www.galaxies.se - by Ivar Hamberg

Sheliak, Beta Lyrae A: 

SPECTRUM:

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. The magnitude is variable 3.25-4.36, spectral type B6-B8 (or "B7").

   - Beta Lyrae Aa1 and Aa2 is an eclipsing binary, 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 primary, and Aa2 is the secondary component

   - Beta Lyrae Ab is another 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.

In high resolution spectra, one can easily see changes in the spectral lines depending on the actual phase of the 12.9 day period. 

More facts:

Beta Lyrae Aa1 is a fainter Giant (less massive, but larger radius, luminosity 6.500 suns)

Beta Lyrae Aa2 is a brighter Dwarf, (more massive and brighter but smaller radius, luminosity 26.300 suns)

Aa1 has transferred material to Aa2. Aa2 has an accretion disc with bipolar jets enabling strong emission lines (see spectrum). It is said that about 20% of the luminosity is from the accretion disc. So the prominent emission lines seen in the spectrum should be a substantial contribution from the accretion. 

Observations in the spectrogram, and some current general understandings:

Ca II 3934 Å - from the photosphere of the B7 larger giant Aa1 star.

He I 4471, 4713, 4922, 5016, 5876, 6678, 7065. From mass transfer and the accretion disc (and jets?) associated with the Aa2 star.

H beta 4861 (emission), H alpha 6563 (emission). From mass transfer and the accretion disc (and jets?) associated with the Aa2 star.

H gamma, delta, epsilon (absorption). From the photosphere of the B7 giant Aa1 star.

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.)

Higher Resolution - Sheliak, Beta Lyrae A: 

SPECTRUM:

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