Sun, 07/12/2020 - 18:43
Hi there
First, thanks to all the organisers and presenters of the EB webinar - I learned a lot!
As I was listening, I wondered if it is possible to detect changes in the spectrum of an EB if it is comprised of two widely different spectral types? If so, and you track it over a minimum, there should be some interesting dynamics to observe. I do spectroscopy and have just started to do do the simulatneous photometry so it might be a nice project...
Thanks
Kevin
I have no experience with spectroscopy but I think this should be possible. I would suggest starting with a deep total eclipse. During totality, the light from the brighter star is completely blocked so the spectrum of the fainter star can be recorded. At maximum, the spectrum of the brighter star will dominate and you should be able to digitally subtract out the spectrum of the fainter star.
I few suggested candidates for summer are V342 Aql, W Del, and U Sge. In autumn, ST Per, Z Per, and RW Tau should also work. For all of these stars, the totality lasts an hour or longer so you will have time to record the spectrum at minimum.
SAM
I have no experience with spectroscopy but I think this should be possible. I would suggest starting with a deep total eclipse. During totality, the light from the brighter star is completely blocked so the spectrum of the fainter star can be recorded. At maximum, the spectrum of the brighter star will dominate and you should be able to digitally subtract out the spectrum of the fainter star.
I few suggested candidates for summer are V342 Aql, W Del, and U Sge. In autumn, ST Per, Z Per, and RW Tau should also work. For all of these stars, the totality lasts an hour or longer so you will have time to record the spectrum at minimum.
SAM
Thanks for suggestions,
I managed to track down an article on V342 Aql. ( Erdem et al. New AStronomy , 2007) which gives the spectra of the two components - A4II+[K0IV] (at least that's how I interpreted this information).
A are K very distinguishable, so maybe this is a starting point..
Kevin
If you use BV or BVI you can get a sense of differences in color by calculating B-V and/or V-I for each data point pair (BV pair, VI pair) during the drop to minimum. Since the B amd V (or V and I) are taken at slightly different times there will not be precision, but you will get an idea of basic color changes, if any.
Ed
I visualised this in a different way recently by plotting two phase curves simultaneously, one from data with a B filter and the other with a V filter, taken on two different nights. The target was an EW star. Because of the short period it was easy to capture an entire cycle each night.
Roy
Hello Kevin,
Something you didn't explicitly ask, but is one of the main spectroscopic measurements for EBs, is changes in wavelength due to the doppler shift of the moving components. Using this you can measure radial velocities for the two components, which is crucial in defining a full binary solution. I recommend you look into this further if you are going to be taking spectra of EBs as this is a sought after measurement (especially by me).
Thanks,
Bert Pablo
Staff Astronomer, AAVSO
My understanding is that the high spectral resolution needed to achieve really useful radial velocity mesurements of eclipsing systems requires professional level instrumentation. I'm doubtful that the telescopes and spectrographs used by most amateurs in private observatories could achieve this.
Roy
Hey Roy,
That really depends on the sorts of stars and orbital periods you are talking about. While a star analyzer is insufficient for this kind of analysis, you don't need echelle level spectra either. I have used many spectra taken by home observatories when analyzing brighter binaries such as UW CMa. For massive stars brighter than 7th magnitude and orbital periods of ~10 days or less, radial velocity variations are quite achievable with resolutions in the range of 5000, maybe less (this is all ball park, but you get the idea). Depending on your equipment and how much effort you want to put in with stacking spectra it is definitely possible, especially for the sort of research that I personally do.
Thanks,
Bert Pablo
Staff Astronomer, AAVSO
Hi Bert. Thank you. It's good that amateurs can do that. The targets are, however, limited. Among those studied by Variable Stars South a ballpark figure of about 8% have minima between 7 and 8 V mag, and very few are brighter.
Roy
Hi, Kevin:
Yes, changes in spectrum are somtimes observable with small-telescope spectroscopy (and multi-color photometry). If you are in the upcoming Spectroscopy Workshop "ALPY" session, I will show (briefly) an example. BO Mon has a deep flat-bottom eclipse, and the two stars are quite different. Do photometry in B-V-R through the eclipse and you see very different eclipse depths in the three colors. A series of spectra through eclipse are fun - at the bottom of the eclipse you can get a decent spectrum of the secondary star, which is a much later (redder/cooler) spectral type than the primary.
An easier target (not eclipsing...) is the vsual double Alberio. You already know that they are yellow (gold?) and blue, so it is neat to see the how the spectrum difference correlates with your visual impression.
Cheers,
Bob B.