Hello, fellow astronomers,
My long-term astronomy project starting as of now is the photometric and spectroscopic survey of selected Be stars visible in the Southern hemisphere. These will be selected from the ones presently displaying Balmer emission lines. Be stars in the Southern skies are in great need of attention for many of these objects have not been observed, ever, being merely putative Be stars, or just superficially looked at.
I currently have the photometric filters Astrodon B, Rc (dated June and August 2019), and Baader V (being received at the end of the month, https://www.astroshop.eu/pass-filters/baader-filters-ubvri-bessel-v-1-25-/p,73898).
Would I need any additional photometric filter for the purpose delineated above?
If I were to buy Sloan photometric filters (u', g', r', i', and z'), which ones should I start with in order to do the most useful work with Be stars? Or would they be entirely unneeded or not recommended at this point of the J-C <-> Sloan affairs?
Thanks in advance for your kind comments.
Since these are hot stars, the bluer filters are going to be more useful in terms of the changing characteristics of the stars. Thus for most folks just the B and V will be satisfactory. The Sloan u filter could be even more useful, but that requires your telescope to have the uv sensitivity. If you have some ordinary transmitting glass involved, like a corrector plate, near-focus corrector, or even simply just a camera lens, then you won't have much throughput in the violet. Most of the activity in the Be stars is going to be evident in the H-alpha line itself, so either a narrow H-alpha filter or perhaps a low-dispersion spectrum is going to be diagnostic.
Not ever observed? You might want to seek out the older ASAS-3 survey data, or the current ASAS-SN data, which will contain long runs of photometry of at the least the brighter reasonably isolated stars of any sort.
I believe having understood the points you've made, thank you.
When I said "not ever observed" I was referring mainly to spectroscopy. Many Be stars detected in the Southern hemisphere have been so by wide-field photometry done with space telescopes, without detailed confirmation or follow-up. There have been numerous cases of "Be stars" which later were better classified as B[e] or Herbig Ae/Be. A paper by Labadie-Bartz et al., 2017 (Photometric Variability of the Be Star Population, Astronomical Journal,153:252) details this issue with respect to the data from the light curves of 610 known Be stars in the KELT transit survey.
In a recent survey of the BeSS database (http://basebe.obspm.fr/basebe/ - 2330 objects) and ArasBeAm database (http://arasbeam.free.fr/?lang=en - 2021 objects), I detected that out of the 1,313 Be, Herbig Ae/Be, and B[e] stars registered to date in the Southern celestial hemisphere, 673 objects (51%) have not had a single spectrum recorded; 429 have 1 to 5 spectra. Ninety-three Southern stars have been extensively studied, with 50 or more spectra deposited.
If one searches the AAVSO, quite often Be stars listed in the BeSS database are not represented in VSX or do not show more than very few - if any - photometric records.
I will be checking the ASAS-3 and/or the ASAS-SN, thank you. Maybe also Gaia? Gaia's photometric instruments allow data acquisition over the 320–1000 nm spectral band, of all stars brighter than magnitude 20. The Blue Photometer operates in the range 330–680 nm; the Red Photometer covers 640–1050 nm. I will see how to access Gaia's photometric data.
You have made a very good point: although my camera, a ZWO ASI 533 MM Pro is quite capable in the near UV: (https://astronomy-imaging-camera.com/product/asi533mM-pro), my scope is a Schmidt-Cassegrain with its characteristic corrector plate. UV will be blocked out.
Thank you so much for your valuable input.
The GAIA3 data are readily accessed through the CDS-Strasbourg VizieR catalogue-query utility:
All the GAIA DR3 stuff is under item I/355. There are many sub-files under this directory. The main astrometric, photometric, and radial-velocity file is under I/355/gaiadr3. The spectra, which I have only recently found were available, are under I/355/spectra. The link given in reports from the latter show the rather coarse fluxed spectra. Having looked at ~1000 of these in the past ten days for stars of all types all over the sky, I am now relatively confident about what can be seen in them. The faintest stars with good spectra are about mag 14, though there is some range at the faint end. Things get unreliable brighter than about mag 7. Reasonably strong H-alpha in Be (and other) stars is readily identifiable when S/N is good. Spectral classification is possible for stars from about K5 and cooler. For bluer stars I don't think you can do better getting than a whole letter class in most cases.