Be stars are monitored spectroscopically (overwhelmingly at H-alpha) by amateurs probably more than any other group of variable stars, but there has been little virtually simultaneous photometric and spectroscopic monitoring of these stars done by amateurs. That's a fertile, pretty much wide-open field for amateurs, much as eclipsing binaries were 50 years ago. It also provides opportunities for collaborative programs amongst amateur photometrists and spectroscopists, as well as for pro-am co-operation. Here's a link to an interesting paper that points up the need for simultaneous photometry and spectroscopy of Be stars, and the science that can come from those observations:
The Correlation Between H-alpha Emission and Visual Magnitude During Long-Term Variations in Classical Be Stars
T. A. A. Sigut and P. Patel
Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, CANADA N6A 3K7
H-alpha equivalent widths and UBV magnitudes are calculated for Be star disk models that grow in size and/or density with time. We show that these simple models are consistent with the known Be star classes of positive and inverse correlations between long-term variations in H-alpha and V magnitude as identified by Harmenac. We support the conclusion of Harmenac that the distinction is controlled by the inclination of the disk to the line of sight. We demonstrate that the strength of these correlations, particularly those of an inverse correlation where the system becomes fainter as the H-alpha emission strength grows, is strongly influenced by the scale height of the inner Be star disk and the extent of the gravitational darkening of the central B star due to rapid rotation. This dependence may allow coordinated spectroscopic and photometric observations to better constrain these poorly known Be star parameters.
Accepted by The Astrophysical Journal
Preprints from: asigut@uwo.ca
or on the web at: arXiv:1301.3721
The "Visual Magnitude" in the title refers to V-filtered photometry, but long-term visual monitoring of Be stars is equally important as, similar to CVs or symbiotics, can go into "outburst" on a more or less regular basis, depending on the star.
Cheers,
Thom Gandet (GTN)
Dear Thom,
my colleagues and me have performed a very similar investigation.
See:
Halpha-emission and V-correlations as probes of Be stars disks
(by Ernst Pollmann, Wolfgang Vollmann & Ferenc Puscas)
Published in:
BAV-Rundbrief (1/2012), Bundesdeutsche Arbeitsgemeinschaft Veränderliche Sterne, Germany
http://astrospectroscopy.de/HalphaversusV.pdf
Best wishes,
Ernst
This is very interesting work, Ernst.
Do you have some further details on the experimental method, equipment used etc., for measuring Ha-EW?
Go well!
Jeremy
Hi Jeremy,
the experimental way is the method of the spectroscopy.
I am using the spectrograph LHIRES III of the french firm SHELIAK, connected at an Celstron C14 (please have a look at my home page http://www.astrospectroscopy.de
The evaluation of the Halpha equivalent width is always performed with the standard method of the professional astro spectroscopy.
Best wishes, Ernst
This is quite interesting. I would find this process very simple. I currently have a LISA spectrograph and UBVRI equipped CCD side by side on my 2 scopes. I am slowly surveying many Be stars in the far south down to mag 12 and taking spectra of them with a resolution of R =800. These are then submitted to BeSS.
I could very easily take photometry measurements at the same time providing I have comp mags to use. Lots of the Be stars are not recognised as variable in the VSX so are not reportable to the AAVSO.
Is there any point in doing this?
Cheers
Terry
Hi Terry,
Definitely worth doing. Go for it! Very little is known about the faint Be stars, especially about the correlations between the photometric and spectroscopic behavior, and there are also some rather fun and weird faint Be stars (e.g., the Be stars with warm dust disks) that are not at all well-known. The paper I mentioned is just the most recent professional study using simultaneous photometry and spectroscopic observations that I found.
I forgot that Ernst is now an AAVSO member. (Sorry, Ernst!) He has done a lot of Be star spectroscopy and found or confirmed periodicity in Be stars. He has been observing Be stars spectroscopically for several years, participated in several pro-am Be star projects and has also contributed many spectra to BeSS.
As you may know, most amateur spectroscopy is currently being done in the UK and Europe, mostly of stars brighter than about 8th or so, as I recall, and not a whole lot of amateur long-term photometry anywhere north of the equator. Long-term multi-color amateur photometry of even bright southern Be stars also lags behind the north, and U-band observations are much less numerous than BVRI ones. Since CCD cameras have now replaced photoelectric photometers, U-band has become a kind of "orphan", and there is as much good science that can be done there as at V-band, for example.
There is no single database of photometric *and* spectroscopic observations, such as the AID, yet. The AAVSO is looking into ways to implement one, but there are some knotty problems to solve there. If you can demonstrate that a Be star is variable, please do submit your photometry to the VSX folks, but I wouldn't let the lack of official comp stars stop me from starting to observe. If you observe them, the comp stars will come!
Even without official comps, differential ensemble photometry will allow determining variability. Either way, typical photometric cycle times for Be stars run from about a hundred days to 1500 days or so, so there might be a bit of a wait before you see a positive result.
Best wishes,
Thom
Thanks for the
Thom
Thanks for the encouragement.
Taking the simultaneous images is simple and there are comp stars around on the AAVSO database thanks to APASS although they only work for the dimmer stars. Even U is possible but comp stars do become a problem as there isn't always another nearby star visible in U.
I might just take images and archive them. If the star changes the spectra then I can go back and measure the magnitudes then.
My plan is to survey the B stars ~annually as they become visible in the southern evening sky.
Terry
... I would neither add further comments.
Thom´s statement decribes fairly comprehensive the link between spectroscopy and photometry of Be stars.
Best wishes, Ernst
Sorry to come late to this, but I'd like to add that this is a worth while project. There is still work to do understanding the Be phenomenon and more data helps. But there is a caveat. There has been a lot of work done on the short-term (days to months) trends and activity in Be stars. There is a tendancy for observers to spend a few weeks or a season on a star, publish and move on. Where more data and effort is really needed is in consistent long-term monitoring. Consistency is important because changes in instrument and technique can make it difficult to compare data over many years.
I'd encourage people with a spectrograph to adopt a Be star or two as part of a long term spectroscopic/photometric program. It might not bear fruit even in a few years but it could be very useful in the longterm. It is also worthwhile to maybe check-in on and follow Be-stars that are not in their "active" Be phase. It is often useful to professionals and other observers to catch these stars when they transition from in-active to active or active to inactive. It is hoped that catching those transitions and carefully observing them can provide vital clues about what causes the Be phenomenon in those stars spectifically and all Be stars in general.
[quote=uis01]
Sorry to come late to this, but I'd like to add that this is a worth while project. There is still work to do understanding the Be phenomenon and more data helps. But there is a caveat. There has been a lot of work done on the short-term (days to months) trends and activity in Be stars. There is a tendancy for observers to spend a few weeks or a season on a star, publish and move on. Where more data and effort is really needed is in consistent long-term monitoring. Consistency is important because changes in instrument and technique can make it difficult to compare data over many years.
I'd encourage people with a spectrograph to adopt a Be star or two as part of a long term spectroscopic/photometric program. It might not bear fruit even in a few years but it could be very useful in the longterm. It is also worthwhile to maybe check-in on and follow Be-stars that are not in their "active" Be phase. It is often useful to professionals and other observers to catch these stars when they transition from in-active to active or active to inactive. It is hoped that catching those transitions and carefully observing them can provide vital clues about what causes the Be phenomenon in those stars spectifically and all Be stars in general.
[/quote]
This is the "raison d'etre" behind the Pro-Am BeSS database
http://basebe.obspm.fr/basebe/Accueil.php?flag_lang=en
Consistency of data is addressed by contributions being moderated (and contributors given help to improve their quality where needed) and the requirement for the data to be reduced according to a specified protocol and supplied in a specified format.
The requested observing interval for each Be star and which need spectra taken currently can be found here as well as reports on several specific long term monitoring campaigns.
http://arasbeam.free.fr/?lang=en
Monthly reports of specific observations from the data (eg changes in activity etc) are published here
http://www.astrosurf.com/aras/surveys/beactu/index.htm
Cheers
Robin
There is another example of successful supplement of photometry and spectroscopy:
The campaign "Photometry and Spectroscopy of P Cyg".
See:
http://astrospectroscopy.de/PCYG_AAVSO.pdf
Ernst