendar dates. I've made notes for several stars that I am observing, and have given some a priority number (in the 1st column), so I'd consider these the highest priority to observe, but spectra of other targets will also have value. For example, gam_Cas and V442_And are two important targets at the moment, but there are many others (6_Cep, EM_Cep, HD_208682, phi_Per...).

Generally the idea is that even low-cadence H-alpha-only spectra of Be stars provide important context for interpreting the space photometry from TESS. This is the only way to know if a star was ejecting mass or not, or if it has a disk or not, during the TESS observational baseline. This is necessary to interpret some of the photometric signals (i.e. circumstellar vs. pulsational).

There are some interesting fast changes in EM Cep currently (disc loss?)
Cheers
Robin