34 Cygni an unusual star in Cygnus the Swan

 

34 Cygni aka P Cygni in the constellation Cygnus.
PIRATE robotic telescope with BVR filters, Mount Teide, Teneriffe.
Data credit: telescope.org. Open Observatories, Open University.
Image Credit: Pip Stakkert at the JPO.

Annotated Image credit Astrometry .net.

Why is 34 Cygni unusual:

• 34 Cygni is unusual because it is not a single star, but a symbiotic binary system. That means it’s made of two very different stars orbiting each other:
• A cool red giant, which has a very extended, bloated atmosphere.
• A hot companion (likely a white dwarf), which shines with intense ultraviolet light.
• The giant loses gas, and the hot companion excites and ionizes this gas, producing a glowing nebula-like envelope around the system. Because of this, 34 Cygni shows features of both a cool star and a hot star mixed together in its spectrum.

34 Cygni is classified as a symbiotic star of type S. Its peculiarities arise from the interaction between its components:

Binary Composition

• M-type red giant donor: contributes strong molecular bands (TiO, VO, CN), characteristic of a cool photosphere (T_eff ≈ 3200–3600 K).
• Hot compact companion (white dwarf): provides ionizing radiation (T_eff > 50,000 K) that excites emission lines in the red giant’s wind.

Spectral Profile Features

• Cool star absorption spectrum:
• Broad molecular bands (TiO, VO) dominating the optical.
• Strong continuum slope toward the red.
• Superposed emission spectrum:
• Hydrogen Balmer lines (Hα, Hβ, Hγ, etc.) in strong emission.
• Helium lines (He I, sometimes He II) from higher excitation regions.
• Forbidden lines ([O III] 5007 Å, [Ne III], [N II]) from the ionized nebular gas around the binary.
• Occasionally, Raman-scattered O VI lines around 6825 Å and 7082 Å, which are diagnostic of symbiotic systems.

Why Kurt Thrust and his team want to capture 34 Cygni's spectrum as a 'try out' for the new diffraction grating affixed to the Seestar S30.

• Most stars show either an absorption spectrum (normal stars) or an emission-line spectrum (nebulae, hot stars with winds).
• 34 Cygni shows a hybrid spectrum, with both molecular absorption and nebular emission simultaneously.
• Its spectral variability over time reflects mass transfer episodes, changes in the red giant wind, and accretion activity on the white dwarf.
• The JPO team has not captured spectral data for this star before and Kurt loves a challenge.

 Summary:

• 34 Cygni is unusual because it is a symbiotic binary, displaying both red giant absorption bands and nebular emission lines. In a low-resolution spectrum you’d see molecular TiO absorption from the cool star, plus bright emission lines of hydrogen, helium, and forbidden ions, giving it a “mixed identity” unlike normal stars.
• Prof  G.P.T Chat has theoretically constructed the following spectral profile simulation for a binary star system like 34  Cygni. We shall compare the theoretical profile with the actual profile captured at the JPO."

- Joel Cairo CEO of the Jodrell Plank Observatory.

Stop press: 

• The clouds cleared and the Seestar S30 plus diffraction grating captured zero and first order spectra for 34 Cygni together with a calibration set for Vega. Yet to see if we can create meaningful profiles from the data using BASS software. This will be the subject of a future post. Jolene, has used the feedback from the performance of the prototype, to make some minor modifications to the design of the grating holder, in order to reduce the overall length of spectra on the Seestar S30's sensor.

"Astronomy is temporarily on hold at the JPO as its sponsor, Anita Roberts will be 75 years old this week and she is the JPO Team's favourite star. There will be much jollity and partying in the JPO Visitor Centre this week!! Give Comet the Cat another 'goldfish'! " - Kurt Thrust current Director of the Jodrell Plank Observatory.