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.

Revenant of the Swan

 

P Cygni (34 Cygni) and also known as the ' Revenant of the Swan' - Hyper Giant Blue Variable Star in the Constellation Cygnus the Swan - 66mm Altair Starwave refractor with 0.6 x focal reducer and field flattener - Canon 600d DSLR at ISO 800. 3 minute RAW exposures. Credit: Pip Stakkert.

Plate solving. Credit:  Astrometry.net

"This interesting and highly luminous star is located between 5000 and 6000 light years distant and is moving away from us at nearly 9 km/sec. The star has a current magnitude of  4.8  (Absolute Mag -7.9) and may be seen from a dark site with the naked eye. This is incredible considering its vast distance from our Solar System.  P Cygni is extraordinary in many ways! It has a mass 37 times  and radius 76 times that of our Sun. It is 610,000 times more luminous than the Sun and this is the reason it can be seen from such a great distance. It is one of the most luminous stars known in the Milky Way.

The star is an irregular variable and has, over the past 500 years, shown major brightening. In recent times the variability has been less extreme and visual brightening is occurring at 0.15 of a magnitude per century. P Cygni is thought to be burning hydrogen in a shell around its core and if so is moving from hyper giant blue to red super giant stage all part of an evolutionary process as the star moves closer to its likely supernova. The life of a blue hyper giant star is short and violent and measured in millions rather than billions of years when compared with our Sun.

Because of its variability and extreme outbursts in the 17th century, the star was thought to be a recurring nova. Presumably it was named the the 'Revenant of the Swan' because it exhibited a repeated and unexpected return to life after multiple deaths or novae.

P Cygni gives it's name to a type of stellar spectrum that shows both absorption and emission in the profile. The emission line arises from a dense stellar wind near to the star, while the blue shifted absorption lobe is created where the radiation passes through circumstellar material rapidly expanding in the direction of the observer. As the star is quite bright we are hoping to use our transmission grating to obtain a spectrum later in the summer when Cygnus is on the meridian". - Kurt Thrust Director of the Jodrell Plank Observatory.