Galaxies for Fun Astronomical CMOS and CCD photos of peculiar galaxies and other astronomical stuff.
www.galaxies.se - by Ivar Hamberg
Beta Lyrae A - a very complex binary system:
Beta Lyrae A is maybe one of the most studied eclipsing binaries in the sky, but still enigmatic. The two stars in this binary system revolve in 12.9 days. By going deep into several publications from the last 30 years or so, one can get a good idea of how this system works.
Beta Lyrae Aa1 is a fainter Giant. The star is less massive, but with a larger radius and a luminosity of 6.500 suns.
Beta Lyrae Aa2 is a brighter but obscured Dwarf. It is more massive and brighter but with smaller radius and with a luminosity of 26.300 suns.
Aa1 (the Donor) has transferred material to Aa2 (the Gainer).
Aa2 has an accretion disc with bipolar jets and hot spots enabling strong emission lines.
The spectrum shows both strong emission and absorption lines. It is said that about 20% of the luminosity is from the accretion disc. A substantial part of the emission lines are from this accretion area.
Two different spectra were taken in 2022 with my spectrograph. I have tried to illustrate what the different features in these spectra relate to.
Sheliak, Beta Lyrae A:
SPECTRUM #1:
Date: 2022-08-22, 21:00-21:16 UTC
Exp: This is a 720 sec spectrum, combined from four 180 sec images.
Instrument: 12" RC telescope. 300 L/mm grating spectrograph.
Spectrum dark field adjusted, flattened and calibrated to known lines.
The spectrum has both prominent emission and absorption lines. A quite interesting combination!
Facts:
Beta Lyrae is a multiple star system. It is said to have 6 main components, A-F.
Beta Lyrae A is named Sheliak.
- Beta Lyrae A has 3 components (Aa1+Aa2 and Ab.). The magnitude is variable 3.25-4.36, spectral type B6-B8 (or "B7").
- Beta Lyrae Aa1 and Aa2 is an eclipsing binary pair, with the eclipses giving the magnitude variations given above.
The orbital axis is perpendicular to us. The separation is said to be only 0.865 milli arcseconds.
Aa1 is the Donor star, and Aa2 is the Gainer star.
- Beta Lyrae Ab is a 3rd component that was discovered in 2006. It is separated by 0.54 arcseconds from Aa.
Aa1 and Aa2 orbits each other within 12.9 days. Aa1 is a B6-B8 star. Aa2 is smaller in radius and said to be a B0.5V star, much hidden by a luminous accretion disc.
- Beta Lyrae B, mag 7.19, is of type B7V (probably a single star, but previously thought of as a spectral binary), and is 45" away.
- Beta Lyrae C, D, E, F are from mag 7 to 15 and believed to be single stars.
- Beta Lyrae A, B and F are believed to be physically at similar distance. Components C, D, E are only in the line of sight.
In high resolution spectra, one can easily see changes in the spectral lines depending on the actual phase of the 12.9 day period.
Observations in the spectrogram, and some current general understandings:
ABSORPTION: Ca II 3934 Å - from the photosphere of the B7 larger giant Aa1 star.
EMISSION/ABS: He I 4471, 4713, 4922, 5016, 5876, 6678, 7065. From mass transfer and the jets and accretion disc associated with the Aa2 star. (However, complicated profiles.)
EMISSION: H-beta 4861 (emission), H-alpha 6563 (emission). From mass transfer and the jets and accretion disc associated with the Aa2 star.
ABSORPTION: H-gamma, H-delta, H-epsilon (absorption). From the photosphere of the B7 giant Aa1 star.
NOTE: For B-stars in a Be-phase it is said to be common that H-alpha and H-beta are seen in emission, but not H-gamma, H-delta or H-epsilon.
Several lines show complex double peaks, with a combination blue-shifted red-shifted parts, due to high rotational speeds. This is typical for this star, and changes with the phase of the orbit.
The Sodium lines are seen separated (the high res spectrum) and may be due to both interstellar absorption far from the star system and close to the obscure disc.
Period. 2456897.16 + N *12.9414 This gave the phase Phi=0.42 for my exposure (I have seen two published periods 12.9414 and 12.94062. They give 0.417 and 0.431, quite similar.) Ph=0.5 refers to second minima where the Donor star is in front of the Gainer star.
See also references at the Wikipedia reference list, Shelyak Instruments website, AAVSO, Buil, the Walker Atlas and elsewhere. -It is maybe one of the most observed and analyzed star systems but still not fully understood.
Some references:
Mennickent, Galaxies 2022 - Acretion Disks and Long Cycles in Beta Lyrae-Type Binaries
Broz, Mourard et al, Astronomy & Astrophysics 2021 - Optically thin circumstellar medium in the Beta Lyr A system
Mourard et al, Astronomy & Astrophysics 2018 - Physical properties of Beta Lyr A and its accretion disk
Ak et al, Astronomy & Astrophysics 2007 - New findings supporting the presence of a thick disc and bipolar jets in the Beta Lyrae system
Higher Resolution - Sheliak, Beta Lyrae A:
SPECTRUM #2:
Date: 2022-09-17, 21:42-22:00 UTC
Exp: This is a 300 sec spectrum, combined from five 60 sec images.
Instrument: 12" RC telescope. 600 L/mm grating spectrograph.
Spectrum dark field adjusted, flattened and calibrated to known lines.
The spectrum shows much more of the delicate details of this complex star system.
The phase is calculated to be 0.43. (2459840.41667 - 2456897.16 = 2943.25667 Divide by 12.9414 => 277.43